Application of nonlinear ultrasonic method for monitoring of stress state in concrete
Energy Technology Data Exchange (ETDEWEB)
Kim, Gyu Jin; Kwak, Hyo Gyoung [Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of); Park, Sun Jong [Dept. of Structural System and Site Safety Evaluation, Korea Institute of Nuclear Safety, Daejeon (Korea, Republic of)
2016-04-15
As the lifespan of concrete structures increases, their load carrying capacity decreases owing to cyclic loads and long-term effects such as creep and shrinkage. For these reasons, there is a necessity for stress state monitoring of concrete members. Particularly, it is necessary to evaluate the concrete structures for behavioral changes by using a technique that can overcome the measuring limitations of usual ultrasonic nondestructive evaluation methods. This paper proposes the use of a nonlinear ultrasonic method, namely, nonlinear resonant ultrasonic spectroscopy (NRUS) for the measurement of nonlinearity parameters for stress monitoring. An experiment compared the use of NRUS method and a linear ultrasonic method, namely, ultrasonic pulse velocity (UPV) to study the effects of continuously increasing loads and cyclic loads on the nonlinearity parameter. Both NRUS and UPV methods found a similar direct relationship between load level and that parameter. The NRUS method showed a higher sensitivity to micro-structural changes of concrete than UPV method. Thus, the experiment confirms the possibility of using the nonlinear ultrasonic method for stress state monitoring of concrete members.
Directory of Open Access Journals (Sweden)
A. Tata
2009-01-01
Full Text Available This paper presents a nonlinear finite element modeling and analysis of rectangular normal-strength reinforced concrete columns confined with transverse steel under axial compressive loading. In this study, the columns were modeled as discrete elements using ANSYS nonlinear finite element software. Concrete was modeled with 8-noded SOLID65 elements that can translate either in the x-, y-, or z-axis directions from ANSYS element library. Longitudinal and transverse steels were modeled as discrete elements using 3D-LINK8 bar elements available in the ANSYS element library. The nonlinear constitutive law of each material was also implemented in the model. The results indicate that the stress-strain relationships obtained from the analytical model using ANSYS are in good agreement with the experimental data. This has been confirmed with the insignificant difference between the analytical and experimental, i.e. 5.65 and 2.80 percent for the peak stress and the strain at the peak stress, respectively. The comparison shows that the ANSYS nonlinear finite element program is capable of modeling and predicting the actual nonlinear behavior of confined concrete column under axial loading. The actual stress-strain relationship, the strength gain and ductility improvement have also been confirmed to be satisfactorily.
Energy Technology Data Exchange (ETDEWEB)
Shokoohfar, Ahmad; Rahai, Alireza, E-mail: rahai@aut.ac.ir
2016-03-15
Highlights: • This paper describes nonlinear analyses of a 1:4 scale model of a (PCCV). • Coupled temp-disp. analysis and concrete damage plasticity are considered. • Temperature has limited effects on correct failure mode estimation. • Higher pre-stressing forces have limited effects on ultimate radial displacements. • Anchorage details of liner plates leads to prediction of correct failure mode. - Abstract: This paper describes the nonlinear analyses of a 1:4 scale model of a pre-stressed concrete containment vessel (PCCV). The analyses are performed under pressure and high temperature effects with considering anchorage details of liner plate. The temperature-time history of the model test is considered as an input boundary condition in the coupled temp-displacement analysis. The constitutive model developed by Chang and Mander (1994) is adopted in the model as the basis for the concrete stress–strain relation. To trace the crack pattern of the PCCV concrete faces, the concrete damage plasticity model is applied. This study includes the results of the thermal and mechanical behaviors of the PCCV subject to temperature loading and internal pressure at the same time. The test results are compared with the analysis results. The analysis results show that the temperature has little impact on the ultimate pressure capacity of the PCCV. To simulate the exact failure mode of the PCCV, the anchorage details of the liner plates around openings should be maintained in the analytical models. Also the failure mode of the PCCV structure hasn’t influenced by hoop tendons pre-stressing force variations.
Nonlinear dynamic acousto-elasticity measurement by Rayleigh wave in concrete cover evaluation
Vu, Quang Anh; Garnier, Vincent; Payan, Cédric; Chaix, Jean-François; Lott, Martin; Eiras, Jesús N.
2015-10-01
This paper presents local non-destructive evaluation of concrete cover by using surface Rayleigh wave in nonlinear Dynamic Acousto-Elasticity (DAE) measurement. Dynamic non classical nonlinear elastic behavior like modulus decrease under applied stress and slow dynamic process has been observed in many varieties of solid, also in concrete. The measurements conducted in laboratory, consist in qualitative evaluation of concrete thermal damage. Nonlinear elastic parameters especially conditioning offset are analyzed for the cover concrete by Rayleigh wave. The results of DAE method show enhanced sensitivity when compared to velocity measurement. Afterward, this technique broadens measurements to the field.
Nonlinear pushover analysis of infilled concrete frames
Institute of Scientific and Technical Information of China (English)
Chao Hsun Huang; Yungting Alex Tuan; Ruo Yun Hsu
2006-01-01
Six reinforced concrete frames with or without masonry infills were constructed and tested under horizontal cyclic loads. All six frames had identical details in which the transverse reinforcement in columns was provided by rectangular hoops that did not meet current ACI specifications for ductile frames. For comparison purposes, the columns in three of these frames were jacketed by carbon-fiber-reinforced-polymer (CFRP) sheets to avoid possible shear failure. A nonlinear pushover analysis, in which the force-deformation relationships of individual elements were developed based on ACI 318, FEMA 356,and Chen's model, was carried out for these frames and compared to test results. Both the failure mechanisms and impact of infills on the behaviors of these frames were examined in the study. Conclusions from the present analysis provide structural engineers with valuable information for evaluation and design of infilled concrete frame building structures.
Potential of Nonlinear Ultrasonic Indicators for Nondestructive Testing of Concrete
Directory of Open Access Journals (Sweden)
C. Payan
2010-01-01
Full Text Available In the context of a growing need for safety and reliability in Civil Engineering, acoustic methods of nondestructive testing provide answers to a real industrial need. Linear indicators (wave speed and attenuation exhibit a limited sensitivity, unlike nonlinear ones which usually have a far greater dynamic range. This paper illustrates the potential of these indicators, and evaluates its potential for in situ applications. Concrete, a structurally heterogeneous and volumetrically, mechanically damaged material, is an example of a class of materials that exhibit strong multiple scattering as well as significant elastic nonlinear response. In the context of stress monitoring in pre-stressed structures, we show that intense scattering can be applied to robustly determine velocity changes at progressively increasing applied stress using coda wave interferometry and thereby extract nonlinear coefficients. In a second part, we demonstrate the high sensitivity of nonlinear parameters to thermal damage as regard with linear ones. Then, the influence of water content and porosity on these indicators is quantified allowing to uncouple the effect of damage from environmental or structural parameters.
Energy Technology Data Exchange (ETDEWEB)
Byers, Loren W. [Los Alamos National Laboratory; Ten Cate, James A. [Los Alamos National Laboratory; Johnson, Paul A. [Los Alamos National Laboratory
2012-06-28
Nonlinear resonance ultrasound spectroscopy experiments conducted on concrete cores, one chemically and mechanically damaged by alkali-silica reactivity, and one undamaged, show that this material displays highly nonlinear wave behavior, similar to many other damaged materials. They find that the damaged sample responds more nonlinearly, manifested by a larger resonant peak and modulus shift as a function of strain amplitude. The nonlinear response indicates that there is a hysteretic influence in the stress-strain equation of state. Further, as in some other materials, slow dynamics are present. The nonlinear response they observe in concrete is an extremely sensitive indicator of damage. Ultimately, nonlinear wave methods applied to concrete may be used to guide mixing, curing, or other production techniques, in order to develop materials with particular desired qualities such as enhanced strength or chemical resistance, and to be used for damage inspection.
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Lavrov Kirill
2016-01-01
Full Text Available The hyperelastic orthotropic material model is proposed to describe the nonlinear behavior of concrete under monotonic multiaxial loading with taking into account the tension-compression anisotropy. The orthotropy is introduced for the correct description of concrete cracking. The hyperelasticity provides unconditional thermodynamical consistency and advantages in numerical solving of boundary value problems. Identification of model parameters is based on four experimental deformation diagrams of concrete: axial stress - axial strain and axial stress - transverse strain under uniaxial tension and compression. The results of the hyperelastic orthotropic model are compared with Karpenko’s orthotropic model and experimental data for multiaxial loading.
Nonlinear elastic model for compacted clay concrete interface
Institute of Scientific and Technical Information of China (English)
R. R. SHAKIR; Jungao ZHU
2009-01-01
In this paper, a nonlinear elastic model was developed to simulate the behavior of compacted clay concrete interface (CCCI) based on the principle of transition mechanism failure (TMF). A number of simple shear tests were conducted on CCCI to demonstrate different failure mechanisms; i.e., sliding failure and deformation failure. The clay soil used in the test was collected from the "Shuang Jang Kou" earth rockfill dam project. It was found that the behavior of the interface depends on the critical water contents by which two failure mechanisms can be recognized. Mathematical relations were proposed between the shear at failure and water content in addition to the transition mechanism indicator.The mathematical relations were then incorporated into the interface model. The performance of the model is verified with the experimental results. The verification shows that the proposed model is capable of predicting the interface shear stress versus the total shear displacement very well.
Nonlinear Finite Element Analysis of Reinforced Concrete Shells
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Mustafa K. Ahmed
2013-05-01
Full Text Available This investigation is to develop a numerical model suitable for nonlinear analysis of reinforced concrete shells. A nine-node Lagrangian element Figure (1 with enhanced shear interpolation will be used in this study. Table (1 describes shape functions and their derivatives of this element.An assumed transverse shear strain is used in the formulation of this element to overcome shear locking. Degenerated quadratic thick plate elements employing a layered discrelization through the thickness will be adopted. Different numbers of layers for different thickness can be used per element. A number of layers between (6 and 10 have proved to be appropriate to represent the nonlinear material behavior in structures. In this research 8 layers will be adequate. Material nonlinearities due to cracking of concrete, plastic flow or crushing of concrete in compression and yield condition of reinforcing steel are considered. The maximum tensile strength is used as a criterion for crack initiation. Attention is given to the tension stiffening phenomenon and the degrading effect of cracking on the compressive and shear strength of concrete. Perfect bond between concrete and steel is assumed. Attention is given also to geometric nonlinearities. An example have been chosen in order to demonstrate the suitability of the models by comparing the predicted behaviour with the experimental results for shell exhibiting various modes of failure.
SA-based concrete seismic stress monitoring: a case study for normal strength concrete
Hou, S.; Zhang, H. B.; Ou, J. P.
2016-09-01
The stress history of concrete structures that have survived an earthquake can serve as a critical index to evaluate the health of the structure. There are currently few reliable monitoring methods to assess concrete stress after a seismic event. Piezoelectric-based smart aggregate (SA) provides an innovative experimental approach to monitor stress on concrete. The principle of SA-based concrete seismic stress monitoring is based on the assumption that concrete stress can be reliably predicted by the average output voltages of limited SAs with an acceptable margin of error. In this study, the meso-scale randomness of concrete was evaluated throughout the overall stress range of concrete and the influence of different load paths was considered. Four cylindrical specimens of normal strength concrete were embedded with a total of 24 SAs. The SA output sensitivity curve in the paths of loading-unloading with different amplitudes and monotonic loading up to failure was obtained. Monitoring errors were analyzed during pre- and post-peak stages from the experimental results. This research suggests that SA-based concrete seismic stress monitoring for normal strength concrete is reliable.
3D Nonlinear Numerical Simulation of Intact and Debonded Reinforced Concrete Beams
Institute of Scientific and Technical Information of China (English)
Chen Quan(陈权); Marcus L.
2004-01-01
To study the behaviour of reinforced concrete (RC) structures with sections of concrete removed and the reinforcement exposed, 3D nonlinear numerical analysis was performed upon both intact and debonded RC beams by using finite element techniques. The deformational characteristics and the ultimate loads were obtained through numerical models, as well as crack and stress distributions. The failure modes can also be deduced from computational results. Compared with intact beams, the normal assumptions of plane section behaviour is not hold true and the patterns of stress and strain are different in debonded RC beams. The numerical results show good consistency with experimental data. This kind of numerical simulation is a supplement to existing codes.
Non-linearities in tensile creep of concrete at early age
DEFF Research Database (Denmark)
Hauggaard-Nielsen, Anders Boe; Damkilde, Lars
1997-01-01
A meterial model for creep is proposed which takes into consideration some of the couplings in early age concrete. The model is in incremental form and reflect the hydration process where new layers of cement gel are formed in a stress free state. In the present context attention is on non......-linear creep at high stress levels. The parameteres in the model develop in time as a result of hydration. The creep model has been used to analyse the tensile experiments at different stress levels carried out in the HETEK project. The tests were made on dogbone shaped specimen and the test procedure...... is described. Furthermore, compressive creep at high stress levels are fitted....
Siu, Sam; Ji, Qing; Wu, Wenhao; Song, Gangbing; Ding, Zhi
2014-12-01
In this paper, we explore the characteristics of a concrete block as a communication medium with piezoelectric transducers. Lead zirconate titanate (PZT) is a piezoceramic material used in smart materials intended for structural health monitoring (SHM). Additionally, a PZT based smart aggregate (SA) is capable of implementing stress wave communications which is utilized for investigating the properties of an SA based concrete channel. Our experiments characterize single-input single-output and multiple-input multiple-output (MIMO) concrete channels in order to determine the potential capacity limits of SAs for stress wave communication. We first provide estimates and validate the concrete channel response. Followed by a theoretical upper bound for data rate capacity of our two channels, demonstrating a near-twofold increase in channel capacity by utilizing multiple transceivers to form an MIMO system. Our channel modeling techniques and results are also helpful to researchers using SAs with regards to SHM, energy harvesting and stress wave communications.
Analysis of factors influencing fire damage to concrete using nonlinear resonance vibration method
Energy Technology Data Exchange (ETDEWEB)
Park, Gang Kyu; Park, Sun Jong; Kwak, Hyo Gyoung [Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, KAIST, Daejeon (Korea, Republic of); Yim, Hong Jae [Dept. of Construction and Disaster Prevention Engineering, Kyungpook National University, Sangju (Korea, Republic of)
2015-04-15
In this study, the effects of different mix proportions and fire scenarios (exposure temperatures and post-fire-curing periods) on fire-damaged concrete were analyzed using a nonlinear resonance vibration method based on nonlinear acoustics. The hysteretic nonlinearity parameter was obtained, which can sensitively reflect the damage level of fire-damaged concrete. In addition, a splitting tensile strength test was performed on each fire-damaged specimen to evaluate the residual property. Using the results, a prediction model for estimating the residual strength of fire-damaged concrete was proposed on the basis of the correlation between the hysteretic nonlinearity parameter and the ratio of splitting tensile strength.
Nonlinear analysis of concrete beams strengthened by date palm fibers
Bouzouaid, Samia; Kriker, Abdelouahed
2017-02-01
The behaviour of concrete beams strengthened with date palm fibers was studied by Nonlinear Finite Element Analysis using ANSYS software. Five beams that were experimentally tested in a previous research were considered. The results obtained from the ANSYS finite element analysis are compared with the experimental data for the five beams with different amounts of fibres, ranging from 0.2% to 0.5% by a step equal to 0.1% and with a fibre length of 0.04 m. The results obtained by FEA showed good agreement with those obtained by the experimental program. This research demonstrates the ability of FEA in predicting the behaviour of beams strengthened with Date Palm fibers. It will help researchers in studying beams with different configurations without the need to go through the lengthy experimental testing programs.
Nonlinear fracture mechanics investigation on the ductility of reinforced concrete beams
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A. Carpinteri
Full Text Available In the present paper, a numerical algorithm based on the finite element method is proposed for the prediction of the mechanical response of reinforced concrete (RC beams under bending loading. The main novelty of such an approach is the introduction of the Overlapping Crack Model, based on nonlinear fracture mechanics concepts, to describe concrete crushing. According to this model, the concrete dam- age in compression is represented by means of a fictitious interpenetration. The larger is the interpenetration, the lower are the transferred forces across the damaged zone. The well-known Cohesive Crack Model in tension and an elastic-perfectly plastic stress versus crack opening displacement relationship describing the steel reinforcement behavior are also integrated into the numerical algorithm. The application of the proposed Cohesive-Overlapping Crack Model to the assessment of the minimum reinforcement amount neces- sary to prevent unstable tensile crack propagation and to the evaluation of the rotational capacity of plastic hinges, permits to predict the size-scale effects evidenced by several experimental programs available in the literature. According to the obtained numerical results, new practical design formulae and diagrams are proposed for the improvement of the current code provisions which usually disregard the size effects.
Nonlinear analysis of massive concrete at successive construction
2013-01-01
The presented doctoral thesis deals with numerical analysis of fresh mass concrete, that is concrete whose temperature rise due to heat of cement hydration must be controlled. The thesis consists of two parts. In the first part, a numerical model which solves a fully coupled problem of water, moist air, and heat transfer in fresh concrete and mechanical analysis is presented. Basic equations are deduced from the model of the porous body, which describes concrete as a material, composed of ...
Surface Wave Velocity-Stress Relationship in Uniaxially Loaded Concrete
DEFF Research Database (Denmark)
Shokouhi, Parisa; Zoëga, Andreas; Wiggenhauser, Herbert
2012-01-01
loading cycles revealed that the velocities show a stress-memory effect in good agreement with the Kaiser effect. Comparing the velocities measured during loading and unloading, the effects of stress and damage on the measured velocities could be differentiated. Moreover, the stress dependency of surface......The sonic surface wave (or Rayleigh wave) velocity measured on prismatic concrete specimens under uniaxial compression was found to be highly stress-dependent. At low stress levels, the acoustoelastic effect and the closure of existing microcracks results in a gradual increase in surface wave...... velocities. At higher stress levels, concrete suffers irrecoverable damage: the existing microcracks widen and coalesce and new microcracks form. This progressive damage process leads first to the flattening and eventually the drop in the velocity-stress curves. Measurements on specimens undergoing several...
A macro-meso constitutive law for concrete having imperfect interface and nonlinear matrix
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
The overall behavior of concrete depends on its meso structures such as aggregate shape, interface status, and mortar matrix property. The two key meso structure characters of concrete, bond status of interface and nonlinear property of matrix, are considered in focus. The variational structure principle is adopted to establish the macro-meso constitutive law of concrete. Specially, a linear reference composite material is selected to make its effective behavior approach the nonlinear overall behavior of concrete. And the overall property of linear reference composite can be estimated by classical estimation method such as self-consistent estimates method and Mori-Tanaka method. This variational structure method involves an optimum problem ultimately. Finally, the macro-meso constitutive law of concrete is established by optimizing the shear modulus of matrix of the linear reference composite. By analyzing the constitutive relation of concrete established, we find that the brittleness of concrete stems from the imperfect interface and the shear dilation property of concrete comes from the micro holes contained in concrete.
Effect of Stress Amplitude on the Damping of Recycled Aggregate Concrete
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Chaofeng Liang
2015-08-01
Full Text Available Damping characterizes the energy dissipation capacity of materials and structures, and it is affected by several external factors such as vibrating frequency, stress history, temperature, and stress amplitude. This study investigates the relationship between the damping and the stress amplitude of environment-friendly recycled aggregate concrete (RAC. First, a function model of a member’s loss factor and stress amplitude was derived based on Lazan’s damping-stress function. Then, the influence of stress amplitude on the loss tangent of RAC was experimentally investigated. Finally, parameters used to determine the newly derived function were obtained by numerical fitting. It is shown that the member’s loss factor is affected not only by the stress amplitude but also by factors such as the cross section shapes, boundary conditions, load types, and loading positions. The loss tangent of RAC increases with the stress amplitude, even at low stress amplitude. The damping energy exponent of RAC is not identically equal to 2.0, indicating that the damping is nonlinear. It is also found that the energy dissipation capacity of RAC is superior to that of natural aggregate concrete (NAC, and the energy dissipation capacity can be further improved by adding modified admixtures.
Stress wave propagation in reinforced concrete piles during driving
Zorn, N.F.
1983-01-01
The aim of this report is to give an insight into what happens in a reinforced concrete pile during driving, and to contribute to design requirements for the loading case pile driving. Since the behaviour of stress waves in piles is influenced by a various number of parameters, the fewest of which r
Stress wave propagation in reinforced concrete piles during driving
Zorn, N.F.
1983-01-01
The aim of this report is to give an insight into what happens in a reinforced concrete pile during driving, and to contribute to design requirements for the loading case pile driving. Since the behaviour of stress waves in piles is influenced by a various number of parameters, the fewest of which
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Jianda Xin
2015-01-01
Full Text Available For concrete under short-term loading, effect of reinforcement on concrete crack resistance capability is usually negligible; however, recent research results show that extension of this viewpoint to concrete under long-term loading (temperature variation may be unsuitable. In order to investigate this phenomenon, this paper presents the experimental and analytical results of early-age reinforced concrete temperature stress development under uniaxial restraint. The experiments were carried out on a temperature stress testing machine (TSTM. Experimental results show that the coupling of reinforcement and concrete creep behavior influenced the concrete temperature stress development, and nearly 16% of concrete stress was reduced in the current research. Moreover, the cracking time of reinforced concrete was also delayed. Finally, based on the principle of superposition, analytical simulations of effect of reinforcement on concrete temperature stress have been performed.
Hong, Wan; Lv, Kui; Li, Bing; Jiang, Yuchen; Hu, Xiamin; Qu, Qizhong
2017-10-01
Deflection determination of concrete structures using distributed long-gauge strain sensors is investigated in this paper. Firstly, the relationship between deflection and distributed long-gauge strain of concrete beams is presented, and the method is independent of external load and takes account of structural nonlinearity. The deflection distribution along the span of a beam-like structure can be predicted from strain response for the whole process of loading (elastic stage, concrete cracking stage and steel yielding stage). Secondly, experiment of a reinforced concrete beam has been conducted to verify the accuracy of the method. Experimental results show that the relative error between the estimated and actual deflection can be controlled within about 5% while the error can reach up to about 70% if structural nonlinearity is not considered. Finally, the influence of error of material parameters and sensor gauge length on deflection estimation has been analyzed. The error of concrete compression strength has a limited influence on deflection prediction while the contribution of tensile concrete should be considered before concrete cracking. The error of area of tensile bars will affect the deflection accuracy after concrete cracking.
The stress-induced surface wave velocity variations in concrete
Spalvier, Agustin; Bittner, James; Evani, Sai Kalyan; Popovics, John S.
2017-02-01
This investigation studies the behavior of surface wave velocity in concrete specimens subjected to low levels of compressive and tensile stress in beams from applied flexural loads. Beam specimen is loaded in a 4-point-load bending configuration, generating uniaxial compression and tension stress fields at the top and bottom surfaces of the beam, respectively. Surface waves are generated through contactless air-coupled transducers and received through contact accelerometers. Results show a clear distinction in responses from compression and tension zones, where velocity increases in the former and decreases in the latter, with increasing load levels. These trends agree with existing acoustoelastic literature. Surface wave velocity tends to decrease more under tension than it tends to increase under compression, for equal load levels. It is observed that even at low stress levels, surface wave velocity is affected by acoustoelastic effects, coupled with plastic effects (stress-induced damage). The acoustoelastic effect is isolated by means of considering the Kaiser effect and by experimentally mitigating the viscoelastic effects of concrete. Results of this ongoing investigation contribute to the overall knowledge of the acoustoelastic behavior of concrete. Applications of this knowledge may include structural health monitoring of members under flexural loads, improved high order modelling of materials, and validation of results seen in dynamic acoustoelasticity testing.
STUDIES ON STRESS TRANSFERENCE MECHANISM OF STEEL FIBRE REINFORCED CONCRETE
Institute of Scientific and Technical Information of China (English)
杨佑发; 许绍乾; 钟正华
2001-01-01
The stress transfer mechanism of steel fibre reinforced concrete is studied. The solutions for the stress and displacement were regarded as the superposition of "the elementary solutions" and "the improved solutions". The elementary solutions were found by using two-dimensional elastic theory and the improved solutions were found by using the Love displacement function method. The calculated results indicate that the solutions possess good convergence. By comparing the three-dimensional solutions with the shear-lag solutions, evident difference may be found.
Probabilistic Nonlinear Analysis of Reinforced Concrete Bubbler Tower Structure Failure
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Králik Juraj
2014-06-01
Full Text Available This paper describes the reliability analysis of concrete bubbler tower structure of nuclear power plant with the reactor WWER 440 under high internal overpressure. There is showed summary of calculation models and calculation methods for the probability analysis of the structural integrity considering degradation effects and high internal overpressure. The uncertainties of the resistance and the calculation model were taking in the account in the RSM method.
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C. E. M. Oliveira
Full Text Available This work investigates the response of two reinforced concrete (RC plane frames after the loss of a column and their potential resistance for progressive collapse. Nonlinear dynamic analysis is performed using a multilayered Euler/Bernoulli beam element, including elasto-viscoplastic effects. The material nonlinearity is represented using one-dimensional constitutive laws in the material layers, while geometrical nonlinearities are incorporated within a corotational beam formulation. The frames were designed in accordance with the minimum requirements proposed by the reinforced concrete design/building codes of Europe (fib [1-2], Eurocode 2 [3] and Brazil (NBR 6118 [4]. The load combinations considered for PC analysis follow the prescriptions of DoD [5]. The work verifies if the minimum requirements of the considered codes are sufficient for enforcing structural safety and robustness, and also points out the major differences in terms of progressive collapse potential of the corresponding designed structures.
Nonlinear analysis of RC cylindrical tank and subsoil accounting for a low concrete strength
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Lewiński Paweł M.
2017-01-01
Full Text Available The paper discusses deformational and incremental approaches to a nonlinear FE analysis of soil-structure interaction including the description of behaviour of the RC structure and the subsoil under short-term loading. Two kinds of constitutive models for ground and structure were adopted for a nonlinear interaction analysis of the RC cylindrical tank with subsoil. The constitutive laws for concrete and subsoil were developed in compliance with the deformational and flow theories of plasticity. Moreover, a non-linear elastic-brittle-plastic analysis of RC axi-symmetric structures using finite element iterative techniques is presented. The results of the two types of FE analysis of soil-structure interaction are compared taking into account a low concrete strength of tank structure.
Concrete damage diagnosed using the non-classical nonlinear acoustic method
Institute of Scientific and Technical Information of China (English)
Zhou Dao; Liu Xiao-Zhou; Gong Xiu-Fen; Nazarov V E; Ma Li
2009-01-01
It is known that the strength of concrete is seriously affected by damage and cracking. In this paper, six concrete samples under different damage levels are studied. The experimental results show a linear dependence of the resonance frequency shift on strain amplitude at the fundamental frequency, and approximate quadratic dependence of the am-plitudes of the second and third harmonics on strain amplitude at the fundamental frequency as well. In addition, the amplitude of the third harmonics is shown to increase with the increase of damage level, which is even higher than that of the second harmonics in samples with higher damage levels. These are three properties of non-classical nonlinear acoustics. The nonlinear parameters increase from 106 to 108 with damage level, and are more sensitive to the damage level of the concrete than the linear parameters obtained by using traditional acoustics methods. So, this method based on non-classical nonlinear acoustics may provide a better means of non-destructive testing (NDT) of concrete and other porous materials.
GEOMETRIC AND MATERIAL NONLINEAR ANALYSIS OF REINFORCED CONCRETE SLABS AT FIRE ENVIRONMENT
Directory of Open Access Journals (Sweden)
Ayad A. Abdul -Razzak
2013-05-01
Full Text Available In the present study a nonlinear finite element analysis is presented to predict the fire resistance of reinforced concrete slabs at fire environment. An eight node layered degenerated shell element utilizing Mindlin/Reissner thick plate theory is employed. The proposed model considered cracking, crushing and yielding of concrete and steel at elevated temperatures. The layered approach is used to represent the steel reinforcement and discretize the concrete slab through the thickness. The reinforcement steel is represented as a smeared layer of equivalent thickness with uniaxial strength and rigidity properties.Geometric nonlinear analysis may play an important role in the behavior of reinforced concrete slabs at high temperature. Geometrical nonlinearity in the layered approach is considered in the mathematical model, which is based on the total Lagrangian approach taking into account Von Karman assumptions.Finally two examples for which experimental results are available are analyzed, using the proposed model .The comparison showed good agreement with experimental results.
Field test on temperature field and thermal stress for prestressed concrete box-girder bridge
Institute of Scientific and Technical Information of China (English)
Baoguo CHEN; Rui DING; Junjie ZHENG; Shibiao ZHANG
2009-01-01
A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete (PC) box-girder bridge. The change of hydration heat temperature consists of four periods: temperature rising period, constant temperature period, rapid temperature fall period and stow temperature fall period. The peak value of hydration heat temperature increases with the increasing casting temperature of concrete; the relation between them is approximately linear. According to field tests, the thermal stress incurred by hydration heat may induce temperature cracks on the PC box-girder. Furthermore, the nonlinear distribution of temperature gradient and the fluctuation of thermal stress induced by exposure to sunlight were also obtained based on continuous in-situ monitoring. Such results show that the prevailing Chinese Code (2004) is insufficient since it does not take into account the temperature gradient of the bottom slab. Finally, some preventive measures against temperature cracks were proposed based on related studies. The conclusions can provide valuable reference for the design and construction of PC box-girder bridges.
STRENGTH CRITERION FOR PLAIN CONCRETE UNDER MULTIAXIAL STRESS BASED ON DAMAGE POISSON'S RATIO
Institute of Scientific and Technical Information of China (English)
Ding Faxing; Yu Zhiwu
2006-01-01
A new unified strength criterion in the principal stress space has been proposed for use with normal strength concrete (NC) and high strength concrete (HSC) in compressioncompression-tension, compression-tension-tension, triaxial tension, and biaxial stress states. The study covers concrete with strengths ranging from 20 to 130 Mpa. The conception of damage Poisson's ratio is defined and the expression for damage Poisson's ratio is determined basically.The failure mechanism of concrete is illustrated, which points out that damage Poisson's ratio is the key to determining the failure of concrete. Furthermore, for the concrete under biaxial stress conditions, the unified strength criterion is simplified and a simplified strength criterion in the form of curves is also proposed. The strength criterion is physically meaningful and easy to calculate, which can be applied to analytic solution and numerical solution of concrete structures.
RESEARCH OF THE STRESS STATE OF A MODIFIED IN-SITU CONCRETE
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D. V. Rudenko
2016-12-01
Full Text Available Purpose. The article focuses on investigation of the stress state of a modified in-situ concrete of natural hardening. Methodology. To achieve the aim, the research of the microstructure of the modified cement matrix of concrete, as well as the mechanism of structure formation of modified concrete with natural hardening was conducted; the methods for reliable evaluation of concrete strength were defined. Findings. The development of internal stresses affects the properties of concretedifferently. With an increase in temperature-shrinkage deformations in time and, thus, with increasing structural stresses in the cement sheath around the grains of the filler two opposite processes may develop: zone of plastic flow or cracking. Originality. It was established that the structural features complex of the modified concrete when the load transfer leads to the formation of extensive zones of prefracture which is able to absorb a significant amount of elastic strain energy that provides the design deformation properties of the concrete for special purposes. Ideas about the definition of the criteria of cracking modified concrete, hardening under natural conditions had further development. Practical value. The resulting equations allow to solve the problem about the minimum level of structural stress in monolithic concrete in a saturated large placeholder, as well as to assess the influence of structural stresses on the properties of concrete. In normal concrete with a relatively thin cement sheath at temperature-shrinkage deformations, high tangential and low radial tension occur. In vivo, this stress is higher as a result of higher values of Δε(τ, which is not observed in the modified concrete. In the modified concretes only tangential stresses are the greatest danger to structures. The change of shrinkage stress with time is straightforward. The total temperature-shrinkage deformations have a sawtooth graph. For modified concrete the amplitude is 48
Directory of Open Access Journals (Sweden)
A. E. P. G. De Avila Jacintho
Full Text Available The bond stress between steel and concrete is the essential condition to the good behaviour of reinforced concrete structures. To preview the use of concrete with waste incorporation for structural aims, the verification of its quality control is necessary, whether of compression strength and bond. This paper presents the study results about the viability use of APULOT tests, that is a bond tests, to prevent the compression strength of concrete with rubber addition. The purpose of APULOT tests become study in many laboratories in France and Brazil, where is to estimate the compression strength using the bond stress obtained in tests execute inside of building construction. Also the use of concrete with rubber addition to structural use has been made with safe because this kind of addition makes the concrete compression strength decrease. To study its compression strength behavior is also make part of this research. This work aims to contribute with standardization of APULOT tests, and also give conditions to use the concrete with rubber addition in structural elements with more safe.
Early age stress-crack opening relationships for high performance concrete
DEFF Research Database (Denmark)
Østergaard, Lennart; Lange, David A.; Stang, Henrik
2004-01-01
Stress–crack opening relationships for concrete in early age have been determined for two high performance concrete mixes with water to cementitious materials ratios of 0.307 and 0.48. The wedge splitting test setup was used experimentally and the cracked nonlinear hinge model based on the fictit...
Directory of Open Access Journals (Sweden)
Husain M. Husain
2013-05-01
Full Text Available In this work a program is developed to carry out the nonlinear analysis (material nonlinearity of prestressed concrete beams using tendons of carbon fiber reinforced polymer (CFRP instead of steel. The properties of this material include high strength, light weight, and insusceptibility to corrosion and magnetism. This material is still under investigation, therefore it needs continuous work to make it beneficial in concrete design. Four beams which are tested experimentally by Yan et al. are examined by the developed computer program to reach a certain analytical approach of the design and analysis of such beams because there is no available restrictions or recommendations covering this material in the codes. The program uses the finite element analysis by dividing the beams into isoparametric 20-noded brick elements. The results obtained are good in comparison with experimental results.
Abd El Baky, Hussien
--slip relation is developed considering the interaction between the interfacial normal and shear stress components along the bonded length. A new approach is proposed to describe the entire tau-s relationship based on three separate models. The first model captures the shear response of an orthotropic FRP laminate. The second model simulates the shear characteristics of an adhesive layer, while the third model represents the shear nonlinearity of a thin layer inside the concrete, referred to as the interfacial layer. The proposed bond--slip model reflects the geometrical and material characteristics of the FRP, concrete, and adhesive layers. Two-dimensional and three-dimensional nonlinear displacement-controlled finite element (FE) models are then developed to investigate the flexural and FRP/concrete interfacial responses of FRP-strengthened reinforced concrete beams. The three-dimensional finite element model is created to accommodate cases of beams having FRP anchorage systems. Discrete interface elements are proposed and used to simulate the FRP/concrete interfacial behaviour before and after cracking. The FE models are capable of simulating the various failure modes, including debonding of the FRP either at the plate end or at intermediate cracks. Particular attention is focused on the effect of crack initiation and propagation on the interfacial behaviour. This study leads to an accurate and refined interpretation of the plate-end and intermediate crack debonding failure mechanisms for FRP-strengthened beams with and without FRP anchorage systems. Finally, the FE models are used to conduct a parametric study to generalize the findings of the FE analysis. The variables under investigation include two material characteristics; namely, the concrete compressive strength and axial stiffness of the FRP laminates as well as three geometric properties; namely, the steel reinforcement ratio, the beam span length and the beam depth. The parametric study is followed by a statistical
How simple can nonlinear finite element modelling be for structural concrete?
Directory of Open Access Journals (Sweden)
Argirova, G.
2014-12-01
Full Text Available This paper discusses on the required level of simplicity for suitable modelling of structural concrete. Traditional equilibrium- based approaches (as strut-and-tie models are too coarse in some cases, as they account for the cracking state of concrete in a sometimes excessively simplified manner. The alternative of complex nonlinear numerical modelling is also not always satisfactory for design as the number of parameters required, their definition and the sensitivity of the structural response to them is complex and requires a high level of experience. Contrary to these approaches, this paper introduces the elastic plastic stress field method. This method is grounded on the theory of plasticity but allows considering deformation compatibility. The results are consistent both in terms of the strength and deformation field of the member. It also has the advantage of requiring only two physical material properties (modulus of elasticity and plastic strength which can be easily determined by designers.Este artículo discute sobre el nivel de sencillez ideal para un análisis no lineal de elementos de hormigón estructural. Los métodos de cálculo basados únicamente en condiciones de equilibrio (como los modelos de bielas-y-tirantes no son siempre adecuados ya que el estado de fisuración del hormigón se considera a veces de una manera excesivamente simplificada. Los análisis no lineales complejos tampoco son siempre adecuados, ya que el número de parámetros requeridos, su definición y la sensibilidad de la respuesta del elemento a sus variaciones requieren una gran experiencia. Como alternativa, se presenta el método de los campos de tensiones elasto-plásticos. Este método se basa en la teoría de la plasticidad pero incorporando condiciones de compatibilidad. Los resultados son coherentes en términos de resistencia y de deformaciones. Además, sólo necesita la definición de dos parámetros mecánicos (módulo de elasticidad y
2010-05-21
... International Trade Administration Pre-Stressed Concrete Steel Wire Strand from the People's Republic of China... countervailable subsidies are being provided to producers and exporters of pre-stressed concrete steel wire strand... Determination on October 27, 2009. See Pre-Stressed Concrete Steel Wire Strand from the People's Republic...
2015-01-01
Concrete is a component of coherent transition between a concrete base and a wooden construction. The structure is based on a quantity of investigations of the design possibilities that arise when combining digital fabrication tools and material capacities.Through tangible experiments the project discusses materiality and digitally controlled fabrications tools as direct expansions of the architect’s digital drawing and workflow. The project sees this expansion as an opportunity to connect th...
Numerical Study on Nonlinear Semiactive Control of Steel-Concrete Hybrid Structures Using MR Dampers
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Long-He Xu
2013-01-01
Full Text Available Controlling the damage process, avoiding the global collapse, and increasing the seismic safety of the super high-rise building structures are of great significance to the casualties’ reduction and seismic losses mitigation. In this paper, a semiactive control platform based on magnetorheological (MR dampers comprising the Bouc-Wen model, the semi-active control law, and the shear wall damage criteria and steel damage material model is developed in LS-DYNA program, based on the data transferring between the main program and the control platform; it can realize the purpose of integrated modeling, analysis, and design of the nonlinear semi-active control system. The nonlinear seismic control effectiveness is verified by the numerical example of a 15-story steel-concrete hybrid structure; the results indicate that the control platform and the numerical method are stable and fast, the relative displacement, shear force, and damage of the steel-concrete structure are largely reduced using the optimal designed MR dampers, and the deformations and shear forces of the concrete tube and frame are better consorted by the control devices.
Energy Technology Data Exchange (ETDEWEB)
Chachoua, A
1999-07-01
The cyclic behaviour of reinforced concrete structures under high-level solicitations is of prime importance for the para-seismic studies and dimensioning of nuclear facility buildings. The main characteristics of concrete materials are: the non-linear relationship between stresses and deformations, and the development of cracks leading to a loss of tightness and to the occurrence of plastic or residual deformations. The aim of this study is to find the most suitable method for the modeling of the behaviour of concrete under aleatory loading, and the modeling of the seismic excitation source using models based on pulse signals and white noise. (J.S.)
Karimi, Mohammad M.; Tabatabaee, Nader; Jahanbakhsh, H.; Jahangiri, Behnam
2016-11-01
Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery's nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.
Karimi, Mohammad M.; Tabatabaee, Nader; Jahanbakhsh, H.; Jahangiri, Behnam
2017-08-01
Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery's nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.
Research on temperature field and temperature stress of prestressed concrete girders
Directory of Open Access Journals (Sweden)
Chen Cheng
2011-02-01
Full Text Available This paper introduces the establishment and simplification of the temperature field and the general calculation method of temperature stress of the prestressed concrete box girders. Three kinds of sunshine temperature gradient models were loaded to a real bridge respectively, and got stress and displacement curves. Research data of several prestressed concrete box girders were selected from different regions of China to compare the relative error of the calculated and measured value. We indicate that the study of temperature field and thermal stress of prestressed concrete box girders is necessary, and will help engineers to solve the problem in structure design.
Reliability Index for Reinforced Concrete Frames using Nonlinear Pushover and Dynamic Analysis
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Ahmad A. Fallah
2009-12-01
Full Text Available In the conventional design and analysis methods affecting parameters loads, materials' strength, etc are not set as probable variables. Safety factors in the current Codes and Standards are usually obtained on the basis of judgment and experience, which may be improper or uneconomical. In technical literature, a method based on nonlinear static analysis is suggested to set Reliability Index on strength of structural systems. In this paper, a method based on Nonlinear Dynamic analysis with rising acceleration (or Incremental Dynamic Analysis is introduced, the results of which are compared with those of the previous (Static Pushover Analysis method and two concepts namely Redundancy Strength and Redundancy Variations are proposed as an index to these impacts. The Redundancy Variation Factor and Redundancy Strength Factor indices for reinforced concrete frames with varying number of bays and stories and different ductility potentials are computed and ultimately, Reliability Index is determined using these two indices.
Meng, Yi; Yi, Weijian
2011-06-01
Polyvinylidene fluoride (PVDF) piezoelectric material has been successfully applied in many engineering fields and scientific research. However, it has rarely been used for direct measurement of concrete stresses under impact loading. In this paper, a new PVDF-based stress gauge was developed to measure concrete stresses under impact loading. Calibrated on a split Hopkinson pressure bar (SHPB) with a simple measurement circuit of resistance strain gauges, the PVDF gauge was then used to establish dynamic stress-strain curves of concrete cylinders from a series of axial impact testing on a drop-hammer test facility. Test results show that the stress curves measured by the PVDF-based stress gauges are more stable and cleaner than that of the stress curves calculated with the impact force measured from a load cell.
2010-07-07
... International Trade Administration Pre-Stressed Concrete Steel Wire Strand from the People's Republic of China... concrete steel wire strand (PC strand) from the People's Republic of China (PRC). On June 22, 2010, the ITC...-Stressed Concrete Steel Wire Strand from the People's Republic of China, USITC Pub. 4162, Inv. Nos....
Nonlinear Analysis of External Prestressed Reinforced Concrete Beams with BFRP and CFRP
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Haleem K. Hussain
2017-05-01
Full Text Available The traditional strengthening methods for concrete structure (girders, beams, columns…. consuming time and could be an economical, a new modern repair methods using the Carbon Fiber Reinforced Polymers (CFRP and Basalt Fiber Reinforced Polymer (BFRP as a laminate strips or bars,and considered a competitive solution that will increase the life-cycle of repaired structures. This study investigated the strengthen reinforced concrete girder. Nonlinear analysis have been adopted to the models using FEM analysis (ANSYS to simulate the theoretical results compared with experimental results.Using finite element packages, more efficient and better analyses can be made to fully understand the response of individual structural components and their contribution to a structure as a whole.Three type of material are used in this study as an external prestressed wire (steel, CFRP and BFRP. The prestressed beam is modeled as simply supported beam with two concentrated point load. The results showed that all tested strengthening beam increased the load carryingcapacity of the beams depend on prestressing force. Obtained Result was compared for different type of beam.This study also was enlarged to include using CFRP and BFRPbarwhich are light weight and moredurable, lead to ease of handling and maintenance. The research conducted analytical work to evaluate the effectiveness of concrete beams reinforced normally by the use of CFRP and BFRP bars. The results showed a significant gain in the beam’s ultimate capacities using CFRP bars comparing with beam reinforced with BFRP bar and reference beam
3-D Temperature and Stress Simulations of Hardening Concrete
DEFF Research Database (Denmark)
Jensen, Poul; Buhr, Birit; Thorborg, Jesper
2003-01-01
When concrete is cast, heat develops. When the concrete cools down there is a risk that thermal gradients induce cracks in the structure. In the Middle East this is especially important as extensive heat builds up due to the high ambient temperatures. Possible formed cracks will have a detrimenta...
3-D Temperature and Stress Simulations of Hardening Concrete
DEFF Research Database (Denmark)
Jensen, Poul; Buhr, Birit; Thorborg, Jesper
2003-01-01
When concrete is cast, heat develops. When the concrete cools down there is a risk that thermal gradients induce cracks in the structure. In the Middle East this is especially important as extensive heat builds up due to the high ambient temperatures. Possible formed cracks will have a detrimenta...
Experimental Study on Common and Steel Fiber Reinforced Concrete Under Dynamic Tensile Stress
Institute of Scientific and Technical Information of China (English)
董新龙; 陈江瑛; 高培正; 祁振林; 王永忠; 王永刚; 王礼立
2004-01-01
Split Hopkinson technique has been developed to test the strength of common concrete and steel fiber reinforced concrete under dynamic tensile stress. Two types of test methods are considered, the splitting tensile test and a modified spalling test in which a specimen is loaded under uniaxial stress. The result shows that the dynamic strength enhancement of concrete is remarkable by using the reinforcing fiber. But for the common concrete, the base of compressive strength seems to show little effect on the tensile strength under dynamic loading. The experimental results also show that the resistance to tensile fracture of the steel fiber reinforced concrete for C100-mix is higher than those of C40-mix.
Study of the stress-strain state of compressed concrete elements with composite reinforcement
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Bondarenko Yurii
2017-01-01
Full Text Available The efficiency analysis of the application of glass composite reinforcement in compressed concrete elements as a load-carrying component has been performed. The results of experimental studies of the deformation-strength characteristics of this reinforcement on compression and compressed concrete cylinders reinforced by this reinforcement are presented. The results of tests and mechanisms of sample destruction have been analyzed. The numerical analysis of the stress-strain state has been performed for axial compression of concrete elements with glasscomposite reinforcement. The influence of the reinforcement percentage on the stressed state of a concrete compressed element with the noted reinforcement is estimated. On the basis of the obtained results, it is established that the glass-composite reinforcement has positive effect on the strength of the compressed concrete elements. That is, when calculating the load-bearing capacity of such structures, the function of composite reinforcement on compression should not be neglected.
Narayanan, Arun; Subramaniam, Kolluru V. L.
2016-09-01
The influence of stress and induced damage in concrete on the electro-mechanical (EM) impedance response of bonded PZT patches is evaluated for applied compressive loading. Full field displacements obtained from digital image correlation are used to evaluate the level of stress-induced damage in concrete. Stress in the substrate produces an imposed strain on the PZT. A change in the imposed strain produces a rightward frequency shift and an increase in the amplitude of the resonant peak in the EM conductance spectrum of the PZT. An increase in the substrate compliance produces a decrease in the resonant frequency and an increase in the amplitude of the resonant peak. Changes in the resonant peak in the conductance spectrum induced by increasing substrate stress are of a significant magnitude when compared with the changes induced by damage. In the early stages of damage associated with distributed microcracking, the counteracting influences of increasing level of damage and increasing stress on the resonant peak result in no shift in frequency for measurements under applied load. There is however an increase in the amplitude of the resonance peak. When the applied stress is removed, there is a net decrease in frequency resulting from damage in the form of distributed microcracks. Measures of changes in the resonant peak based on root mean square deviation (RMSD), do not show any observable change when measurements are performed under applied loading. There is a consistent increase in RMSD values and frequency shift with increasing damage when the applied stress is removed. The centroidal measure of the normalized frequency spectrum reflects changes in substrate stress. At higher applied stress levels, there is a nonlinear increase in damage, leading to localization and cracking. The influence of damage is dominant in this region and significant changes are obtained in the RMSD values in both loaded and unloaded conditions.
Králik, Juraj
2011-01-01
This paper describes the reliability analysis of a concrete containment for VVER 440 under a high internal overpressure. The probabilistic safety assessment (PSA) level 3 aims at an assessment of the probability of the concrete structure failure under the excessive overpressure. The non-linear analysis of the concrete structures was considered. The uncertainties of the loads level (long-time temperature and dead loads), the material model (concrete cracking and crushing, behavior of the reinf...
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Hokeš Filip
2015-12-01
Full Text Available The subject of this paper is to describe some of the aspects manifesting in the use of the elastoplastic material model library multiPlas, which was developed to support non-linear computations in the ANSYS system. The text focuses on the analysis of numerical simulations of a virtual tension test in several case studies, thereby the text endeavours to describe the problems connected with modelling non-linear behaviour of concrete in a tensile area.
Directory of Open Access Journals (Sweden)
Králik Juraj
2016-12-01
Full Text Available This paper describes the nonlinear analysis of the reinforced concrete hermetic containment under an accidental temperature. The scenario of the hard accident in NPP and the methodology of the calculation of the failure temperature using the safety assessment are presented. The experimental and project material properties are taken into account in the safety assessment.
Damage in Concrete and its Detection by Use of Stress-Volumetric Strain Diagram
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Jerga Ján
2014-05-01
Full Text Available The reliable determination of the damage degree of concrete in the structure is difficult and not seldom short-term compressive strengths are considered as real strengths of concrete. Because the load history of the construction is generally unknown, we do not know, whether there have been reached values in the vicinity of the peak of the stress-strain diagram. The strength at the sustained or repeated loading would be then significantly lower, as obtained from tests performed on intact samples. The diagnostic of concrete damage is impeded by environmental effects, resulting in the anisotropy of the development of micro cracks. The possibility is pointed out to use the characteristics of the stress volumetric strain diagram for the assessment of the condition of the material, with the perspective of the application for the determination of the residual long-term strength of concrete
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F.M. Almeida Filho
Full Text Available The present study evaluates the bond behavior between steel bars and concrete by means of a numerical analysis based on Finite Element Method. Results of a previously conducted experimental program on reinforced concrete beams subjected to monotonic loading are also presented. Two concrete types, self-compacting concrete and ordinary concrete, were considered in the study. Non-linear constitutive relations were used to represent concrete and steel in the proposed numerical model, aiming to reproduce the bond behavior observed in the tests. Experimental analysis showed similar results for the bond resistances of self-compacting and ordinary concrete, with self-compacting concrete presenting a better performance in some cases. The results given by the numerical modeling showed a good agreement with the tests for both types of concrete, especially in the pre-peak branch of the load vs. slip and load vs. displacement curves. As a consequence, the proposed numerical model could be used to estimate a reliable development length, allowing a possible reduction of the structure costs.
On the Determination of Concrete Armour Unit Stress including Specific Results related to Dolosse
DEFF Research Database (Denmark)
Burcharth, H. F.; Howell, G.L.; Liu, Z.
1991-01-01
Failures of rubble mound breakwaters armoured with complex types of unreinforced concrete armour units are often due to breakage. This happens when the stresses exceed the material strength. Sufficient parametric studies of the stresses are not yet available to produce design diagrams for structu......Failures of rubble mound breakwaters armoured with complex types of unreinforced concrete armour units are often due to breakage. This happens when the stresses exceed the material strength. Sufficient parametric studies of the stresses are not yet available to produce design diagrams...... for structural integrity. The paper presents a general discussion of the problems related to stress etermination and describes the results and the analyses of model tests with 200 kg and 200 g load-cell instrumented Dolosse. Static stresses, wave-generate stresses due to impacts were studied as well as model...
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Muhammet Karaton
2014-01-01
Full Text Available A beam-column element based on the Euler-Bernoulli beam theory is researched for nonlinear dynamic analysis of reinforced concrete (RC structural element. Stiffness matrix of this element is obtained by using rigidity method. A solution technique that included nonlinear dynamic substructure procedure is developed for dynamic analyses of RC frames. A predicted-corrected form of the Bossak-α method is applied for dynamic integration scheme. A comparison of experimental data of a RC column element with numerical results, obtained from proposed solution technique, is studied for verification the numerical solutions. Furthermore, nonlinear cyclic analysis results of a portal reinforced concrete frame are achieved for comparing the proposed solution technique with Fibre element, based on flexibility method. However, seismic damage analyses of an 8-story RC frame structure with soft-story are investigated for cases of lumped/distributed mass and load. Damage region, propagation, and intensities according to both approaches are researched.
Karaton, Muhammet
2014-01-01
A beam-column element based on the Euler-Bernoulli beam theory is researched for nonlinear dynamic analysis of reinforced concrete (RC) structural element. Stiffness matrix of this element is obtained by using rigidity method. A solution technique that included nonlinear dynamic substructure procedure is developed for dynamic analyses of RC frames. A predicted-corrected form of the Bossak-α method is applied for dynamic integration scheme. A comparison of experimental data of a RC column element with numerical results, obtained from proposed solution technique, is studied for verification the numerical solutions. Furthermore, nonlinear cyclic analysis results of a portal reinforced concrete frame are achieved for comparing the proposed solution technique with Fibre element, based on flexibility method. However, seismic damage analyses of an 8-story RC frame structure with soft-story are investigated for cases of lumped/distributed mass and load. Damage region, propagation, and intensities according to both approaches are researched.
Analysis of Load Stress for Asphalt Pavement of Lean Concrete Base
Lijun, Suo; Xinwu, Wang
The study revealed that whether it is early distresses in asphalt pavement or not depends largely on working performance of base. In the field of asphalt pavement, it is widely accepted that lean concrete base, compared with the general semi-rigid base, has better working performance, such as high strength and good eroding resistance. Problem of early distresses in asphalt pavement, which caused by more traffic loadings, can be settled effectively when lean concrete is used in asphalt pavement. Traffic loading is important parameter used in the analysis of the new pavement design. However, few studies have done extensive and intensive research on the load stress for asphalt pavement of lean concrete base. Because of that, it is necessary to study the load stress for the asphalt pavement. In the paper, first of all, three-dimension finite element model of the asphalt pavement is created for the aim of doing mechanical analysis for the asphalt pavement. And then, the two main objectives of this study are investigated. One is analysis for load stress of lean concrete base, and the other is analysis for load stress of asphalt surface. The results show that load stress of lean concrete base decreases, decrease and increase with increase of base's thickness, surface's thickness and ratio of base's modulus to foundation's modulus respectively. So far as the asphalt surface is concerned, maximum shearing stress, which is caused by load, is evident in asphalt surface which is located in transverse contraction joint of lean concrete base of asphalt pavement. Maximum shearing stress decrease, decrease, decrease and increase respectively with increase of the surface's modulus, the surface's thickness, base's thickness and ratio of base's modulus to foundation's modulus.
Mäkelä, J T A; Korhonen, R K
2016-06-14
Modern fibril-reinforced computational models of articular cartilage can include inhomogeneous tissue composition and structure, and nonlinear mechanical behavior of collagen, proteoglycans and fluid. These models can capture well experimental single step creep and stress-relaxation tests or measurements under small strains in unconfined and confined compression. Yet, it is known that in indentation, especially at high strain velocities, cartilage can express highly nonlinear response. Different fibril reinforced poroelastic and poroviscoelastic models were used to assess measured highly nonlinear stress-relaxation response of rabbit articular cartilage in indentation. Experimentally measured depth-dependent volume fractions of different tissue constituents and their mechanical nonlinearities were taken into account in the models. In particular, the collagen fibril network was modeled using eight separate models that implemented five different constitutive equations to describe the nonlinearity. These consisted of linear elastic, nonlinear viscoelastic and multiple nonlinear elastic representations. The model incorporating the most nonlinearly increasing Young׳s modulus of collagen fibrils as a function of strain captured best the experimental data. Relative difference between the model and experiment was ~3%. Surprisingly, the difference in the peak forces between the experiment and the model with viscoelastic collagen fibrils was almost 20%. Implementation of the measured volume fractions did not improve the ability of the model to capture the measured mechanical data. These results suggest that a highly nonlinear formulation for collagen fibrils is needed to replicate multi-step stress-relaxation response of rabbit articular cartilage in indentation with high strain rates.
An Embedded Stress Sensor for Concrete SHM Based on Amorphous Ferromagnetic Microwires
Jesús Olivera; Margarita González; José Vicente Fuente; Rastislav Varga; Arkady Zhukov; José Javier Anaya
2014-01-01
A new smart concrete aggregate design as a candidate for applications in structural health monitoring (SHM) of critical elements in civil infrastructure is proposed. The cement-based stress/strain sensor was developed by utilizing the stress/strain sensing properties of a magnetic microwire embedded in cement-based composite (MMCC). This is a contact-less type sensor that measures variations of magnetic properties resulting from stress variations. Sensors made of these materials can be design...
Estimation of in-situ stresses in concrete members using polarized ultrasonic shear waves
Chen, Andrew; Schumacher, Thomas
2014-02-01
Ultrasonic testing is commonly used to detect flaws, estimate geometries, and characterize properties of materials and structures. Acoustoelasticity refers to the dependency of stress wave velocity with applied stresses and is a phenomenon that has been known by geophysicists since the 1960s. A way to capitalize on this effect for concrete applications is by using ultrasonic shear waves which are particularly sensitive to applied stresses when polarized in the direction of the applied stress. The authors conducted an experiment on a 150 mm (6 in.) diameter concrete cylinder specimen with a length of 305 mm (12 in.) that was loaded in discrete load steps to failure. At each load step two ultrasonic shear waves were transmitted through the specimen, one with the polarization perpendicular and the other transverse to the applied stress. The velocity difference between the two sets of polarized shear waves was found to correlate with the applied stress in the specimen. Two potential applications for this methodology include estimation of stresses in pre-stressed concrete bridge girders and investigation of load redistribution in structural support elements after extreme events. This paper introduces the background of the methodology, presents an analysis of the collected data, and discusses the relationship between the recorded signals and the applied stress.
Li, Mengxing; Anderson, Neil; Sneed, Lesley; Torgashov, Evgeniy
2016-12-01
Two stress-wave based techniques, ultrasonic surface wave (USW) and impact echo (IE), as well as ground penetrating radar (GPR) were used to assess the condition of a segment of concrete pavement that includes a layer of concrete, a granular base and their interface. Core specimens retrieved at multiple locations were used to confirm the accuracy and reliability of each non-destructive testing (NDT) result. Results from this study demonstrate that the GPR method is accurate for estimating the pavement thickness and locating separations (air voids) between the concrete and granular base layers. The USW method is a rapid way to estimate the in-situ elastic modulus (dynamic elastic modulus) of the concrete, however, the existence of air voids at the interface could potentially affect the accuracy and reliability of the USW test results. The estimation of the dynamic modulus and the P-wave velocity of concrete was improved when a shorter wavelength range (3 in. to 8.5 in.) corresponding to the concrete layer thickness was applied instead of the full wavelength rage (3 in. to 11 in.) based on the standard spacing of the receiver transducers. The IE method is proved to be fairly accurate in estimating the thickness of concrete pavements. However, the flexural mode vibration could affect the accuracy and reliability of the test results. Furthermore, the existence of air voids between the concrete and granular base layers could affect the estimation of the compression wave velocity of concrete when the full wavelength range was applied (3 in. to 11 in.). Future work is needed in order to improve the accuracy and reliability of both USW and IE test results.
Impact of rockfill deformation on stress-strain state on dam reinforced concrete face
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Sainov Mikhail Petrovich
2015-03-01
Full Text Available The author considered the results of the numerical studies of stress-strain state of a 100 m high rockfill dam with a reinforced concrete face. In the analysis, the dam construction sequence and loads applied to it were considered; it was assumed that the reinforced concrete face was constructed after filling the dam. The calculations were carried out in the elastic formulation at various moduli of deformation and Poisson’s ratio. It was revealed that at rockfill settlement under the action of hydrostatic pressure the reinforced concrete face not only bends but also is subject to longitudinal force. The development of these forces is connected not only with rockfill shear deformation in horizontal direction. Depending on the value of rockfill Poisson’s ratio these longitudinal forces may be both compressive and tensile. At the Poisson’s ratio exceeding 0.25 the longitudinal forces are tensile, and when it is equal to 0.2 - they are compressive. Evidently these particular longitudinal forces are the course of crack formation in reinforced concrete faces of a number of constructed dams. The indirect confirmation of the development of tensile forces on the face is the fact that actually in all the dams with reinforced concrete face opening of perimeter joint was observed. Thus, in order to provide the strength of reinforced concrete it is important to increase rockfill shear modulus. Only the decrease of stone compressibility (i.e. increase of linear deformation modulus E will slightly improve the stress state of the face, as the value of E has less effect on settlements and shear of the dam than Poisson’s ratio. High rockfill dams with reinforced concrete face may have a favorable stress state only at narrow site when the face horizontal displacements are inconsiderable and due to the settlements of rockfill in the face the forces are compressive but not tensile longitudinal forces.
NONLINEAR FINITE ELEMENT ANALYSIS OF REINFORCED CONCRETE BEAMS IN FIRE%火灾下钢筋混凝土梁非线性有限元分析
Institute of Scientific and Technical Information of China (English)
廖艳芬; 漆雅庆; 马晓茜
2011-01-01
Through numerical simulation of the whole process of heat transfer and deformation on three different conditions groups of reinfored concrete beams,it is analysed the non-linear changing process of the temperature distribution and structural deformation of reinfored concrete beams in fire.Based on thermal characteristics and the temperature-strain-stress constitutive characteristics of reinforced concrete beams it is analysied the influences of the evolutionary processes of the reinfored concrete beams temperature distribution in fire,as well as reinforcement ratio,initial load and heating time on the fire resistance capacity of reinfored concrete beams.Results show that the overall instability of the beams is caused by the reduction of material strength,weight and the initial load,as well as the internal stress because of the uneven heating in fire.The influences of initial load on the residual bearing capacity is little,but increase the number of rebars can effectively improve the fire resistance capacity of reinforced concrete beams.%为分析钢筋混凝土梁在火灾过程中的温度分布、结构变形非线性变化过程,在三组不同条件下对火灾后钢筋混凝土梁构件内部传热及变形过程进行全过程仿真。基于钢筋混凝土热工特性、温度-应变-应力本构特性,分析钢筋混凝土梁在受火时的温度分布演化过程,以及配筋率、初始载荷和受火时间等参数对钢筋混凝土梁防火承载力的影响。结果表明：火灾中材料强度的降低,自重和初始载荷以及不均匀升温引起的内部应力共同作用引起了构件的整体失稳。初始载荷对梁剩余承载力的影响不大,提高混凝土中钢筋数量能有效地提高钢筋混凝土梁的防火承载力。
Estimation of Peak Wave Stresses in Slender Complex Concrete Armor Units
DEFF Research Database (Denmark)
Howell, G.L.; Burcharth, H. F.; Rhee, Joon R
1991-01-01
Recent methods for the structural design of concrete armor units divide the forces into static loads, impact loads, and wave or pulsating loads. Physical model technology is being developed at several laboratories to measure wave loads on model armor units. While this technology represents...... significant progress, structural designers require a maximum stress value to design armor units....
Diffuse ultrasound monitoring of stress and damage development on a 15-ton concrete beam.
Zhang, Yuxiang; Planès, Thomas; Larose, Eric; Obermann, Anne; Rospars, Claude; Moreau, Gautier
2016-04-01
This paper describes the use of an ultrasonic imaging technique (Locadiff) for the Non-Destructive Testing & Evaluation of a concrete structure. By combining coda wave interferometry and a sensitivity kernel for diffuse waves, Locadiff can monitor the elastic and structural properties of a heterogeneous material with a high sensitivity, and can map changes of these properties over time when a perturbation occurs in the bulk of the material. The applicability of the technique to life-size concrete structures is demonstrated through the monitoring of a 15-ton reinforced concrete beam subject to a four-point bending test causing cracking. The experimental results show that Locadiff achieved to (1) detect and locate the cracking zones in the core of the concrete beam at an early stage by mapping the changes in the concrete's micro-structure; (2) monitor the internal stress level in both temporal and spatial domains by mapping the variation in velocity caused by the acousto-elastic effect. The mechanical behavior of the concrete structure is also studied using conventional techniques such as acoustic emission, vibrating wire extensometers, and digital image correlation. The performances of the Locadiff technique in the detection of early stage cracking are assessed and discussed.
Nonlinear seismic response analysis of reinforced concrete tube in tube structure
Institute of Scientific and Technical Information of China (English)
WANG Hai-bo; SHEN Pu-sheng
2005-01-01
Super-highly reinforced concrete tube in tube structure is a developing structure system of high-rise building. The more reasonable derivation process of the multi-vertical-line-element model stiffness matrix is given.On the premise of pointing out the problems of present multi-spring element model, combined with present multivertical-line-element model for analyzing on shear wall, the model is expanded to spatial one, and the stiffness matrix of which is derived. Combined with hysteretic axial model and hysteretic shear model, it is suitable for columns,wall limbs and beams with all kinds of section form. Some examples are calculated and compared with test results,which shows that the models have relatively good accuracy. On the base of the experimental phenomenon and failure mechanism for tube in tube structure specimen, nonlinear seismic responses analysis program on the basis of the advantaged element model for tube in tube structure is developed. Calculation results are in good agreement with those of the pseudo-dynamic tests and the failure mechanism can be well reflected.
Stress and Sliding Stability Analysis of Songlin Rock-Filled Concrete Gravity Dam
Sundström, Max; Ivedal, Max
2016-01-01
The construction of Songlin rock-filled concrete gravity dam, located in the Yunnan province, China began in the end of 2015. In this master thesis the finite element method (FEM) based software Abaqus has been used to perform a computational analysis on tension stresses, compression stresses and sliding stability for static conditions. One overflow section and one non-overflow section of the dam have been analysed. The results of the analysis have been evaluated by comparing with Chinese sta...
Generalized non-linear strength theory and transformed stress space
Institute of Scientific and Technical Information of China (English)
YAO Yangping; LU Dechun; ZHOU Annan; ZOU Bo
2004-01-01
Based on the test data of frictional materials and previous research achievements in this field, a generalized non-linear strength theory (GNST) is proposed. It describes non-linear strength properties on the π-plane and the meridian plane using a unified formula, and it includes almost all the present non-linear strength theories, which can be used in just one material. The shape of failure function of the GNST is a smooth curve between the SMP criterion and the Mises criterion on the π-plane, and an exponential curve on the meridian plane. Through the transformed stress space based on the GNST, the combination of the GNST and various constitutive models using p and q as stress parameters can be realized simply and rationally in three-dimensional stress state.
Institute of Scientific and Technical Information of China (English)
YU Hongfa; SUN Wei; ZHANG Yunsheng; GUO Liping; LI Meidan
2008-01-01
Freeze-thaw durabilities of three types of concretes-normal portland cement concrete (OPC),high strength concrete (HSC) and steel fiber reinforced high strength concrete (SFRHSC)were systemically investigated under the attacks of chemical solution,and combination of external flexural stress and chemical solution.Four kinds of bitterns from salt lakes in Sinkiang,Qinghai,Inner Mongolia and Tibet provinces of China were used as chemical attack solutions.The relative dynamic modulus (RDM) was used as an index for evaluating the damage degree during the course of chemical attack and stress corrosion.The experimental results show that the freeze-thaw durability of concrete is visibly reduced in the present of the flexural stress,i e,stress accelerates the damage process.In order to quantify the stress accelerated effect,a stress accelerating coefficient was proposed.The stress accelerating coefficient is closely related with the types of bitterns and the numbers of freeze-thaw cycles is.The more numbers of freeze-thaw cycles is,the greater the stress accelerating coefficient for various concretes will be.In addition,there also exists a critical ratio of external stress to the maximum flexural stress.If the stress ratio exceeds the critical one,the freeze-thaw durability of various concretes will be greatly decreased compared to the responding concretes without applied stress.The critical stress ratio of OPC,HSC and SFRHSC is 0.30,0.40 and 0.40,respectively,indicating that HSC and SFRHSC have advantages over OPC and are suitable to use in the bittern erosion regions.
Façade Greening: High-rise apartment building in Milan using pre-stressed concrete slab
Sun, Wenning; Li, Mingxin; Han, Yinong; Wang, Moqi; Ansourian, Peter
2016-08-01
In this project, one single level of the Façade Greening was designed and modelled using finite element method in Strand7. A static analysis was performed in order to understand the deflection and the stress due to the extra loads imposed by the soil and plants. The results produced by the linear static solver are compared with the strength of the materials and the European limitations. The maximum tension stress which exceeds the tensile strength in concrete is found in the root of the cantilever balcony. An alternative design of the cantilevered balcony with pre-stressed concrete slab is modelled separately for the balcony. Decrease is found in the tension stress and the significant improvement of deflection of the balcony with pre-stressed concrete slab. The dynamic loads such as wind and earthquake did not suggest significant effect on the pre-stressed concrete slab.
Stress-enhanced Gelation: A Dynamic Nonlinearity of Elasticity
Yao, Norman Y.; Broedersz, Chase P.; Depken, Martin; Becker, Daniel J.; Pollak, Martin R.; MacKintosh, Frederick C.; Weitz, David A.
2013-01-01
A hallmark of biopolymer networks is their sensitivity to stress, reflected by pronounced nonlinear elastic stiffening. Here, we demonstrate a distinct dynamical nonlinearity in biopolymer networks consisting of F-actin cross-linked by α-actinin-4. Applied stress delays the onset of relaxation and flow, markedly enhancing gelation and extending the regime of solid-like behavior to much lower frequencies. We show that this macroscopic network response can be accounted for at the single molecule level by the increased binding affinity of the cross-linker under load, characteristic of catch-bond-like behavior. PMID:23383843
Stress-Strain Relationship and Failure Criterion for Concrete after Freezing and Thawing Cycles
Institute of Scientific and Technical Information of China (English)
Luo Xin; Wei Jun
2006-01-01
The research of the failure criterion and one-dimensional stress-strain relationship of deteriorated concrete were carried out.Based on the damage mechanics theory, the damage which reflects the alternation of internal state of material were introduced into the formula presented by Desayi and Krishman and the weighted twin-shear strength theory. As a nondestructive examination method in common use, the ultrasonic technique was adopted in the study, and the ultrasonic velocity was used to establish the damage variable. After that, the failure criterion and one-dimensional stress-strain relationship for deteriorated concrete were obtained.Eventually, tests were carried out to study the evolution laws on the damage. The results show that the more freezing and thawing cycles are, the more apparently the failure surface shrinks. Meanwhile, the comparison between theoretical data and experimental data verifies the rationality of the damage-based one-dimensional stress-strain relationship proposed.
An embedded stress sensor for concrete SHM based on amorphous ferromagnetic microwires.
Olivera, Jesús; González, Margarita; Fuente, José Vicente; Varga, Rastislav; Zhukov, Arkady; Anaya, José Javier
2014-10-24
A new smart concrete aggregate design as a candidate for applications in structural health monitoring (SHM) of critical elements in civil infrastructure is proposed. The cement-based stress/strain sensor was developed by utilizing the stress/strain sensing properties of a magnetic microwire embedded in cement-based composite (MMCC). This is a contact-less type sensor that measures variations of magnetic properties resulting from stress variations. Sensors made of these materials can be designed to satisfy the specific demand for an economic way to monitor concrete infrastructure health. For this purpose, we embedded a thin magnetic microwire in the core of a cement-based cylinder, which was inserted into the concrete specimen under study as an extra aggregate. The experimental results show that the embedded MMCC sensor is capable of measuring internal compressive stress around the range of 1-30 MPa. Two stress sensing properties of the embedded sensor under uniaxial compression were studied: the peak amplitude and peak position of magnetic switching field. The sensitivity values for the amplitude and position within the measured range were 5 mV/MPa and 2.5 µs/MPa, respectively.
An Embedded Stress Sensor for Concrete SHM Based on Amorphous Ferromagnetic Microwires
Directory of Open Access Journals (Sweden)
Jesús Olivera
2014-10-01
Full Text Available A new smart concrete aggregate design as a candidate for applications in structural health monitoring (SHM of critical elements in civil infrastructure is proposed. The cement-based stress/strain sensor was developed by utilizing the stress/strain sensing properties of a magnetic microwire embedded in cement-based composite (MMCC. This is a contact-less type sensor that measures variations of magnetic properties resulting from stress variations. Sensors made of these materials can be designed to satisfy the specific demand for an economic way to monitor concrete infrastructure health. For this purpose, we embedded a thin magnetic microwire in the core of a cement-based cylinder, which was inserted into the concrete specimen under study as an extra aggregate. The experimental results show that the embedded MMCC sensor is capable of measuring internal compressive stress around the range of 1–30 MPa. Two stress sensing properties of the embedded sensor under uniaxial compression were studied: the peak amplitude and peak position of magnetic switching field. The sensitivity values for the amplitude and position within the measured range were 5 mV/MPa and 2.5 µs/MPa, respectively.
Spline Nonparametric Regression Analysis of Stress-Strain Curve of Confined Concrete
Directory of Open Access Journals (Sweden)
Tavio Tavio
2008-01-01
Full Text Available Due to enormous uncertainties in confinement models associated with the maximum compressive strength and ductility of concrete confined by rectilinear ties, the implementation of spline nonparametric regression analysis is proposed herein as an alternative approach. The statistical evaluation is carried out based on 128 large-scale column specimens of either normal-or high-strength concrete tested under uniaxial compression. The main advantage of this kind of analysis is that it can be applied when the trend of relation between predictor and response variables are not obvious. The error in the analysis can, therefore, be minimized so that it does not depend on the assumption of a particular shape of the curve. This provides higher flexibility in the application. The results of the statistical analysis indicates that the stress-strain curves of confined concrete obtained from the spline nonparametric regression analysis proves to be in good agreement with the experimental curves available in literatures
Stress corrosion failure of large diameter pressure pipelines of prestressed concrete
Energy Technology Data Exchange (ETDEWEB)
Valiente, A. [Universidad Politecnico de Madrid (Spain). Dpto. de Ciencia de Materiales
2001-07-01
The failure of a 1.5 m diameter prestressed concrete line for water supply was examined. The water pressure opened a hole of 0.5 m{sup 2} in the pipe wall by breaking the concrete into fragments and by tensile severing of a number of coils of the wire winding. Flexural and tensile testing of samples of the broken materials showed no damage to the concrete, but showed significant losses of strength and ductility in the prestressing steel wire. The SEM analysis of the external and fracture surfaces of the circumferential wires revealed shallow cracking and corroded areas as expected from a stress corrosion cracking process. The failure analysis presented in this paper shows that such a process was able to exhaust the damage tolerance of the affected tube until the pipeline burst under the work pressures. (author)
Directory of Open Access Journals (Sweden)
Chepurnenko Anton Sergeevich
2016-12-01
Full Text Available The task of comprehensive analysis presented in this article is a development of theory of calculation of shrinkage stresses in cellular concrete wall panels; such stresses occur due to carbonation of concrete because of the creep of material. Analytical dependences characterizing the influence of carbonation on the modulus of elasticity, shrinkage and creep of autoclaved cellular concrete, as well as the regularity of variation of carbonation degree as per thickness of the wall panels depending on time, were obtained. The proposed theory of calculation of shrinkage stresses in cellular concrete wall panels, with account of concrete creep, makes it possible to predict the influence of carbonation processes on crack resistance thereof, and thus to develop measures of technological and structural nature, in order to improve their operational reliability and durability.
Wang, Yuhang; Nie, Jianguo; Fan, Jiansheng
2016-06-01
An experimental study on concrete filled steel tube columns with rectangular section subjected to compressionflexure-torsion combined action has been carried out. The failure modes and load-deformation hysteretic relations were obtained. Based on the principles of classical material mechanics, the relations between the torsion curvature of the section and the shear strain of the fiber on the section were established. Then the strain distribution on the rectangular section of concrete filled steel tube columns subjected to torsion was analyzed. The three-dimensional refined finite element model was also built, in order to make the precision verification. The matrix forms of the relation between the torsion curvature of the section and the shear strain of the fiber on the section were derived, and introduced into the fiber beam model considering nonlinear torsion effect on the section. The comparison between test results and calculation results showed that the fiber beam model considering nonlinear torsion effect had high modeling efficiency and solution precision for predicting the torsion behavior of concrete filled steel tube columns with rectangular sections, and was suitable for analyzing the dynamic response of various structures subjected to the combined cyclic load caused by the earthquake load.
Directory of Open Access Journals (Sweden)
AHMER ALI
2013-02-01
Full Text Available In recent years steel-concrete composite shear walls have been widely used in enormous high-rise buildings. Due to high strength and ductility, enhanced stiffness, stable cycle characteristics and large energy absorption, such walls can be adopted in the auxiliary building; surrounding the reactor containment structure of nuclear power plants to resist lateral forces induced by heavy winds and severe earthquakes. This paper demonstrates a set of nonlinear numerical studies on I-shaped composite steel-concrete shear walls of the nuclear power plants subjected to reverse cyclic loading. A three-dimensional finite element model is developed using ABAQUS by emphasizing on constitutive material modeling and element type to represent the real physical behavior of complex shear wall structures. The analysis escalates with parametric variation in steel thickness sandwiching the stipulated amount of concrete panels. Modeling details of structural components, contact conditions between steel and concrete, associated boundary conditions and constitutive relationships for the cyclic loading are explained. Later, the load versus displacement curves, peak load and ultimate strength values, hysteretic characteristics and deflection profiles are verified with experimental data. The convergence of the numerical outcomes has been discussed to conclude the remarks.
Monitoring of applied stress in concrete using ultrasonic full-waveform comparison techniques
Hafiz, Ali; Schumacher, Thomas
2017-04-01
Ultrasonic testing is a non-destructive approach commonly used to evaluate concrete structures. A challenge with concrete is that it is heterogeneous, which causes multiple wave scattering resulting in longer and more complex wave paths. The recorded ultrasonic waveform can be divided into two portions: the coherent (or early) and the diffuse (or Coda) portion. While conventional methods only use the coherent portion, e.g. the first wave arrival to determine the wave velocity, we are interested in the entire waveform, i.e. until the wave amplitude is completely dampened out. The objective of this study was to determine what portion of the signal is most sensitive to applied stress and the associated formation and propagation of cracks. For this purpose, the squared Pearson correlation coefficient, R2 was used, which provides a measure for the strength of the linear relationship (or similarity) between a reference waveform under no stress and a waveform recorded at a certain level of applied stress. Additionally, a signal energy-based filter was developed and used to detect signals that captured acoustic emissions generated during the loading process. The experimental work for this study consisted of an active monitoring approach by employing a pitch-catch setup with two ultrasonic transducers, one transmitter and one receiver, that were attached to (nullset) 152 x 305 mm concrete cylinder specimens, which were loaded monotonically to failure. Our results show that applied stress correlates well with the R2 with remarkable sensitivity to small applied stresses. Also, the relationship between R2 and applied stress is linear for an applied stress that is less than 50% of the ultimate stress.
Nonlinear Reynolds stress models and the renormalization group
Rubinstein, Robert; Barton, J. Michael
1990-01-01
The renormalization group is applied to derive a nonlinear algebraic Reynolds stress model of anisotropic turbulence in which the Reynolds stresses are quadratic functions of the mean velocity gradients. The model results from a perturbation expansion that is truncated systematically at second order with subsequent terms contributing no further information. The resulting turbulence model applied to both low and high Reynolds number flows without requiring wall functions or ad hoc modifications of the equations. All constants are derived from the renormalization group procedure; no adjustable constants arise. The model permits inequality of the Reynolds normal stresses, a necessary condition for calculating turbulence-driven secondary flows in noncircular ducts.
Wobble friction coefficient in post-stressed concrete
Directory of Open Access Journals (Sweden)
Diego Ernesto Dueñas Puentes
2010-04-01
Full Text Available This work was aimed at establishing a wobble friction coefficient (K from records regarding some post-stressed bridges built in Colombia. Such records were arranged and analysed together with stress diagrams resulting from the corres-ponding plans, calculations and reports. Suitable records were produced from this review to make the analysis. Once the records had been selected, the probable wobble friction coefficient (K was then calculated for each case and this coefficient was related to the length of the cable and the total area of the strands composing the cable. These records and their results were subsequently grouped according to the type of bridge to produce a wobble friction coefficient (K for each specific structure. The study indicated that the wobble friction coefficient was lower than that indicated by the Colombian Seismic Bridge Design Code, Instituto Nacional De Vías, 1995]. The influence of tensioning equipment, materials and labour suggested a format for recording tensioning to reduce inaccuracy when readings are being taken. A reduction in the costs of tensioning would arise from taking the forgoing into account.
Stress measurement in thick plates using nonlinear ultrasonics
Energy Technology Data Exchange (ETDEWEB)
Abbasi, Zeynab, E-mail: zabbas5@uic.edu, E-mail: dozevin@uic.edu; Ozevin, Didem, E-mail: zabbas5@uic.edu, E-mail: dozevin@uic.edu [University of Illinois at Chicago, Civil and Materials Engineering, 842 W Taylor Street ERF 2095, Chicago, IL 60607 (United States)
2015-03-31
In this paper the interaction between nonlinear ultrasonic characteristics and stress state of complex loaded thick steel plates using fundamental theory of nonlinear ultrasonics is investigated in order to measure the stress state at a given cross section. The measurement concept is based on phased array placement of ultrasonic transmitter-receiver to scan three angles of a given cross section using Rayleigh waves. The change in the ultrasonic data in thick steel plates is influenced by normal and shear stresses; therefore, three measurements are needed to solve the equations simultaneously. Different thickness plates are studied in order to understand the interaction of Rayleigh wave penetration depth and shear stress. The purpose is that as the thickness becomes smaller, the shear stress becomes negligible at the angled measurement. For thicker cross section, shear stress becomes influential if the depth of penetration of Rayleigh wave is greater than the half of the thickness. The influences of plate thickness and ultrasonic frequency on the identification of stress tensor are numerically studied in 3D structural geometry and Murnaghan material model. The experimental component of this study includes uniaxial loading of the plate while measuring ultrasonic wave at three directions (perpendicular, parallel and angled to the loading direction). Instead of rotating transmitter-receiver pair for each test, a device capable of measuring the three angles is designed.
Stress measurement in thick plates using nonlinear ultrasonics
Abbasi, Zeynab; Ozevin, Didem
2015-03-01
In this paper the interaction between nonlinear ultrasonic characteristics and stress state of complex loaded thick steel plates using fundamental theory of nonlinear ultrasonics is investigated in order to measure the stress state at a given cross section. The measurement concept is based on phased array placement of ultrasonic transmitter-receiver to scan three angles of a given cross section using Rayleigh waves. The change in the ultrasonic data in thick steel plates is influenced by normal and shear stresses; therefore, three measurements are needed to solve the equations simultaneously. Different thickness plates are studied in order to understand the interaction of Rayleigh wave penetration depth and shear stress. The purpose is that as the thickness becomes smaller, the shear stress becomes negligible at the angled measurement. For thicker cross section, shear stress becomes influential if the depth of penetration of Rayleigh wave is greater than the half of the thickness. The influences of plate thickness and ultrasonic frequency on the identification of stress tensor are numerically studied in 3D structural geometry and Murnaghan material model. The experimental component of this study includes uniaxial loading of the plate while measuring ultrasonic wave at three directions (perpendicular, parallel and angled to the loading direction). Instead of rotating transmitter-receiver pair for each test, a device capable of measuring the three angles is designed.
Directory of Open Access Journals (Sweden)
Fukada Saiji
2015-01-01
Full Text Available The prestressed concrete (PC stress ribbon footbridge is a type of suspension bridge without towers, which has been applied in Japan and all over the world for years in light of its low construction cost and aesthetic merit. It generally consists of the precast concrete slabs with embedded cables. However, the walking-induced lateral vibration trouble of the Millennium Bridge in London in 2000 gave a lesson to the engineers that the lateral vibration feature must be taken into consideration for the footbridge vibration evaluation. In this sense, the field investigations on the lateral vibration features of 14 pre-stressed concrete stress ribbon footbridge in Japan was carried out by artificial impact and damping free vibration tests. According to the investigations, the larger the bridge span, the lower the frequencies of lateral-related vibration modes. In addition, based on the damping-free vibration field tests, there was a tendency toward the damping constant degradation when bridge span became larger.
Institute of Scientific and Technical Information of China (English)
HUO Kaicheng; SHUI Zhonghe; LI Yue
2006-01-01
By using the uptodate temperatuer-stress testing machine, the thermal expansion coefficient of concrete at early ages was studied and indicative conclusions were achieved: temperature rising due to hydration heat is not directly correlated with cracking, but the temperature and stress evolution process should be taken into consideration in the same time. Proper chemical admixtures and mineral compositions can improve the mechanical properties of concrete such as thermal expansion coefficient, which is very indicative in practice.
Nonlinear/linear unified thermal stress formulations - Transfinite element approach
Tamma, Kumar K.; Railkar, Sudhir B.
1987-01-01
A new unified computational approach for applicability to nonlinear/linear thermal-structural problems is presented. Basic concepts of the approach including applicability to nonlinear and linear thermal structural mechanics are first described via general formulations. Therein, the approach is demonstrated for thermal stress and thermal-structural dynamic applications. The proposed transfinite element approach focuses on providing a viable hybrid computational methodology by combining the modeling versatility of contemporary finite element schemes in conjunction with transform techniques and the classical Bubnov-Galerkin schemes. Comparative samples of numerical test cases highlight the capabilities of the proposed concepts.
Directory of Open Access Journals (Sweden)
Song Bing
2016-01-01
Full Text Available Taking the mixing amount of diatomite calcined and vitrified micro bubbles(VMB as the main changing parameters, experiment studies the properties of the vitrified micro bubbles recycled concrete blocks; then this paper adopts the finite element software ANSYS to analyze the square double skin steel stub short columns filled with recycled concrete under axial compression. According to the vertical stress distribution, strain and bearing capacity of the steel tube and core concrete, we make a contrastive axial compression properties analysis on the different hollow ratio χ(0,0.35and the VMB content(0%,100%,130% of square double skin steel stub short columns filled with recycled concrete. The result shows that: Compressive strength of VMB recycled concrete increases with the increase of diatomite calcined content, when mixing amount of diatomite calcined is 3%,the compressive strength of 130% VMB content test specimen can reach 32.45 MPa;Because of the inner circular steel tube is setted which strengthening component buckling capacity and improving the ductility of the component, stress distribution of hollow components is more balance than solid components, and their axial displacements decrease by 5.6% compared with the solid components when they reach ultimate bearing capacity; When the hollow ratio is same, ultimate bearing capacity of 130% VMB content test specimen compared with the content is 0% only reduces by about 3.5%; When the VMB content is same, ultimate bearing capacity of hollow components compared with solid components increases by about 2.5%, which reducing weight as well as improving the anti-seismic performance.
Roseires Dam Heightening Project in Sudan Works of Pre-tensioned Pre-stressed Concrete Beams
Institute of Scientific and Technical Information of China (English)
黄志敏
2014-01-01
Works of pre-tensioned and pre-stressed concrete beams at dam crest of Roseires Dam Heightening Project located on Nile Riv-er in the Country of Sudan was in a big quantity, complexity and tight completion time. For pre-tensioning operation, frame type pedestal was built. Strict work method statement and applicable work procedure were also developed to assure high work quality and timely completion. All these have become precious experience in the field of pre-tensioning and pre-stressing beams.
Design of reinforced concrete walls casted in place for the maximum normal stress of compression
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T. C. Braguim
Full Text Available It is important to evaluate which designing models are safe and appropriate to structural analysis of buildings constructed in Concrete Wall system. In this work it is evaluated, through comparison of maximum normal stress of compression, a simple numerical model, which represents the walls with frame elements, with another much more robust and refined, which represents the walls with shells elements. The designing of the normal stress of compression it is done for both cases, based on NBR 16055, to conclude if the wall thickness initially adopted, it is enough or not.
Directory of Open Access Journals (Sweden)
Neela Deshpande
2014-12-01
Full Text Available In the recent past Artificial Neural Networks (ANN have emerged out as a promising technique for predicting compressive strength of concrete. In the present study back propagation was used to predict the 28 day compressive strength of recycled aggregate concrete (RAC along with two other data driven techniques namely Model Tree (MT and Non-linear Regression (NLR. Recycled aggregate is the current need of the hour owing to its environmental friendly aspect of re-use of the construction waste. The study observed that, prediction of 28 day compressive strength of RAC was done better by ANN than NLR and MT. The input parameters were cubic meter proportions of Cement, Natural fine aggregate, Natural coarse Aggregates, recycled aggregates, Admixture and Water (also called as raw data. The study also concluded that ANN performs better when non-dimensional parameters like Sand–Aggregate ratio, Water–total materials ratio, Aggregate–Cement ratio, Water–Cement ratio and Replacement ratio of natural aggregates by recycled aggregates, were used as additional input parameters. Study of each network developed using raw data and each non dimensional parameter facilitated in studying the impact of each parameter on the performance of the models developed using ANN, MT and NLR as well as performance of the ANN models developed with limited number of inputs. The results indicate that ANN learn from the examples and grasp the fundamental domain rules governing strength of concrete.
Zreiki, Jihad; Chaouche, Mohend; Moranville, Micheline
2008-01-01
Early age behaviour of concrete is based on complex multi-physical and multiscale phenomena. The predication of both cracking risk and residual stresses in hardened concrete structures is still a challenging task. We propose in this paper a practical method to characterize in the construction site the material parameters and to identify a macroscopic model from simple tests. We propose for instance to use a restrained shrinkage ring test to identify a basic early age creep model based on a simple ageing visco-elastic Kelvin model. The strain data obtained from this test can be treated through an early age finite element incremental procedure such that the fitting parameters of the creep law can be quickly identified. The others properties of concrete have been measured at different ages (elastic properties, hydration kinetics, and coefficient of thermal expansion). From the identified early age model, we computed the temperature rise and the stress development in a non reinforced concrete stress for nuclear w...
STUDY ON STRESS-STRAIN PROPERTIES OF REACTIVE POWDER CONCRETE UNDER UNIAXIAL COMPRESSION
Directory of Open Access Journals (Sweden)
M.V.SESHAGIRI RAO
2010-11-01
Full Text Available Reactive Powder Concrete(RPC which is a new type of improved high strength concrete, is a recent development in concrete technology. Because the material is intrinsically strong in compression, the stress-strain behaviour of RPC under compression is of considerable interest in the design of RPC members and accurate prediction of their structural behaviour. An attempt has been made in the present study to determine the complete stress-strain curves from uniaxial compression tests. The effect of material composition on the stressstrain behaviour and the compression toughness are presented in the paper. The highest cylinder compressive strength of 171.3 MPa and elastic modulus of 44.8 GPa were recorded for 2% 13 mm Fibres. The optimum Fibre content was found to be 3% of 6mm or 2% of 13 mm. A new measure of compression toughness known as MTI (modified toughness index is proposed and it is found to range from 2.64 to 4.65 for RPC mixes.
Directory of Open Access Journals (Sweden)
Chunhua Lu
2009-01-01
Full Text Available Two artificial neural networks (ANN, back-propagation neural network (BPNN and the radial basis function neural network (RBFNN, are proposed to predict the carbonation depth of prestressed concrete. In order to generate the training and testing data for the ANNs, an accelerated carbonation experiment was carried out, and the influence of stress level of concrete on carbonation process was taken into account especially. Then, based on the experimental results, the BPNN and RBFNN models which all take the stress level of concrete, water-cement ratio, cement-fine aggregate, cement-coarse aggregate ratio and testing age as input parameters were built and all the training and testing work was performed in MATLAB. It can be found that the two ANN models seem to have a high prediction and generalization capability in evaluation of carbonation depth, and the largest absolute percentage errors of BPNN and RBFNN are 10.88% and 8.46%, respectively. The RBFNN model shows a better prediction precision in comparison to BPNN model.
Institute of Scientific and Technical Information of China (English)
ZHU Jin-song; GAO Chang-e; SONG Yu-pu
2005-01-01
The effects of different lateral confinement stress on the fatigue behavior and cumulative damage of plain concrete were investigated experimentally. Eighty 100mm × 100mm × 100mm specimens of ordinary strength concrete were tested with constant-or variable-amplitude cyclic compression and lateral confinement pressure in two orthogonal directions. A fatigue equation was gained by modifying the classical Aas-Jakobsen SN equation and used for taking into account the effect of the confined stress on fatigue strength of plain concrete. The present study indicates that the fatigue failure is greatly influenced by the sequence of applied variable-amplitude fatigue loading, and Miner's rule is inapplicable to predict the residual fatigue life, especially in the sequence of low to high. The present research also shows that the exponent d of the Corten-Dolan's damage formula is a constant depending on the materials and the levels of load spectrum, and d can be determined through the two-stage fatigue tests. The residual fatigue lives predicted by Corten-Dolan' s damage formula are found to be in good agreement with the results of the experiments.
High stress monitoring of prestressing tendons in nuclear concrete vessels using fibre-optic sensors
Energy Technology Data Exchange (ETDEWEB)
Perry, M., E-mail: marcus.perry@strath.ac.uk [Institute for Energy and Environment, University of Strathclyde, 204 George Street, Glasgow G1 1XW (United Kingdom); Yan, Z.; Sun, Z.; Zhang, L. [Aston Institute of Photonic Technologies, Aston University, Birmingham B4 7ET (United Kingdom); Niewczas, P. [Institute for Energy and Environment, University of Strathclyde, 204 George Street, Glasgow G1 1XW (United Kingdom); Johnston, M. [Civil Design Group, EDF Energy, Nuclear Generation, East Kilbride G74 5PG (United Kingdom)
2014-03-15
Highlights: • We weld radiation-resistant optical fibre strain sensors to steel prestressing tendons. • We prove the sensors can survive 1300 MPa stress (80% of steel's tensile strength). • Mechanical relaxation of sensors is characterised under 1300 MPa stress over 10 h. • Strain transfer between tendon and sensor remains at 69% after relaxation. • Sensors can withstand and measure deflection of tendon around a 4.5 m bend radius. - Abstract: Maintaining the structural health of prestressed concrete nuclear containments is a key element in ensuring nuclear reactors are capable of meeting their safety requirements. This paper discusses the attachment, fabrication and characterisation of optical fibre strain sensors suitable for the prestress monitoring of irradiated steel prestressing tendons. The all-metal fabrication and welding process allowed the instrumented strand to simultaneously monitor and apply stresses up to 1300 MPa (80% of steel's ultimate tensile strength). There were no adverse effects to the strand's mechanical properties or integrity. After sensor relaxation through cyclic stress treatment, strain transfer between the optical fibre sensors and the strand remained at 69%. The fibre strain sensors could also withstand the non-axial forces induced as the strand was deflected around a 4.5 m bend radius. Further development of this technology has the potential to augment current prestress monitoring practices, allowing distributed measurements of short- and long-term prestress losses in nuclear prestressed-concrete vessels.
DEFF Research Database (Denmark)
Halding, Philip Skov; Hertz, Kristian Dahl; Schmidt, Jacob Wittrup
2014-01-01
In the first part of the 20th century concrete hinges developed by Freyssinet and Mesnager were widely tested and implemented in concrete structures. The concrete hinges were used a great deal in closed-spandrel arch bridges. Since such a bridge type has not been competitive for the past 40 years......, the research in concrete hinges has not evolved significantly in that period. But introducing a new state-of-the-art concrete arch bridge solution (Pearl-Chain arches invented at the Technical University of Denmark) creates a necessity of a concrete hinge research based on modern standards. Back when research...... in concrete hinges was more common different designs were proposed for the geometry and reinforcement. Previous research focused on fatigue, multi-axial stresses around the hinge throat, and the relation between rotation- and moment. But many different test-setups were proposed by different researchers...
Setareh, Mehdi
2017-01-01
This revised, fully updated second edition covers the analysis, design, and construction of reinforced concrete structures from a real-world perspective. It examines different reinforced concrete elements such as slabs, beams, columns, foundations, basement and retaining walls and pre-stressed concrete incorporating the most up-to-date edition of the American Concrete Institute Code (ACI 318-14) requirements for the design of concrete structures. It includes a chapter on metric system in reinforced concrete design and construction. A new chapter on the design of formworks has been added which is of great value to students in the construction engineering programs along with practicing engineers and architects. This second edition also includes a new appendix with color images illustrating various concrete construction practices, and well-designed buildings. The ACI 318-14 constitutes the most extensive reorganization of the code in the past 40 years. References to the various sections of the ACI 318-14 are pro...
NUMERICAL METHOD AND RANDOM ANALYSIS OF CEMENT CONCRETE EXPANSION
Institute of Scientific and Technical Information of China (English)
无
2000-01-01
The numerical method and random analysis of cement concrete expansion are given. A mathematical procedure is presented which includes the nonlinear characteristics of the concrete. An expression is presented to predict the linear restrained expansion of expansive concrete bar restrained by a steel rod. The results indicate a rapid change in strains and stresses within initial days, after which the change gradually decreases. A reliable and accurate method of predicting the behavior of the concrete bulkheads in drifts is presented here. Extensive sensitivity and parametric studies have been performed. The random density distributions of expansive concrete are given based on the restricted or unrestricted condition. These studies show that the bulkhead stress fields are largely influenced by the early modulus of the concrete and the randomness of the ultimate unrestrained expansion of the concrete.
MICROMECHANICAL DAMAGE MODEL FOR ROCKS AND CONCRETES SUBJECTED TO COUPLED TENSILE AND SHEAR STRESSES
Institute of Scientific and Technical Information of China (English)
Zhongjun Ren; Xianghe Peng; Chunhe Yang
2008-01-01
Based on the analysis of the deformation in an infinite isotropic elastic matrix with an embedded elliptic crack under far field coupled tensile and shear stresses,the energy release rate and a mixed fracture criterion are obtained using an energy balance approach.The additional compliance tensor induced by a single opening elliptic microcrack in a representative volume element is derived,and the effect of microcracks with random orientations is analyzed with the Taylor's scheme by introducing an appropriate probability density function.A micromechanical damage model for rocks and concretes is obtained and is verified with experimental results.
Zhao Cheng; Zhao Chunfeng; Gong Hui
2013-01-01
The behaviour of the soil-structure interface is crucial to the design of a pile foundation. Radial unloading occurs during the process of hole boring and concrete curing, which will affect the load transfer rule of the pile-soil interface. Through large shear tests on the interface between clay and concrete, it can be concluded that the normal stress history significantly influences the shear behaviour of the interface. The numerical simulation of the bored shaft-soil interaction problem req...
Dong, Biqin; Liu, Yuqing; Qin, Lei; Wang, Yaocheng; Fang, Yuan; Xing, Feng; Chen, Xianchuan
2015-10-01
In this paper, the application of a novel cement-based piezoelectric ceramic sensor is stated for the in situ stress monitoring of the reinforced concrete beam under static loading. Smart beam composite structures were designed and characterised by a range of experimental methods. Finite element analysis is used to analyse the mechanical response of the concrete beam under static loading. The results show that the mechanical-electrical response of sensors embedded in reinforced concrete beams follows a linear relationship under various loading conditions. The sensors are able to record the stress history of the beam under static loads. Moreover, the measured stress data agree well with the simulated results and the smart structures are found to be capable of reliably monitoring the response of a beam during stress testing for static loading modes to real concrete structures. The study indicates that such cement-based piezoelectric composites have a high feasibility and applicability to the in situ stress monitoring of reinforced concrete structures.
Directory of Open Access Journals (Sweden)
M. Boudjema
2003-01-01
Full Text Available The elastic response of many rocks to quasistatic stress changes is highly nonlinear and hysteretic, displaying discrete memory. Rocks also display unusual nonlinear response to dynamic stress changes. A model to describe the elastic behavior of rocks and other consolidated materials is called the Preisach-Mayergoyz (PM space model. In contrast to the traditional analytic approach to stress-strain, the PM space picture establishes a relationship between the quasistatic data and a number density of hysteretic mesoscopic elastic elements in the rock. The number density allows us to make quantitative predictions of dynamic elastic properties. Using the PM space model, we analyze a complex suite of quasistatic stress-strain data taken on Berea sandstone. We predict a dynamic bulk modulus and a dynamic shear modulus surface as a function of mean stress and shear stress. Our predictions for the dynamic moduli compare favorably to moduli derived from time of flight measurements. We derive a set of nonlinear elastic constants and a set of constants that describe the hysteretic behavior of the sandstone.
Energy Technology Data Exchange (ETDEWEB)
Gerard, B.; Ulm, F. [Service Ensembles de Production, Departement Surveillance Diagnostic Maintenance, Direction des Etudes et Recherches, Electricite de France (EDF), 92 - Clamart (France)
1997-11-01
This document presents an analysis of the different calculation methods for pre-stressed concrete structure which can be performed by using finite element methods. Two methods of calculating the pre-stressing of concrete structures with finite elements have been determined. The equivalent method which consists of replacing the action of pre-stressing the concrete by equivalent forces. These method is well suited to dimensioning and studying the overall stability of a structure. It is not an easy matter to take into account the coupled or time-varying phenomena. This approach ignores the evolution of the interaction between the pre-stressing and the concrete. The explicit method which consists of including the mechanical resolution of the pre-stressed cables in that of a concrete structure. Not only does this allow a local study of the pre-stressed to be made, it also allows the coupling which developed over time to be determined, e.g. slip, deferred deformation and coupling between the steel and concrete behaviours. This method enables non-linear phenomena with varying degrees of complexity, such as fracture or yielding of the steels, drying out of the concrete, creep, etc to be described. The two methods are complementary. This document presents the mathematical and computer developments relating to each of this method. In the case of the explicit method, certain of the Code-Aster functions already make it possible to meet several EDF application requirements. Several couplings can be taken into account, such as thermomechanical, shrinkage in drying, creep, relaxation and injection of the cables. Three immediate developments of Code-Aster are proposed for the following applications: - a procedure for calculating the pre-stress losses along the pre-stressing cables; - a command to allocate these forces in the form of an initial force field in the bar elements associated with the cables; - a procedure for linking elements whose nodes do not coincide with each other
On the prediction of stress relaxation from known creep of nonlinear materials
Energy Technology Data Exchange (ETDEWEB)
Touati, D.; Cederbaum, G. [Ben-Gurion Univ. of the Negev, Beer Sheva (Israel)
1997-04-01
A method to predict the nonlinear relaxation behavior from creep experiments of nonlinear viscoelastic materials is presented. It is shown that for given nonlinear creep properties, and creep compliance represented by the Prony series, the Schapery creep model can be transformed into a set of first order nonlinear equations. The solution of these equations enables the obtaining of the nonlinear stress relaxation curves. The strain-dependent constitutive equation can then be constructed for a given nonlinear viscoelastic model, as needed for engineering applications. A comparison example of the calculated stress relaxation curves, with test data for polyurethane demonstrates the very good accuracy of the proposed method.
Nonlinear cosmological consistency relations and effective matter stresses
Energy Technology Data Exchange (ETDEWEB)
Ballesteros, Guillermo [Museo Storico della Fisica e Centro Studi e Ricerche ' ' Enrico Fermi' ' , Piazza del Viminale 1, I-00184 Rome (Italy); Hollenstein, Lukas; Jain, Rajeev Kumar; Kunz, Martin, E-mail: guillermo.ballesteros@pd.infn.it, E-mail: lukas.hollenstein@unige.ch, E-mail: rajeev.jain@unige.ch, E-mail: martin.kunz@unige.ch [Département de Physique Théorique and Center for Astroparticle Physics, Université de Genève, Quai E. Ansermet 24, CH-1211 Genève 4 (Switzerland)
2012-05-01
We propose a fully nonlinear framework to construct consistency relations for testing generic cosmological scenarios using the evolution of large scale structure. It is based on the covariant approach in combination with a frame that is purely given by the metric, the normal frame. As an example, we apply this framework to the ΛCDM model, by extending the usual first order conditions on the metric potentials to second order, where the two potentials start to differ from each other. We argue that working in the normal frame is not only a practical choice but also helps with the physical interpretation of nonlinear dynamics. In this frame, effective pressures and anisotropic stresses appear at second order in perturbation theory, even for ''pressureless'' dust. We quantify their effect and compare them, for illustration, to the pressure of a generic clustering dark energy fluid and the anisotropic stress in the DGP model. Besides, we also discuss the effect of a mismatch of the potentials on the determination of galaxy bias.
Nonlinear response of plain concrete shear walls with elastic-damaging behavior
Energy Technology Data Exchange (ETDEWEB)
Yazdani, S.; Schreyer, H.L.
1997-02-01
This report summarizes the theoretical and computational efforts on the modeling of small scale shear walls. Small scale shear walls are used extensively in the study of shear wall behavior because the construction and testing of full size walls are rather expensive. A finite element code is developed which incorporates nonlinear constitutive relations of damage mechanics. The program is used to obtain nonlinear load-deformation curves and to address the initial loss of stiffness due to shrinkage cracking. The program can also be used to monitor the continuous degradation of the fundamental frequency due to progressive damage.
Institute of Scientific and Technical Information of China (English)
YAO Zhi-shu; CHANG Hua; RONG Chuan-xin
2007-01-01
High strength reinforced concrete drilling shaft linings have been adopted to solve the difficult problem of supporting coal drilling shafts penetrating through thick top soils. Through model experiments the stress and strength of such shaft linings are studied. The test results indicate that the load bearing capacity of the shaft lining is very high and that the main factors affecting the load bearing capacity are the concrete strength, the ratio of lining thickness to inner radius and the reinforcement ratio. Based on the limit equilibrium conditions and the strength theory of concrete under multi-axial compressive stressed state, a formula for calculating the load-bearing capacity of a high strength reinforced concrete shaft lining was obtained. Because the concrete in a shaft lining is in a multi-axial compressive stress state the compressive strength increases to a great extent compared to uni-axial loading. Based on experiment a formula for the gain factor in compressive strength was obtained: it can be used in the structural design of the shaft lining. These results have provided a basis for sound engineering practice when designing this kind of shaft lining structure.
A non-linear analytic stress model for the analysis on the stress interaction between TSVs
Directory of Open Access Journals (Sweden)
Ming-Han Liao
2015-06-01
Full Text Available Thermo-elastic strain is induced by through silicon vias (TSV due to the difference of thermal expansion coefficients between the copper (∼18 ppm/◦C and silicon (∼2.8 ppm/◦C when the structure is exposed to a thermal budget in the three dimensional integrated circuit (3DIC process. These thermal expansion stresses are high enough to induce the delamination on the interfaces between the copper, silicon, and isolated dielectric. A compact analytic model for the strain field induced by different layouts of thermal copper filled TSVs with the linear superposition principle is found to result in large errors due to the strong stress interaction between TSVs. In this work, a nonlinear stress analytic model with different TSV layouts is demonstrated by the finite element method and Mohr’s circle analysis. The stress characteristics are also measured by the atomic force microscope-raman technique at a nanometer level resolution. This nonlinear stress model for the strong interactions between TSVs results in an electron mobility change ~2-6% smaller than that resulting from a model that only considers the linear stress superposition principle.
Directory of Open Access Journals (Sweden)
Zheng LU
2014-12-01
Full Text Available In this research work, a method to estimate the dynamic characteristics of a multilayered pavement with bituminous or concrete materials is proposed. A mechanical model is established to investigate the dynamic displacement and stress of the multi-layered pavement structure. Both the flexible and the rigid pavements, corresponding to bituminous materials and concrete materials, respectively, are studied. The theoretical solutions of the multi-layered pavement structure are deduced considering the compatibility condition at the interface of the structural layers. By introducing FFT (Fast Fourier Transform algorithm, some numerical results are presented. Comparisons of the theoretical and experimental result implied that the proposed method is reasonable in predicting the stress and displacement of a multi-layered pavement with bituminous or concrete materials. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.6071
Energy Technology Data Exchange (ETDEWEB)
Guerrero, H.; Restivo, M.
2011-08-01
In-situ decommissioning of Reactors P- and R- at the Savannah River Site will require filling the reactor vessels with a special concrete based on materials such as magnesium phosphate, calcium aluminate or silica fume. Then the reactor vessels will be overlain with an 8 ft. thick layer of Ordinary Portland Cement (OPC) steel reinforced concrete, called the 'Cap Concrete'. The integrity of this protective layer must be assured to last for a sufficiently long period of time to avoid ingress of water into the reactor vessel and possible movement of radioactive contamination into the environment. During drying of this Cap Concrete however, shrinkage strains are set up in the concrete as a result of diffusion and evaporation of water from the top surface. This shrinkage varies with depth in the poured slab due to a non-uniform moisture distribution. This differential shrinkage results in restraint of the upper layers with larger shrinkage by lower layers with lesser displacements. Tensile stresses can develop at the surface from the strain gradients in the bulk slab, which can lead to surface cracking. Further, a mechanism called creep occurs during the curing period or early age produces strains under the action of restraining forces. To investigate the potential for surface cracking, an experimental and analytical program was started under TTQAP SRNL-RP-2009-01184. Slab sections made of Cap Concrete mixture were instrumented with embedded strain gages and relative humidity sensors and tested under controlled environmental conditions of 23 C and relative humidities (RH) of 40% and 80% over a period of 50 days. Calculation methods were also developed for predictions of stress development in the full-scale concrete placement over the reactor vessels. These methods were evaluated by simulating conditions for the test specimens and the calculation results compared to the experimental data. A closely similar test with strain gages was performed by Kim and Lee for
Directory of Open Access Journals (Sweden)
Lei Zhang
2015-01-01
Full Text Available In the concrete dam construction, it is very necessary to strengthen the real-time monitoring and scientific management of concrete temperature control. This paper constructs the analysis and inverse analysis system of temperature stress simulation, which is based on various useful data collected in real time in the process of concrete construction. The system can produce automatically data file of temperature and stress calculation and then achieve the remote real-time simulation calculation of temperature stress by using high performance computing techniques, so the inverse analysis can be carried out based on a basis of monitoring data in the database; it fulfills the automatic feedback calculation according to the error requirement and generates the corresponding curve and chart after the automatic processing and analysis of corresponding results. The system realizes the automation and intellectualization of complex data analysis and preparation work in simulation process and complex data adjustment in the inverse analysis process, which can facilitate the real-time tracking simulation and feedback analysis of concrete temperature stress in construction process and enable you to discover problems timely, take measures timely, and adjust construction scheme and can well instruct you how to ensure project quality.
Zhu, F. H.; Fu, Y. M.
2008-12-01
By considering the effect of interfacial damage and using the variation principle, three-dimensional nonlinear dynamic governing equations of the laminated plates with interfacial damage are derived based on the general six-degrees-of-freedom plate theory towards the accurate stress analysis. The solutions of interlaminar stress and nonlinear dynamic response for a simply supported laminated plate with interfacial damage are obtained by using the finite difference method, and the results are validated by comparison with the solution of nonlinear finite element method. In numerical calculations, the effects of interfacial damage on the stress in the interface and the nonlinear dynamic response of laminated plates are discussed.
Directory of Open Access Journals (Sweden)
Ming-chao Li
2015-10-01
Full Text Available This study used the finite element method (FEM to analyze the stress field and seepage field of a roller-compacted concrete (RCC dam, with an upstream impervious layer constructed with different types of concrete materials, including three-graded RCC, two-graded RCC, conventional vibrated concrete (CVC, and grout-enriched vibrated RCC (GEVR, corresponding to the design schemes S1 through S4. It also evaluated the anti-seepage performance of the imperious layer in the four design schemes under the normal water level and flood-check level. Stress field analysis of a retaining section and discharge section shows that the maximum tensile stress occurs near the dam heel, the maximum compressive stress occurs near the dam toe, and the stress distributions in the four schemes can satisfy the stress control criteria. Seepage field analysis shows that the uplift pressure heads in schemes S3 and S4 descend rapidly in the anti-seepage region, and that the calculated results of daily seepage flow under the steady seepage condition in these two schemes are about 30% to 50% lower than those in the other two schemes, demonstrating that CVC and GEVR show better anti-seepage performance. The results provide essential parameters such as the uplift pressure head and seepage flow for physical model tests and anti-seepage structure selection in RCC dams.
M., Abdel-Mooty
2011-01-01
Autoclaved Aerated Concrete (AAC) block are used mainly as non-load-bearing walls that provide heat insulation. This results in considerable saving in cooling energy particularly in hot desert environment with large variation of daily and seasonal temperatures. However, due to the relatively low strength there use load bearing walls is limited to single storey and low-rise construction. A system to enhance the strength of the AAC masonry wall in resisting both inplane vertical and combined vertical and lateral loads using ferrocement technology is proposed in this research. The proposed system significantly enhances the load carrying capacity and stiffness of the AAC wall without affecting its insulation characteristics. Ferrocement is made of cement mortar reinforced with closely spaced wire mesh. Full scale wall specimens with height of 2100mm and width of 1820mm were tested with different configuration of ferrocement. A finite elementmodel is developed and verified against the experimentalwork. The results of the finite element model correlates well with the experimental results.
Directory of Open Access Journals (Sweden)
Zhao Cheng
2013-01-01
Full Text Available The behaviour of the soil-structure interface is crucial to the design of a pile foundation. Radial unloading occurs during the process of hole boring and concrete curing, which will affect the load transfer rule of the pile-soil interface. Through large shear tests on the interface between clay and concrete, it can be concluded that the normal stress history significantly influences the shear behaviour of the interface. The numerical simulation of the bored shaft-soil interaction problem requires proper modelling of the interface. By taking the energy accumulated on the interface as a hardening parameter and viewing the shearing process of the interface as the process of the energy dissipated to do work, considering the influence of the normal stress history on the shearing rigidity, a mechanical model of the interface between clay and concrete is proposed. The methods to define the model parameters are also introduced. The model is based on a legible mathematical theory, and all its parameters have definite physical meaning. The model was validated using data from a direct shear test; the validation results indicated that the model can reproduce and predict the mechanical behaviour of the interface between clay and concrete under an arbitrary stress history.
Stress and strain analysis for concrete face sand-gravel dam with extruded wall%挤压边墙式混凝土面板砂砾石坝应力变形分析
Institute of Scientific and Technical Information of China (English)
刘思远; 刘晓娟
2013-01-01
As emerging technology in the world dam engineering history, there are a lot of respects need to be supplemented and perfected about extruded wall. Focused on a concrete face sand - gravel dam with concrete extruded wall engineering, the paper carried out the analysis of 3 - D nonlinear finite element and the calculation during construction period and impoundment period, and obtained stress-strain appearance of the dam and concrete face status. The results show that the stress and strain values of concrete face sand-gravel dam with extruded wall under the two conditions can satisfy safety requirement.%挤压边墙作为世界坝工史上一门比较新兴的技术,还有许多方面有待研究和完善.结合某一采用挤压边墙施工技术的混凝土面板砂砾石坝工程,对其进行三维非线性有限元分析,分别对竣工期和蓄水期两种工况进行计算,得到了坝体以及混凝土面板的应力变形状态.研究结果表明:采用挤压边墙式混凝土面板砂砾石坝在竣工期和蓄水期应力应变值能够满足安全要求.
Breakdown of nonlinear elasticity in stress-controlled thermal amorphous solids
Dailidonis, Vladimir; Ilyin, Valery; Procaccia, Itamar; Shor, Carmel A. B. Z.
2017-03-01
In recent work it was clarified that amorphous solids under strain control do not possess nonlinear elastic theory in the sense that the shear modulus exists but nonlinear moduli exhibit sample-to-sample fluctuations that grow without bound with the system size. More relevant, however, for experiments are the conditions of stress control. In the present Rapid Communication we show that also under stress control the shear modulus exists, but higher-order moduli show unbounded sample-to-sample fluctuation. The unavoidable consequence is that the characterization of stress-strain curves in experiments should be done with a stress-dependent shear modulus rather than with nonlinear expansions.
Tian, Zhen; Huo, Linsheng; Gao, Weihang; Li, Hongnan; Song, Gangbing
2017-10-01
Wave-based concrete structural health monitoring has attracted much attention. A stress wave experiences significant attenuation in concrete, however there is a lack of a unified method for predicting the attenuation coefficient of the stress wave. In this paper, a simple and effective absorption attenuation model of stress waves in concrete is developed based on the Rayleigh damping model, which indicates that the absorption attenuation coefficient of stress waves in concrete is directly proportional to the square of the stress wave frequency when the damping ratio is small. In order to verify the theoretical model, related experiments were carried out. During the experiments, a concrete beam was designed in which the d33-model piezoelectric smart aggregates were embedded to detect the propagation of stress waves. It is difficult to distinguish direct stress waves due to the complex propagation paths and the reflection and scattering of stress waves in concrete. Hence, as another innovation of this paper, a new method for computing the absorption attenuation coefficient based on the time-reversal method is developed. Due to the self-adaptive focusing properties of the time-reversal method, the time-reversed stress wave focuses and generates a peak value. The time-reversal method eliminates the adverse effects of multipaths, reflection, and scattering. The absorption attenuation coefficient is computed by analyzing the peak value changes of the time-reversal focused signal. Finally, the experimental results are found to be in good agreement with the theoretical model.
estimating formwork striking time for concrete mixes estimating ...
African Journals Online (AJOL)
eobe
Nonlinear regression analysis performed on each experimental data set produced. 0.57. Nonlinear .... concrete age in form of charts for different grades of concrete made from ..... age', Cement and Concrete Association, Technical. Report 42 ...
Measuring nonlinear stresses generated by defects in 3D colloidal crystals
Lin, Neil Y C; Schall, Peter; Sethna, James P; Cohen, Itai
2016-01-01
The mechanical, structural and functional properties of crystals are determined by their defects and the distribution of stresses surrounding these defects has broad implications for the understanding of transport phenomena. When the defect density rises to levels routinely found in real-world materials, transport is governed by local stresses that are predominantly nonlinear. Such stress fields however, cannot be measured using conventional bulk and local measurement techniques. Here, we report direct and spatially resolved experimental measurements of the nonlinear stresses surrounding colloidal crystalline defect cores, and show that the stresses at vacancy cores generate attractive interactions between them. We also directly visualize the softening of crystalline regions surrounding dislocation cores, and find that stress fluctuations in quiescent polycrystals are uniformly distributed rather than localized at grain boundaries, as is the case in strained atomic polycrystals. Nonlinear stress measurements ...
Directory of Open Access Journals (Sweden)
Fei LENG
2008-09-01
Full Text Available This paper discusses the seismic analysis of concrete dams with consideration of material nonlinearity. Based on a consistent rate-dependent model and two thermodynamics-based models, two thermodynamics-based rate-dependent constitutive models were developed with consideration of the influence of the strain rate. They can describe the dynamic behavior of concrete and be applied to nonlinear seismic analysis of concrete dams taking into account the rate sensitivity of concrete. With the two models, a nonlinear analysis of the seismic response of the Koyna Gravity Dam and the Dagangshan Arch Dam was conducted. The results were compared with those of a linear elastic model and two rate-independent thermodynamics-based constitutive models, and the influences of constitutive models and strain rate on the seismic response of concrete dams were discussed. It can be concluded from the analysis that, during seismic response, the tensile stress is the control stress in the design and seismic safety evaluation of concrete dams. In different models, the plastic strain and plastic strain rate of concrete dams show a similar distribution. When the influence of the strain rate is considered, the maximum plastic strain and plastic strain rate decrease.
Dynamic Stress-Strain Behaviour of Steel Fiber Reinforced High-Performance Concrete with Fly Ash
Directory of Open Access Journals (Sweden)
Tan Chien Yet
2012-01-01
Full Text Available The addition of steel fibers into concrete mix can significantly improve the engineering properties of concrete. The mechanical behaviors of steel fiber reinforced high-performance concrete with fly ash (SFRHPFAC are studied in this paper through both static compression test and dynamic impact test. Cylindrical and cube specimens with three volume fractions of end-hooked steel fibers with volume fraction of 0.5%, 1.0%, and 1.5% (39.25, 78.50, and 117.75 kg/m3 and aspect ratio of 64 are used. These specimens are then tested for static compression and for dynamic impact by split Hopkinson pressure bar (SHPB at strain rate of 30–60 s−1. The results reveal that the failure mode of concrete considerably changes from brittle to ductile with the addition of steel fibers. The plain concrete may fail under low-strain-rate single impact whereas the fibrous concrete can resist impact at high strain rate loading. It is shown that strain rate has great influence on concrete strength. Besides, toughness energy is proportional to the fiber content in both static and dynamic compressions.
Institute of Scientific and Technical Information of China (English)
F. H. Zhu; Y. M. Fu
2008-01-01
By considering the effect of interfacial damage and using the variation principle, three-dimensional nonli-near dynamic governing equations of the laminated plates with interfacial damage are derived based on the general six-degrees-of-freedom plate theory towards the accurate stress analysis. The solutions of interlaminar stress and nonlinear dynamic response for a simply supported laminated plate with interfacial damage are obtained by using the finite dif-ference method, and the results are validated by compari-son with the solution of nonlinear finite element method. In numerical calculations, the effects of interfacial damage on the stress in the interface and the nonlinear dynamic response of laminated plates are discussed.
Directory of Open Access Journals (Sweden)
Ghader Rezazadeh
2007-07-01
Full Text Available In this paper, the effect of residual stress on divergence instability of a rectangular microplate subjected to a nonlinear electrostatic pressure for different geometrical properties has been presented. After deriving the governing equation and using of Step-by-Step Linearization Method (SSLM, the governing nonlinear equation has been linearized. By applying the finite difference method (FDM to a rectangular mesh, the linearized equation has been discretized. The results show, residual stresses have considerable effects on Pull-in phenomena. Tensile residual stresses increase pull-in voltage and compressive decrease it. The effect of different geometrical properties on divergence instability has also been studied.
A hybrid-stress solid-shell element for non-linear analysis of piezoelectric structures
Institute of Scientific and Technical Information of China (English)
SZE; K; Y
2009-01-01
This paper presents eight-node solid-shell elements for geometric non-linear analyze of piezoelectric structures. To subdue shear, trapezoidal and thickness locking, the assumed natural strain method and an ad hoc modified generalized laminate stiffness matrix are employed. With the generalized stresses arising from the modified generalized laminate stiffness matrix assumed to be independent from the ones obtained from the displacement, an extended Hellinger-Reissner functional can be derived. By choosing the assumed generalized stresses similar to the assumed stresses of a previous solid ele- ment, a hybrid-stress solid-shell element is formulated. The presented finite shell element is able to model arbitrary curved shell structures. Non-linear numerical examples demonstrate the ability of the proposed model to analyze nonlinear piezoelectric devices.
Directory of Open Access Journals (Sweden)
Baek-Il Bae
2016-01-01
Full Text Available Although mechanical properties of concrete under uniaxial compression are important to design concrete structure, current design codes or other empirical equations have clear limitation on the prediction of mechanical properties. Various types of fiber-reinforced reactive powder concrete matrix were tested for making more usable and accurate estimation equations for mechanical properties for ultra high strength concrete. Investigated matrix has compressive strength ranged from 30 MPa to 200 MPa. Ultra high strength concrete was made by means of reactive powder concrete. Preventing brittle failure of this type of matrix, steel fibers were used. The volume fraction of steel fiber ranged from 0 to 2%. From the test results, steel fibers significantly increase the ductility, strength and stiffness of ultra high strength matrix. They are quantified with previously conducted researches about material properties of concrete under uniaxial loading. Applicability of estimation equations for mechanical properties of concrete was evaluated with test results of this study. From the evaluation, regression analysis was carried out, and new estimation equations were proposed. And these proposed equations were applied into stress-strain relation which was developed by previous research. Ascending part, which was affected by proposed equations of this study directly, well fitted into experimental results.
Gravemeijer, Koeno
2011-01-01
If we want to make something concrete in mathematics education, we are inclined introduce, what we call, "manipulatives", in the form of tactile objects or visual representations. If we want to make something concrete in a everyday-life conversation, we look for an example. In the former, we try to make a concrete model of our own,…
Non-linear Elasticity and Monitoring of Stress in the Focus of an Earthquake
Bakulin, V.; Bakulin, A.
2001-05-01
Non-linear elasticity proved to give comprehensive framework for relating seismic velocities in rocks to stress. This powerful theory allows attacking the problem of estimating stress state at the focus of earthquakes. Such idea has been proposed long time ago [Kostrov and Nikitin, 1968] however its implementation requires a-priori knowledge of non-linear rock properties. Three non-linear constants needed to describe variation of any velocity with stress are typically estimated from core measurements [Bakulin et al., 2000]. More reliable estimates can be obtained from multi-mode inversions of borehole acoustic data [Sinha, 1996]. Nevertheless database of non-linear formation constants is still very limited. More measurements are required to estimate non-linear rock properties on larger scale and with independent stress constraints. Such measurements can be done in mines [Bakulin and Bakulin, 1999] or in hydrocarbon reservoirs where time-dependent pressure measurements are available. Without knowledge of non-linear rock properties seismic waves can still bring information about directions of tectonic stresses. In particular, shear wave polarizations can deliver directions of principal stresses in the focus of an earthquake, provided the overburden effects were removed. If rock non-linear properties are independently derived then estimation of stress magnitudes becomes feasible. Such techniques were applied in mining environment [Bakulin and Bakulin, 1999]. They may become routine for monitoring stress state in the focus of earthquakes and therefore can be used for forecasting the seismic activity. Bakulin, A. V., Troyan, V. N., and Bakulin, V. N., 2000, Acoustoelasticity of rocks, St. Petersburg (in Russian). Bakulin, V. and Bakulin, A., 1999, Acoustopolarizational method of measuring stress in rock mass and determination of Murnaghan constants: 69th Annual Internat. Mtg., Soc. Expl. Geophys., 1971-1974. Kostrov, B.V., and Nikitin, L.V., 1968, Influence of initial
Directory of Open Access Journals (Sweden)
Fabian Lamus
2011-01-01
Full Text Available This work describes a numerical model of fibre reinforced concrete elastic behaviour implemented using the finite elements method (Hughes, 2000. In structures made of this material, each point is formed by steel fibres embedded into a simple concrete matrix. The reinforced concrete is represented inside a finite element as an orthotropic material having random material direction based on the vanishing diameter fibre model (Dvorak and Bahei-el-Din, 1982 and the mixing theory modified for short length reinforcement (Oller, 2003. Statistical analysis consisted of repeating the problem’s numerical simulation where the direction of fibres was modified by a random function to set up a sampling database from the results and measure their variability. A sensitivity study of finite element size and the number of sampling data was then carried out in terms of total strain energy. Finite element size and sampling data are recommended. The average structural response of a reinforced concrete beam with different quantities of steel fibres where minimum data dispersion was observed is given as an example of applying the above.
Vibration of piezoelectric nanobeams with an internal residual stress and a nonlinear strain
Energy Technology Data Exchange (ETDEWEB)
Jiang, Hao; Wang, Chengyuan, E-mail: cywang@ujs.edu.cn; Luo, Ying
2015-10-23
This Letter reports the effect of an internal residual stress and the local geometric nonlinearity on the vibration of piezoelectric nanowires (NWs). A dynamic equation is derived based on Hamilton's principle, which enables one to capture the above-mentioned effects and the influence of all lateral surfaces of a rectangular NW. Vibration frequencies are obtained for the NWs under an electrical voltage and compared with those given by the existing Young–Laplace model where zero internal stress, a linear strain and the effects of top and bottom surfaces of rectangular NWs are considered. It is found that the internal residual stress can extinguish the effect of the surface-induced residual stress and substantially down shift the frequency or qualitatively alter the size-dependence of the frequency. In addition, with a nonlinear strain the piezoelectric effect is found to be able to exert a direct impact on the bending stiffness of piezoelectric NWs. - Highlights: • A dynamic equation is derived for piezoelectric nanowires (PNs) by considering a nonlinear strain and an internal stress. • A nonlinear strain extends the piezoelectric effects to the bending stiffness of the PNs. • An internal stress decreases PN frequency and alters its thickness-dependence. • All lateral surfaces of PNs contribute substantially to the effect of surface piezoelectricity.
Nonlinear morphoelastic plates I: Genesis of residual stress
McMahon, J.
2011-04-28
Volumetric growth of an elastic body may give rise to residual stress. Here a rigorous analysis is given of the residual strains and stresses generated by growth in the axisymmetric Kirchhoff plate. Balance equations are derived via the Global Constraint Principle, growth is incorporated via a multiplicative decomposition of the deformation gradient, and the system is closed by a response function. The particular case of a compressible neo-Hookean material is analyzed, and the existence of residually stressed states is established. © SAGE Publications 2011.
Melillo, Paolo; Bracale, Marcello; Pecchia, Leandro
2011-11-07
This study investigates the variations of Heart Rate Variability (HRV) due to a real-life stressor and proposes a classifier based on nonlinear features of HRV for automatic stress detection. 42 students volunteered to participate to the study about HRV and stress. For each student, two recordings were performed: one during an on-going university examination, assumed as a real-life stressor, and one after holidays. Nonlinear analysis of HRV was performed by using Poincaré Plot, Approximate Entropy, Correlation dimension, Detrended Fluctuation Analysis, Recurrence Plot. For statistical comparison, we adopted the Wilcoxon Signed Rank test and for development of a classifier we adopted the Linear Discriminant Analysis (LDA). Almost all HRV features measuring heart rate complexity were significantly decreased in the stress session. LDA generated a simple classifier based on the two Poincaré Plot parameters and Approximate Entropy, which enables stress detection with a total classification accuracy, a sensitivity and a specificity rate of 90%, 86%, and 95% respectively. The results of the current study suggest that nonlinear HRV analysis using short term ECG recording could be effective in automatically detecting real-life stress condition, such as a university examination.
Directory of Open Access Journals (Sweden)
Melillo Paolo
2011-11-01
Full Text Available Abstract Background This study investigates the variations of Heart Rate Variability (HRV due to a real-life stressor and proposes a classifier based on nonlinear features of HRV for automatic stress detection. Methods 42 students volunteered to participate to the study about HRV and stress. For each student, two recordings were performed: one during an on-going university examination, assumed as a real-life stressor, and one after holidays. Nonlinear analysis of HRV was performed by using Poincaré Plot, Approximate Entropy, Correlation dimension, Detrended Fluctuation Analysis, Recurrence Plot. For statistical comparison, we adopted the Wilcoxon Signed Rank test and for development of a classifier we adopted the Linear Discriminant Analysis (LDA. Results Almost all HRV features measuring heart rate complexity were significantly decreased in the stress session. LDA generated a simple classifier based on the two Poincaré Plot parameters and Approximate Entropy, which enables stress detection with a total classification accuracy, a sensitivity and a specificity rate of 90%, 86%, and 95% respectively. Conclusions The results of the current study suggest that nonlinear HRV analysis using short term ECG recording could be effective in automatically detecting real-life stress condition, such as a university examination.
Propagation of Nonlinear Waves in Waveguides and Application to Nondestructive Stress Measurement
Nucera, Claudio
Propagation of nonlinear waves in waveguides is a field that has received an ever increasing interest in the last few decades. Nonlinear guided waves are excellent candidates for interrogating long waveguide like structures because they combine high sensitivity to structural conditions, typical of nonlinear parameters, with large inspection ranges, characteristic of wave propagation in bounded media. The primary topic of this dissertation is the analysis of ultrasonic waves, including ultrasonic guided waves, propagating in their nonlinear regime and their application to structural health monitoring problems, particularly the measurement of thermal stress in Continuous Welded Rail (CWR). Following an overview of basic physical principles generating nonlinearities in ultrasonic wave propagation, the case of higher-harmonic generation in multi-mode and dispersive guided waves is examined in more detail. A numerical framework is developed in order to predict favorable higher-order generation conditions (i.e. specific guided modes and frequencies) for waveguides of arbitrary cross-sections. This model is applied to various benchmark cases of complex structures. The nonlinear wave propagation model is then applied to the case of a constrained railroad track (CWR) subjected to thermal variations. This study is a direct response to the key need within the railroad transportation community to develop a technique able to measure thermal stresses in CWR, or determine the rail temperature corresponding to a null thermal stress (Neutral Temperature -- NT). The numerical simulation phase concludes with a numerical study performed using ABAQUS commercial finite element package. These analyses were crucial in predicting the evolution of the nonlinear parameter beta with thermal stress level acting in the rail. A novel physical model, based on interatomic potential, was developed to explain the origin of nonlinear wave propagation under constrained thermal expansion. In fact
General job stress: a unidimensional measure and its non-linear relations with outcome variables.
Yankelevich, Maya; Broadfoot, Alison; Gillespie, Jennifer Z; Gillespie, Michael A; Guidroz, Ashley
2012-04-01
This article aims to examine the non-linear relations between a general measure of job stress [Stress in General (SIG)] and two outcome variables: intentions to quit and job satisfaction. In so doing, we also re-examine the factor structure of the SIG and determine that, as a two-factor scale, it obscures non-linear relations with outcomes. Thus, in this research, we not only test for non-linear relations between stress and outcome variables but also present an updated version of the SIG scale. Using two distinct samples of working adults (sample 1, N = 589; sample 2, N = 4322), results indicate that a more parsimonious eight-item SIG has better model-data fit than the 15-item two-factor SIG and that the eight-item SIG has non-linear relations with job satisfaction and intentions to quit. Specifically, the revised SIG has an inverted curvilinear J-shaped relation with job satisfaction such that job satisfaction drops precipitously after a certain level of stress; the SIG has a J-shaped curvilinear relation with intentions to quit such that turnover intentions increase exponentially after a certain level of stress.
Peterson, D.
1979-01-01
Rod-beam theories are founded on hypotheses such as Bernouilli's suggesting flat cross-sections under deformation. These assumptions, which make rod-beam theories possible, also limit the accuracy of their analysis. It is shown that from a certain order upward terms of geometrically nonlinear deformations contradict the rod-beam hypotheses. Consistent application of differential geometry calculus also reveals differences from existing rod theories of higher order. These differences are explained by simple examples.
Institute of Scientific and Technical Information of China (English)
SONG Yupu; SONG Xiaoruan; FENG Sheng
2000-01-01
This paper presents an experimental study of a prestressed lightweight concrete platform model with a tank and five steel-columns. This platform can be used not only for extraction but also for storage ofoil and is suitable tor the Bohai Sea and other shallow seas of China. The platform is subjected to tem perature, load, or both. The corresponding temperature distribution, strains, cracks, and vulnerable parts of the platform are analyzed respectively. By use of the finite elemenl method and empirical formulas, the temperalare field of the model is analyzed. The results agree with the experimental results, thereby verifying the reliability of these two calculating methods. The paper provides an experimental basis for the design of the bearing capacity and normal service state of prestressed concrete platforms.
Directory of Open Access Journals (Sweden)
Likhacheva Svetlana Yur'evna
2012-12-01
The findings of the prototype testing include identification of the two areas of deformations: areas of elastic deformations and areas of intensive development of deformations. The first area of partial elastic deformations is characterized by the linear stress function, while the second area demonstrates that this relationship is nonlinear. Permanent deformations appear as of the startup of the loading process and disproportionate stress is demonstrated throughout the deformation process. However, in the first area (partial elastic deformations residual deformations are so small that this area is considered as the area of "the area of incomplete elasticity".
An Elastoplastic Damage Constitutive Model for Concrete
Institute of Scientific and Technical Information of China (English)
LIU Jun; LIN Gao; ZHONG Hong
2013-01-01
An elastoplastic damage constitutive model to simulate nonlinear behavior of concrete is presented.Similar to traditional plastic theory,the irreversible deformation is modeled in effective stress space.In order to better describe different stiffness degradation mechanisms of concrete under tensile and compressive loading conditions,two damage variables,i.e.,tension and compression are introduced,to quantitatively evaluate the degree of deterioration of concrete structure.The rate dependent behavior is taken into account,and this model is derived firmly in the framework of irreversible thermodynamics.Fully implicit backward-Euler algorithm is suggested to perform constitutive integration.Numerical results of the model accord well with the test results for specimens under uniaxial tension and compression,biaxial loading and triaxial loading.Failure processes of double-edge-notched (DEN) specimen are also simulated to further validate the proposed model.
An elastoplastic damage constitutive model for concrete
Liu, Jun; Lin, Gao; Zhong, Hong
2013-04-01
An elastoplastic damage constitutive model to simulate nonlinear behavior of concrete is presented. Similar to traditional plastic theory, the irreversible deformation is modeled in effective stress space. In order to better describe different stiffness degradation mechanisms of concrete under tensile and compressive loading conditions, two damage variables, i.e., tension and compression are introduced, to quantitatively evaluate the degree of deterioration of concrete structure. The rate dependent behavior is taken into account, and this model is derived firmly in the framework of irreversible thermodynamics. Fully implicit backward-Euler algorithm is suggested to perform constitutive integration. Numerical results of the model accord well with the test results for specimens under uniaxial tension and compression, biaxial loading and triaxial loading. Failure processes of double-edge-notched (DEN) specimen are also simulated to further validate the proposed model.
Institute of Scientific and Technical Information of China (English)
李悦; 颜超; 辜中伟
2013-01-01
It is a key point in current research of concrete durability to calculate and analyze the expansion stress generated due to corrosion of steel bars in reinforced concrete. Considering the uneven rust on steel bars in reinforced concrete, finite element analysis software ABAQUS is used for numerical simulation of stress in concrete due to rusting of steel bar and distribution law of the main tensile stress of concrete is summarized.%计算分析钢筋混凝土中钢筋锈蚀量产生的膨胀应力是目前混凝土耐久性研究的重点问题.考虑混凝土中钢筋的不均匀锈蚀现象,应用有限元分析软件ABAQUS对钢筋锈蚀引起的混凝土内应力进行数值模拟,总结混凝土主拉应力的分布规律.
The effective wavenumber of a pre-stressed nonlinear microvoided composite
Energy Technology Data Exchange (ETDEWEB)
Parnell, W J; Abrahams, I D, E-mail: William.Parnell@manchester.ac.uk [School of Mathematics, Alan Turing Building, University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom)
2011-01-01
By using nonlinear elasticity and a modified version of classical multiple scattering theory we derive an explicit form for the effective wavenumber for horizontally polarized shear (SH) elastic waves propagating through a pre-stressed inhomogeneous material consisting of well-separated cylindrical voids embedded in a neo-Hookean rubber host phase. The resulting effective (incremental) antiplane shear modulus is thus also derived.
Jiang, X. T.; Wang, Y. D.; Dai, C. H.; Ding, M.
2017-08-01
The finite element model of concrete-filled steel tubular member was established by the numerical analysis software considering material nonlinearity to analyze concrete creep effect on the dynamic responses of the member under axial compression and lateral impact. In the model, the constitutive model of core concrete is the plastic damage model, that of steel is the Von Mises yield criterion and kinematic hardening model, and the creep effect at different ages is equivalent to the change of concrete elastic modulus. Then the dynamic responses of concrete-filled steel tubular member considering creep effects was simulated, and the effects of creep on contact time, impact load, deflection, stress and strain were discussed. The fruits provide a scientific basis for the design of the impact resistance of concrete filled steel tubular members.
Topology optimization of reinforced concrete structures
DEFF Research Database (Denmark)
Amir, Oded
Recent advances regarding topology optimization procedures of reinforced concrete structures are presented. We discuss several approaches to the challenging problem of optimizing the distribution of concrete and steel reinforcement. In particular, the consideration of complex nonlinear constitutive...
Giles, G. L.; Wallas, M.
1981-01-01
User documentation is presented for a computer program which considers the nonlinear properties of the strain isolator pad (SIP) in the static stress analysis of the shuttle thermal protection system. This program is generalized to handle an arbitrary SIP footprint including cutouts for instrumentation and filler bar. Multiple SIP surfaces are defined to model tiles in unique locations such as leading edges, intersections, and penetrations. The nonlinearity of the SIP is characterized by experimental stress displacement data for both normal and shear behavior. Stresses in the SIP are calculated using a Newton iteration procedure to determine the six rigid body displacements of the tile which develop reaction forces in the SIP to equilibrate the externally applied loads. This user documentation gives an overview of the analysis capabilities, a detailed description of required input data and an example to illustrate use of the program.
STUDY ON COUPLING MODEL OF SEEPAGE-FIELD AND STRESS-FIELD FOR ROLLED CONTROL CONCRETE DAM
Institute of Scientific and Technical Information of China (English)
GU Chong-shi; SU Huai-zhi; ZHOU Hong
2005-01-01
Based on the construction interfaces in rolled control concrete dam(RCCD),the methods were proposed to calculate the influence thickness of construction interfaces and the corresponding physical mechanics parameters.The principle on establishing the coupling model of seepage-field and stress-field for RCCd was presented.A 3-D Finite Element Method(FEM)program was developed.Study shows that such parameters as the thickness of construction interfaces ,the elastic ration and the Poisson's ratio obtained by tests and theoretical analysis are more resasonable ,the coupling model of seepage-field and stress-field for RCCD may indicate the coupling effect between the two fields scientifically,and the develpped 3-D FEM program can feflect the effect of the construction interfaces more adequately.According to the stydy,many scientific opinions are given both to analyze the influence of the construction interfaces to the dam's characteristic,and to reveal the interaction between the stress-field and the seepage-field.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
The self-stress trial of the fifteen high-strength, low-heat and micro-expansion concrete-filled steel tube(CFST) is introduced, and the generating and distributing features of pre-stress and its relation to adding quantity of expansive agent, which provides persuasive dependences for optimal design of high-strength, low-heat and micro-expansion CFST were investigated, especially for the design of added quantity of expansive agent.
Linear and nonlinear interactions between the earth tide and a tectonically stressed earth
Beaumont, C.
1978-01-01
In the vincinity of earthquake focal regions, conditions may not be equal. Crustal rocks stressed to more than approximately 0.6 of their failure strength exhibit material properties over and above that of linear elasticity. Interactions between the earth tide and crustal rocks that are under high tectonic stress are discussed in terms of simple phenomenological models. In particular, the difference between a nonlinear elastic model of dilatancy and a dilatancy model that exhibits hysteresis is noted. It is concluded that the small changes in stress produced by the earth tide act as a probe of the properties of crustal rocks. Observations of earth tide tilts and strains in such high stress zones may, therefore, provide keys to the constitutive properties and the tectonic stress rate tensor of these zones.
2010-01-01
If we want to make something concrete in mathematics education, we are inclined introduce, what we call, ‘manipulatives’, in the form of tactile objects or visual representations. If we want to make something concrete in a everyday-life conversation, we look for an example. In the former, we try to make a concrete model of our own, abstract, knowledge; in the latter, we try to find an example that the others will be familiar with. This article first looks at the tension between these tw...
Directory of Open Access Journals (Sweden)
Koeno Gravemeijer
2010-07-01
Full Text Available If we want to make something concrete in mathematics education, we are inclined introduce, what we call, ‘manipulatives’, in the form of tactile objects or visual representations. If we want to make something concrete in a everyday-life conversation, we look for an example. In the former, we try to make a concrete model of our own, abstract, knowledge; in the latter, we try to find an example that the others will be familiar with. This article first looks at the tension between these two different ways of making things concrete. Next another role of manipulatives, will be discussed, namely that of means for scaffolding and communication. In this role, manipulatives may function as means of support in a process that aims at helping students to build on their own thinking while constructing more sophisticated mathematics
Institute of Scientific and Technical Information of China (English)
履之
1994-01-01
Although concrete is an excellent building material because of its abili-ty to withstand stress and compression, it is susceptible to cracking. Car-olyn Dry, an associate professor of architecture at the University of Illinois
Effects of stress and physical ageing on nonlinear creep behavior of poly(methyl methacrylate)
Institute of Scientific and Technical Information of China (English)
赵荣国; 陈朝中; 李其抚; 罗文波
2008-01-01
The effects of stress,ageing time and ageing temperature on creep behavior of poly(methyl methacrylate) were studied.After annealing above its glass transition temperature for a period of time to eliminate the stress and thermal history,the specimens were quenched and aged at various ageing temperatures for different ageing time,and then the short-term creep tests under different stress levels were carried out at room temperature.The creep strains were modeled by means of time-ageing time equivalence and time-stress equivalence,and the master creep curves were constructed via ageing time shift factors and stress shift factors.The results indicate that the creep rate increases with stress,while decreases with ageing time,and the ageing temperature history obviously affects the creep rate.For linear viscoelastic material,the ageing shift rate is independent on imposed stress,while for nonlinear viscoelastic material,the ageing shift rate decreases with increasing stress.The unified master creep curve up to 540 d at reference state was constructed by shifting the creep curves horizontally along the logarithmic time axis to overlap each other.It is demonstrated that the time-stress equivalence,united with the time-ageing time equivalence,provides an effective accelerated characterization technique in the laboratory to evaluate the long-term creep behavior of physical ageing polymers.
Hemanth, M; Deoli, Shilpi; Raghuveer, H P; Rani, M S; Hegde, Chatura; Vedavathi, B
2015-09-01
Simulation of periodontal ligament (PDL) using non-linear finite element method (FEM) analysis gives better insight into understanding of the biology of tooth movement. The stresses in the PDL were evaluated for intrusion and lingual root torque using non-linear properties. A three-dimensional (3D) FEM model of the maxillary incisors was generated using Solidworks modeling software. Stresses in the PDL were evaluated for intrusive and lingual root torque movements by 3D FEM using ANSYS software. These stresses were compared with linear and non-linear analyses. For intrusive and lingual root torque movements, distribution of stress over the PDL was within the range of optimal stress value as proposed by Lee, but was exceeding the force system given by Proffit as optimum forces for orthodontic tooth movement with linear properties. When same force load was applied in non-linear analysis, stresses were more compared to linear analysis and were beyond the optimal stress range as proposed by Lee for both intrusive and lingual root torque. To get the same stress as linear analysis, iterations were done using non-linear properties and the force level was reduced. This shows that the force level required for non-linear analysis is lesser than that of linear analysis.
Teruna, D. R.
2017-03-01
Pushover analysis or also known as nonlinear static procedures (NSP) have been recognized in recent years for practical evaluation of seismic demands and for structural design by estimating a structural building capacities and deformation demands. By comparing these demands and capacities at the performance level interest, the seismic performance of a building can be evaluated. However, the accuracy of NSP for assessment irregular building is not yet a fully satisfactory solution, since irregularities of a building influence the dynamic responses of the building. The objective of the study presented herein is to understand the nonlinear behaviour of six story RC building with mass irregularities at different floors and stiffness irregularity at first story (soft story) using NSP. For the purpose of comparison on the performance level obtained with NSP, nonlinear time history analysis (THA) were also performed under ground motion excitation with compatible to response spectra design. Finally, formation plastic hinges and their progressive development from elastic level to collapse prevention are presented and discussed.
An analysis of the stress formula for energy-momentum methods in nonlinear elastodynamics
Romero, Ignacio
2012-11-01
The energy-momentum method, a space-time discretization strategy for elastic problems in nonlinear solid, structural, and multibody mechanics relies critically on a discrete derivative operation that defines an approximation of the internal forces that guarantees the discrete conservation of energy and momenta. In the case of nonlinear elastodynamics, the formulation for general hyperelastic materials is due to Simo and Gonzalez, dating back to the mid-nineties. In this work we show that there are actually infinite second order energy-momentum methods for elastodynamics, all of them deriving from a modified midpoint integrator by an appropriate redefinition of the stress tensor at equilibrium. Such stress tensors can be interpreted as the solutions to local convex projections, whose precise definitions lead to different methods. The mathematical requirements of such projections are identified. Based on this geometrical interpretation several conserving methods are examined.
Strain-enhanced stress relaxation impacts nonlinear elasticity in collagen gels.
Nam, Sungmin; Hu, Kenneth H; Butte, Manish J; Chaudhuri, Ovijit
2016-05-17
The extracellular matrix (ECM) is a complex assembly of structural proteins that provides physical support and biochemical signaling to cells in tissues. The mechanical properties of the ECM have been found to play a key role in regulating cell behaviors such as differentiation and malignancy. Gels formed from ECM protein biopolymers such as collagen or fibrin are commonly used for 3D cell culture models of tissue. One of the most striking features of these gels is that they exhibit nonlinear elasticity, undergoing strain stiffening. However, these gels are also viscoelastic and exhibit stress relaxation, with the resistance of the gel to a deformation relaxing over time. Recent studies have suggested that cells sense and respond to both nonlinear elasticity and viscoelasticity of ECM, yet little is known about the connection between nonlinear elasticity and viscoelasticity. Here, we report that, as strain is increased, not only do biopolymer gels stiffen but they also exhibit faster stress relaxation, reducing the timescale over which elastic energy is dissipated. This effect is not universal to all biological gels and is mediated through weak cross-links. Mechanistically, computational modeling and atomic force microscopy (AFM) indicate that strain-enhanced stress relaxation of collagen gels arises from force-dependent unbinding of weak bonds between collagen fibers. The broader effect of strain-enhanced stress relaxation is to rapidly diminish strain stiffening over time. These results reveal the interplay between nonlinear elasticity and viscoelasticity in collagen gels, and highlight the complexity of the ECM mechanics that are likely sensed through cellular mechanotransduction.
Development of Tensile Softening Model for Plain Concrete
Energy Technology Data Exchange (ETDEWEB)
Lee, S.K.; Song, Y.C. [Korea Electric Power Research Institute, Taejon (Korea)
2002-07-01
Large-scale direct tensile softenng tests using plate concrete specimens(4000, 5000psi) with notch were performed under uniaxial stress. There were presented the basic physical properties and the complete load-CMOD(Crack Mouth Opening Displacement) curves for them And them the fracture energy was evaluated using the complete load-CMOD curves respectively, and there was presents optimal tensile softening model which is modified by a little revision of an existing one. Therefore, here provided the real verification data through the tests for developing other nonlinear concrete finite element models. (author). 32 refs., 38 figs., 4 tabs.
A nonlinear constitutive model for stress relaxation in ligaments and tendons.
Davis, Frances M; De Vita, Raffaella
2012-12-01
A novel constitutive model that describes stress relaxation in transversely isotropic soft collagenous tissues such as ligaments and tendons is presented. The model is formulated within the nonlinear integral representation framework proposed by Pipkin and Rogers (J. Mech. Phys. Solids. 16:59-72, 1968). It represents a departure from existing models in biomechanics since it describes not only the strain dependent stress relaxation behavior of collagenous tissues but also their finite strains and transverse isotropy. Axial stress-stretch data and stress relaxation data at different axial stretches are collected on rat tail tendon fascicles in order to compute the model parameters. Toward this end, the rat tail tendon fascicles are assumed to be incompressible and undergo an isochoric axisymmetric deformation. A comparison with the experimental data proves that, unlike the quasi-linear viscoelastic model (Fung, Biomechanics: Mechanics of Living Tissues. Springer, New York, 1993) the constitutive law can capture the observed nonlinearities in the stress relaxation response of rat tail tendon fascicles.
Non-linear analysis and the design of Pumpkin Balloons: stress, stability and viscoelasticity
Rand, J. L.; Wakefield, D. S.
Tensys have a long-established background in the shape generation and load analysis of architectural stressed membrane structures Founded upon their inTENS finite element analysis suite these activities have broadened to encompass lighter than air structures such as aerostats hybrid air-vehicles and stratospheric balloons Winzen Engineering couple many years of practical balloon design and fabrication experience with both academic and practical knowledge of the characterisation of the non-linear viscoelastic response of the polymeric films typically used for high-altitude scientific balloons Both companies have provided consulting services to the NASA Ultra Long Duration Balloon ULDB Program Early implementations of pumpkin balloons have shown problems of geometric instability characterised by improper deployment and these difficulties have been reproduced numerically using inTENS The solution lies in both the shapes of the membrane lobes and also the need to generate a biaxial stress field in order to mobilise in-plane shear stiffness Balloons undergo significant temperature and pressure variations in flight The different thermal characteristics between tendons and film can lead to significant meridional stress Fabrication tolerances can lead to significant local hoop stress concentrations particularly adjacent to the base and apex end fittings The non-linear viscoelastic response of the envelope film acts positively to help dissipate stress concentrations However creep over time may produce lobe geometry variations that may
Optimization of reinforced concrete slabs
Ferritto, J. M.
1979-01-01
Reinforced concrete cells composed of concrete slabs and used to limit the effects of accidental explosions during hazardous explosives operations are analyzed. An automated design procedure which considers the dynamic nonlinear behavior of the reinforced concrete of arbitrary geometrical and structural configuration subjected to dynamic pressure loading is discussed. The optimum design of the slab is examined using an interior penalty function. The optimization procedure is presented and the results are discussed and compared with finite element analysis.
Optimization of reinforced concrete slabs
Ferritto, J. M.
1979-01-01
Reinforced concrete cells composed of concrete slabs and used to limit the effects of accidental explosions during hazardous explosives operations are analyzed. An automated design procedure which considers the dynamic nonlinear behavior of the reinforced concrete of arbitrary geometrical and structural configuration subjected to dynamic pressure loading is discussed. The optimum design of the slab is examined using an interior penalty function. The optimization procedure is presented and the results are discussed and compared with finite element analysis.
Cheilakou, E.; Theodorakeas, P.; Koui, M.; Zeris, C.
2014-03-01
The present study evaluates the potential of GPR for the inspection of pre-stressed concrete bridges and its usefulness to provide non visible information of the interior structural geometry and condition, required for strengthening and rehabilitation purposes. For that purpose, different concrete blocks of varying dimensions with embedded steel reinforcement bars, tendon ducts and fabricated voids, were prepared and tested by means of GPR in a controlled laboratory environment. 2D data acquisition was carried out in reflection mode along single profile lines of the samples in order to locate the internal structural elements. 3D surveys were also performed in a grid format both along horizontal and vertical lines, and the individual profiles collected were interpolated and further processed using a 3D reconstruction software, in order to provide a detailed insight into the concrete structure. The obtained 2D profiles provided the accurate depth and position of the embedded rebars and tendon ducts, verifying the original drawings. 3D data cubes were created enabling the presentation of depth slices and providing additional information such as shape and localization of the internal elements. The results obtained from this work showed the effectiveness and reliability of the GPR technique for pre-stressed concrete bridge investigations.
Fogarassy, Paul; Cofino, Bruno; Millet, Pierre; Lodini, Alain
2005-07-01
The thermal deposition of hydroxyapatite (HA) on titanium alloy substrate (Ti-6A1-4V) leads to a structure that has very good osseointegration properties. However, clinical failures have been occasionally reported at the interface between substrate and coating. Lifetime is the main parameter in such prostheses; therefore, in order to improve their quality, it is necessary to evaluate the level of stresses near the interface. The high-energy synchrotron radiation combines the advantages of a bulk analysis and reduced volume of the gauge. The objective of our study was to calculate the residual stress using a nonlinear finite-element model and to measure residual stress level near the interface, in the hydroxyapatite coating and in titanium alloy substrate with a nondestructive and high-resolution experiment. The high-energy synchrotron radiation of the BM16 beam-line at ESRF (Grenoble-France) was used with a resolution of down to 10 micrometers. The experimental measurements validate the results found by means of nonlinear finite-element analysis of the plasma spraying induced stress.
有渗透水作用时混凝土坝的实测应力分析%Measured Stress for Concrete Dams with Seepage Water Effect
Institute of Scientific and Technical Information of China (English)
彭虹
2012-01-01
The stress and strain monitoring of concrete dam is the one of monitoring for dam safety, the dam heel is the furthest sensitive emphases place for stress and strain. Recur to elasticity mechanical analysis for porous material, processed research for component elements at measured stress and strain in stress gauge and strain gauge embedded concrete dams. The available stress, that act on framework of concrete and part of pore water pressure rip included in measured stress by stress gauge, and the pore water pressure is full hydraulic head（lifting pressure） p for stress gauge, that embedded on the seam with body of dam and it＇s foundation or the seamed face of body are Indicated. The strain gauge embedded with the same body of dam, the available stress-strain will only included in measured strain, and the part of strain by the pore water pressure without proceed. The theoretic basis provided that rightly applying monitoring data at stress and strain of concrete dams for evaluating character of dam safety.%混凝土坝的应力、应变监测是大坝安全监测的项目之一,大坝坝踵是应力、应变最敏感的重点部位。借助于多孔材料弹性力学的分析,对埋设于混凝土坝中的应力计和应变计实测应力、应变中的构成成分进行了研究,指出了应力计实测应力中包含有作用于混凝土骨架的有效应力和部分孔隙水压力;埋设在建基面和接缝面上的应力计,其孔隙水压力为全水头扬压力。同样埋设在坝体混凝土中的应变计,实测应变中则仅包含有效应力应变,而没有因孔隙水压力产生的变形分量,为正确应用混凝土坝应力、应变监测成果评估大坝安全性状提供了理论依据。
Directory of Open Access Journals (Sweden)
Jianjun Luo
2016-10-01
Full Text Available In recent years, a big number of large diameter pre-stressed concrete cylinder pipe (PCCP lines have been applied to the Mid-route of the South-to-North Water Transfer Project. However, the leakage problem of PCCP causes annually heavy economic losses to our country. In such a context of situation, how to detect leaks rapidly and precisely after pipes appear cracks in water supply system has great significance. Based on the study and analysis of the characteristic structure of large diameter PCCP, a new leak detection system using fiber Bragg grating sensors, which can capture signals of water pressure change, is proposed. The feasibility, reliability and practicability of the system could be acceptable according to data achieved from in–situ tests. Moreover, the leak detection system can monitor in real-time of dynamic change of water pressure. The equations of the leakage quantity and water pressure have been presented in this paper, which can provide technical guidelines for large diameter PCCP lines maintenance.
Liu, Xi; Dong, Xinjun; Wang, Yang
2016-04-01
In structural sensing applications, wireless sensing systems have drawn great interest owing to faster installation process and lower system cost compared to the traditional cabled systems. As a new-generation wireless sensing system, Martlet features high-speed data acquisition and extensible layout, which allows easy interfacing with various types of sensors. This paper presents a field test of the Martlet sensing system installed at an in-service pre-stressed concrete highway bridge on SR113 over Dry Creek in Bartow County, Georgia. Four types of sensors are interfaced with Martlet in this test, including accelerometers, strain gages, strain transducers and magnetostrictive displacement sensors. In addition, thermocouples are used to monitor the temperature change of the bridge through the day. The acceleration, strain and displacement response of the bridge due to traffic and ambient excitations are measured. To obtain the modal properties of the bridge, hammer impact tests are also performed. The results from the field test demonstrate the reliability of the Martlet wireless sensing system. In addition, detailed modal properties of the bridge are extracted from the acceleration data collected in the test.
Nonlinear Creep Model for Deep Rock under High Stress and High Pore Water Pressure Condition
Directory of Open Access Journals (Sweden)
Xie Yuanguang
2016-05-01
Full Text Available Conventional triaxial compression creep experiments for deep sandstone under high confining pressure and high pore water pressure were carried out, in order to predict the creep response of deep rock under these conditions. A nonlinear viscoelastic-plastic creep constitutive model was proposed based on the experimental results. The theory of component model was used as a basis for the formulation of this model. First, by using mathematical fitting and analogy, a new nonlinear viscous component was introduced based on the properties of the creep curves during the tertiary stage. Second, a timer component to judge whether the creep can get into the tertiary stage was presented. Finally, a nonlinear creep model was proposed. Results showed good agreement between theory curves from the nonlinear creep model and experimental data. This model can be applied to predict deep rock creep responses under high stress and high pore water pressure conditions. Hence, the obtained conclusions in this study are beneficial to deep rock engineering.
Simanjuntak, T. D. Y. F.; Marence, M.; Schleiss, A. J.; Mynett, A. E.
2016-11-01
This paper presents the mechanical and hydraulic behaviour of passively prestressed concrete-lined pressure tunnels embedded in elastic transversely isotropic rocks subjected to non-uniform in situ stresses. Two cases are distinguished based on whether the in situ vertical stress in the rock mass is higher, or lower than the in situ horizontal stress. A two-dimensional finite element model was used to study the influence of dip angle, α, and horizontal-to-vertical stress ratio, k, on the bearing capacity of prestressed concrete-lined pressure tunnels. The study reveals that the in situ stress ratio and the orientation of stratifications in the rock mass significantly affect the load sharing between the rock mass and the lining. The distribution of stresses and deformations as a result of tunnel construction processes exhibits a symmetrical pattern for tunnels embedded in a rock mass with either horizontal or vertical stratification planes, whereas it demonstrates an unsymmetrical pattern for tunnels embedded in a rock mass with inclined stratification planes. The results obtained for a specific value α with coefficient k are identical to that for α + 90° with coefficient 1/ k by rotating the tunnel axis by 90°. The maximum internal water pressure was determined by offsetting the prestress-induced hoop strains at the final lining intrados against the seepage-induced hoop strains. As well as assessing the internal water pressure, this approach is capable of identifying potential locations where longitudinal cracks may occur in the final lining.
Rong, Youmin; Zhang, Guojun; Huang, Yu
2016-10-01
Inherent strain analysis has been successfully applied to predict welding deformations of large-scale structural components, while thermal-elastic-plastic finite element method is rarely used for its disadvantages of long calculation period and large storage space. In this paper, a hybrid model considering nonlinear yield stress curves and multi-constraint equations to thermal-elastic-plastic analysis is further proposed to predict welding distortions and residual stresses of large-scale structures. For welding T-joint structural steel S355JR by metal active gas welding, the published experiment results of temperature and displacement fields are applied to illustrate the credibility of the proposed integration model. By comparing numerical results of four different cases with the experiment results, it is verified that prediction precision of welding deformations and residual stresses is apparently improved considering the power-law hardening model, and computational time is also obviously shortened about 30.14% using multi-constraint equations. On the whole, the proposed hybrid method can be further used to precisely and efficiently predict welding deformations and residual stresses of large-scale structures.
Structural Precast Concrete Handbook
DEFF Research Database (Denmark)
Kjærbye, Per Oluf H
Structural concept for precast concrete systems. Design og precast reinforced concrete components. Design of precast concrete connections. Illustrations on design of precast concrete buildings. Precast concrete assembly....
Institute of Scientific and Technical Information of China (English)
牛坤
2014-01-01
The study of the impervious concrete wall body stress deformation characteristics of an earth -rockfill dam under different plastic modulus , wall thickness and dam height working conditions gives a reference to design of a similar hydraulic project .Taking the optimized design of the impervious wall reinforcement scheme of the dan-ger-removing and reinforcement project of a certain clay core dam in Zhejiang Province as the basis , the stress de-formation characteristics of the impervious wall were analyzed by means of 2-dimensional nonlinearity .The wall body stress is significantly affected by plastic modulus and dam height and less affected by wall thickness , while its horizontal displacement is significantly affected by dam height and very little by either plastic modulus or wall thick -ness.When a dam impervious wall is designed , importance should be attached to selection of wall body concrete plastic modulus.In general ordinary concrete could be used for the low dams with a height of 20m or less, and the plastic modulus should be controlled to be ess than 5,000 MPa for the 40 –60m high dams.%以浙江省某粘土心墙坝除险加固工程防渗墙加固方案优化设计为背景，采用二维非线性对防渗墙的应力变形特性进行分析。研究土石坝坝体混凝土防渗墙在不同弹性模量、墙厚和坝高工况下的墙体应力变形特性。墙体应力受弹性模量及坝高的影响显著，受墙厚的影响微小；水平位移受坝高的影响显著，受弹性模量和墙厚的影响很小。坝体防渗墙设计时，应重视墙体混凝土弹性模量的选择。对一般20 m级的低坝可采用普通混凝土材料，对于40～60 m级中坝，应控制弹性模量不超过5000 MPa。
Constitutive Behavior and Finite Element Analysis of FRP Composite and Concrete Members
Directory of Open Access Journals (Sweden)
Ki Yong Ann
2013-09-01
Full Text Available The present study concerns compressive and flexural constitutive models incorporated into an isoparametric beam finite element scheme for fiber reinforced polymer (FRP and concrete composites, using their multi-axial constitutive behavior. The constitutive behavior of concrete was treated in triaxial stress states as an orthotropic hypoelasticity-based formulation to determine the confinement effect of concrete from a three-dimensional failure surface in triaxial stress states. The constitutive behavior of the FRP composite was formulated from the two-dimensional classical lamination theory. To predict the flexural behavior of circular cross-section with FRP sheet and concrete composite, a layered discretization of cross-sections was incorporated into nonlinear isoparametric beam finite elements. The predicted constitutive behavior was validated by a comparison to available experimental results in the compressive and flexural beam loading test.
Numerical analysis of ultimate strength of concrete filled steel tubular arch bridges
Institute of Scientific and Technical Information of China (English)
XIE Xu; CHEN Heng-zhi; Li Hui; SONG Shi-rui
2005-01-01
The calculation of ultimate bearing capacity is a significant issue in the design of Concrete Filled Steel Tubular (CFST)arch bridges. Based on the space beam theory, this paper provides a calculation method for determining the ultimate strength of CFST structures. The accuracy of this method and the applicability of the stress-strain relationships were validated by comparing different existing confined concrete uniaxial constitutive relationships and experimental results. Comparison of these results indicated that this method using the confined concrete uniaxial stress-strain relationships can be used to calculate the ultimate strength and CFST behavior with satisfactory accuracy. The calculation results are stable and seldom affected by concrete constitutive relationships. The method is therefore valuable in the practice of engineering design. Finally, the ultimate strength of an arch bridge with span of 330 m was investigated by the proposed method and the nonlinear behavior was discussed.
Institute of Scientific and Technical Information of China (English)
潘金龙; 鲁冰; 顾大伟; 夏正昊; 夏天阳
2015-01-01
In order to improve the seismic performance, deformation ability and ultimate load-carrying capacity of columns with rectangular cross section, engineered cementitious composite (ECC) is introduced to partially substitute concrete in the edge zone of reinforced concrete columns and form reinforced ECC/concrete composite columns. Firstly, based on the assumption of plane remaining plane and the simplified constitutive models, the calculation method of the load-carrying capacity of reinforced ECC/concrete columns is proposed. The stress and strain distribu-tions and crack propagation of the composite columns in different states of eccentric compressive loading are ana-lyzed. Then, nonlinear finite element analysis is conducted to study the mechanical performance of reinforced ECC/concrete composite columns with rectangular cross section. It is found that the simulation results are in good agreement with the theoretical results, indicating that the proposed method for calculating the load-carrying capacity of concrete/ECC composite columns is valid. Finally, based on the proposed method, the effects of ECC thickness, com-pressive strength of concrete and longitudinal reinforcement ratio on the mechanical performance of reinforced ECC/concrete composite columns are analyzed. Calculation results indicate that increasing the thickness of ECC layer or longitudinal reinforcement ratio can effectively increase the ultimate load-carrying capacity of the composite column with both small and large eccentricity, but increasing the strength of concrete can only increase the ultimate load-carrying capacity of the composite column with small eccentricity.
Energy Technology Data Exchange (ETDEWEB)
Ameler, J.
1997-12-31
In this work, an analytical material model was developed, based on the finite element (FE) method, with which the material behaviour of a normal quartzite concrete under temperature stress can be described. Starting from natural fires, the short term area and temperatures between the normal temperature and about 800 C are of special interest. Altogether, it was found that important processes reducing the strength, which occur in high temperature stresses of concrete, can be directly traced back to the additive or the mortar phase, while others are due to the interaction between the two partners. In this attempted model, the compound material concrete is therefore regarded as a system consisting of two components, the additive and the mortar matrix. The mortar matrix is defined as the part consisting of the cement, the water and the fine proportion of the additive (diameter{<=}4 mm). (orig./MM) [Deutsch] In der vorliegenden Arbeit wurde ein analytisches Werkstoffmodell auf der Basis der FE-Methode entwickelt, mit dem das Werkstoffverhalten eines quarzitischen Normalbetons unter einer Temperaturbeanspruchung beschrieben werden kann. Ausgehend vom natuerlichen Brandgeschehen, interessieren besonders der Kurzzeitbereich und Temperaturen zwischen Normaltemperatur und ca. 800 C. In der Summe zeichnet sich ab, dass wesentliche festigkeitsmindernde Prozesse, die sich bei einer Hochtemperaturbeanspruchung von Beton abspielen, direkt dem Zuschlag bzw. der Moertelphase zugeordnet werden koennen, waehrend andere auf die Interaktion zwischen den beiden Partnern zurueckzufuehren sind. Im vorliegenden Modellansatz wird der Verbundwerkstoff Beton deshalb als ein aus zwei Komponenten bestehendes System betrachtet, dem Zuschlag und der Moertelmatrix. Die Moertelmatrix wird als der aus dem Zement, dem Wasser und dem Feinanteil des Zuschlags (Durchmesser{<=}4 mm) zusammengesetzte Teil definiert. (orig./MM)
NONLINEAR ANALYSIS OF CONCRETE WALL AT HIGH TEMPERATURE%高温条件下混凝土墙体的非线性分析研究
Institute of Scientific and Technical Information of China (English)
李荣涛
2011-01-01
论文建立了一个弹塑性-损伤耦合本构模型用于数值模拟高温下混凝土的真实破坏过程.导出了一个利用Newton-Raphson迭代的一般的直接应力返回映射算法.同时求解应力向量和塑性、损伤的内状态变量.并推导了用于化学-热-湿-力学耦合分析的全局守恒方程Newton-Raphson迭代过程的一致性切线模量矩阵.建议了一个用于弹塑性-损伤耦合分析的两级求解过程.给出的数值例题结果显示了所提出的算法和公式的正确性,表明了所发展的弹塑性-损伤耦合本构模型在模拟高温下混凝土墙体中复杂破坏过程的能力.%A coupled elastoplastic-damage constitutive model for the numerical simulation of realistic failure in concretes at high temperature is developed in this paper. A general direct stress return mapping algorithm, using Newton-Raphson iteration, is derived. The stress vector and scalar internal state variables quantifying the incremental plasticity and damage are updated simultaneously. The consistent tangent modulus matrices for coupled chemo-thermo-hygro-mechanical analysis are formulated for use in the global Newton iterative procedure. A solution procedure with two hierarchical phases for the coupled elastoplastic-damage analysis is proposed. Numerical examples are given to demonstrate the validity of the presented algorithm and formulations, illustrate the capability of the proposed constitutive model in reproducing coupled chemo-thermo-hygro-mechanical behavior in concrete wall subjected to fire and thermal radiation.
Energy Technology Data Exchange (ETDEWEB)
Bahedi, K., E-mail: bahedikhadija@yahoo.fr [Laboratoire Optoelectronique et Physico-chimie des Materiaux.Unite de recherche associe au CNRST-URAC-14. Universite Ibn Tofail, Faculte des Sciences BP 133 Kenitra 14000 (Morocco); Addou, M.; Jouad, M. El; Sofiani, Z. [Laboratoire Optoelectronique et Physico-chimie des Materiaux.Unite de recherche associe au CNRST-URAC-14. Universite Ibn Tofail, Faculte des Sciences BP 133 Kenitra 14000 (Morocco); Oauzzani, H. EL; Sahraoui, B. [Institute of Sciences and Molecular Technologies of Angers, MOLTECH Anjou - UMR CNRS 6200, 2 bd Lavoisier 49045 ANGERS cedex2 (France)
2011-07-01
Nanocrystalline ZnO:Al thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 450 deg. C to study their crystalline structure, composition, strain, stress, roughness characteristics and nonlinear optical susceptibility as a function of Al concentration (0, 2, 3, 5 at.%). The films were characterized by X-ray diffractometer (XRD), EDAX 9100 analyser, atomic force microscopy (AFM) and third harmonic generation (THG). The Al (3 at.%) doped ZnO thin films exhibited the lower strain/stress than undoped films. The nonlinear properties of the ZnO:Al thin films have been found to be influenced by the films strain/stress.
Polymer concrete patching materials
Energy Technology Data Exchange (ETDEWEB)
Fontana, J.J.
1977-09-01
The increased use of deicing salts is causing rapid deterioration of portland cement concrete bridge decks. Soluble chlorides cause corrosion of the steel reinforcing rods with a corresponding increase in volume of the rods. This expansion causes stresses in the concrete which result in delaminations and surface spalling. The repair of surface spalls with portland cement concrete can only be made if traffic can be avoided for several days. A patching material which would allow traffic to resume over the repaired area in a few hours was needed. Polymer concrete (PC) was developed to repair deteriorated portland cement concrete. Polymer concrete is defined as a composite material in which the aggregate is bound together in a dense matrix with a polymer binder. The aggregate is mixed with a monomer mixture and subsequently cured in place. Polymer concrete combines the premix characteristics of portland cement concrete with high strength, long term durability properties and fast cure times. PC placed at temperatures between 35/sup 0/F and 95/sup 0/F attains strengths greater than 5000 psi in 2 hours. The high early strength of PC is suitable for use in the repair of highway structures where traffic conditions allow closing of the area for only a few hours.
2012-01-01
Pervious concrete is a type of concrete with little or no fines which give a large void. This enables high permeability and because of this it enables water to percolate through the concrete. Pervious concrete have been used in many years both as pavement material and on several other applications in the U.S and in other countries in Western Europe. In Norway pervious concrete is not currently in use. This thesis aims to investigate if pervious concrete can withstand the harsh Norwegian clima...
Institute of Scientific and Technical Information of China (English)
Cai-Wan Chang-Jian; Her-Terng Yau
2007-01-01
This study performs a dynamic analysis of a rotor supported by two squeeze couple stress fluid film journal bearings with nonlinear suspension. The numerical results show that the stability of the system varies with the non-dimensional speed ratios and the dimensionless parameter l*. It is found that the system is more stable with higher dimensionless parameter l*.Thus it can conclude that the rotor-bearing system lubricated with the couple stress fluid is more stable than that with the conventional Newtonian fluid. The modeling results thus obtained by using the method proposed in this paper can be used to predict the stability of the rotor-bearing system and the undesirable behavior of the rotor and bearing center can be avoided.
The Design and Analysis of Long-Span and Low-Depth Prestressed Composite Steel-Concrete Beam Bridge
Institute of Scientific and Technical Information of China (English)
张俊平; 黄海云; 黄道沸
2002-01-01
The design scheme of long-span and low-depth composite steel-concrete beams is introduced, and the methods of avoiding the cracking of concrete deck in the negative moment regions are proposed. Moreover, significant exploration for problems of the composite beams has been made, such as optimizing construction steps to regulate the stress, applying jacking technique to exert prestress on the concrete deck, investigating the uplifting force principle of the shear connectors by means of model test and non-linear finite element analysis, and pointing out the countermeasure to reduce tension force of the shear connectors.
Chlorine signal attenuation in concrete.
Naqvi, A A; Maslehuddin, M; ur-Rehman, Khateeb; Al-Amoudi, O S B
2015-11-01
The intensity of prompt gamma-ray was measured at various depths from chlorine-contaminated silica fume (SF) concrete slab concrete specimens using portable neutron generator-based prompt gamma-ray setup. The intensity of 6.11MeV chloride gamma-rays was measured from the chloride contaminated slab at distance of 15.25, 20.25, 25.25, 30.25 and 35.25cm from neutron target in a SF cement concrete slab specimens. Due to attenuation of thermal neutron flux and emitted gamma-ray intensity in SF cement concrete at various depths, the measured intensity of chlorine gamma-rays decreases non-linearly with increasing depth in concrete. A good agreement was noted between the experimental results and the results of Monte Carlo simulation. This study has provided useful experimental data for evaluating the chloride contamination in the SF concrete utilizing gamma-ray attenuation method.
Directory of Open Access Journals (Sweden)
Zhen Chen
2016-01-01
Full Text Available Accelerated degradation test (ADT has been widely used to assess highly reliable products’ lifetime. To conduct an ADT, an appropriate degradation model and test plan should be determined in advance. Although many historical studies have proposed quite a few models, there is still room for improvement. Hence we propose a Nonlinear Generalized Wiener Process (NGWP model with consideration of the effects of stress level, product-to-product variability, and measurement errors for a higher estimation accuracy and a wider range of use. Then under the constraints of sample size, test duration, and test cost, the plans of constant-stress ADT (CSADT with multiple stress levels based on the NGWP are designed by minimizing the asymptotic variance of the reliability estimation of the products under normal operation conditions. An optimization algorithm is developed to determine the optimal stress levels, the number of units allocated to each level, inspection frequency, and measurement times simultaneously. In addition, a comparison based on degradation data of LEDs is made to show better goodness-of-fit of the NGWP than that of other models. Finally, optimal two-level and three-level CSADT plans under various constraints and a detailed sensitivity analysis are demonstrated through examples in this paper.
Structural Precast Concrete Handbook
DEFF Research Database (Denmark)
Kjærbye, Per Oluf H
Structural concept for precast concrete systems. Design og precast reinforced concrete components. Design of precast concrete connections. Illustrations on design of precast concrete buildings. Precast concrete assembly.......Structural concept for precast concrete systems. Design og precast reinforced concrete components. Design of precast concrete connections. Illustrations on design of precast concrete buildings. Precast concrete assembly....
Characterization and Stress-Strain Relationship of Leached Concrete%溶蚀混凝土的表征及应力-应变关系
Institute of Scientific and Technical Information of China (English)
黄蓓; 钱春香
2011-01-01
溶蚀作用导致水泥基材料的孔隙率增加从而影响材料的传输及力学性能.对于结构中的既有混凝土,采用非破损和局部破损方法测量和评估溶蚀混凝士的承载力是非常重要的.采用酚酞指示剂法、孔隙溶液pH测量法、超声波无损检测法,对溶蚀混凝土进行了溶蚀损伤程度表征;试验测试了溶蚀混凝七的单轴应力一应变关系:采用XRD和压汞分析研究了混凝土溶蚀机理.研究表明:酚酞指示剂法可以较为直观的表征溶蚀损伤深度,测量的溶蚀程度与强度衰减较为接近:Ca(OH)2和C-S-H凝胶在溶蚀过程中同时溶出,Ca(OH)2是造成早期溶蚀质量损伤的主要原因:混凝土溶蚀后有害孔的数量增加,对混凝土的耐久性产生不利影响;溶蚀混凝土的应力-应变关系曲线形状与普通混凝土相似,但表现出良好的延性及韧性.%Leaching of cementitious materials leads to an increase in porosity, which has important consequences on transport and mechanical properties. It is thus important to investigate the methods that can be used in unleached concrete to evaluate the residual bearing capacity of leached concrete. In this paper, the degradation degree of leached concrete was characterized by three methods (i.e., spraying phenolphthalein, pH value of pore solution, velocity of supersonic). The stress-strain curve of leached concrete under unaxial loads was examined by a material test system. The kinetics of degradation was analyzed by X-ray diffraction and mercury intrusion test. The results show that spraying phenolphthalein is an effective way to characterize the leaching degradation related to attenuation of compressive strength. The dissolution happened both in portlandite and C-S-H gel during the leaching duration and the dissolution of portlandite is a main cause of mass loss at the early stages of leaching. A number of harmful pores with the size above 200 nm increased in the leaching of
Enos, David George
Assessment of the effect of cathodic protection on a chloride contaminated bridge pile involves the definition of the hydrogen embrittlement behavior of the pearlitic reinforcement combined with quantification of the local (i.e., at the steel/concrete interface) chemical and electrochemical conditions, both prior to and throughout the application of cathodic protection. The hydrogen embrittlement behavior of the reinforcement was assessed through a combination of Devanathan/Stachurski permeation experiments to quantify subsurface hydrogen concentrations, CsbH, as a function of the applied hydrogen overpotential, eta, and crack initiation tests for bluntly notched and fatigue pre-cracked tensile specimens employing elastic-plastic finite element analysis and linear elastic fracture mechanics, respectively. A threshold mobile lattice hydrogen concentration for embrittlement of 2×10sp{-7} mol/cmsp3 was established for bluntly notched and fatigue pre-cracked specimens. Crack initiation occurred by the formation of shear cracks oriented at an angle approaching 45sp° from the tensile axis, as proposed by Miller and Smith (Miller, 1970), in regions where both the longitudinal and shear stresses were maximized (i.e., near the notch root). These Miller cracks then triggered longitudinal splitting which continued until fast fracture of the remaining ligament occurred. Instrumented laboratory scale piles were constructed and partially immersed in ASTM artificial ocean water. With time, localized corrosion (crevicing) was initiated along the reinforcement, and was accompanied by an acidic shift in the pH of the occluded environment due to ferrous ion hydrolysis. Cathodic protection current densities from -0.1 muA/cmsp2 to -3.0 muA/cmsp2 were applied via a skirt anode located at the waterline. Current densities as low as 0.66 muA/cmsp2 were sufficient to deplete the dissolved oxygen concentration at the steel/concrete interface and result in the observance of hydrogen
Jeong, Hyunjo; Zhang, Shuzeng; Li, Xiongbing
2017-02-01
In this work, we employ a focused beam theory to modify the phase reversal at the stress-free boundary, and consequently enhance the second harmonic generation during its back-propagation toward the initial source position. We first confirmed this concept through experiment by using a spherically focused beam at the water-air interface, and measuring the reflected second harmonic and comparing with a planar wave reflected from the same stress-free or a rigid boundary. In order to test the feasibility of this idea for measuring the nonlinearity parameter of solids in a reflection mode, a focused nonlinear ultrasonic beam is modeled for focusing at and reflection from a stress-free boundary. A nonlinearity parameter expression is then defined together with diffraction and attenuation corrections.
DEFF Research Database (Denmark)
Bache, Anja Margrethe
2010-01-01
Why glazed concrete? Concrete hardens and finds its strength at room temperature whereas clay products must first be fired before they achieve this strength. They are stronger and three times as durable as clay products, which is a weighty reason for choosing concrete.5 Another reason, which....... If this succeeds, it will be possible to manufacture thin, large-scale glazed concrete panels comparable in size to concrete sandwich construction and larger which, with or without back-casting, can work as load-bearing construction elements....
DEFF Research Database (Denmark)
Bache, Anja Margrethe
2010-01-01
Why glazed concrete? Concrete hardens and finds its strength at room temperature whereas clay products must first be fired before they achieve this strength. They are stronger and three times as durable as clay products, which is a weighty reason for choosing concrete.5 Another reason, which....... If this succeeds, it will be possible to manufacture thin, large-scale glazed concrete panels comparable in size to concrete sandwich construction and larger which, with or without back-casting, can work as load-bearing construction elements....
Bond behaviour of GFRP reinforced geopolymer cement concrete
Directory of Open Access Journals (Sweden)
Hailu Tekle Biruk
2017-01-01
Full Text Available Bond plays a key role in the performance of reinforced concrete structures. Glass fibre reinforced polymer (GFRP reinforcing bar and Geopolymer cement (GPC concrete are promising alternative construction materials for steel bars and Ordinary Portland Cement (OPC concrete respectively. In this study, the bond behaviour between these two materials is investigated by using beam-end specimen tests. The bond behaviour of 15.9 mm diameter sand-coated GFRP bar was investigated. An embedment length of six and nine times the bar diameter were used. The free end and the loaded end bond-slip-relationships, the bond failure mode and the average bond stress were used to analyse each of the specimens. Additionally, the distribution of tensile and bond stress along the embedment length was investigated by installing strain gauges along the embedment length in some of the specimens. Test results indicate that a significant difference exists between the free end and loaded end bond-slip curves, which is due to the lower elastic modulus of the GFRP bars. Furthermore, it was found that the tensile and bond stress distribution along the embedment length is nonlinear and the nonlinearity changes with the load.
Nonlinear feedback drives homeostatic plasticity in H2O2 stress response
Goulev, Youlian; Morlot, Sandrine; Matifas, Audrey; Huang, Bo; Molin, Mikael; Toledano, Michel B; Charvin, Gilles
2017-01-01
Homeostatic systems that rely on genetic regulatory networks are intrinsically limited by the transcriptional response time, which may restrict a cell’s ability to adapt to unanticipated environmental challenges. To bypass this limitation, cells have evolved mechanisms whereby exposure to mild stress increases their resistance to subsequent threats. However, the mechanisms responsible for such adaptive homeostasis remain largely unknown. Here, we used live-cell imaging and microfluidics to investigate the adaptive response of budding yeast to temporally controlled H2O2 stress patterns. We demonstrate that acquisition of tolerance is a systems-level property resulting from nonlinearity of H2O2 scavenging by peroxiredoxins and our study reveals that this regulatory scheme induces a striking hormetic effect of extracellular H2O2 stress on replicative longevity. Our study thus provides a novel quantitative framework bridging the molecular architecture of a cellular homeostatic system to the emergence of nonintuitive adaptive properties. DOI: http://dx.doi.org/10.7554/eLife.23971.001 PMID:28418333
Levy, Lawrence R; Yao, Weiguang; McGuire, George; Vollick, Dan N; Jette, Jennifer; Shanahan, Matthew J; Hay, James M; Neufeld, Richard W J
2012-10-01
Dynamical systems analysis is applied to a nonlinear model of stress and coping (Neufeld, 1999). The model is composed of 6 order parameters and 11 control parameters, and integrates core constructs of the topic domain, including variants of cognitive appraisal, differential stress susceptibility, stress activation, and coping propensity. In part owing to recent advances in Competitive Modes Theory (Yao, Yu & Essex, 2002), previously intractable but substantively significant dynamical properties of the 6-dimensional model are identified. They include stable and unstable fixed-point equilibria (higher-dimensional saddle-node bifurcation), oscillatory patterns attending fixed-point de-stabilization, and chaotic behaviors. Examination of the nature of system fixed-point de-stabilization, in relation to its control parameters, unveils mechanisms of re-stabilization, and dynamic stability control. All identified dynamics emerge naturally from a system whose construction guideposts are lodged in the addressed content domain. Dynamical complexities therefore may be intrinsic to the present content domain, possibly no less so than in other disciplines where the presence of such attributes has been established.
Nonlinear effect of elastic vortexlike motion on the dynamic stress state of solids
Shilko, Evgeny V.; Grinyaev, Yurii V.; Popov, Mikhail V.; Popov, Valentin L.; Psakhie, Sergey G.
2016-05-01
We present a theoretical analysis of the dynamic stress-strain state of regions in a solid body that are involved in a collective elastic vortexlike motion. It is shown that the initiation of elastic vortexlike motion in the material is accompanied by the appearance of dilatancy and equivalent strain, the magnitudes of which are proportional to the square of the ratio of linear velocity on the periphery of the elastic vortex to the velocity of longitudinal elastic waves (P wave). Under conditions of dynamic loading the described dynamic effects are able to initiate inelastic deformation or destruction of the material at loading speeds of a few percent of the P -wave speed. The obtained analytical estimates suggest that dynamic nonlinear strains can make a significant contribution in a number of widely studied nonlinear dynamic phenomena in solids. Among them are the effect of acoustic (dynamic) dilatancy in solids and granular media, which leads to the generation of longitudinal elastic waves by transverse waves [V. Tournat et al., Phys. Rev. Lett. 92, 085502 (2004), 10.1103/PhysRevLett.92.085502] and the formation of an array of intense "hot spots" (reminiscent of shear-induced hydrodynamic instabilities in fluids) in adiabatic shear bands [P. R. Guduru et al., Phys. Rev. E 64, 036128 (2001), 10.1103/PhysRevE.64.036128].
Micromechanism Underlying Nonlinear Stress-Dependent K0 of Clays at a Wide Range of Pressures
Directory of Open Access Journals (Sweden)
Xiang-yu Shang
2015-01-01
Full Text Available In order to investigate the mechanism underlying the reported nonlinear at-rest coefficient of earth pressure, K0 of clays at high pressure, a particle-scale model which can be used to calculate vertical and horizontal repulsion between clay particles has been proposed. This model has two initial states which represent the clays at low pressure and high pressure, and the particles in this model can undergo rotation and vertical translation. The computation shows that the majority of particles in a clay sample at high pressure state would experience rotation during one-dimensional compression. In addition, rotation of particles which tends to form a parallel structure causes an increase of the horizontal interparticle force, while vertical translation leads to a decrease in it. Finally, the link between interparticle force, microstructure, and macroscopic K0 is analyzed and it can be used to interpret well the nonlinear changes in K0 with both vertical consolidation stress and height-diameter ratio.
Strength and Deformation of Axially Loaded Fiber-Reinforced Polymer Sheet Confined Concrete Columns
Institute of Scientific and Technical Information of China (English)
李静; 钱稼茹; 蒋剑彪
2004-01-01
Experimental results of 29 axially loaded fiber-reinforced polymer sheet (FS) confined concrete columns and two reference plain concrete columns are introduced. Twenty four column specimens were confined with carbon fiber sheet (CFS) and five column specimens were hybrid confined with both CFS and glass fiber sheet (GFS). The influence of aspect ratio, FS material, initial axial force ratio, and FS confinement degree on the strength and deformation of columns were studied. Based on the experimental results, the equations of complete stress-strain curve of CFS confined concrete are proposed. These equations are suitable for the nonlinear analysis of square and rectangular section columns. Suggestions of applying FS to confine concrete columns are presented.
Application of artificial neural networks to predict the deflections of reinforced concrete beams
Kaczmarek, Mateusz; Szymańska, Agnieszka
2016-06-01
Nonlinear structural mechanics should be taken into account in the practical design of reinforced concrete structures. Cracking is one of the major sources of nonlinearity. Description of deflection of reinforced concrete elements is a computational problem, mainly because of the difficulties in modelling the nonlinear stress-strain relationship of concrete and steel. In design practise, in accordance with technical rules (e.g., Eurocode 2), a simplified approach for reinforced concrete is used, but the results of simplified calculations differ from the results of experimental studies. Artificial neural network is a versatile modelling tool capable of making predictions of values that are difficult to obtain in numerical analysis. This paper describes the creation and operation of a neural network for making predictions of deflections of reinforced concrete beams at different load levels. In order to obtain a database of results, that is necessary for training and testing the neural network, a research on measurement of deflections in reinforced concrete beams was conducted by the authors in the Certified Research Laboratory of the Building Engineering Institute at Wrocław University of Science and Technology. The use of artificial neural networks is an innovation and an alternative to traditional methods of solving the problem of calculating the deflections of reinforced concrete elements. The results show the effectiveness of using artificial neural network for predicting the deflection of reinforced concrete beams, compared with the results of calculations conducted in accordance with Eurocode 2. The neural network model presented in this paper can acquire new data and be used for further analysis, with availability of more research results.
Developing the phenomenological equations triaxial deformation of concrete under dynamic loads
Directory of Open Access Journals (Sweden)
Berlinov Mikhail
2017-01-01
Full Text Available The basic assumptions and hypotheses construction of the computational model studies, taking into account the peculiarities of the work force imperfections of materials under dynamic loading, based on the phenomenological laws of nonlinear rheology and deformable elastic-creeping body. The values for the coefficient vibrocreep computational model under triaxial stress-strain state on the basis of the hypothesis of central symmetry of the hysteresis loop. The basic phenomenological equations allow the calculation of concrete elements in the conditions of triaxial stress-strain state under dynamic impacts and taking into account the non-linearity of the rheology of deformation.
Lifespan and oxidative stress show a non-linear response to atmospheric oxygen in Drosophila.
Rascón, Brenda; Harrison, Jon F
2010-10-15
Oxygen provides the substrate for most ATP production, but also serves as a source of reactive oxygen species (ROS), which can induce cumulative macromolecular oxidative damage and cause aging. Pure oxygen atmospheres (100 kPa) are known to strongly reduce invertebrate lifespan and induce aging-related physiological changes. However, the nature of the relationship between atmospheric oxygen, oxidative stress, and lifespan across a range of oxygen levels is poorly known. Developmental responses are likely to play a strong role, as prior research has shown strong effects of rearing oxygen level on growth, size and respiratory system morphology. In this study, we examined (1) the effect of oxygen on adult longevity and (2) the effect of the oxygen concentration experienced by larvae on adult lifespan by rearing Drosophila melanogaster in three oxygen atmospheres throughout larval development (10, 21 and 40 kPa), then measuring the lifespan of adults in five oxygen tensions (2, 10, 21, 40, 100 kPa). We also assessed the rate of protein carbonyl production for flies kept at 2, 10, 21, 40 and 100 kPa as adults (all larvae reared in normoxia). The rearing of juveniles in varying oxygen treatments affected lifespan in a complex manner, and the effect of different oxygen tensions on adult lifespan was non-linear, with reduced longevity and heightened oxidative stress at extreme high and low atmospheric oxygen levels. Moderate hypoxia (10 kPa) extended maximum, but not mean lifespan.
Continuous Reinforced Concrete Beams
DEFF Research Database (Denmark)
Hoang, Cao Linh; Nielsen, Mogens Peter
1996-01-01
This report deals with stress and stiffness estimates of continuous reinforced concrete beams with different stiffnesses for negative and positive moments e.g. corresponding to different reinforcement areas in top and bottom. Such conditions are often met in practice.The moment distribution...
Bond-slip behavior of CFRP plate-concrete interface
Cho, D. Y.; Park, S. K.; Hong, S. N.
2011-11-01
The paper deals with evaluation of the bond performance between a CFRP plate and concrete with respect to various compressive strengths of concrete and bond lengths of the CFRP plate as parameters. To consider stress conditions in the tensile zone of reinforced concrete (RC) structures, double-lap axial tension tests were conducted for eight specimens with CFRP plates bonded to concrete prisms. In addition, a simple linear bond-slip model for the CFRP plate/concrete joints, developed from the bond tests, was used. To verify the model proposed, a total of seven RC beams were strengthened with CFRP plates and tested in flexure employing various bond lengths, strengthening methods, and numbers of CFRP plates. A nonlinear finite-element analysis, with the bond-slip model incorporated in the DIANA program, was performed for the strengthened RC beams. Also, the results of flexural test and analytical predictions are found to be in close agreement in terms of yield and ultimate loads and ductility.
Directory of Open Access Journals (Sweden)
B. M. Khroustalev
2015-01-01
Full Text Available One of the main directions in construction material science is the development of next generation concrete that is ultra-dense, high-strength, ultra-porous, high heat efficient, extra corrosion-resistant. Selection of such direction is caused by extreme operational impacts on the concrete, namely: continuously increasing load on the concrete and various dynamics of such loads; the necessity in operation of concrete products in a wide temperature range and their exposure to various chemical and physical effects.The next generation concrete represents high-tech concrete mixtures with additives that takes on and retain the required properties when hardening and being used under any operational conditions. A differential characteristic of the next generation concrete is its complexity that presumes usage of various mineral dispersed components, two- and three fractional fine and coarse aggregates, complex chemical additives, combinations of polymer and iron reinforcement.Design strength and performance properties level of the next generation concrete is achieved by high-quality selection of the composition, proper selection of manufacturing techniques, concrete curing, bringing the quality of concrete items to the required level of technical condition during the operational phase. However, directed formation of its structure is necessary in order to obtain high-tech concrete.Along with the traditional methods for regulation of the next generation concrete structure, modification of concrete while using silica nanoparticles is also considered as a perspective one because the concrete patterning occurs due to introduction of a binder in a mineral matrix. Due to this it is possible to obtain nano-modified materials with completely new properties.The main problem with the creation of nano-modified concrete is a uniform distribution of nano-materials in the volume of the cement matrix which is particularly important in the cases of adding a modifier in
Directory of Open Access Journals (Sweden)
Yijie Huang
2015-01-01
Full Text Available A new mechanical model for analysing the behaviour of axially loaded recycled aggregate concrete filled steel tubes (RACFSTs stub columns is presented in this study. The model is derived from the typical elastoplasticity, the nonlinear elastic mechanics, and the properties of materials. Based on the mechanical model, a novel numerical program is developed. The mechanical model and the numerical program are adopted to study the effect of recycled coarse aggregate (RCA replacement percentage on RACFST mechanical behaviour. The complete load-deformation relationship of specimens, the steel tube axial and circumferential stresses, and the performance of the confined core concrete and the variation of interaction are also investigated. The analytical results indicate that this model is able to capture the mechanical behaviour of RACFST. It is also found that the axial and circumferential stresses of steel tube change nonlinearly during the loading stages. It is concluded that the behaviour of the confined core concrete is significantly influenced by the confining pressure. The steel tube confinement could improve the mechanical behaviour of RAC effectively and the RCA replacement percentage slightly changes the response of core concrete. Finally, the relations between confined core concrete and confining pressure are analysed.
Measurements of resonance frequencies on prestressed concrete beams during post-tensioning
Energy Technology Data Exchange (ETDEWEB)
Lundqvist, P. [Div. of Structural Engineering, Lund University (Sweden); Ryden, N. [Div. of Engineering Geology, Lund University (Sweden)
2011-07-01
The reactor containment, which is a concrete structure prestressed vertically and horizontally, is the most essential safety barrier in a nuclear power plant and is designed to withstand a severe internal accident. The safety of the containment depends on the induced compressive stresses in the concrete, however due to various long-term mechanisms the tendon forces will decrease with time. Today, no methods exist for measuring these prestress losses in containments with bonded tendons and thus there is a need for non-destructive methods for estimating the losses in these structures. Recent results from non-linear ultrasonic measurements during uniaxial loading have demonstrated a strong acoustic and elastic effect in concrete. The present research applies resonant acoustic spectroscopy (RAS) during static loading and unloading of three prestressed concrete beams. At each load step multiple modes of vibration are measured using an accelerometer and a small impact source. Measured resonant frequencies increase with increasing compressive stress. The stress dependency of the modulus of elasticity indicates that the change in state of stress in a simple concrete structure can be estimated by simply measuring the resonance frequency
Mesos-scale modeling of irradiation in pressurized water reactor concrete biological shields
Energy Technology Data Exchange (ETDEWEB)
Le Pape, Yann [ORNL; Huang, Hai [Idaho National Laboratory (INL)
2016-01-01
Neutron irradiation exposure causes aggregate expansion, namely radiation-induced volumetric expansion (RIVE). The structural significance of RIVE on a portion of a prototypical pressurized water reactor (PWR) concrete biological shield (CBS) is investigated by using a meso- scale nonlinear concrete model with inputs from an irradiation transport code and a coupled moisture transport-heat transfer code. RIVE-induced severe cracking onset appears to be triggered by the ini- tial shrinkage-induced cracking and propagates to a depth of > 10 cm at extended operation of 80 years. Relaxation of the cement paste stresses results in delaying the crack propagation by about 10 years.
Siringi, Gideon Momanyi
better damage tolerance but the Elastic Modulus would be reduced. After evaluation of rubberized concrete at elevated temperatures, it has been found that very high temperature would have adverse effects to the concrete like excessive spalling, pop-outs and cracking on the surface and therefore it is proposed to use this kind of concrete where temperature would not exceed 100°C (212°F) for extended periods. Observation of concrete at microscopic level showed that it consists of three phases; interfacial transition zone (ITZ), bulk hydrated cement paste and aggregate. The ITZ was seen to contain micro pores and microcracks and was considered the weakest phase in concrete therefore exercises a far greater influence on the mechanical behavior of concrete than is reflected by its size. Existence of the ITZ explains why concrete strength is lower and behaves inelastically while the aggregate and cement paste if tested separately behave elastically and have higher strength than concrete. A 3-Dimensional nonlinear Finite Element Model (FEM) for a concrete beam is proposed and developed using ABAQUS. Smeared crack model in ABAQUS is used to define material properties. The developed FEM is capable of predicting the ultimate load, deflections, Stress-deflection/strain curves and crack initiation which are all verified against the experimental tests. ABAQUS was found to be a useful tool for modeling of concrete. In conclusion, this research provides a clear understanding on the effects of using scrap tires as an aggregate in concrete. The pros and cons of TDA are explored, ways of overcoming the shortcomings suggested and a way of predicting concrete properties when using TDA provided.
Performance Analysis and Optimization of Dowels in Jointed Concrete Floors
Ghauch, Ziad; Tabbara, Mazen
2012-01-01
This study examines the performance of traditional round dowels in concrete floors and attempts to optimize the design of dowels through Finite Element (FE) analysis. A new type of Double-Tapered Round (DTR) dowels is proposed, and the performance of DTR dowels is compared to that of traditional cylindrical dowels. Linear Elastic (LE) analysis are performed in Abaqus (v-6.11) order to identify the optimized geometry of DTR dowels that would achieve (1) highest load transfer across adjacent slabs through shear action, and (2) lowest bearing stresses on the concrete. LE analyses are complemented by nonlinear FE analysis. The Riks method available in Abaqus/Standard, coupled with the Concrete Damaged Plasticity (CDP) model is used to simulate the degradation of concrete surrounding both DTR the traditional cylindrical dowels. Results obtained show that the use of DTR dowels can reduce bearing stresses at the face of the joint by as much 2.2 times as compared to traditional cylindrical dowels. While adequate load...
Behavior of high strength concrete columns under eccentric loads
Directory of Open Access Journals (Sweden)
Hany A. Kottb
2015-04-01
Full Text Available In recent decades, high strength concrete (HSC has been widely accepted by designers and contractors to be used in concrete structures, especially in high compressive stress elements. The research aims to study the behavior of high strength concrete columns under eccentric compression using experimental and analytical programs. The research is divided into two main parts; the first part is an experimental investigation for ten square columns tested at the Cairo University Concrete Research Laboratory. The main studied parameters were eccentricity of the applied load, column slenderness ratio; and ratios of longitudinal and transverse reinforcement. The second part is analytical analysis using nonlinear finite element program ANSYS11 on nineteen columns (ten tested square columns and nine rectangular section columns to study the effect of the previous parameters on the column ultimate load, mid-height displacement, and column cracking patterns. The analyzed columns revealed a good agreement with the experimental results with an average difference of 16% and 17% for column ultimate load and mid-height displacement respectively. Results showed an excellent agreement for cracking patterns. Predictions of columns capacities using the interaction diagrams based on ACI 318-08 stress block parameters indicated a safe design procedure of HSC columns under eccentric compression, with ACI 318-08 being more conservative for moderate reinforced HSC columns.
DEFF Research Database (Denmark)
Burcharth, H. F.; Liu, Zhou
1989-01-01
Recent breakwater failures revealed the shortcomings of the traditional design procedures for concrete armour units. This paper deals with one of them, which can be expressed as the "lack of balance between the hydraulic stability of the armour layer and the mechanical strength or integrity...
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
A numerical model is developed in this paper to calculate the bending moments of flexural members through integration in 3D solid finite element analyses according to the nonlinear constitutive model of concrete and the elastoplastic constitutive model of steel,utilizing the stress condition of the cross-section,considering the destruction characteristic of reinforced concrete members,and based on the plane cross-section assumption.The results of this model give good agreement with those of the classical me...
DEFF Research Database (Denmark)
Dich, Nadya; Doan, Stacey N; Kivimäki, Mika
2014-01-01
Previous research suggests that high levels of negative emotions may affect health. However, it is likely that the absence of an emotional response following stressful events may also be problematic. Accordingly, we investigated whether a non-linear association exists between negative emotional...... cardiovascular, metabolic and immune function biomarkers at three clinical follow-up examinations. A non-linear association between negative emotional response and allostatic load was observed: being at either extreme end of the distribution of negative emotional response increased the risk of physiological...
Institute of Scientific and Technical Information of China (English)
2008-01-01
A multiphase mesostructure mechanical model is proposed to study the deformation and failure process of concrete considering its heterogeneity at the meso scopic level.Herein,concrete is taken as a type of three-component composite material composed of mortar matrix,aggregates and interfaces on the meso-scale.First,an efficient approach to the disposition of aggregates of concrete and a state matrix method to generate mesh coordinates for aggregates are proposed.Secondly,based on the nonlinear continuum damage mechanics,a meso-scale finite element model is presented with damage softening stress-strain relationship for describing the mechanical behavior of different components of concrete.In this method,heterogeneities of each component in the concrete are considered by assuming the material properties of three components conform to the Weibull distribution law.Finally,based on this multiphase meso-mechanics model,a simulation analysis of fracture behavior of a rock-fill concrete(RFC) beam is accomplished.The study includes experimental tests for determining basic mechanical parameters of three components of RFC and four-point flexural beam tests for verification of the model.It is preliminarily shown that the numerical model is applicable to studying failure mechanisms and process of concrete type material.
Fatigue of concrete under compression: Database and proposal for high strength concrete
Lantsoght, E.O.L.
2014-01-01
The compressive strength of concrete decreases as an element is subjected to cycles of loading. In a typical fatigue test for the concrete compressive strength, a concrete specimen (typically a cylinder) is loaded between a lower and upper stress limit. These limits are expressed as a fraction of th
Fatigue of concrete under compression: Database and proposal for high strength concrete
Lantsoght, E.O.L.
2014-01-01
The compressive strength of concrete decreases as an element is subjected to cycles of loading. In a typical fatigue test for the concrete compressive strength, a concrete specimen (typically a cylinder) is loaded between a lower and upper stress limit. These limits are expressed as a fraction of
2014-01-01
Today bituminous concrete is a conventional paving material. Among its advantages one can name dustlessness and noiselessness, fine wear (up to 1 mm a year) and fine maintainability. As the main disadvantages of this material one can name high slipperiness under humidification, low durability and weather resistance. Besides that, during placement of the bituminous concrete a lot of different air pollutants are emitted, which are harmful for environment and human’s health (they are listed in t...
Directory of Open Access Journals (Sweden)
Lyapidevskaya Ol'ga Borisovna
2014-02-01
Full Text Available Today bituminous concrete is a conventional paving material. Among its advantages one can name dustlessness and noiselessness, fine wear (up to 1 mm a year and fine maintainability. As the main disadvantages of this material one can name high slipperiness under humidification, low durability and weather resistance. Besides that, during placement of the bituminous concrete a lot of different air pollutants are emitted, which are harmful for environment and human’s health (they are listed in the paper according to the US Environmental Protection Agency materials. As an alternative, one can use cement-concrete pavement, which is in many ways more efficient than the bituminous concrete. It is proposed to enhance environmental performance of the cement-concrete pavement via usage of photocatalysis. The mechanism of different photocatalytic reactions is described in the paper, namely heterogeneous and homogeneous photocatalysis, photo-induces, photoactivated catalysis and catalytical photoreactions. It is pro-posed to use heterogeneous photocatalysis with titanium dioxide as a photocatalyst. The mechanism of photo oxidation of air contaminants, with the usage of titanium dioxide is2described. The paper sets problems, connected with the sensibilization of TiOto thevisible light (it is proposed to use titanium dioxide, doped with the atoms of certain elements to increase its sensibility to the visible light and with the development of a new photocatalytic paving concrete, which will meet the requirements, specified for paving in the climatic and traffic conditions of the Russian Federation.
Institute of Scientific and Technical Information of China (English)
张常光; 陈新栋; 范文
2016-01-01
The overturning stability is vital for the retaining wall design of foundation pits, where the surrounding soils are usually unsaturated due to water draining. Moreover, the intermediate principal stress does affect the unsaturated soil strength; meanwhile, the relationship between the unsaturated soil strength and matric suction is nonlinear. This work is to present closed-form equations of critical embedment depth for a rigid retaining wall against overturning by means of moment equilibrium. Matric suction is considered to be distributed uniformly and linearly with depth. The unified shear strength formulation for unsaturated soils under the plane strain condition is adopted to characterize the intermediate principal stress effect, and strength nonlinearity is described by a hyperbolic model of suction angle. The result obtained is orderly series solutions rather than one specific answer; thus, it has wide theoretical significance and good applicability. The validity of this present work is demonstrated by comparing it with a lower bound solution. The traditional overturning designs for rigid retaining walls, in which the saturated soil mechanics neglecting matric suction or the unsaturated soil mechanics based on the Mohr-Coulomb criterion are employed, are special cases of the proposed result. Parametric studies about the intermediate principal stress, matric suction and its distributions along with two strength nonlinearity methods on a new defined critical buried coefficient are discussed.
Reservoir water effects on earthquake performance evaluation of Torul Concrete-Faced Rockfill Dam
Institute of Scientific and Technical Information of China (English)
Alemdar BAYRAKTAR; Murat Emre KARTAL; Hasan Basri BASAGA
2009-01-01
This study presents earthquake performance analysis of the Torul Concrete-Faced Rockfill (CFR) Dam with two-dimensional dam-soil and dam-soil-reservoir finite element models. The Lagrangian approach was used with fluid elements to model impounded water. The interface elements were used to simulate the slippage between the concrete face slab and the rockfill. The horizontal component of the 1992 Erzincan earthquake, with a peak ground acceleration of 0.515g, was considered in time-history analysis. The Drucker-Prager model was preferred in nonlinear analysis of the concrete slab, rockfill and foundation soil. The maximum principal stresses and the maximum displacements in two opposite directions were compared by the height of the concrete slab according to linear time-history analysis to reveal the effect of reservoir water. The changes of critical displacements and principal stresses with time are also shown in this paper. According to linear and nonlinear time-history analysis, the effect of the reservoir water on the earthquake performance of the Torul CFR Dam was investigated and the possible damage situation was examined. The results show that the hydrodynamic pressure of reservoir water leads to an increase in the maximum displacements and principal stresses of the dam and reduces the earthquake performance of the dam. Although the linear time-history analysis demonstrates that the earthquake causes a momentous damage to the concrete slab of the Torul CFR Dam, the nonlinear time-history analysis shows that no evident damage occurs in either reservoir case.
ECT Team, Purdue
2007-01-01
Certain concrete pours have areas where the congestion of reinforcing bars make placement of concrete almost impossible. Using conventional placing and vibration techniques, the resulting concrete can have considerable honeycombing due to the development of voids. Self-placing concrete is a possible solution to the problem. Also known as self-compactable concrete, self-consolidating concrete, flowable concrete, and non-vibration concrete. These concretes eliminate the need for vibration in a ...
Bond interface crack propagation of fresh foundation concrete and rock under blasting load
Institute of Scientific and Technical Information of China (English)
WU Liang; LU Wen-bo; ZHONG Dong-wang
2009-01-01
According to concrete age,the dynamic stress intensity factors of bond inter-face crack of concrete-rock was calculated.Result shows that the propagation of concrete interface crack is mainly caused by tensile stress and shear stress for stress wave reflec-tion.With the growth of concrete age,interface crack fracture toughness increases,and its capacity of resisting blasting load strengthens.Therefore,blasting vibration should be strictly controlled for fresh concrete.
Baek-Il Bae; Hyun-Ki Choi; Bong-Seop Lee; Chang-Hoon Bang
2016-01-01
Although mechanical properties of concrete under uniaxial compression are important to design concrete structure, current design codes or other empirical equations have clear limitation on the prediction of mechanical properties. Various types of fiber-reinforced reactive powder concrete matrix were tested for making more usable and accurate estimation equations for mechanical properties for ultra high strength concrete. Investigated matrix has compressive strength ranged from 30 MPa to 200 M...
Baek-Il Bae; Hyun-Ki Choi; Bong-Seop Lee; Chang-Hoon Bang
2016-01-01
Although mechanical properties of concrete under uniaxial compression are important to design concrete structure, current design codes or other empirical equations have clear limitation on the prediction of mechanical properties. Various types of fiber-reinforced reactive powder concrete matrix were tested for making more usable and accurate estimation equations for mechanical properties for ultra high strength concrete. Investigated matrix has compressive strength ranged from 30 MPa to 200 M...
Viscoelastic behavior of concrete pile
Institute of Scientific and Technical Information of China (English)
丁科; 唐小弟
2008-01-01
Based on constitutive theory of viscoelasticity,the viscoelastic behaviour of concrete pile was investigated.The influence of viscosity coefficient on the stress,displacement and velocity response was discussed.With the increase of viscosity coefficient,the amplitude of stress wave decreases,and the maximum value of the stress wave shifts to deeper position of the pile.In other words,the viscosity coefficient behaves as lag effect to stress wave.
Concrete under Impact Loading, Tensile Strength and Bond
Reinhardt, H.W.
1982-01-01
Uniaxial impact tensile tests on plain concrete were carried out with the aid of Split Hopkinson Bar equipment with stress rates of up to 60000 N/mm2. s. Various concrete mixes were investigated under. dry and wet conditions. All the concretes showed an increase in strength with increasing stress
Concrete under Impact Loading, Tensile Strength and Bond
Reinhardt, H.W.
1982-01-01
Uniaxial impact tensile tests on plain concrete were carried out with the aid of Split Hopkinson Bar equipment with stress rates of up to 60000 N/mm2. s. Various concrete mixes were investigated under. dry and wet conditions. All the concretes showed an increase in strength with increasing stress ra
An Analysis of Zhamao Concrete Faced Rock-fill Dams by Means of Nonlinear FEM%扎毛水库混凝土面板坝结构非线性有限元分析
Institute of Scientific and Technical Information of China (English)
解晓峰; 王正中; 刘诠鸿; 毛渐
2012-01-01
基于邓肯E—B模型对扎毛水库混凝土面板堆石坝进行了结构非线性有限元分析，给出了坝体和面板在竣工期、蓄水期的应力变形及分布规律。计算结果表明：坝体的总体变形较小，最大沉降量为44．67cm，约为坝高的0．6％；面板最大拉应力和压应力分别为1．53MPa和2．32MPa，均未超过混凝土的极限抗拉-抗压值；面板的最大挠度为12．4cm，周边缝的变形也不大，均在已建工程实测值范围内。%With the finite element simulation based on Duncan-Zhang E -B model, an analysis is made of the stress and strain of Zhamao rock-fill dams with concrete face slab during construction and impoundment periods. The calculation results show that .. the overall deformation of the dam is relatively small, the maximum dam settlements are 44. 67cm, which accounts for 0. 6% of the height of the dam, the maximum tensile stresses and compressive stresses are 2.57 MPa and 1.86MPa, which do not exceed the limit of the concrete tensile-compressive value. The maximum deflection is 12. 4 cm, the deformation of surrounding seam in the normal range. The distribution of stress and deformation is similar with the prototype observations of other projects under construction.
2015-01-01
From the Back Cover: The emphasis throughout the present volume is on the practical application of theoretical mathematical models helping to unravel the underlying mechanisms involved in processes from mathematical physics and biosciences. It has been conceived as a unique collection of abstract methods dealing especially with nonlinear partial differential equations (either stationary or evolutionary) that are applied to understand concrete processes involving some important applications re...
混凝土徐变应力计算方法及应用%Calculation Method for Concrete Creep Stress and Its Application
Institute of Scientific and Technical Information of China (English)
陈江; 段会文
2011-01-01
The strain gauge(s) within dam concrete can only monitor the strain(s) on the direction of buried gauge, and in engineering practice, the monitoring data need to be converted to creep stress. The conversion is based on the creep test of strain gauge(s). The Stress Increment Method used for the data conversion was improved and the principal stress calculation was increased. MATLAB-based program package of computing and graphics for data conversion was developed. After applying the package to Jin'anqiao RCC gravity dam, the time-history curve of stress can be quickly and easily represented by graphics. The practice shows that the program is effective.%采用应变计(组)只能监测应变计埋设方向的坝体内部混凝土应变,工程应用中需要把监测成果转换为徐变应力.通过对转换方法--应力增量法进行改进,增加主应力计算,并基于MATLAB编写计算及绘图程序.把程序应用到金安桥水电站碾压混凝土重力坝,可方便快捷地得到测点各监测时刻的应力状态及时程曲线.实践结果表明,该程序快捷、有效,值得推广.
Theoretical study for Bond between Reinforcement steel and Concrete
Directory of Open Access Journals (Sweden)
usama mostafa mahran
2013-04-01
Full Text Available The behavior and load carrying behavior of reinforced concrete structures is influence by the interaction between the concrete and reinforcement. The stress transfer between reinforcement and concrete in the longitudinal direction of the bars is called bond. An essential feature of reinforced concrete is the bond between steel and concrete. Anchorage of reinforcement depends on the bond between steel and concrete, crack width and crack spacing are mainly governed by it. So, stiffness, deformation and dynamic behavior are influenced by it, and in reverse loading damping and energy dissipation is a function of bond. This is one of the reasons why bond has been, and still is, a topic of fundamental and applied research. Bond stress is the equivalent unit shear stress acting in parallel to the reinforcing bar on the interface between reinforcing steel bar and concrete. Due to the transfer of forces through bond stress, between the reinforcing rebar and concrete, the force in the reinforcing bar changes along its length. Because bond stress is thought of as stress per unit area of bar surface, it is related to the rate of change of steel stress. Consequently, to have bond stress it is necessary to have a changing steel stress. In cases of high stress at the contact interface, near cracks or end anchorages, the bond stresses are related to relative displacements between concrete and steel. These relative displacements, which are caused by different average strains in the concrete and the steel, are usually called bond-slip (t-d.
Historic Concrete: From Concrete Repair to Concrete Conservation
Heinemann, H.A.
2013-01-01
Concrete like materials were already applied during the Roman Empire. After the decline of the Roman Empire, a wide scale application of concrete only reappeared in the 19th century. Here lies also the origin of modern (reinforced) concrete. Since then, both concrete application and composition have
Institute of Scientific and Technical Information of China (English)
雷拓; 钱江; 刘伯权
2013-01-01
A fiber beam-column element in conjunction with zero-length elements attached to its ends was proposed to simulate the flexural and shear mechanism respectively .Based on the Limit State Material model and the Shear Limit Curve model provided by OpenSees , the nonlinear shear effect of reinforced concrete column and its coupling with the flexural effect were defined .The reliability of the proposed model was validated by means of comparisons with existing test results .Finally ,a plane frame from in-situ pushover test was simulated .It is shown that the proposed method ,by taking the nonlinear shear effect into account ,produces satisfactory results for frame columns with shear strength and stiffness degradation , w hile the conventional fiber beam-column element can hardly simulate actual flexure-shear failure mechanism for columns characterized by insufficient transverse reinforcement . The proposed method is applicable for nonlinear analysis of reinforced concrete frame structures with shear deficiencies .%采用纤维模型梁柱单元和与之串联的零长度单元，模拟柱的弯曲机制和剪切机制。利用OpenSees提供的Limit State Material和Shear Limit Curve材料模型，定义钢筋混凝土柱的非线性剪切效应及其与弯曲效应的耦合。通过与不同学者的试验结果比较，验证了该方法的可靠性。最后，对笔者完成的原位推覆试验的一榀平面框架进行了Pushover 分析。结果表明，考虑非线性剪切效应的模型化方法能较好地模拟钢筋混凝土柱抗剪承载力和刚度的退化现象，传统的纤维模型梁柱单元难以反映配箍不足的钢筋混凝土柱的弯剪破坏机制。该方法可用于存在抗剪能力缺陷的框架结构的非线性分析。
Institute of Scientific and Technical Information of China (English)
戴建国; 黄承逵
2001-01-01
Based on a series of experiments, this paper studied the fundamental mechanical properties of a new type of high performance fiber reinforced concrete, steel fiber reinforced sulphate-aluminate self-stressing concrete (SFRSC). The direct tensile strength, compressive strength, splitting tensile strength and flexural strength were tested. Through the bonding forces between steel fibers and expansive concrete matrix and the three-dimension limitation of steel fibers, self-stresses are introduced to SFRSC. Owing to this kind of effects, the strengthening effects of steel fibers on concrete strengths are improved by adding another strengthening coefficient ks to original coefficient αm. Based on the current strength design formulation of steel fiber concrete, the strengthening coefficients are obtained through regressing and optimizing analysis on experimental data. It has been attested that SFRSC could be used as a kind of applicable high performance concrete composite in engineering application.%研究了在三维乱向分布钢纤维的限制下，掺有钢纤维的硫铝酸盐自应力混凝土(SFRSC)的直接拉伸、抗压、劈拉、抗折强度特性.由于钢纤维和基体间的摩阻限制所引入的自应力和钢纤维的三向限制作用，使得钢纤维对于自应力混凝土的增强效应要比对于普通混凝土的高.另外，在现有钢纤维混凝土强度计算模式的基础上，通过优化方法得出了对于不同目标自应力等级的自应力混凝土的钢纤维增强效应系数.
On the performance of circular concrete-filled high strength steel columns under axial loading
Directory of Open Access Journals (Sweden)
Mohamed Mahmoud El-Heweity
2012-06-01
Full Text Available This work presents a numerical study to investigate the performance of circular high-strength steel tubes filled with concrete (CFT under monotonic axial loading. A model is developed to implement the material constitutive relationships and non-linearity. Calibration against previous experimental data shows good agreement. A parametric study is then conducted using the model and compared with codes provisions. Strength and ductility of confined concrete are of primary concern. Variables considered are yield stress of steel tube and column diameter. The assessment of column performance is based on axial load carrying capacities and enhancements of both strength and ductility due to confinement. Two parameters namely strength enhancement factor (Kf and ductility index (μ are clearly defined and introduced for assessment. Results indicate that both concrete strength and ductility of CFT columns are enhanced but to different extents. The ductile behaviors are significantly evident. The increase in yield stress of steel tube has a minimal effect on concrete strength but pronounced effect on concrete ductility. However, reduction in ductility is associated with using high-tensile steel of Grade 70. The overall findings indicate that the use of high-strength tube in CFT columns is not promising. This finding may seriously be considered in seismic design.
Directory of Open Access Journals (Sweden)
F.J. Baldenebro-Lopez
2014-07-01
Full Text Available This study presents results from a theoretical-experimental program of beams partially pre-stressed made with continuous recycled PET strip-reinforced concrete (plain concrete strength of 20 MPa. These studies mainly attempted to determine the stripinfluence in altering the flexural strength at first and final crack. Also the load-deflection, ductility, energy absorption capacity of the beams are observed and the studies can be used in predicting the flexural behavior of longitudinally reinforced concrete. The model theory assumes that concrete has a tensile load capacity different from zero, characterized by a uniaxial tensile stress-strain diagram. The need for non-linear geometric and the material models imply the use of numerical methods such as the finite element method; so that, a finite element analysis of reinforced concrete beam with strips-reinforced plastic is performed. The obtained results were compared with computer analysis and experimental data to corroborate the validity of the suggested method, showing that the theory also predicts correctly the post-cracking creep deformation.
Continuous Reinforced Concrete Beams
DEFF Research Database (Denmark)
Hoang, Cao Linh; Nielsen, Mogens Peter
1996-01-01
This report deals with stress and stiffness estimates of continuous reinforced concrete beams with different stiffnesses for negative and positive moments e.g. corresponding to different reinforcement areas in top and bottom. Such conditions are often met in practice.The moment distribution...... at the limit state of serviceability is in some simple cases determined by setting up the statical and the compatibility conditions.With these moment distributions, the maximum deflection and the reinforcement stresses at the span middle and at a support are calculated.The results are compared with results...
Tensile behavior and tension stiffening of reinforced concrete
Energy Technology Data Exchange (ETDEWEB)
Choun, Young Sun; Seo, Jeong Moon
2001-03-01
For the ultimate behavior analysis of containment buildings under severe accident conditions, a clear understanding of tensile behaviors of plain and reinforced concrete is necessary. Nonlinear models for tensile behaviors of concrete are also needed. This report describe following items: tensile behaviors of plain concrete, test results of reinforced concrete panels in uniaxial and biaxial tension, tension stiffening. The tensile behaviors of reinforced concrete are significantly influenced by the properties of concrete and reinforcing steel. Thus, for a more reliable evaluation of tensile behavior and ultimate pressure capacity of a reinforced or prestressed concrete containment building, an advanced concrete model which can be considered rebar-concrete interaction effects should be developed. In additions, a crack behavior analysis method and tension stiffening models, which are based on fracture mechanics, should be developed. The model should be based on the various test data from specimens considering material and sectional properties of the containment building.
Tanev, George; Saadi, Dorthe B; Hoppe, Karsten; Sorensen, Helge B D
2014-01-01
Chronic stress detection is an important factor in predicting and reducing the risk of cardiovascular disease. This work is a pilot study with a focus on developing a method for detecting short-term psychophysiological changes through heart rate variability (HRV) features. The purpose of this pilot study is to establish and to gain insight on a set of features that could be used to detect psychophysiological changes that occur during chronic stress. This study elicited four different types of arousal by images, sounds, mental tasks and rest, and classified them using linear and non-linear HRV features from electrocardiograms (ECG) acquired by the wireless wearable ePatch® recorder. The highest recognition rates were acquired for the neutral stage (90%), the acute stress stage (80%) and the baseline stage (80%) by sample entropy, detrended fluctuation analysis and normalized high frequency features. Standardizing non-linear HRV features for each subject was found to be an important factor for the improvement of the classification results.
Directory of Open Access Journals (Sweden)
M. R. DORIA
Full Text Available ABSTRACTIn inspections of buildings, it is common to find structures that, well before reaching its useful life longer require repairs and reinforcements. This study examined the bond strength between concrete of different ages and between steel and concrete, focusing on the recovery of reinforced concrete structures. To analyze the bond between concrete of different ages, trials with specimens receiving three different types of treatments at the interface between the concrete were performed: brushing; brushing and mortar equal to concrete of substrate and brushing and epoxy layer. Indirect tensile tests and oblique and vertical shear tests at the interface were made . The bond stress between steel and concrete was evaluated by pull out test under the conditions of the bar inserted in the still fresh concrete and when inserted in the hardened concrete with epoxy. Results showed increased bond strength by indirect tensile stress of 15% and 37%; 4% and 12% for the adherence test by oblique shear, and 108% and 178%, for the testing of vertical shear, respectively, for the specimens whose interfaces have received, in addition to brushing, layer of mortar and epoxy bridge, compared to those who received only brushing. Insignificant loss (about 0.52% of bond stress was noticed for pull out test of steel bar when compared with test results of the specimens that had steel bar inserted in the concrete in the hardened state with epoxy adhesion bridge, with those who had inserted steel bar in fresh concrete.
Institute of Scientific and Technical Information of China (English)
2015-01-01
As a highly nonlinear dynamic system, oceanic general circulation models (OGCMs) usually exhibit nonlinear responses to prescribed wind stress forcing. To explore mechanisms for these nonlinear responses, we designed and conducted three idealized numerical experiments with an OGCM with modifi ed wind stress forcing. In the experiments, the climatological mean wind stress was identical, and the only diff erences in external forcing were wind stress anomalies. The wind anomalies were set to zero in a control run, and the observed wind stress anomalies with and without reversed signs were superimposed on the mean climatology in two sensitivity experiments. Forced by the prescribed wind stress anomalies in sensitivity runs, the OGCM well reproduced the El Ni˜no–Southern Oscillation (ENSO) and the Pacifi c and Indian Ocean Dipole (IOD) in the Indian Ocean, as well as the asymmetry between positive and negative phases of these modes. Relative to the control run, the two sensitivity runs exhibited almost identical changes in the mean climate state, although the wind stress anomalies were reversed in these two experiments. Thus, it was concluded that the asymmetry of wind stress anomalies contributes only slightly to the mean state changes and ocean internal dynamics was the main contributor. Further heat budget analysis suggested that nonlinear temperature advection terms, including both mean advection and perturbed advection, favor the ENSO/IOD rectifi ed eff ect on the mean state.
Vulnerability of aged concrete gravity dams
Energy Technology Data Exchange (ETDEWEB)
Gogoi, I. [Assam Engineering Institute, Guwahati (India). Dept. of Civil Engineering; Maity, D. [Indian Institute of Technology, Guwahati (India). Dept. of Civil Engineering
2004-07-01
This paper presented an analysis procedure to predict the effects of aging on the behavior of concrete gravity dams. A time dependent isotropic damage index was determined, presenting the performance of the dam with increasing age. Results revealed that the degradation process is dependent on the design life of the structure. The influence of damage along the dam height was greater than damage observed along its width. In order to consider the time dependent degradation of concrete owing to environmental factors and mechanical loading, an algorithm was presented in order to forecast the behavior of existing dams and to assess the necessity of retrofitting or decommissioning. It was concluded that dam behavior during seismic excitation is influenced by the effects of both the dam reservoir system and initial earthquake damage. With increasing age, dam displacement increases, but hydrodynamic pressures and stresses exerted by reservoirs decrease. It was recommended that more accurate behavior could be determined if further research into the coupled effect of foundation-dam-reservoir interaction with material non-linearity was considered. 15 refs.,15 figs.
Analysis of the stress-strain state of New Exchequer combined damat static loads
Directory of Open Access Journals (Sweden)
Sainov Mikhail Petrovich
Full Text Available In the article the authors analyze numerical modeling results of the stress-strain state of a combined dam created by construction of a higher rockfill dam with a reinforced concrete face behind the downstream face of the concrete dam. The analysis was conducted on the example of the design of 150 meter high New Exchequer dam (USA. Numerical modeling was conducted with consideration of non-linearity of soils deformation as well as non-linear behavior of the interaction “concrete - soil”, “concrete - concrete”. The analysis showed that though in a combined dam the concrete part gets additional displacements and settlements, its stress state remains favorable without appearance of tensile stresses and opening of the contact “concrete - rock”. This is explained by the fact that on the top the concrete dam is weightened by the reservoir hydrostatic pressure. The role of rockfill lateral pressure on the concrete dam stress state is small. There may be expected sliding of soil in relation to the concrete dam downstream face due to the loss of its shear strength. Besides, decompaction of the contact "soil - concrete" may occur, as earthfill will have considerable displacements in the direction from the concrete dam. Due to this fact the loads from the earthfill weight do not actually transfer to the concrete dam. The most critical zone in the combined dam is the interface of the reinforced concrete face with the concrete dam. Under the action of the hydrostatic pressure the earth-fill under the face will have considerable settlements and displacements, because soil slides in relation to the concrete dam downstream face. This results in considerable openings (10 cm and shear displacements (50 сm in the perimeter joint. The results of the numerical modeling are confirmed by the presence of seepage in New Exchequer dam, which led to the necessity of its repair. Large displacements do not allow using traditional sealing like copper water stops
Institute of Scientific and Technical Information of China (English)
叶梅新; 曹建安; 侯文崎; 肖佳
2011-01-01
Adopting the real concrete mix proportion of Ronggui Bridge in Guangzhou- Zhuhai inter-city express railway, the tested creep coefficient of C60 HPC was compared with creep coefficient calculated in terms of different concrete codes, and the calculation method of creep deformation of structures was determined. Through long term observation and examination, development laws of the long term deformation of pre-stressed simple supported beams, including its influencing factors and control measures were studied. The results show that during 762 d observing period, pre-stressing loss of the test beams is too small to be more than 8.63%, which means the long term deformation of pre-stressed concrete beams is mainly caused by concrete creep. After surface loading, deformation of the test beams occurring during the earlier 185 d is about 75% of the total long term deformation, while only about 25% in the later is over 500 d. Concrete strain also becomes stable 400 d after surface loading. Ambient temperature and humidity, pre-stress tension age and surface loading age of concrete are all demonstrated to be important influencing factors of long term deformation of pre-stressed concrete structures. Therefore, measures such as maintaining concrete with high humidity and at low temperature, extending pre-stress tension time and track laying time appropriately, can be applied in controlling long term deformation of pre-stressed concrete beams with ballastless track effectively.%采用广珠(广州-珠海)城际容桂水道特大桥主桥的实际混凝土配比，对比分析C60高性能混凝土实测徐变系数和按各种规范计算所得徐变系数，确定结构徐变变形计算方法。通过长期试验观测，研究预应力混凝土简支梁的长期变形发展规律及其影响因素和控制措施。研究结果表明：在762 d的观测期内，梁体预应力损失很小，最多不超过8.63％，说明预应力混凝土梁后期变形主要由混凝
Institute of Scientific and Technical Information of China (English)
LIU Zheng-Feng; WANG Xiao-Hong
2008-01-01
Adopting Yoshizawa's two-scale expansion technique,the fluctuating field is expanded around the isotropic field.The renormalization group method is applied for calculating the covariance of the fluctuating field at the lower order expansion,A nonlinear Reynolds stress model is derived and the turbulent constants inside are evaluated analytically.Compared with the two-scale direct interaction approximation analysis for turbulent shear flows proposed by Yoshizawa,the calculation is much more simple.The analytical model presented here is close to the Speziale model,which is widely applied in the numerical simulations for the complex turbulent flows.
A Failure Criterion for Concrete
DEFF Research Database (Denmark)
Ottosen, N. S.
1977-01-01
A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace in the devi......A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace...
A Failure Criterion for Concrete
DEFF Research Database (Denmark)
Ottosen, N. S.
1977-01-01
A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace in the devi......A four-parameter failure criterion containing all the three stress invariants explicitly is proposed for short-time loading of concrete. It corresponds to a smooth convex failure surface with curved meridians, which open in the negative direction of the hydrostatic axis, and the trace...
Institute of Scientific and Technical Information of China (English)
DING Fa-xing; YU Zhi-wu
2006-01-01
Based on reanalyzing test results of uniaxial compressive behavior of concrete at constant high temperatures in China,with the compressive cube strength of concrete from 20 to 80 Mpa, unified formulas for uniaxial compressive strength, elastic modulus, strain at peak uniaxial compression and mathematical expression for unaxial compressive stress-strain relations for the concrete at constant high temperatures were studied. Furthermore, the axial stress-axial strain relations between laterally confined concrete under axial compression and multiaxial stress-strain relations for steel at constant high temperatures were studied. Finally,based on continuum mechanics, the mechanics model for concentric cylinders of circular steel tube with concrete core of entire section loaded at constant high temperatures was established. Applying elasto-plastic analysis method, a FORTRAN program was developed, and the concrete-filled circular steel tubular (CFST) stub columns at constant high temperatures were analyzed. The analysis results are in agreement with the experiment ones from references.
Nonlinear Seismic Response Analysis on Concrete-Filled Steel Tubular Frame Piers%框架式钢管混凝土桥墩非线性地震反应分析
Institute of Scientific and Technical Information of China (English)
常山; 朱东生; 何发礼
2013-01-01
以框架式钢管混凝土桥墩及钢筋混凝土空心薄壁墩为研究对象,采用纤维单元建立了框架式钢管混凝土桥墩及钢筋混凝土空心薄壁墩的非线性动力分析模型,输入3条地震波,计算得到了框架式钢管混凝土桥墩与钢筋混凝土空心薄壁墩的线性及非线性地震时程响应,比较了不同类型桥墩地震响应的差异,讨论了框架式钢管混凝土桥墩的地震反应特点.%Taking concrete-filled steel tubular frame pier and hollow thin-walled pier as the research projects,the dynamic time-history analysis models are established by using the fiber element for concrete-filled steel tubular frame pier and hollow thin-walled pier.By inputting 3 actual seismic waves into the analysis models,the linear and nonlinear time-history response is analyzed respectively.Based on the analysis results,the effect of seismic response for different piers is compared,and seismic response characteristics of frame pier are discussed.The results show that shear response appears linear distribution,moment response represents serrated distribution and axial force response emerges stepwise increase along the column height for frame pier under the action of waves.Shear,moment and axial force response of one column of frame pier are relatively smaller compared with hollow thin-walled pier under the action of waves.
Carroll, Laura M; Bergholz, Teresa M; Hildebrandt, Ian M; Marks, Bradley P
2016-07-01
Sublethal heating, which can occur during slow cooking of meat products, is known to induce increased thermal resistance in Salmonella. However, very few studies have addressed the kinetics of this response. Although several recent studies have reported improved thermal inactivation models that include the effect of prior sublethal history on subsequent thermal resistance, none of these models were based on cellular-level responses to sublethal thermal stress. The goal of this study was to determine whether a nonlinear model could accurately portray the response of Salmonella to heat stress induced by prolonged exposure to sublethal temperatures. To accomplish this, stationary-phase Salmonella Montevideo cultures were subjected to various heating profiles (held at either 40 or 45°C for 0, 5, 10, 15, 30, 60, 90, 180, or 240 min) using a PCR thermal cycler. Differential plating on selective and nonselective media was used to confirm the presence of cellular injury. Reverse transcription quantitative PCR was used to screen the transcript levels of six heat stress-related genes to find candidate genes for nonlinear modeling. Injury was detected in populations of Salmonella held at 45°C for 30, 60, and 90 min and at 40°C for 0, 5, and 90 min (P 0.05). The transcript levels of ibpA, which codes for a small heat shock protein associated with the ClpB and DnaK-DnaJ-GrpE chaperone systems, showed the greatest increase relative to the transcript levels at 0 min, which was significant at 5, 10, 15, 30, 60, 90, and 180 min at 45°C and at 5, 10, 15, 30, 60, and 90 min at 40°C (P < 0.05). Using ibpA transcript levels as an indicator of adaptation to thermal stress, a nonlinear model for sublethal injury is proposed. The use of variables indicating the physiological state of the pathogen during stress has the potential to increase the accuracy of thermal inactivation models that must account for prolonged exposure to sublethal temperatures.
Traian Oneţ
2009-01-01
The paper presents the last studies and researches accomplished in Cluj-Napoca related to high performance concrete, high strength concrete and self compacting concrete. The purpose of this paper is to raid upon the advantages and inconveniences when a particular concrete type is used. Two concrete recipes are presented, namely for the concrete used in rigid pavement for roads and another one for self-compacting concrete.
Directory of Open Access Journals (Sweden)
Traian Oneţ
2009-01-01
Full Text Available The paper presents the last studies and researches accomplished in Cluj-Napoca related to high performance concrete, high strength concrete and self compacting concrete. The purpose of this paper is to raid upon the advantages and inconveniences when a particular concrete type is used. Two concrete recipes are presented, namely for the concrete used in rigid pavement for roads and another one for self-compacting concrete.
Chiumenti, Michèle; Cervera Ruiz, Miguel; Agelet de Saracibar Bosch, Carlos; Dialami, Narges
2013-01-01
In this work a novel finite element technology based on a three-field mixed formulation is presented. The Variational Multi Scale (VMS) method is used to circumvent the LBB stability condition allowing the use of linear piece-wise interpolations for displacement, stress and pressure fields, respectively. The result is an enhanced stress field approximation which enables for stress-accurate results in nonlinear computational mechanics. The use of an independent nodal variable for the pressure ...
2014-01-01
This article reflects on a number of liturgical innovations in the worship of Melodi ya Tshwane, an inner-city congregation of the Uniting Reformed Church in Southern Africa (URCSA). The focus of the innovations was to implement the understanding of justice in Article 4 of the Confession of Belhar, a confessional standard of the URCSA. The basic contention of the article is that well designed liturgies that facilitate experiences of beauty can nurture a concrete spirituality to mobilise urba...
Directory of Open Access Journals (Sweden)
MOHD H. MOHD HASHIM
2016-04-01
Full Text Available The existing reinforced concrete structures may require rehabilitation and strengthening to overcome deficiencies due to defect and environmental deterioration. Fibre Reinforced Polymer (FRP-concrete bonding systems can provide solution for the deficiencies, but the durability of the bonded joint needs to be investigated for reliable structural performance. In this research the interfacial bonding behaviour of CFRP-concrete system under tropical climate exposure is main interest. A 300 mm concrete prism was bonded with CFRP plate on its two sides and exposed for 3, 6, and 9 months to laboratory environment, continuous natural weather, and wet-dry exposure in 3.5% saltwater solution at room and 40 °C temperature. The prisms were subjected to tension and compression load under bonding test to measure the strain and determine stress distribution and shear stress transfer behaviour. The results of the bonding test showed that load transfer was fairly linear and uniform at lower load level and changed to non-linear and non- uniform at higher load level. The force transfers causes the shear stress distribution being shifted along the bonded length. The combination of climate effects may have provided better curing of the bonded joints, but longer duration of exposure may be required to weaken the bond strength. Nevertheless, CFRP-concrete bonding system was only minimally affected under the tropical climate and salt solution.
Time-dependent Early-age Behaviors of Concrete under Restrained Condition
Institute of Scientific and Technical Information of China (English)
MA Xinwei; CAO Lixin; R D Hooton; H Lam; NIU Changren
2007-01-01
To investigate the early-age behaviors of concrete under a restrained condition, a set of apparatus was developed. In this way, the tensile creep and other early-age properties can be investigated in depth. By measuring the modulus of elasticity of concrete, synchronous shrinkage of concrete and steel rings and free shrinkage of concrete, the deformations of concrete ring can be quantified respectively. The experimental results show the tensile stress in concrete is time-dependent, and the stress at cracking is much lower than the tensile strength at that age; the tensile creep plays an important role in relaxing the tensile stress and postponing the cracking of concrete.
Zhang, Rui; Schweizer, Kenneth S
2012-04-21
We generalize the microscopic naïve mode coupling and nonlinear Langevin equation theories of the coupled translation-rotation dynamics of dense suspensions of uniaxial colloids to treat the effect of applied stress on shear elasticity, cooperative cage escape, structural relaxation, and dynamic and static yielding. The key concept is a stress-dependent dynamic free energy surface that quantifies the center-of-mass force and torque on a moving colloid. The consequences of variable particle aspect ratio and volume fraction, and the role of plastic versus double glasses, are established in the context of dense, glass-forming suspensions of hard-core dicolloids. For low aspect ratios, the theory provides a microscopic basis for the recently observed phenomenon of double yielding as a consequence of stress-driven sequential unlocking of caging constraints via reduction of the distinct entropic barriers associated with the rotational and translational degrees of freedom. The existence, and breadth in volume fraction, of the double yielding phenomena is predicted to generally depend on both the degree of particle anisotropy and experimental probing frequency, and as a consequence typically occurs only over a window of (high) volume fractions where there is strong decoupling of rotational and translational activated relaxation. At high enough concentrations, a return to single yielding is predicted. For large aspect ratio dicolloids, rotation and translation are always strongly coupled in the activated barrier hopping event, and hence for all stresses only a single yielding process is predicted.
A Non-Linear Upscaling Approach for Wind Turbines Blades Based on Stresses
Castillo Capponi, P.; Van Bussel, G.J.W.; Ashuri, T.; Kallesoe, B.
2011-01-01
The linear scaling laws for upscaling wind turbine blades show a linear increase of stresses due to the weight. However, the stresses should remain the same for a suitable design. Application of linear scaling laws may lead to an upscaled blade that may not be any more a feasible design. In this pap
A Non-Linear Upscaling Approach for Wind Turbines Blades Based on Stresses
Castillo Capponi, P.; Van Bussel, G.J.W.; Ashuri, T.; Kallesoe, B.
2011-01-01
The linear scaling laws for upscaling wind turbine blades show a linear increase of stresses due to the weight. However, the stresses should remain the same for a suitable design. Application of linear scaling laws may lead to an upscaled blade that may not be any more a feasible design. In this
Directory of Open Access Journals (Sweden)
Gabriela Rezende Fernandes
2009-01-01
Full Text Available In this work, non-linear analyses of reinforced concrete plates are performed by using a BEM formulation, based on Kirchhoff’s theory, which has already proved to be a robust technique to deal with plate problems. The non-linear behavior of concrete is modeled by theMazars model, which is based on continuum damage mechanics (CDM and has an easy parametric identification, while the reinforcement is governed by the uniaxial elasto-plastic model with constant hardening. Initially, the different types of damage models and their parametric identification are discussed and the Mazars model is presented. Then the BEM formulation is discussed, which is based on the initial moment technique, where the remaining domain integralsare evaluated by approaching the initial moment field over internal cells. The stress distribution over the plate thickness is obtained by using a Gauss scheme in which the adopted criterion is verified ineach Gauss point defined along the plate. Then, the internal values of moments are approached by numerical integrals along the plate thickness. Finally, some numerical examples of reinforced concrete plates are analyzed, where the potentiality of the Mazars model is verified despite the difficulties of the parametric identification.Nesse trabalho são feitas análises nãolineares de placas de concreto armado,utilizando-se uma formulação do MEC (método dos elementos de contorno baseada nas hipóteses de Kirchhoff. O modelo constitutivo adotado para o concreto é o modelo proposto por Mazars baseado na Mecânica do da Dano Contínuo (MDC, sendo o comportamento não-linear das armaduras governado pelo modelo elastoplástico comencruamento isótropo. Justifica-se a escolha de tal modelo numérico pela simplicidade paramétrica do modelo de dano e pela robustez do MEC, que já provou ser eficiente na análise de placas. Inicialmente, apresenta-se uma revisão dos tipos de modelos de dano e suas implicações na identifica
Numerical simulation of high pressure water jet impacting concrete
Liu, Jialiang; Wang, Mengjin; Zhang, Di
2017-08-01
High pressure water jet technology is an unconventional concrete crushing technology. In order to reveal the mechanism of high pressure water jet impacting concrete, it built a three-dimensional numerical model of high pressure water jet impacting concrete based on fluid mechanics and damage mechanics. And the numerical model was verified by theoretical analysis and experiments. Based on this model, it studied the stress characteristics in concrete under high pressure water jet impacting at different time, and quantified the damage evolution rules in concrete along the water jet radial direction. The results can provide theoretical basis and guidance for the high pressure water jet crushing concrete technology.
Mechanical Properties of Layered Hybrid Fiber Reinforced Concrete
Institute of Scientific and Technical Information of China (English)
YUAN Hai-qing; CHEN Jing-tao; ZHU Ji-dong
2003-01-01
To improve the mechanical properties of concrete,Layered Hybrid Fiber Reinforced Concrete (LHFRC) was developed in this paper.Through comparative tests,the effects of layered hybrid fibers on a series of mechanical properties of concrete were discussed.The mechanical properties include compressive strength,tensile strength,flexural strength,compressive stress-strain relationship,flexural toughness and cracking resistance of concrete.The testing results and analysis demonstrate that layered hybrid fibers can significantly improve the flexural strength,toughness and cracking resistance of concrete while the cost of concrete increases slightly.
Olaya Beracasa, Santiago Eduardo; Flórez Gutiérrez, Richard Daniel
2016-01-01
QUICK CONCRETE es un emprendimiento el cual se planteó como una empresa prestadora de servicios en el sector de la construcción en la ciudad de Ibagué, Colombia. Con ayuda de empresas ya reconocidas a nivel regional como lo son: la distribuidora de materiales y ferretería La Española, A&C y la ladrillera Ladrillos Roma. Se espera impactar en el mercado con un método diferente y un precio competitivo de servicio. El mayor impulso de la construcción puede estar asociado a una mayor demanda de v...
Institute of Scientific and Technical Information of China (English)
王国超; 王伯昕; 赵建宇; 许晓慧
2016-01-01
利用摆锤试验机进行了672块简支弯曲试件的冲击试验，获得了普通混凝土、钢纤维混凝土以及钢纤维自应力混凝土试件冲击破坏的吸收功，并根据各自的耗能值对其抗冲击性能作了比较，发现体积率为1％的钢纤维对于自应力混凝土基体的增强作用强于普通混凝土基体；随着钢纤维体积率的增加，试件吸收功会出现拐点，极值出现在2％到3％之间；并通过K-S检验法和Weibull分布理论对试验结果进行了非参数统计推断，得出钢纤维体积率为0．5％的自应力混凝土试件冲击功为泊松分布而其他钢纤维体积率的自应力混凝土试件冲击功均符合Weibull分布。%A number of 672 specimens were impacted in the three-point bending situation with pendulum machine. The energy absorb-ing of concrete,steel fiber reinforced concrete and steel fiber reinforced self-stressing concrete test specimens were obtained. Compared the impact capacity with respective energy consumption,it concluded that the energy absorbing of steel fiber reinforced self-stressing concrete test specimens with same fiber volume content was higher than that of same volume content steel fiber reinforced concrete specimens. The energy consumption of specimens would come to a inflection point as the volume content raising and the extreme value was between 2%and 3%. Lastly,the results were nonparametric inference by K-S and Weibull examination and all the groups were sat-isfied to Weibull distribution except for those steel fiber reinforced self-stressing concrete test specimens with 0.5%fiber volume con-tent fitted to Poisson distribution properly.
Numerical Analysis of Composite Steel Concrete Structural Shear Walls with Steel Encased Profiles
Directory of Open Access Journals (Sweden)
Daniel Dan
2009-01-01
Full Text Available The use of common reinforced concrete shear walls in high rise buildings is sometimes limited because of the large amount of reinforcement localized at the end of the element. A good alternative in avoiding this disadvantage is to use composite steel concrete structural shear walls with steel encased profiles. This solution used for high rise buildings, offers to designers lateral stiffness, shear capacity and high bending resisting moment of structural walls. The encasement of the steel shapes in concrete is applied also for the following purposes: flexural stiffening and strengthening of compression elements; fire protection; potentially easier repairs after moderate damage; economy with respect both to material and construction. Until now in the national and international literature poor information about nonlinear behaviour of composite steel concrete structural shear walls with steel encased profiles is available. A theoretical and experimental program related to the behaviour of steel concrete structural shear walls with steel encased profiles is developed at “Politehnica” University of Timişoara. The program refers to six different elements, which differ by the shape of the steel encased profile and also by the arrangement of steel shapes on the cross section of the element. In order to calibrate the elements for experimental study some numerical analysis were made. The paper presents the results of numerical analysis with details of stress distribution, crack distribution, structural stiffness at various loads, and load bearing capacity of the elements.
Institute of Scientific and Technical Information of China (English)
廖艳芬; 漆雅庆; 马晓茜
2012-01-01
结合实际民用建筑可燃物特点,基于简化的固体可燃物燃烧模型,利用CFD场模拟软件FLUENT对单室房间进行了火灾模拟,得到了烟气温度场分布情况.在此基础上,结合钢筋混凝土热工特性、温度-应变-应力本构特性,分析对比了钢筋混凝土柱在四种不同火灾条件下的温度场分布及变形规律.结果表明:由于现代建筑物中橡胶、塑料等高热值、易挥发性燃料成分的大量存在,使火灾初期具有快速的升温速率,而且火场整体燃烧温度高过ISO834标准.火灾发生前期,钢筋混凝土柱的轴向形变主要来源于热膨胀,恒载荷下的压应变相对作用较小；火灾发生后期,随着混凝土强度的降低,恒载荷下的压应变作用增强.整体而言,轴向膨胀和回压,耦合径向弯曲变形,导致构件内部破坏失稳.升温速率越大,截面温度梯度越大,破坏前能承受的挠度越小,耐火时间越短.%Based on the characteristics of combustible fuel of actual civil building and a simplified combustion model of solid fuel, through numerical simulation of a single room in fire by use of the CFD simulation software FLUENT, this paper analyses the transient temperature distribution of the flue gas in the room. Then based on the thermal characteristics of reinforced concrete columns, the ternperature-strain-stress constitutive characteristics, the paper analyses the evolutionary processes of the reinforced concrete columns temperature distribution and deformation regulations under four different elevated temperature conditions. The results indicate; because high calorific value and volatile fuel composition exist massively in the civil building, such as rubber and plastics, it makes fires with early rapid heating rate early, and the overall combustion temperature of the room is higher than IS0834 standards. Pre-fire, the axial deformation of reinforced concrete columns is mainly from thermal expansion in the meantime
Concrete construction engineering handbook
Nawy, Edward G
2008-01-01
Provides coverage of concrete construction engineering and technology. This work features discussions focusing on: the advances in engineered concrete materials; reinforced concrete construction; specialized construction techniques; and, design recommendations for high performance.
Flow modelling of steel fibre reinforced self-compacting concrete
DEFF Research Database (Denmark)
Svec, Oldrich
Concrete is one of the most widely used materials in the world. Ordinary concrete composition makes the material strong in compression yet weak and brittle in tension. Steel reinforced concrete successfully eliminates the weak tensile properties of the ordinary concrete. Steel fibres dispersed...... in concrete can efficiently substitute or supplement conventional steel reinforcement, such as reinforcement bars. Ordinary concrete composition further makes the material stiff and non-flowable. Self-compacting concrete is an alternative material of low yield stress and plastic viscosity that does flow...... and fills the formwork with a little or no effort. Steel fibre reinforced self-compacting concrete is a logical combination of the two types of concrete. The combination nevertheless creates several challenges. It has been observed by many authors that steel fibres orient and distribute according...
Directory of Open Access Journals (Sweden)
Hwa Kian Chai
2016-04-01
Full Text Available Concrete is the most ubiquitous construction material. Apart from the fresh and early age properties of concrete material, its condition during the structure life span affects the overall structural performance. Therefore, development of techniques such as non-destructive testing which enable the investigation of the material condition, are in great demand. Tomography technique has become an increasingly popular non-destructive evaluation technique for civil engineers to assess the condition of concrete structures. In the present study, this technique is investigated by developing reconstruction procedures utilizing different parameters of elastic waves, namely the travel time, wave amplitude, wave frequency, and Q-value. In the development of algorithms, a ray tracing feature was adopted to take into account the actual non-linear propagation of elastic waves in concrete containing defects. Numerical simulation accompanied by experimental verifications of wave motion were conducted to obtain wave propagation profiles in concrete containing honeycomb as a defect and in assessing the tendon duct filling of pre-stressed concrete (PC elements. The detection of defects by the developed tomography reconstruction procedures was evaluated and discussed.
SENSITIVITY ANALYSIS OF CONCRETE PERFORMANCE USING FINITE ELEMENT APPROACH
Parjoko, Y. H.
2012-01-01
This study aims to understand the effect of applying several parameters: different axle load configuration, concrete properties, subgrade properties, slab thickness, joint characteristics, shoulder construction, bounded HMA overlay on concrete pavement, and bounded and unbounded CTB foundation over subgrade on the fatigue and erosion related distresses in concrete pavements. KENSLAB, an elaborate finite element program is used to determine the concrete pavement responses: stresses and deflect...
Modeling of concrete cracking due to corrosion process of reinforcement bars
Energy Technology Data Exchange (ETDEWEB)
Bossio, Antonio, E-mail: antonio.bossio@unina.it [Department of Chemical Engineering, Materials and Production, University of Naples “Federico II”, Napoli, Piazzale V. Tecchio 80, I-80125 Italy (Italy); Monetta, Tullio, E-mail: monetta@unina.it [Department of Chemical Engineering, Materials and Production, University of Naples “Federico II”, Napoli, Piazzale V. Tecchio 80, I-80125 Italy (Italy); Bellucci, Francesco, E-mail: bellucci@unina.it [Department of Chemical Engineering, Materials and Production, University of Naples “Federico II”, Napoli, Piazzale V. Tecchio 80, I-80125 Italy (Italy); Lignola, Gian Piero, E-mail: glignola@unina.it [Department of Structures for Engineering and Architecture, University of Naples “Federico II”, Via Claudio 21, I-80125 Napoli (Italy); Prota, Andrea, E-mail: aprota@unina.it [Department of Structures for Engineering and Architecture, University of Naples “Federico II”, Via Claudio 21, I-80125 Napoli (Italy)
2015-05-15
The reinforcement corrosion in Reinforced Concrete (RC) is a major reason of degradation for structures and infrastructures throughout the world leading to their premature deterioration before design life was attained. The effects of corrosion of reinforcement are: (i) the reduction of the cross section of the bars, and (ii) the development of corrosion products leading to the appearance of cracks in the concrete cover and subsequent cover spalling. Due to their intrinsic complex nature, these issues require an interdisciplinary approach involving both material science and structural design knowledge also in terms on International and National codes that implemented the concept of durability and service life of structures. In this paper preliminary FEM analyses were performed in order to simulate pitting corrosion or general corrosion aimed to demonstrate the possibility to extend the results obtained for a cylindrical specimen, reinforced by a single bar, to more complex RC members in terms of geometry and reinforcement. Furthermore, a mechanical analytical model to evaluate the stresses in the concrete surrounding the reinforcement bars is proposed. In addition, a sophisticated model is presented to evaluate the non-linear development of stresses inside concrete and crack propagation when reinforcement bars start to corrode. The relationships between the cracking development (mechanical) and the reduction of the steel section (electrochemical) are provided. Finally, numerical findings reported in this paper were compared to experimental results available in the literature and satisfactory agreement was found.
Vlahinic, Ivan
It has been said that porous materials are like music: the gaps are as important as the filled-in bits. In other words, in addition to the solid structure, pore characteristics such as size and morphology play a crucial role in defining the overall physical properties of the porous materials. This work goes a step further and examines the behaviors of some porous media that arise when the pore network is occupied by two fluids, principally air and water, as a result of drying or wetting. Such a state gives rise to fluid capillarity which can generate significant negative fluid pressures. In the first part, a constitutive model for drying of an elastic porous medium is proposed and then extended to derive a novel expression for effective stress in partially saturated media. The model is motivated by the fact that in a system that is saturated by two different fluids, two different pressure inherently act on the surfaces of the pore network. This causes a non-uniform strain field in the solid structure, something that is not explicitly accounted for in the classic formulations of this problem. We use some standard micromechanical homogenization techniques to estimate the extent of the 'non-uniformity' and on this basis, evaluate the validity of the classic Bishop effective stress expression for partially saturated materials. In the second part, we examine a diverse class of porous materials which behave in an unexpected (and even counterintuitive) way under the internal moisture fluctuations. In particular, during wetting and drying alike, the solid viscosity of these materials appears to soften, sometimes by an order of magnitude or more. Under load, this can lead to significantly increased rates of deformations. On account of the recent experimental and theoretical findings on the nature of water flow in nanometer-size hydrophillic spaces, we provide a physical explanation for the viscous softening and propose a constitutive law on this basis. To this end, it also
Directory of Open Access Journals (Sweden)
Gaspar Tébar, Demetrio
1991-03-01
Full Text Available The evidence that the concrete is not a material for ever was noticed from the beginning of its industrial use. In the present work, the author describes the studies carried out during the last century and the early ages of the present one, mainly devoted to the study of the durability in sea water.
At the present days, and in spite of the numerous papers published from then, the study of the concrete durability continues focusing the research priorities and economical resources of researchers and industries related with this material. Moreover, the new laboratory techniques are allowing to understand old problems and even to open again the discussion on reaction mechanisms which were believed to be completely understood.
The article finalizes with a brief description of the numerous studies carried out at the Institute Eduardo Torroja on concrete durability, mainly those related with the resistance against gypsum attack (so abundant in our country land and against sea water attack.
La realidad de que el hormigón no es un material eterno y es susceptible de sufrir ataques por agentes químicos, fue constatada desde el comienzo mismo de su uso industrial. En el presente trabajo el autor enumera los estudios realizados el siglo pasado y a comienzos del presente sobre la durabilidad del hormigón en agua de mar.
En la actualidad y a pesar de los numerosos trabajos desarrollados desde entonces, el estudio de la durabilidad del hormigón sigue centrando la atención prioritaria y los recursos económicos de los investigadores e industrias relacionadas con este material. Además las nuevas técnicas de estudio están permitiendo comprender antiguos problemas e incluso reabrir la discusión sobre mecanismos de reacción que se creían completamente explicados.
Finaliza el artículo con una descripción somera de los múltiples trabajos realizados en el Instituto Eduardo Torreja sobre la materia, en especial los estudios realizados sobre
Energy Technology Data Exchange (ETDEWEB)
Reineck, K.H.; Lichtenfels, A.; Schlaich, J. [Stuttgart Univ. (Germany). Inst. fuer Konstruktion und Entwurf 2
1998-12-31
In 1996 the two large heat storage tanks in Hamburg-Bramfeld (4,750 cubic metres) and Friedrichshafen-Wiggenhausen (12,000 cubic metres) were built out of concrete with an inner stainless steel lining. This was a big step towards economic efficiency. The research project ``Tight sealing of pit water storage tanks made out of pre-stressed concrete`` was launched by the BMBF in order to show that the concrete construction will not only bear loads but also ensure sealing. Building costs for underground hot water storage tanks could then be reduced by at least 25%. The first results of this research project are presented. The paper also contains recommendations for the further development of heat storage tanks built with pre-stressed concrete. (orig.) [Deutsch] Im Jahre 1996 wurden die beiden grossen Waermespeicher in Hamburg-Bramfeld mit einem Volumen von 4.750 m{sup 3} und in Friedrichshafen-Wiggenhausen mit 12.000 m{sup 3} aus Beton mit innenliegender Edelstahlauskleidung fertiggestellt. Mit dem Bau dieser beiden Grossspeicher konnte ein richtungsweisender Schritt hin zur Wirtschaftlichkeit gemacht werden, wie man es in Studien vor 15 Jahren nicht fuer moeglich hielt. Mit dem BMBF - Forschungsvorhaben `Dichte Heisswasser - Waermespeicher aus Hochleistungsbeton` soll gezeigt werden, dass das Betontragwerk nicht nur Lasten abtragen sondern auch die Funktion der Abdichtung uebernehmen kann. Damit sollen die Baukosten fuer unterirdische Heisswasser-Waermespeicher um mindestens 25% gesenkt werden. Es werden die ersten Ergebnisse dieses Forschungsvorhabens mitgeteilt und Empfehlungen fuer die weitere Entwicklung von Waermespeichern aus Hochleistungsbeton gegeben. (orig.)
Modelling Tension Stiffening in Reinforced Concrete Structures
DEFF Research Database (Denmark)
Christiansen, Morten Bo; Nielsen, Mogens Peter
1997-01-01
flexure.In the first model, the yield zone model, it is assumed that the mean crack distance is a descending function of the reinforcement stress in a crack. Furthermore it is assumed that in certain zones between the cracks the concrete is carrying its full effective tensile strength, i.e. the concrete...... with deformations in reinforced concrete disks subjected to pure shear.A physical model for the shear stress-shear strain behaviour of disks, including tension stiffening, is proposed.In the disk model it is assumed that the tensile principal stress in the concrete decreases linearly from the initiation of cracking...... until a certain load level. At any load level the model can predict the shear strains of the disk and the inclination of the crack system. When regarding tension stiffening this latter parameter will be a function of the load level.The model is compared with experimental data, and in the light...
THE BOND STRESS-SLIP RELATIONSHIP FOR STEEL REINFORCED LIGHTWEIGHT CONCRETE%型钢轻骨料混凝土粘结滑移本构关系研究
Institute of Scientific and Technical Information of China (English)
张建文
2012-01-01
本文研究了型钢与轻骨料混凝土的局部粘结滑移本构关系．在型钢表面刻槽贴应变片，并在与型钢应变片对应位置的混凝土表面贴应变片，由试验结果和分析：得到了型钢表面粘结应力沿锚固长度的负指数分布函数；绘制了局部滑移分布曲线；给出了加载端局部粘结滑移本构关系．局部最大粘结应力主要与混凝土强度、配箍率、混凝土相对保护层厚度有关．引入粘结滑移本构关系的型钢轻骨料混凝土梁有限元分析结果和试验结果吻合较好．%The bond-slip constitutive relationship is studied based on the push-out tests of nine steel reinforced lightweight concrete specimens. The section steel is instrumented with strain gauges in a machined axial cavity at the flanges and webs, and gauges are also stuck on the concrete surface corresponding to the gauge positions of the section steel. According to the test results, the negative exponent distribution function of the bond stress along the anchorage length is analyzed and the local relative slip curves are obtained. The constitutive relationship between the local bond stress and the slip at the loading end is investigated. The maximum local bond stress mainly depends on the strength of the concrete, the stirrup ratio and concrete cover depth. The steel reinforced lightweight aggregate concrete beams are analyzed by introducing the local bond-slip constitutive relationship. The test values agree very well with those obtained with finite element analysis.
Kim, Yu Shin; Galis, Zorina S; Rachev, Alexander; Han, Hai-Chao; Vito, Raymond P
2009-01-01
Arteries adapt to their mechanical environment by undergoing remodeling of the structural scaffold via the action of matrix metalloproteinases (MMPs). Cell culture studies have shown that stretching vascular smooth muscle cells (VSMCs) positively correlates to the production of MMP-2 and -9. In tissue level studies, the expressions and activations of MMP-2 and -9 are generally higher in the outer media. However, homogeneous mechanical models of arteries predict lower stress and strain in the outer media, which appear inconsistent with experimental findings. The effects of heterogeneity may be important to our understanding of VSMC function since arteries exhibit structural heterogeneity across the wall. We hypothesized that local stresses, computed using a heterogeneous mechanical model of arteries, positively correlate to the levels of MMP-2 and -9 in situ. We developed a model of the arterial wall accounting for nonlinearity, residual strain, anisotropy, and structural heterogeneity. The distributions of elastin and collagen fibers in situ, measured in the media of porcine carotid arteries, showed significant nonuniformities. Anisotropy was represented by the direction of collagen fibers measured by the helical angle of VSMC nuclei. The points at which the collagen fibers became load bearing were computed, assuming a uniform fiber strain and orientation under physiological loading conditions, an assumption motivated by morphological measurements. The distributions of circumferential stresses, computed using both heterogeneous and homogeneous models, were correlated to the distributions of expressions and activations of MMP-2 and -9 in porcine common carotid arteries incubated in an ex vivo perfusion organ culture system under physiological conditions for 48 h. While strains computed using incompressibility were identical in both models, the heterogeneous model, unlike the homogeneous model, predicted higher circumferential stresses in the outer layer correlated
Non-linear impact of glutathione depletion on C. elegans life span and stress resistance
Directory of Open Access Journals (Sweden)
Nadine Urban
2017-04-01
Full Text Available The redox environment in cells and organisms is set by low-molecular mass and protein-bound thiols, with glutathione (GSH representing a major intracellular redox buffer. Subtle thiol oxidation elicits signal transduction processes and adaptive responses to cope with stressors, whereas highly oxidizing conditions may provoke cell death. We here tested how thiol depletion affects life span, stress resistance and stress signaling in the model organism Caenorhabditis elegans. Diethyl maleate (DEM, an α,β-unsaturated carbonyl compound that conjugates to GSH and other thiols, decreased C. elegans life span at a concentration of 1 mM. In contrast, low and moderate doses of DEM (10–100 µM increased mean and maximum life span and improved resistance against oxidative stress. DEM-induced life span extension was not detectable in worms deficient in either the FoxO orthologue, DAF-16, or the Nrf2 orthologue, SKN-1, pointing to a collaborative role of the two transcription factors in life span extension induced by thiol depletion. Cytoprotective target genes of DAF-16 and SKN-1 were upregulated after at least 3 days of exposure to 100 µM DEM, but not 1 mM DEM, whereas only 1 mM DEM caused upregulation of egl-1, a gene controlled by a p53-orthologue, CEP-1. In order to test whether depletion of GSH may elicit effects similar to DEM, we suppressed GSH biosynthesis in worms by attenuating γ-glutamylcysteine synthetase (gcs-1 expression through RNAi. The decline in GSH levels elicited by gcs-1 knockdown starting at young adult stage did not impair viability, but increased both stress resistance and life expectancy of the worms. In contrast, gcs-1 knockdown commencing right after hatching impaired nematode stress resistance and rendered young adult worms prone to vulval ruptures during egg-laying. Thus, modest decrease in GSH levels in young adult worms may promote stress resistance and life span, whereas depletion of GSH is detrimental to freshly
Germanium under high tensile stress: nonlinear dependence of direct band gap vs. strain
Guilloy, K.; Pauc, N.; Gassenq, A.; Niquet, Y. M.; Escalante, J. M.; Duchemin, I.; Tardif, S; Dias, G. Osvaldo; Rouchon, D.; Widiez, J.; Hartmann, J.M.; Geiger, R.; Zabel, T.; Sigg, H; Faist, J.
2016-01-01
Germanium is a strong candidate as a laser source for silicon photonics. It is widely accepted that the band structure of germanium can be altered by tensile strain so as to reduce the energy difference between its direct and indirect band gaps. However, the conventional deformation potential model most widely adopted to describe this transformation happens to have been investigated only up to 1 % uniaxially loaded strains. In this work, we use a micro-bridge geometry to uniaxially stress ger...
Del Coz Díaz, J. J.; Nieto, P.J.García; Hernández, J. Domínguez; Álvarez Rabanal, F.P.
2010-01-01
Abstract This paper presents a comparative nonlinear thermal analysis for a total of eighteen different in situ cast floors varying both the constituent materials of the hollow blocks (clay, concrete and lightweight concrete) and the shape and number of recesses (six different block types) using the finite element method (FEM). Based on the non-linear thermal analysis of the different configurations by FEM and considering both upward and downward heat flows, it is possible to choos...
Okamura, Hajime; Ouchi, Masahiro
2003-01-01
Self-compacting concrete was first developed in 1988 to achieve durable concrete structures. Since then, various investigations have been carried out and this type of concrete has been used in practical structures in Japan, mainly by large construction companies. Investigations for establishing a rational mix-design method and self-compactability testing methods have been carried out from the viewpoint of making self-compacting concrete a standard concrete.
Okamura, Hajime; Ouchi, Masahiro
2003-01-01
Self-compacting concrete was first developed in 1988 to achieve durable concrete structures. Since then, various investigations have been carried out and this type of concrete has been used in practical structures in Japan, mainly by large construction companies. Investigations for establishing a rational mix-design method and self-compactability testing methods have been carried out from the viewpoint of making self-compacting concrete a standard concrete.
High-performance hybrid-fibre concrete: development and utilisation
Markovic, I.
2006-01-01
Although concrete is the most utilised building material nowdays, this material has a large shortcoming: it has a good resistance against compressive stresses, but a very low resistance against tensile stresses. Usual way to solve this problem is the application of steel reinforcement in concrete st
Directory of Open Access Journals (Sweden)
Momoh Emmanuel Owoichoechi
2017-06-01
Full Text Available Incorporating scrap tyre rubber particles as partial replacement for aggregates has been found to produce concrete with improved ductility, deformability and damping which are desired characteristics of a viable material for enhancing structural response to earthquake vibrations. An analytical study using Drain-2dX was carried out to investigate the response of 4-storey, 3-bay reinforced concrete frames on innovative rubberised concrete deformable foundation models to simulated earthquake scaled to 5 different peak ground accelerations. Stress-strain properties of 3-layers aramid fibre-reinforced polymer (FRP-confinement for concrete incorporating waste rubber from scrap vehicle tyres were used to model the elements of this foundation models. With a partial decoupling of the superstructure from the direct earthquake force, the models showed up to 70% reduction in base shear, an improved overall q-factor of 7.1, and an estimated frame acceleration of 0.11g for an earthquake peak ground acceleration of 0.44g. This implies that a non-seismically designed reinforced concrete frame on the proposed rubberised concrete deformable foundation system would provide a simple, affordable and equally efficient alternative to the conventional and usually expensive earthquake resistant concrete frames. A supplementary Arrest System (SAS was proposed to anchor the frame from the resulting soft storey at the rubberised concrete foundation. A further research is recommended for the design of concrete hinges with rubberised concrete as used in the model with the most impressive response.
XFEM for Thermal Crack of Massive Concrete
Directory of Open Access Journals (Sweden)
Guowei Liu
2013-01-01
Full Text Available Thermal cracking of massive concrete structures occurs as a result of stresses caused by hydration in real environment conditions. The extended finite element method that combines thermal fields and creep is used in this study to analyze the thermal cracking of massive concrete structures. The temperature field is accurately simulated through an equivalent equation of heat conduction that considers the effect of a cooling pipe system. The time-dependent creep behavior of massive concrete is determined by the viscoelastic constitutive model with Prony series. Based on the degree of hydration, we consider the main properties related to cracking evolving with time. Numerical simulations of a real massive concrete structure are conducted. Results show that the developed method is efficient for numerical calculations of thermal cracks on massive concrete. Further analyses indicate that a cooling system and appropriate heat preservation measures can efficiently prevent the occurrence of thermal cracks.
Fatigue Behavior of Plain Concrete Under Biaxial Compression:Experiments and Theoretical Model
Institute of Scientific and Technical Information of China (English)
朱劲松; 宋玉普; 曹伟
2003-01-01
The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm×100 mm×100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue life predicted by this model is found to be in good agreement with the results of the experimental research.
Energy Technology Data Exchange (ETDEWEB)
Archambeau, C.B. [Univ. of Colorado, Boulder, CO (United States)
1994-01-01
A fractured solid under stress loading (or unloading) can be viewed as behaving macroscopically as a medium with internal, hidden, degrees of freedom, wherein changes in fracture geometry (i.e. opening, closing and extension) and flow of fluid and gas within fractures will produce major changes in stresses and strains within the solid. Likewise, the flow process within fractures will be strongly coupled to deformation within the solid through boundary conditions on the fracture surfaces. The effects in the solid can, in part, be phenomenologically represented as inelastic or plastic processes in the macroscopic view. However, there are clearly phenomena associated with fracture growth and open fracture fluid flows that produce effects that can not be described using ordinary inelastic phenomenology. This is evident from the fact that a variety of energy release phenomena can occur, including seismic emissions of previously stored strain energy due to fracture growth, release of disolved gas from fluids in the fractures resulting in enhanced buoyancy and subsequent energetic flows of gas and fluids through the fracture system which can produce raid extension of old fractures and the creation of new ones. Additionally, the flows will be modulated by the opening and closing of fractures due to deformation in the solid, so that the flow process is strongly coupled to dynamical processes in the surrounding solid matrix, some of which are induced by the flow itself.
An analytical and numerical study of the nonlinear reflection at a stress-free surface
Romer, Anne; Kim, Jin-Yeon; Jacobs, Laurence J.
2015-03-01
Implementation of the ultrasonic second harmonic generation has typically been restricted to simple setups such as through-transmission or Rayleigh surface waves. Recent research has evaluated the second harmonic waves generation in P- and SV- waves reflected from a stress-free surface to enable the single-sided interrogation of a specimen. This research considers the second harmonic generation in an aluminum specimen, which is analytically evaluated using an approach based on a perturbation method. Here, the model is chosen to mimic an experimental setup where the longitudinal wave is generated at oblique angle using a wedge transducer. Due to the mode conversion at the interface of the wedge and the specimen, it is necessary to evaluate longitudinal and shear waves, determining all second harmonic waves generated in the bulk and at the stress-free boundary. The theoretically developed model is then implemented in a commercial finite element code, COMSOL, using increasing fundamental wave amplitudes for different values of third order elastic constants. The results of this computational model verify the analytical approach and the proposed measurement setup, taking into account assumptions and approximations of the solution procedure. Furthermore, the computational model is used to draw important conclusions relevant to the experimental setup, including the need to avoid interaction with diffracted waves.
An analytical and numerical study of the nonlinear reflection at a stress-free surface
Energy Technology Data Exchange (ETDEWEB)
Romer, Anne, E-mail: anne.romer@gmx.net; Kim, Jin-Yeon, E-mail: anne.romer@gmx.net [School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States); Jacobs, Laurence J. [School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA and G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332 (United States)
2015-03-31
Implementation of the ultrasonic second harmonic generation has typically been restricted to simple setups such as through-transmission or Rayleigh surface waves. Recent research has evaluated the second harmonic waves generation in P- and SV- waves reflected from a stress-free surface to enable the single-sided interrogation of a specimen. This research considers the second harmonic generation in an aluminum specimen, which is analytically evaluated using an approach based on a perturbation method. Here, the model is chosen to mimic an experimental setup where the longitudinal wave is generated at oblique angle using a wedge transducer. Due to the mode conversion at the interface of the wedge and the specimen, it is necessary to evaluate longitudinal and shear waves, determining all second harmonic waves generated in the bulk and at the stress-free boundary. The theoretically developed model is then implemented in a commercial finite element code, COMSOL, using increasing fundamental wave amplitudes for different values of third order elastic constants. The results of this computational model verify the analytical approach and the proposed measurement setup, taking into account assumptions and approximations of the solution procedure. Furthermore, the computational model is used to draw important conclusions relevant to the experimental setup, including the need to avoid interaction with diffracted waves.
Energy Technology Data Exchange (ETDEWEB)
Castorena Gonzalez, J.H.; Calderon Guillen, J.A. [Universidad Autonoma de Sinaloa, Los Mochis, Sinaloa (Mexico)]. E-mail: kstor28@yahoo.com.mx; cajoel_99@yahoo.com; Almeraya Calderon, F.; Gaona Tiburcio, C. [Centro de Investigacion en Materiales Avanzados, S.C., Chihuahua, Chihuahua (Mexico)]. E-mail: facundo.almeraya@cimav.edu.mx; citlalli.gaona@cimav.edu.mx; Almaral Sanchez, J.L. [Universidad Autonoma de Sinaloa, Los Mochis, Sinaloa (Mexico)]. E-mail: jalmaral@gmail.com; Martinez Villafane, A. [Centro de Investigacion en Materiales Avanzados, S.C., Chihuahua, Chihuahua (Mexico)]. E-mail: martinez.villafane@cimav.edu.mx
2011-01-15
The corrosion in the reinforcement steel is a problem that diminishes the useful life of reinforced concrete structures, reside committing its structural security. In the available models to estimate the mechanical effect of the corrosion, it is assumed that the corroded steel, through the oxides that grow to its surroundings, exercises a pressure on the surrounding concrete supposing a problem of plane stress or plane strain. In this work, the problem is modeled with three-dimensional finite element starting from an experiment on a subjected cylinder to accelerated corrosion, with strain gage to measure the pressure indirectly in the interface steel-concrete. From the results obtained it can be concluded that the effect of the length of corroded steel, anodic length, has a significant effect on the magnitude of the pressure in the interface steel-concrete, fact that can be used to improve the existing models. [Spanish] La corrosion en el acero de refuerzo es un problema que disminuye la vida util en las estructuras de concreto reforzado, ademas de comprometer su seguridad estructural. En los modelos disponibles para estimar el efecto mecanico de la corrosion, se supone que el acero corroido, a traves de los oxidos que crecen a su alrededor, ejercen una presion sobre el concreto circundante suponiendo un problema de esfuerzos o deformaciones planas, En el presente trabajo, se modela el problema con elemento finito tridimensional a partir de un experimento sobre un cilindro de concreto reforzado sometido a corrosion acelerada, instrumentado para medir indirectamente la presion en la interfase acero-concreto. De los resultados obtenidos se concluye que el efecto de la longitud de acero corroido, longitud anodica, tiene un efecto significativo sobre la magnitud de la presion en la interfase acero-concreto, hecho que puede ser utilizado para mejorar los modelos existentes.
Institute of Scientific and Technical Information of China (English)
程旭东; 孙连方; 马红; 韩明一; 张如林
2015-01-01
During the construction process of large-scale LNG storage tanks, the hydration heat of cement causes a great ther-mal stress to LNG storage tank dome, which leads to concrete cracking and seriously affects the durability of the dome. An improved finite element model for a large-scale LNG storage tank was established using the finite element program ADINA, and the temperature field in tank dome was determined in the process of segmented pouring of concrete, the numerical simu-lation results were compared with the field test results. The temperature field and the structure were coupled by considering concrete creep and age effects, the distributions of thermal stress and crack were determined, and the risks of concrete crack-ing were estimated. Furthermore, the sensitivity of the parameter was analyzed. The results show that a great temperature difference between the inside and the outside of the dome is generated in the process of concrete pouring, which will cause a great thermal stress. The thermal stress of the first pouring is greater than others, the hoop stress is greater than the meridian stress, and it will make the edge of dome produce meridian cracks along the circumferential direction. Types of cement have an important effects on the results of thermal stress.%对于大型LNG储罐，其穹顶因水泥水化热产生较大的热应力，引起混凝土开裂，严重影响储罐的耐久性。以某大型LNG储罐穹顶为研究对象，采用ADINA有限元软件建立精细化的有限元模型，模拟LNG储罐穹顶分段浇筑过程中的早期温度场分布，并将数值计算结果与现场测试结果进行对比；数值分析时考虑了混凝土徐变及龄期效应，对混凝土穹顶的温度场和应力场进行耦合计算，得到穹顶的热应力分布及裂缝开展情况，对穹顶混凝土开裂风险进行评估，进而对参数的敏感性进行分析。结果表明：穹顶内外在混凝土浇筑过程中产生温差较大
Directory of Open Access Journals (Sweden)
Semina Yuliya Anatol'evna
2015-09-01
Full Text Available The behavior of reinforced concrete elements under some types of cyclic loads is described in the paper. The main aim of the investigations is research of the stress-strain state and strength of the inclined sections of reinforced concrete beam elements in conditions of systemic impact of constructive factors and the factor of external influence. To spotlight the problem of cyclic loadings three series of tests were conducted by the author. Firstly, the analysis of the tests showed that especially cyclic alternating loading reduces the bearing capacity of reinforced concrete beams and their crack resistance by 20 % due to the fatigue of concrete and reinforcement. Thus the change of load sign creates serious changes of stress-strain state of reinforced concrete beam elements. Low cycle loads of constant sign effect the behavior of the constructions not so adversely. Secondly, based on the experimental data mathematical models of elements’ strength were obtained. These models allow evaluating the impact of each factor on the output parameter not only separately, but also in interaction with each other. Furthermore, the material spotlighted by the author describes stress-strain state of the investigated elements, cracking mechanism, changes of deflection values, the influence of mode cyclic loading during the tests. Since the data on the subject are useful and important to building practice, the ultimate aim of the tests will be working out for improvement of nonlinear calculation models of span reinforced concrete constructions taking into account the impact of these loads, and also there will be the development of engineering calculation techniques of their strength, crack resistance and deformability.
Analysis of mixed-mode fracture in concrete using interface elements and a cohesive crack model
Indian Academy of Sciences (India)
Víctor O García-Álvarez; Ravindra Gettu; Ignacio Carol
2012-02-01
The paper presents a model, based on nonlinear fracture mechanics, for analysing crack propagation in quasi-brittle materials, such as concrete. The work is limited to two-dimensions, and therefore, the fracture modes of interest are mode I (pure tension) and mode II (pure shear). The constitutive model has been implemented in the context of the ﬁnite element method using interface elements. The fracture is simulated through a discrete crack represented by the interface with a cohesive crack stress-separation relation derived from the model, which is based on a fracture criterion, together with a ﬂow rule and a softening law. The model is used for simulating results from an experimental study on beams with centric and eccentric notches of high and normal strength concretes, and explaining other test results available in the literature.
A micromechanical four-phase model to predict the compressive failure surface of cement concrete
Directory of Open Access Journals (Sweden)
A. Caporale,
2014-07-01
Full Text Available In this work, a micromechanical model is used in order to predict the failure surface of cement concrete subject to multi-axial compression. In the adopted model, the concrete material is schematised as a composite with the following constituents: coarse aggregate (gravel, fine aggregate (sand and cement paste. The cement paste contains some voids which grow during the loading process. In fact, the non-linear behavior of the concrete is attributed to the creation of cracks in the cement paste; the effect of the cracks is taken into account by introducing equivalent voids (inclusions with zero stiffness in the cement paste. The three types of inclusions (namely gravel, sand and voids have different scales, so that the overall behavior of the concrete is obtained by the composition of three different homogenizations; in the sense that the concrete is regarded as the homogenized material of the two-phase composite constituted of the gravel and the mortar; in turn, the mortar is the homogenized material of the two-phase composite constituted of the sand inclusions and a (porous cement paste matrix; finally, the (porous cement paste is the homogenized material of the two-phase composite constituted of voids and the pure paste. The pure paste represents the cement paste before the loading process, so that it does not contain voids or other defects due to the loading process. The abovementioned three homogenizations are realized with the predictive scheme of Mori-Tanaka in conjunction with the Eshelby method. The adopted model can be considered an attempt to find micromechanical tools able to capture peculiar aspects of the cement concrete in load cases of uni-axial and multi-axial compression. Attributing the non-linear behavior of concrete to the creation of equivalent voids in the cement paste provides correspondence with many phenomenological aspects of concrete behavior. Trying to improve this correspondence, the influence of the parameters of the
An Incursion on Punching of Reinforced Concrete Flat Slabs
Directory of Open Access Journals (Sweden)
Dan-Vasile Bompa
2009-01-01
Full Text Available Starting from the early 60s continuous studies have been made regarding punching of concrete flat slabs. The evolution of technology and calculus systems influenced this engineering branch. Nowadays is possible to account in structural analysis all the non-linear behaviour of reinforced and prestressed concrete and to get the most close structural response in comparison with the real behaviour. As a controversy matter, several tests and theories have been developed. Nowadays researchers try to find the most accurate and economic formula for punching. This paper purpose is to make a survey on punching classical model and related nonlinear concrete behaviour regarded to this issue.
Concrete decontamination by Electro-Hydraulic Scabbling (EHS)
Energy Technology Data Exchange (ETDEWEB)
NONE
1994-11-01
EHS is being developed for decontaminating concrete structures from radionuclides, organic substances, and hazardous metals. EHS involves the generation of powerful shock waves and intense cavitation by a strong pulsed electric discharge in a water layer at the concrete surface; high impulse pressure results in stresses which crack and peel off a concrete layer of controllable thickness. Scabbling produces contaminated debris of relatively small volume which can be easily removed, leaving clean bulk concrete. Objective of Phase I was to prove the technical feasibility of EH for controlled scabbling and decontamination of concrete. Phase I is complete.
Directory of Open Access Journals (Sweden)
Carlos Humberto Martins
2008-01-01
Full Text Available Este trabalho apresenta um estudo sobre análise de vigas de concreto armado em que a não-linearidade física para o material é implementada pelo procedimento refinado da NBR-6118. Este modelo considera a não-linearidade física do concreto armado via diagramas de momento x curvatura de uma seção transversal. O modelo de diagramamomento x curvatura apresentado pelos Comentários Técnicos da NBR-6118 - CT-301 do Ibracon (ABNT, 2003 utiliza a deformação média na armadura tracionada, onde se leva em conta a resistência do concreto tracionado entre fissuras (tension stiffening. Portanto, foiimplementado, em linguagem de programação Fortran Power Station, o procedimento dado pela norma para a contribuição do concreto tracionado entre fissuras. Para comprovar a validade do procedimento implementado, são realizados exemplos numéricos.This work presents a study on the analysis of reinforced concrete beams in which the physical non-linearity of the material isimplemented through the refined procedure in the Technical Comments of Brazilian code NBR-6118 - CT 301 / Ibracon. This model considers the physical non-linearity of the reinforced concrete through momentum-curvature diagrams of a cross-section. Themomentum-curvature diagram presented in the CT-301 (ABNT, 2003 uses medium deformation in the reinforcement, in which the tension stiffening of the reinforced concrete is taken into account. Using programming language Fortran Power Station, the expression given by the code for the contribution of the tension stiffening of the reinforced concrete was implemented. Finally, some results are presented to check the validity of the employed calculation process.
Institute of Scientific and Technical Information of China (English)
Jin Wencheng; Zhou Xiaoyong; Li Na
2008-01-01
A numerical model is developed in this paper to calculate the bending moments of flexural members through integration in 3D solid finite element analyses according to the nonlinear constitutive model of concrete and the elastoplastic constitutive model of steel, utilizing the stress condition of the cross-section, considering the destruction characteristic of reinforced concrete members, and based on the plane cross-section assumption. The results of this model give good agreement with those of the classical method. Consequently, we can also deduce the corresponding numerical expression for eccentrically loaded members according to the analysis method.
Behavior of compacted clay-concrete interface
Institute of Scientific and Technical Information of China (English)
R.R. SHAKIR; Jungao ZHU
2009-01-01
Tests of interface between compacted clay and concrete were conducted systematically using interface simple shear test apparatus. The samples, having same dry density with different water content ratio, were prepared.Two types of concrete with different surface roughness, i.e., relatively smooth and relatively rough surface rough-ness, were also prepared. The main objectives of this paper are to show the effect of water content, normal stress and rough surface on the shear stress-shear displacement relationship of clay-concrete interface. The following were concluded in this study: 1) the interface shear sliding dominates the interface shear displacement behavior for both cases of relatively rough and smooth concrete surface except when the clay water content is greater than 16% for the case of rough concrete surface where the shear failure occurs in the body of the clay sample; 2) the results of interface shear strength obtained by direct shear test were different from that of simple shear test for the case of rough concrete surface; 3) two types of interface failure mechanism may change each other with different water content ratio; 4) the interface shear strength increases with increasing water content ratio especially for the case of clay-rough concrete surface interface.
Computation of reinforcement for solid concrete
Hoogenboom, P.C.J.; De Boer, A.
2008-01-01
Reinforcement in a concrete structure is often determined based on linear elastic stresses. This paper considers computation of the required reinforcement when these stresses have been determined by the finite element method with volume elements. Included are both tension reinforcement and compressi
Vu, The Manh; Sulem, Jean; Subrin, Didier; Monin, Nathalie
2013-03-01
A semi-analytical solution based on the transfer matrix technique is proposed to analyze the stresses and displacements in a two-dimensional circular opening excavated in transversely isotropic formation with non-linear behavior. A non-isotropic far field can be accounted for and the process of excavation is simulated by progressive reduction of the internal radial stress. A hyperbolic stress-strain law is proposed to take into account the non-linear behavior of the rock. The model contains seven independent parameters corresponding to the five elastic constants of an elastic material with transverse isotropy and to the friction coefficient and cohesion along the parallel joints (weakness planes). This approach is based on the discretization of the space into concentric rings. It requires the establishment of elementary solutions corresponding to the stress and displacement fields inside each ring for given conditions at its boundaries. These solutions, based on complex variable theory, are obtained in the form of infinite series. The appropriate number of terms to be kept for acceptable approximation is discussed. This non-linear model is applied to back analyze the convergence measurements of Saint-Martin-la-Porte access gallery. Short-term and long-term ground parameters are evaluated.
Fatigue Performance of Fiber Reinforced Concrete
DEFF Research Database (Denmark)
Jun, Zhang; Stang, Henrik
1996-01-01
The objective of the present study is to obtain basic data of fibre reinforced concrete under fatigue load and to set up a theoretical model based on micromechanics. In this study, the bridging stress in fiber reinforced concrete under cyclic tensile load was investigted in details. The damage...... mechanism of the interface between fiber and matrix was proposed and a rational model given. Finally, the response of a steel fiber reinforced concrete beam under fatigue loading was predicted based on this model and compared with experimental results....
Institute of Scientific and Technical Information of China (English)
王海; 穆康; 陈荣淋; 戚志博; 俞缙
2012-01-01
Concrete-cored sand-gravel pile is a new and typical composite material pile. Theoretical a-nalysis of core pile axial stress are carried out based on Mindlin displacement solution in elastic semi-infinite body and composite material mechanics. Regularities of distribution of core pile axial stress under different axial loads, grade of concret and elastic modulus of sandy soil are deduced, theoretical results are compared with field test results. The comparison results show that theoretical analysis results are accordant with field test results and they can be verified each other. Theoretical study has significant value for analysis of performance mechanism of concrete-cored sand-gravel pile.%劲性砂桩是一种新型复合材料桩.基于弹性半无限空间的Mindlin位移解及复合材料力学原理,对劲性砂桩中混凝土芯桩轴向应力分布进行理论分析研究,得到劲性砂石桩芯桩轴力分布函数,讨论了不同荷载、混凝土芯桩标号、砂土弹性模量情况下芯桩轴向应力分布规律,并与现场芯桩轴向应力测试结果进行对比分析.研究表明:该理论分析结果与现场试验所显示的规律基本一致,验证了理论研究的合理性.该研究对于了解劲性砂桩的荷载传递规律和工作机制具有一定的理论价值.
Institute of Scientific and Technical Information of China (English)
刘朵; 张建东; 刘钊
2013-01-01
The steel truss-web and pre-stressed concrete composite girder bridge consists of two parts :steel truss-web and top-and-bottom concrete board .Because the distribution of shear deformation is non-uniform ,the composite box girder bridge has the obvious shear-lag effect under longitudinal bending .Taking a steel truss-web and pre-stressed concrete composite girder bridge for example ,the shear-lag effect and the distribution law of effective width are analyzed by the fi-nite element model of space ,and the effects of top-and-bottom thickness and steel pipe thickness on the shear-lag effect are studied here so as to provide references for the similar design in the future .%钢桁腹预应力混凝土组合梁桥在截面形式上采用桁式腹杆和混凝土顶底板，由于剪切变形的不均匀性，使得组合箱梁在纵向弯曲时产生较为明显的剪滞效应。以某钢桁腹混凝土组合梁桥为例，利用空间实体模型分析了剪滞效应和有效宽度分布规律，并研究了顶底板厚度及钢管壁厚对剪滞效应的影响，为今后同类桥型的设计提供参考。
Properties of Concrete Containing Scrap-Tire Rubber
Directory of Open Access Journals (Sweden)
Mazyad Al-Fadhli
2017-03-01
Full Text Available Solid waste management is one of the major environmental concerns all over the world and in Kuwait. Over 5 billion tons of non-hazardous solid waste materials are generated in Kuwait each year. Of these, more than 2 million scrap-tires (approximately 2 million tons are generated each year. In addition to this, about seven million scrap-tires have been stockpiled. Due to the increasingly serious environmental problems presented by waste tires, the feasibility of using elastic and flexible tire–rubber particles as aggregate in concrete is investigated in this study. Tire–rubber particles composed of tire chips, crumb rubber, and a combination of tire chips and crumb rubber, were used to replace mineral aggregates in concrete. These particles were used to replace 10%, 15%, 20%, and 25% of the total mineral aggregate’s volume in concrete. Cylindrical shape concrete specimens 15 cm in diameter and 30 cm in height were fabricated and cured. The fresh rubberized concrete exhibited lower unit weight and acceptable workability compared to plain concrete. The results of a uniaxial compressive strain control test conducted on hardened concrete specimens indicate large reductions in the strength and tangential modulus of elasticity. A significant decrease in the brittle behavior of concrete with increasing rubber content is also demonstrated using nonlinearity indices. The maximum toughness index, indicating the post failure strength of concrete, occurs in concretes with 25% rubber content. Unlike plain concrete, the failure state in rubberized concrete occurs gently and uniformly, and does not cause any separation in the specimen. Crack width and its propagation velocity in rubberized concrete are lower than those of plain concrete. Ultrasonic analysis reveals large reductions in the ultrasonic modulus and high sound absorption for tire–rubber concrete.
Institute of Scientific and Technical Information of China (English)
刘军; 林皋
2012-01-01
基于不可逆热力学原理提出一种简单的混凝土类准脆性材料的损伤本构模型，具有参数相对少、公式表达简单、易于数值实现等特点。采用双标量损伤变量来描述混凝土的拉伸和压缩不等性、刚度及强度退化特性；通过分解自由能为体积和剪切两部分，在体积部分引入单边效应函数来考虑裂纹闭合效应；通过对损伤变量的黏性化处理以及附加弹性条件来考虑率相关性。给出混凝土试件在单轴拉伸和压缩、双轴加载、三轴压缩以及应变率影响的不同加载条件下的数值计算结果，与试验结果比较吻合。通过对缺口梁三点弯曲加载破坏过程和重力坝地震响应的数值模拟，验证损伤模型在大尺度混凝土结构的非线性分析方面，具有较好的收敛性和计算能力。%A simple damage constitutive model for concrete-like quasi-brittle materials within the framework of irreversible thermodynamics is developed. The model needs fewer parameters, is simpler in mathematical expression and more convenient for numerical calculation. Different responses under tensile and compressive loadings as well as degradation of stiffness and strength are considered by employing two scalar damage variables. In order to take the microcrack closure effect into consideration, the Helmholtz free energy is decomposed into hydrostatic and deviatoric components, and a unilateral effect function is introduced in the hydrostatic part. The rate effect is considered by introducing viscous regularizations into the damage variable and combined with an additional elastic condition. The cases of uniaxial tensile and compressive, biaxial and triaxial compressive loadings for a concrete specimen are studied. The results agree well with the experiment. The proposed model is employed in the analyses of a three-point bending beam and a gravity dam subjected to earthquake loading. Numerical results show that the
Cohesive Zone Model Based Numerical Analysis of Steel-Concrete Composite Structure Push-Out Tests
Directory of Open Access Journals (Sweden)
J. P. Lin
2014-01-01
Full Text Available Push-out tests were widely used to determine the shear bearing capacity and shear stiffness of shear connectors in steel-concrete composite structures. The finite element method was one efficient alternative to push-out testing. This paper focused on a simulation analysis of the interface between concrete slabs and steel girder flanges as well as the interface of the shear connectors and the surrounding concrete. A cohesive zone model was used to simulate the tangential sliding and normal separation of the interfaces. Then, a zero-thickness cohesive element was implemented via the user-defined element subroutine UEL in the software ABAQUS, and a multiple broken line mode was used to define the constitutive relations of the cohesive zone. A three-dimensional numerical analysis model was established for push-out testing to analyze the load-displacement curves of the push-out test process, interface relative displacement, and interface stress distribution. This method was found to accurately calculate the shear capacity and shear stiffness of shear connectors. The numerical results showed that the multiple broken lines mode cohesive zone model could describe the nonlinear mechanical behavior of the interface between steel and concrete and that a discontinuous deformation numerical simulation could be implemented.
Self-desiccation Effect of High Performance Concrete
Institute of Scientific and Technical Information of China (English)
JIANG Zheng-wu; SUN Zhen-ping; WANG Pei-ming
2004-01-01
Effects of water to binder ratio (mW/mB), types and addition content of mineral admixtures on the autogenous relative humidity (ARH) change of concrete resulting from self-desiccation were studied. The parameters of coefficient of mineral self-desiccation-effect k and efficient water to binder ratio re were proposed, and experimental results were fitted non-linearly and analyzed using these proposed parameters. The experimental results indicate that ARH reduction of concrete at different ages increases with the decrease of mW/mB. The ARH change laws of concrete with mW/mB lower than 0.4 can be expressed with a non-linear equation. The extent of the effect of types and addition content of mineral admixtures on ARH reduction of concrete resulting from self-desiccation can be reflected by the non-linear equation with the parameter of efficient water to binder ratio re effectively.
Fracture mechanical analysis of strengthened concrete tension members with one crack
DEFF Research Database (Denmark)
Hansen, Christian Skodborg; Stang, Henrik
2012-01-01
A concrete tension member strengthened 2 with fiber reinforced polymer plates on two sides 3 is analyzed with non-linear fracture mechanics. The 4 analysis of the strengthened tension member incorpo5 rates cohesive properties for both concrete and inter6 face between concrete and strengthening...... the structural classification parameters, is inves13 tigated in a non-dimensional analysis, and found to 14 depend strongly on the ratio between interfacial and 15 concrete fracture energies....
Flexural Strength Evaluation of Reinforced Concrete Members with Ultra High Performance Concrete
Directory of Open Access Journals (Sweden)
Baek-Il Bae
2016-01-01
Full Text Available Flexural strength evaluation models for steel fiber reinforced ultra high strength concrete were suggested and evaluated with test results. Suggested flexural strength models were composed of compression stress blocks and tension stress blocks. Rectangular stress block, triangular stress block, and real distribution shape of stress were used on compression side. Under tension, rectangular stress block distributed to whole area of tension side and partial area of tension side was used. The last model for tension side is realistic stress distribution. All these models were verified with test result which was carried out in this study. Test was conducted by four-point loading with 2,000 kN actuator for slender beam specimen. Additional verifications were carried out with previous researches on flexural strength of steel fiber reinforced concrete or ultra high strength concrete. Total of 21 test specimens were evaluated. As a result of comparison for flexural strength of section, neutral axis depth at ultimate state, models with triangular compression stress block, and strain-softening type tension stress block can be used as exact solution for ultra high performance concrete. For the conservative and convenient design of section, modified rectangular stress block model can be used with strain softening type tension stress block.
Recycling of demolished concrete
Energy Technology Data Exchange (ETDEWEB)
Nagataki, S. [Niigata Univ., Niigata (Japan). Dept. of Civil Engineering; Iida, K. [Technology Centre of Taisei Corp., Yokohama (Japan)
2001-07-01
There is a significant amount of research being conducted in Japan on ways to recycle demolished concrete. The material is already being used for road bases and foundations, but in the future, the concrete will have to be recycled as concrete aggregate. Recycling may also include the cement in the concrete in order to address the issue of global warming and carbon dioxide reductions. This initiative is in response to predictions that in the future there will be tremendous quantities of demolished concrete to deal with. Recycling of cement is also necessary in terms of resolving environmental problems and promoting sustainable development. The properties of concrete made with recycled aggregates were described and were compared with original concrete made of known materials. The paper also proposed an approach that should be taken to recycling concrete in the twenty-first century in which reduced limestone was used to reclaim cement. Recycled concrete with cement requires more energy, but uses less resources and discharges less carbon dioxide. Currently, recycled aggregate does not meet the Japanese Industrial Standard for concrete aggregate. The resistance to freeze/thaw cycles was not adequate. The amount of mortar adhered to the recycled aggregate had little affect on the strength and durability of recycled concrete. It was concluded that the quality of recycled concrete aggregate depends on the quality of original concrete. 11 refs., 12 tabs., 11 figs.
Review of constitutive models and failure criteria for concrete
Energy Technology Data Exchange (ETDEWEB)
Seo, Jeong Moon; Choun, Young Sun [Korea Atomic Energy Research Institute, Taejeon (Korea)
2000-03-01
The general behavior, constitutive models, and failure criteria of concrete are reviewed. The current constitutive models for concrete cannot satisfy all of mechanical behavior of concrete. Among several constitutive models, damage models are recommended to describe properly the structural behavior of concrete containment buildings, because failure modes and post-failure behavior are important in containment buildings. A constitutive model which can describe the concrete behavior in tension is required because the containment buildings will reach failure state due to ultimate internal pressure. Therefore, a thorough study on the behavior and models under tension stress state in concrete and reinforced concrete has to be performed. There are two types of failure criteria in containment buildings: structural failure criteria and leakage failure criteria. For reinforced or prestressed concrete containment buildings, concrete cracking does not mean the structural failure of containment building because the reinforcement or post-tensioning system is able to resist tensile stress up to yield stress. Therefore leakage failure criteria will be prior to structural failure criteria, and a strain failure criterion for concrete has to be established. 120 refs., 59 figs., 1 tabs. (Author)
Institute of Scientific and Technical Information of China (English)
陈波; 孙伟; 丁建彤
2013-01-01
The working principle and development history of cracking frame and temperature stress testing machine were introduced. Some research work on the crack resistance of early age concretes based on thermal stress test during the past 40 years were reviewed. According to the previous studies in Nanjing Hydraulic Research Institute, the influence of aggregate types and temperature histories on the crack resistance by temperature stress testing machine were investigated. Some main aspects for thermal stress test that need to be further investigated were discussed, including standardization of testing machine and test method, controlling of restraint degree, measuring accuracy of Young's modulus, quantification of concrete cumulative damage induced by to-and-fro movements, and calcu-lation method of early age creep, et al.% 阐述了开裂试验架和温度–应力试验机的工作原理、仪器设备发展和完善的过程。介绍了过去40年里基于温度–应力试验的早龄期混凝土抗裂性研究的进展情况。给出了采用温度–应力试验机考察骨料品种和温度历程对早龄期混凝土抗裂性影响的两个研究案例。对温度–应力试验需要进一步深入研究的几个问题进行了探讨，如：试验设备和试验方法的标准化、约束度控制、弹性模量测试精度、试件的损伤累积及早龄期徐变计算方法等。
Microscopic examination of deteriorated concrete
Nijland, T.G.; Larbi, J.A.
2010-01-01
Concrete petrography is the integrated microscopic and mesoscale (hand specimen size) investigation of hardened concrete, that can provide information on the composition of concrete, the original relationships between the concrete's various constituents, and any changes therein, whether as a result
THE FATIGUE DURABILITY OF THE MODIFIED ASPHALT CONCRETE UNDER THE EFFECT OF INTENSIVE TRAFFIC LOADS
Directory of Open Access Journals (Sweden)
Yuri KALGIN
2016-06-01
Full Text Available The problem of prediction of the service life of asphalt concrete surface constructed with modified asphalt concrete application onto a traffic lane is examined. Asphalt concrete behaviour in road surface under the traffic loads was analysed. There were shown The results of experiments and their mathematical analysis of the assessment of standard and modified cold asphalt concrete fatigue life on road surface were shown. The service life of an asphalt concrete surface covered with standard and modified cold asphalt concrete is examined. The prediction has been received with an account of stress relaxation processes in asphalt concrete pavement and unevenness of traffic load application.
Rigid-plastic seismic design of reinforced concrete structures
DEFF Research Database (Denmark)
Costa, Joao Domingues; Bento, R.; Levtchitch, V.
2007-01-01
In this paper a new seismic design procedure for Reinforced Concrete (R/C) structures is proposed-the Rigid-Plastic Seismic Design (RPSD) method. This is a design procedure based on Non-Linear Time-History Analysis (NLTHA) for systems expected to perform in the non-linear range during a lifetime...
Special Concrete with Polymers
National Research Council Canada - National Science Library
Nicolae Angelescu; Ioana Ion; Darius Stanciu; José Barroso Aguiar; Elena Valentina Stoian; Vasile Bratu
2016-01-01
.... They were prepared epoxy resin polymer concrete, Portland cement, coarse and fine aggregate and to evaluate the influence of resin dosage on microstructures and density of such structures reinforced concrete mixtures...
Sustainable Concrete Technology
Directory of Open Access Journals (Sweden)
Sim J.
2015-12-01
Full Text Available The growing concern over global warming and significant ecological changes requires sustainable development in all fields of science and technology. Concrete not only consumes huge amount of energy and natural sources, but also emits large amount of CO2, mainly due to the production of cement. It is evident that such large amount of concrete production has put significant impact on the energy, resource, environment, and ecology of the society. Hence, how to develop the concrete technology in a sustainable way has become a significant issue. In this paper, some of Korean researches for sustainable development of concrete are presented. These are sustainable strengthening for deteriorated concrete structure, sustainable reinforcement of new concrete structure, sustainable concrete using recycled aggregate and supplementary cementing materials and finally application of each technique to precast concrete.
Concrete Pavement Joint Deterioration
2016-01-01
Concrete pavements are an important part of our national infrastructure. In recent years the relatively small number of reported joints deteriorating prematurely in concrete pavements around Indiana has increased. Changes over the past 45 years in INDOT specification, pavement materials, designs and construction practices, and current de-icing materials were examined and related to the durability of concrete at the joints of existing pavements. A survey of concrete pavements across the state ...
RESEARCH OF ADHESIVE STRENGTH OF NEW CONCRETE LAYER WITH A SURFACE OF OLD CONCRETE
Directory of Open Access Journals (Sweden)
Bulgakov Boris Igorevich
2016-04-01
Full Text Available Concrete is a material very commonly used in modern construction, each year over 4 billion m3 of concrete is used around the world. In the recent years high-quality fine grain and other types of concrete allow giving the modern creation city buildings new architectural expressivity, meeting the requirements of the XXI century. The trend of using of these new types of concrete is also applied in the construction of tunnel systems and the subway. The fine-grained high performance concrete obtained by using a mixture of organo-mineral additives and fiber reinforcement, compares fovourably with ordinary fine-grained concrete, namely its bending and tensile strength is higher, it has good resistance to shock impacts and fatigue, as well as crack resistance, water resistance and resistance to erosion. So this type of fine-grained high performance concrete is suitable for the construction of subway tunnels and other special objects. When evaluating the concrete performance in underground rock layers subjected to complex mechanical forces, it is important to take into account the stress of metro upon departure and stopping at the stations. The article presents a new experimental method of determining the adhesion strength of fine-grained high performance concrete layer freshly poured on the surface of old concrete in the process of construction and repair of underground. The result of this method application showed that fine-grained high performance concrete is capable of skid resistance higher than 55 % compared to regular fine-grained concrete without additives.
Self-adjustment of Carrying Capacity of Concrete Embedded with CFRC
Institute of Scientific and Technical Information of China (English)
Wu YAO
2006-01-01
By heating up the embedded carbon fiber reinforced cement based material (CFRC), the carrying capacity and deformation of concrete member could be adjusted. The relationship between temperature difference and expansion strain of CFRC was demonstrated, and the temperature-deformation-load effect of concrete embedded with CFRC was studied. Heating the CFRC up to different temperatures resulted in different degree of inner pre-stress in concrete. Thus, the load capacity of concrete could be regulated owing to counteracting the pre-stress.
Gorb, Yuliya
2010-11-01
We model and analyze the response of nonlinear, residually stressed elastic bodies subjected to small amplitude vibrations superimposed upon large deformations. The problem derives from modeling the use of intravascular ultrasound (IVUS) imaging to interrogate atherosclerotic plaques in vivo in large arteries. The goal of this investigation is twofold: (i) introduce a modeling framework for residual stress that unlike traditional Fung type classical opening angle models may be used for a diseased artery, and (ii) investigate the sensitivity of the spectra of small amplitude high frequency time harmonic vibrations superimposed on a large deformation to the details of the residual stress stored in arteries through a numerical simulation using physiologic parameter values under both low and high blood pressure loadings. The modeling framework also points the way towards an inverse problem using IVUS techniques to estimate residual stress in healthy and diseased arteries. © 2010 Elsevier Ltd. All rights reserved.
Deterioration of Concrete Structures
DEFF Research Database (Denmark)
Thoft-Christensen, Palle
Chloride ingress is a common cause of deterioration of reinforced concrete bridges. Concrete may be exposed to chloride by seawater or de-icing salts. The chloride initiates corrosion of the reinforcement, which through expansion disrupts the concrete. In addition, the corrosion reduces the cross...
Deterioration of Concrete Structures
DEFF Research Database (Denmark)
Thoft-Christensen, Palle
Chloride ingress is a common cause of deterioration of reinforced concrete bridges. Concrete may be exposed to chloride by seawater or de-icing salts. The chloride initiates corrosion of the reinforcement, which through expansion disrupts the concrete. In addition, the corrosion reduces the cross...
Uzayr, Sufyan bin
2014-01-01
Whether you have had some previous experience with concrete5 or are entirely new to it, this book will help you understand all that you need to know in order to get started with concrete5 development. A background in PHP is required; some knowledge of HTML/CSS is needed in order to fully grasp the concepts underlying concrete5 theme development.
Directory of Open Access Journals (Sweden)
Fangping Liu
2016-01-01
Full Text Available Concrete fatigue strain evolution plays a very important role in the evaluation of the material properties of concrete. To study fatigue strain and fatigue damage of concrete in reinforced concrete beams under constant amplitude bending fatigue loading, constant amplitude bending fatigue experiments with reinforced concrete beams with rectangular sections were first carried out in the laboratory. Then, by analyzing the shortcomings and limitations of existing fatigue strain evolution equations, the level-S nonlinear evolution model of fatigue strain was constructed, and the physical meaning of the parameters was discussed. Finally, the evolution of fatigue strain and fatigue damage of concrete in the compression zone of the experimental beam was analyzed based on the level-S nonlinear evolution model. The results show that, initially, fatigue strain grows rapidly. In the middle stages, fatigue strain is nearly a linear change. Because the experimental data for the third stage are relatively scarce, the evolution of the strain therefore degenerated into two phases. The model has strong adaptability and high accuracy and can reflect the evolution of fatigue strain. The fatigue damage evolution expression based on fatigue strain shows that fatigue strain and fatigue damage have similar variations, and, with the same load cycles, the greater the load level, the larger the damage, in line with the general rules of damage.
Seismic Analysis of Pre-Stressed Reinforced Concrete Wind-Turbine Tower%预应力钢筋混凝土风力发电塔架的地震响应分析
Institute of Scientific and Technical Information of China (English)
毕继红; 任洪鹏; 尹元彪
2011-01-01
随着风力发电机向海上风力发电和单机大容量的趋势发展,预应力钢筋混凝土塔架将有更广阔的前景.为此,以功率2 Mw的大型风力发电塔架为例,参考日本土木学会的风力发电塔架结构设计指南,提出了一种预应力钢筋混凝土塔架的设计方案,建立了结构计算模型,对其动力性能进行了研究,并做了地震响应分析.采用EL Centro实测地震波,对预应力钢筋混凝土塔架结构的有限元模型进行了仿真计算,并将时程分析结果与按设计指南提出的地震反应谱方法得出的设计值进行了比较分析;讨论了安全检查用工作洞口的设置对塔架结构抗震性能的影响;研究了不同的地震波入射角时塔架结构的地震响应,对该结构的抗震性能进行了详细的分析.结果表明,所提出的预应力钢筋混凝土结构形式不仅可以避免由叶轮脉动激励的共振响应,且具有较好的抗震性能,工作洞口的设置并不影响其抗震性能.研究结果将为预应力钢筋混凝土塔架的设计提供重要的理论依据.%With the development of offshore wind farm and large-capacity wind turbine, prestressed reinforced concrete tower will have a wide prospect. Based on the guidelines on the design of wind-turbine compiled by Japan Society of Civil Engineers, the design proposed of pre-stressed reinforced concrete tower was put forward and its calculation model was established in the paper. Moreover, the investigation of dynamic behavior and the seismic response analysis of a pre-stressed reinforced concrete tower for a 2 MW wind-turbine were presented. Comparative analysis of the time-history value obtained through simulation calculation using actual measured EL Centro , and the design value obtained by the method of seismic response spectrum presented in the guidelines was carried out. Subsequently,research on seismic behavior of setting up working hole for security inspection was discussed. The
Mohammadimehr, M.; Mohammadi-Dehabadi, A. A.; Maraghi, Z. Khoddami
2017-04-01
In this research, the effect of non-local higher order stress on the nonlinear vibration behavior of carbon nanotube conveying viscous nanoflow resting on elastic foundation is investigated. Physical intuition reveals that increasing nanoscale stress leads to decrease the stiffness of nanostructure which firstly established by Eringen's non-local elasticity theory (previous nonlocal method) while many of papers have concluded otherwise at microscale based on modified couple stress, modified strain gradient theories and surface stress effect. The non-local higher order stress model (new nonlocal method) is used in this article that has been studied by few researchers in other fields and the results from the present study show that the trend of the new nonlocal method and size dependent effect including modified couple stress theory is the same. In this regard, the nonlinear motion equations are derived using a variational principal approach considering essential higher-order non-local terms. The surrounded elastic medium is modeled by Pasternak foundation to increase the stability of system where the fluid flow may cause system instability. Effects of various parameters such as non-local parameter, elastic foundation coefficient, and fluid flow velocity on the stability and dimensionless natural frequency of nanotube are investigated. The results of this research show that the small scale parameter based on higher order stress help to increase the natural frequency which has been approved by other small scale theories such as strain gradient theory, modified couple stress theory and experiments, and vice versa for previous nonlocal method. This study may be useful to measure accurately the vibration characteristics of nanotubes conveying viscous nanoflow and to design nanofluidic devices for detecting blood Glucose.
Energy Technology Data Exchange (ETDEWEB)
Mohammadimehr, M., E-mail: mmohammadimehr@kashanu.ac.ir [Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan (Iran, Islamic Republic of); Mohammadi-Dehabadi, A.A. [Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan (Iran, Islamic Republic of); Department of Mechanical Engineering, Iran University of Science and Technology, Narmak, Tehran (Iran, Islamic Republic of); Maraghi, Z. Khoddami [Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-53153, Kashan (Iran, Islamic Republic of)
2017-04-01
In this research, the effect of non-local higher order stress on the nonlinear vibration behavior of carbon nanotube conveying viscous nanoflow resting on elastic foundation is investigated. Physical intuition reveals that increasing nanoscale stress leads to decrease the stiffness of nanostructure which firstly established by Eringen's non-local elasticity theory (previous nonlocal method) while many of papers have concluded otherwise at microscale based on modified couple stress, modified strain gradient theories and surface stress effect. The non-local higher order stress model (new nonlocal method) is used in this article that has been studied by few researchers in other fields and the results from the present study show that the trend of the new nonlocal method and size dependent effect including modified couple stress theory is the same. In this regard, the nonlinear motion equations are derived using a variational principal approach considering essential higher-order non-local terms. The surrounded elastic medium is modeled by Pasternak foundation to increase the stability of system where the fluid flow may cause system instability. Effects of various parameters such as non-local parameter, elastic foundation coefficient, and fluid flow velocity on the stability and dimensionless natural frequency of nanotube are investigated. The results of this research show that the small scale parameter based on higher order stress help to increase the natural frequency which has been approved by other small scale theories such as strain gradient theory, modified couple stress theory and experiments, and vice versa for previous nonlocal method. This study may be useful to measure accurately the vibration characteristics of nanotubes conveying viscous nanoflow and to design nanofluidic devices for detecting blood Glucose.
Bond Properties and Experimental Methods of Textile Reinforced Concrete
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
Textile reinforced concrete(TRC, for short) allows the low size production and offers a high effectiveness of the reinforcement by using continuous roving instead of short-chopped fibers. However, whether textiles can cooperate with concrete very well depends on the bond between them. In this paper, the bonding mechanism that the stress was transferred from fine concrete to textile was analyzed, and the influences of the initial bond length of textile, the surface treatment of textile, the strength and workability of concrete as well as the level of prestressing force on bond behavior were investigated on the basis of pull-out tests. The results reveal that with initial bond length increasing, the maximum pull force increases, and increasing concrete strength and improving workability of concrete matrix, epoxy resin impregnating and sand covering of textile as well as prestressing textile can obviously increase the bond strength between the textile and concrete.
Quality control chart for crushed granite concrete
Directory of Open Access Journals (Sweden)
Ewa E. DESMOND
2016-07-01
Full Text Available A chart for assessing in-situ grade (strength of concrete, has been developed in this study. Four grades of concrete after the Nigerian General Specification for Roads and bridges (NGSRB-C20, C25, C30 and C35, is studied at different water-cement ratios for medium and high slump range. The concrete mixes are made from crushed granite rock as coarse aggregate with river sand as fine aggregate. Compression test on specimens are conducted at curing age of 1, 3, 7, 14, 21, 28 and 56 days. Results on concrete workability from slump values, and water-cement ratios revealed that specimens with lower water-cement ratio were less workable but had higher strength, compared to mixes with higher water cement ratio. A simple algorithm using nonlinear regression analysis performed on each experimental data set produced Strength-Age (S-A curves which were used to establish a quality control chart. The accuracy of these curves were evaluated by computing average absolute error (AAS, the error of estimate (EoE and the average absolute error of estimate (Abs EoE for each concrete mix. These were done based on the actual average experimental strengths to measure how close the predicted values are to the experimental data set. The absolute average error of estimate (Abs. EoE recorded was less than ±10% tolerance zone for concrete works.
Institute of Scientific and Technical Information of China (English)
叶恒梅
2016-01-01
The loss of frictional resistance in post -tesioning pre-stressed concrete beam pipe is a big problem during the construction of post-tesioning pre-stressed concrete bridge. The test of frictional resistance loss is important to the quality security and persistence of bridge construction. The formula of beam pipe frictional resistance loss co-effi-cient was calculated by least square method. This formula was applied on the xianhu bridge construction ,then the project of frictional resistance loss test of beam pipe was proposed to reduce the loss of pre-stress and analyze the practical data in the xianhu bridge construction.%在后张法预应力混凝土桥梁结构的建设中，预应力孔道摩阻损失问题十分突出。孔道摩阻测试对确保桥梁结构的施工质量、安全性和耐久性有着重要意义。以仙葫大桥为例，在公式分析的基础上结合最小二乘法原理，推导出孔道摩阻参数的计算公式，为减少预应力损失，提出了孔道摩阻试验检测的方案，同时对该桥现场测试数据进行了计算和分析。研究结果可为同类施工提供参考。
Mechanical properties of concrete containing a high volume of tire-rubber particles.
Khaloo, Ali R; Dehestani, M; Rahmatabadi, P
2008-12-01
Due to the increasingly serious environmental problems presented by waste tires, the feasibility of using elastic and flexible tire-rubber particles as aggregate in concrete is investigated in this study. Tire-rubber particles composed of tire chips, crumb rubber, and a combination of tire chips and crumb rubber, were used to replace mineral aggregates in concrete. These particles were used to replace 12.5%, 25%, 37.5%, and 50% of the total mineral aggregate's volume in concrete. Cylindrical shape concrete specimens 15 cm in diameter and 30 cm in height were fabricated and cured. The fresh rubberized concrete exhibited lower unit weight and acceptable workability compared to plain concrete. The results of a uniaxial compressive strain control test conducted on hardened concrete specimens indicate large reductions in the strength and tangential modulus of elasticity. A significant decrease in the brittle behavior of concrete with increasing rubber content is also demonstrated using nonlinearity indices. The maximum toughness index, indicating the post failure strength of concrete, occurs in concretes with 25% rubber content. Unlike plain concrete, the failure state in rubberized concrete occurs gently and uniformly, and does not cause any separation in the specimen. Crack width and its propagation velocity in rubberized concrete are lower than those of plain concrete. Ultrasonic analysis reveals large reductions in the ultrasonic modulus and high sound absorption for tire-rubber concrete.
Steady-State Creep of Asphalt Concrete
Directory of Open Access Journals (Sweden)
Alibai Iskakbayev
2017-02-01
Full Text Available This paper reports the experimental investigation of the steady-state creep process for fine-grained asphalt concrete at a temperature of 20 ± 2 °С and under stress from 0.055 to 0.311 MPa under direct tension and was found to occur at a constant rate. The experimental results also determined the start, the end point, and the duration of the steady-state creep process. The dependence of these factors, in addition to the steady-state creep rate and viscosity of the asphalt concrete on stress is satisfactorily described by a power function. Furthermore, it showed that stress has a great impact on the specific characteristics of asphalt concrete: stress variation by one order causes their variation by 3–4.5 orders. The described relations are formulated for the steady-state of asphalt concrete in a complex stressed condition. The dependence is determined between stress intensity and strain rate intensity.
Liang, Liang; Liu, Minliang; Sun, Wei
2017-09-20
Biological collagenous tissues comprised of networks of collagen fibers are suitable for a broad spectrum of medical applications owing to their attractive mechanical properties. In this study, we developed a noninvasive approach to estimate collagenous tissue elastic properties directly from microscopy images using Machine Learning (ML) techniques. Glutaraldehyde-treated bovine pericardium (GLBP) tissue, widely used in the fabrication of bioprosthetic heart valves and vascular patches, was chosen to develop a representative application. A Deep Learning model was designed and trained to process second harmonic generation (SHG) images of collagen networks in GLBP tissue samples, and directly predict the tissue elastic mechanical properties. The trained model is capable of identifying the overall tissue stiffness with a classification accuracy of 84%, and predicting the nonlinear anisotropic stress-strain curves with average regression errors of 0.021 and 0.031. Thus, this study demonstrates the feasibility and great potential of using the Deep Learning approach for fast and noninvasive assessment of collagenous tissue elastic properties from microstructural images. In this study, we developed, to our best knowledge, the first Deep Learning-based approach to estimate the elastic properties of collagenous tissues directly from noninvasive second harmonic generation images. The success of this study holds promise for the use of Machine Learning techniques to noninvasively and efficiently estimate the mechanical properties of many structure-based biological materials, and it also enables many potential applications such as serving as a quality control tool to select tissue for the manufacturing of medical devices (e.g. bioprosthetic heart valves). Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
ANALYSIS OF EXPOSURE OF REINFORCED CONCRETE BUILDINGS TO TEMPERATURE LOADS
2012-01-01
The co-authors consider the problem of analysis of building structures in respect of combined effects of forces and temperatures. Results of fire tests of reinforced concrete walls and slabs are presented. Overview of the analysis of the fire resistance of reinforced-concrete buildings is also provided. As a result of the research, numerical solutions were obtained in respect of deflections, stresses, deformations and internal forces arising in a reinforced concrete bearing wall and plate...
Institute of Scientific and Technical Information of China (English)
郭锐
2015-01-01
Taking the large cantilever pre-stressed concrete cap beam construction of a viaduct as an example,from the structure modeling,pre-stressed steel beam system,stress monitoring and other aspects,introduced the construction monitoring technology of bridge structure engineer-ing,through the stress and displacement monitoring analysis of construction process,pointed out that the theory calculated value of large cantile-ver cap beam model in line with construction measured value.%以某高架桥大悬臂预应力混凝土盖梁施工为例，从结构建模、预应力钢束体系、应力监测等方面，介绍了桥梁结构工程的施工监测技术，通过对施工过程中应力和位移的监测分析，指出大悬臂盖梁模型的理论计算值与施工实测值比较吻合。
Autogenous Deformation of Concrete
DEFF Research Database (Denmark)
Autogenous deformation of concrete can be defined as the free deformation of sealed concrete at a constant temperature. A number of observed problems with early age cracking of high-performance concretes can be attributed to this phenomenon. During the last 10 years , this has led to an increased...... focus on autogenous deformation both within concrete practice and concrete research. Since 1996 the interest has been significant enough to hold international, yearly conferences entirely devoted to this subject. The papers in this publication were presented at two consecutive half-day sessions...... at the American Concrete Institute’s Fall Convention in Phoenix, Arizona, October 29, 2002. All papers have been reviewed according to ACI rules. This publication, as well as the sessions, was sponsored by ACI committee 236, Material Science of Concrete. The 12 presentations from 8 different countries indicate...
Autogenous Deformation of Concrete
DEFF Research Database (Denmark)
Autogenous deformation of concrete can be defined as the free deformation of sealed concrete at a constant temperature. A number of observed problems with early age cracking of high-performance concretes can be attributed to this phenomenon. During the last 10 years , this has led to an increased...... focus on autogenous deformation both within concrete practice and concrete research. Since 1996 the interest has been significant enough to hold international, yearly conferences entirely devoted to this subject. The papers in this publication were presented at two consecutive half-day sessions...... at the American Concrete Institute’s Fall Convention in Phoenix, Arizona, October 29, 2002. All papers have been reviewed according to ACI rules. This publication, as well as the sessions, was sponsored by ACI committee 236, Material Science of Concrete. The 12 presentations from 8 different countries indicate...
Institute of Scientific and Technical Information of China (English)
程高; 刘永健; 俞文龙; 龙刚
2015-01-01
T he nonlinear finite element analysis of X‐connections w as done to study the mechanics of square steel tube connections influenced by axial load and concrete .Based on the experiment of con‐crete‐filled square steel tube X‐connections subjected to tension ,the axial load ratio ,thickness ratio of chord and width ratio between branch and chord were changed .Twelve concrete‐filled square steel tube X‐connections and 12 square steel tube X‐connections were designed for the numerical model . The differences among joints ability ,tensile stiffness and stress distribution in branch and chord were analyzed .T he results show that the joints ability of concrete‐filled square steel tube X‐connections is higher than that of square steel tube X‐connections under the compression on chord .T here is no sig‐nificant enhancement in joints ability of square steel tube X‐connections filled with concrete in differ‐ent axial tensile ratio ,thickness ratio of chord and width ratio between branch and chord .Compared with square steel tube ,concrete‐filled square steel tube X‐connections have higher tensile stiffness and better anti‐fatigue performance .%为研究主管轴力、内填混凝土对方钢管节点受拉力学性能的影响，文章进行了X型节点受拉的非线性有限元分析。以方钢管混凝土X型节点受拉试验为研究原型，改变主管的轴力比、宽厚比、支主管宽度比等参数，设计了12个方钢管混凝土和12个方钢管X型受拉节点试件，分别从节点承载力、抗拉刚度、支主管应力分布等方面进行了对比分析。结果表明：改变主管轴拉比、支主管宽度比及主管宽厚比，方钢管混凝土相对于方钢管的节点承载力提高均不显著；主管受轴压力作用时，方钢管混凝土节点承载力高于方钢管节点；方钢管混凝土节点的抗拉刚度、抗疲劳性能显著高于方钢管节点。
Experimental Study on Voided Reinforced Concrete Beams with Polythene Balls
Sivaneshan, P.; Harishankar, S.
2017-07-01
The primary component in any structure is concrete, that exist in buildings and bridges. In present situation, a serious problems faced by construction industry is exhaustive use of raw materials. Recent times, various methods are being adopted to limit the use of concrete. In structural elements like beams, polythene balls can be induced to reduce the usage of concrete. A simply supported reinforced concrete beam has two zones, one above neutral axis and other below neutral axis. The region below neutral axis is in tension and above neutral axis is in compression. As concrete is weak in tension, steel reinforcements are provided in tension zone. The concrete below the neutral axis acts as a stress transfer medium between the compression zone and tension zone. The concrete above the neutral axis takes minimum stress so that we could partially replace the concrete above neutral axis by creating air voids using recycled polythene balls. Polythene balls of varying diameters of 75 mm, 65 mm and 35 mm were partially replaced in compression zone. Hence the usage of concrete in beams and self-weight of the beams got reduced considerably. The Load carrying capacity, Deflection of beams and crack patterns were studied and compared with conventional reinforced concrete beams.
High performance polymer concrete
Directory of Open Access Journals (Sweden)
Frías, M.
2007-06-01
Full Text Available This paper studies the performance of concrete whose chief components are natural aggregate and an organic binder —a thermosetting polyester resin— denominated polymer concrete or PC. The material was examined macro- and microscopically and its basic physical and mechanical properties were determined using mercury porosimetry, scanning electron microscopy (SEM-EDAX, X-ray diffraction (XRD and strength tests (modulus of elasticity, stress-strain curves and ultimate strengths. According to the results of these experimental studies, the PC exhibited a low density (4.8%, closed pore system and a concomitantly continuous internal microstructure. This would at least partially explain its mechanical out-performance of traditional concrete, with average compressive and flexural strength values of 100 MPa and over 20 MPa, respectively. In the absence of standard criteria, the bending test was found to be a useful supplement to compressive strength tests for establishing PC strength classes.Este trabajo de investigación aborda el estudio de un hormigón de altas prestaciones, formado por áridos naturales y un aglomerante orgánico constituido por una resina termoestable poliéster, denominado hormigón polimérico HP. Se describe el material a nivel microscópico y macroscópico, presentando sus propiedades físicas y mecánicas fundamentales, mediante diferentes técnicas experimentales, tales como: porosimetría de mercurio, microscopía electrónica (SEM-EDAX, difracción de rayos X (DRX y ensayos mecánicos (módulo de elasticidad, curvas tensión- deformación y resistencias últimas. Como consecuencia del estudio experimental llevado a cabo, se ha podido apreciar cómo el HP está formado por porosidad cerrada del 4,8%, proporcionando una elevada continuidad a su microestructura interna, lo que justifica, en parte, la mejora de propiedades mecánicas respecto al hormigón tradicional, con unos valores medios de resistencia a compresión de 100
Pressure-tension test for assessing fatigue in concrete
Soleimani, Sayed M.; Boyd, Andrew J.; Komar, Andrew J. K.
2017-04-01
In a pressure-tension test, a cylindrical concrete specimen is inserted into a cylindrical steel jacket, with a rubber ``O'' ring seal at each end to prevent gas leakage. Gas pressure is then applied to the curved surface of the concrete cylinder, leaving the ends free. As the gas pressure is increased, the specimen eventually fractures across a single plane transverse to the axis of the cylinder. The gas pressure at fracture may then be considered as the tensile strength of the concrete. In this study, the pressure-tension test is used to study fatigue in concrete. A total of 22 standard concrete cylinders (100 mm × 200 mm) were tested. Both dry and wet specimens have been studied. Low-cycle loading, which involves the application of a few load cycles at high stress levels - such as a concrete structure under earthquake load - has been used in this study. It was found that the concrete specimens in a low-cycle loading fail after only a few cycles of loading and interestingly at a stress level lower than the maximum value applied in the cyclic loading. In addition, non-destructive testing (NDT) was performed to determine the progressive damage due to tensile load in concrete cylinders using Ultrasonic Pulse Velocity (UPV). It was found that UPV can be used to evaluate the damage in concrete even after the application of a very low-level of tensile stress - as low as 10% of its tensile strength.
Nagode, Marko; Šeruga, Domen
An approach is presented that enables the calculation of elastic strain energy in linear and nonlinear elastic solids during arbitrary thermomechanical load cycles. The approach uses the simple fact that the variation of both strain and complementary energies always forms a rectangular shape in stress-strain space, hence integration is no longer required to calculate the energy. Furthermore, the approach considers the mean stress effect so that predictions of fatigue damage are more realistically representative of real-life experimental observations. By doing so, a parameter has been proposed to adjust the mean stress effect. This parameter α is based on the well-known Smith-Watson-Topper energy criterion, but allows consideration of other arbitrary mean stress effects, e.g. the Bergmann type criterion. The approach has then been incorporated into a numerical method which can be applied to uniaxial and multiaxial, proportional and non-proportional loadings to predict fatigue damage. The end result of the method is the cyclic evolution of accumulated damage. Numerical examples show how the method presented in this paper could be applied to a nonlinear elastic material.
Mechanical Analysis of Concrete Specimen under Restrained Condition
Institute of Scientific and Technical Information of China (English)
MA Xinwei; NIU Changren; R D Hooton
2005-01-01
In order to quantify the development of the tensile stresses and obtain a reliable estimation of the cracking risk, the concrete was subjected to restrained conditions. The fully restrained condition was achieved by keeping the length constant of a concrete specimen. Comparing the free shrinkage with the restrained shrinkage,tensile creep could be discriminated from shrinkage. The testing method was introduced in details, and the mechanical behaviors under tensile load were analyzed. Results show that concrete exhibits a pronounced viscoelasticity. Under restrained condition, the self induced tensile stress increases with time. The lower the water to cement ratio, the larger the tensile stress at the same age. The tensile creep of hardening concrete is much larger than that of hardened concrete. The relationships among autogenous shrinkage under free condition, elastic strain and creep under restrained condition are described, and the mathematical model for the calculation of elastic strain and creep is proposed.
Modelling of elastoplastic damage in concrete due to desiccation shrinkage
Bourgeois, F.; Burlion, N.; Shao, J. F.
2002-07-01
We present a numerical modelling of elastoplastic damage due to drying shrinkage of concrete in the framework of mechanics of partially saturated porous media. An elastoplastic model coupled with isotropic damage is first formulated. Two plastic flow mechanisms are involved, controlled by applied stress and suction, respectively. A general concept of net effective stress is used in take into account effects of capillary pressure and material damage on stress-controlled plastic deformation. Damage evolution depends both on elastic and plastic strains. The model's parameters are determined or chosen from relevant experimental data. Comparisons between numerical simulations and experimental data are presented to show the capacity of model to reproduce mains features of concrete behaviour under mechanical loading and during drying shrinkage of concrete. An example of application concerning drying of a concrete wall is finally presented. The results obtained allow to show potential capacity of proposed model for numerical modelling of complex coupling processes in concrete structures.
Design Basis for Fibre Reinforced Concrete (FRC) Pavements
DEFF Research Database (Denmark)
Bendixen, Søren; Stang, Henrik
1996-01-01
-crack opening relationship can beused to descibe the properties of fibre reinforced concrete (FRC) intension and how the stress-crack opening relationship can beapplied in a simple design scheme for pavements. The projectincludes development of design tools, experiments to determine thestress-crack opening......The paper summarises a Ph.D. project on development of a new design basis for fibre reinforced concrete ground slabs. The stress-crack openingrelationship is a well know basic material property of theso-called fictitious crack model for concrete. In the presentstudy it is shown how the stress...
Modelling autogenous expansion for magnesia concrete in arch dams
Institute of Scientific and Technical Information of China (English)
Feng JIN; Guoxin ZHANG; Xiaoqing LUO; Chuhan ZHANG
2008-01-01
Magnesia Concrete is a kind of expansive con-crete used in Chinese hydraulic engineering more and more widely. To evaluate the effects of autogenous expan-sion on the stresses of arch dams, a simple model of auto-genous expansion for Magnesia Concrete in dam engineering is presented. This model is based on three assumptions: 1) the total amount of autogenous expan-sion of Magnesia Concrete is related only to the properties of materials and mixing of concrete; 2) the autogenous expansion of Magnesia Concrete is irreversible due to the irreversibility of hydration reaction of Magnesia in the concrete; 3) the autogenous expansion strain rates of Magnesia Concrete bear a relation between temperature and residual Magnesia per unit volume of concrete. The model is verified by some experimental data of autogen-ous expansion of Magnesia Concrete and field-measured data of an arch dam in China. Embedded into finite ele-ment arch dam simulation software, this model is employed to simulate the effects of autogenous expansion of Magnesia Concrete in hydraulic engineering.
Concrete Hydration Heat Analysis for RCB Basemat Considering Solar Radiation
Energy Technology Data Exchange (ETDEWEB)
Lee, Seong-Cheol; Son, Yong-Ki [KEPCO International Nuclear Graduate School, Ulsan (Korea, Republic of); Choi, Seong-Cheol [Chung-Ang University, Seoul (Korea, Republic of)
2015-05-15
The NPP especially puts an emphasis on concrete durability for structural integrity. It has led to higher cementitious material contents, lower water-cementitious-material ratios, and deeper cover depth over reinforcing steel. These requirements have resulted in more concrete placements that are subject to high internal temperatures. The problem with high internal temperatures is the increase in the potential for thermal cracking that can decrease concrete's long-term durability and ultimate strength. Thermal cracking negates the benefits of less permeable concrete and deeper cover by providing a direct path for corrosion-causing agents to reach the reinforcing steel. The purpose of this study is to develop how to analyze and estimate accurately concrete hydration heat of the real-scale massive concrete with wide large plane. An analysis method considering concrete placement sequence was studied and solar radiation effects on the real-scale massive concrete with wide large plane were reviewed through the analytical method. In this study, the measured temperatures at the real scale structure and the analysis results of concrete hydration heat were compared. And thermal stress analysis was conducted. Through the analysis, it was found that concrete placement duration, sequence and solar radiation effects should be considered to get the accurate concrete peak temperature, maximum temperature differences and crack index.
Reinforced concrete bridges: effects due to corrosion and concrete young modulus variation
Directory of Open Access Journals (Sweden)
P. T. C. Mendes
Full Text Available Most of the Brazilian bridges of federal road network are made of reinforced concrete and are more than 30 years old, with little information about the mechanical properties of their constitutive materials. Along the service life of these bridges much modification occurred on vehicles load and geometry and in design standard. Many of them show signs of concrete and steel deterioration and their stability conditions are unknown. With the aim of contributing to the structural evaluation of reinforced concrete bridges it was decided to analyze the stresses in reinforced concrete bridge sections to verify the effects due to reinforcement corrosion and variation of the concrete Young modulus on the stress distribution regarding several load patterns and cracking effects in a representative bridge of the Brazilian road network with different longitudinal reinforcement taxes and two concrete Young modulus, Ec and 0.5Ec, and with different percentage of reinforcement corrosion. The analysis considered two finite element models: frame and shell elements as well as solid elements. The results indicate that these variation effects are more significant in reinforcement bars than in concrete.
Lunar concrete: Prospects and challenges
Khitab, Anwar; Anwar, Waqas; Mehmood, Imran; Kazmi, Syed Minhaj Saleem; Munir, Muhammad Junaid
2016-02-01
The possibility of using concrete as a construction material at the Moon surface is considered. Dissimilarities between the Earth and the Moon and their possible effects on concrete are also emphasized. Availability of constituent materials for concrete at lunar surface is addressed. An emphasis is given to two types of materials, namely, hydraulic concrete and sulfur concrete. Hydraulic concrete necessitates the use of water and sulfur concrete makes use of molten sulfur in lieu of cement and water.
Energy Technology Data Exchange (ETDEWEB)
Mohanty, Subhasish, E-mail: smohanty@anl.gov; Majumdar, Saurindranath
2015-10-15
Highlights: • High temperature gas cooled reactor. • Finite element based stress analysis. • H-451 graphite. • Irradiation creep model. • Graphite reflector stress analysis. - Abstract: Irradiation creep plays a major role in the structural integrity of the graphite components in high temperature gas cooled reactors. Finite element procedures combined with a suitable irradiation creep model can be used to simulate the time-integrated structural integrity of complex shapes, such as the reactor core graphite reflector and fuel bricks. In the present work a comparative study was undertaken to understand the effect of linear and nonlinear irradiation creep on results of finite element based stress analysis. Numerical results were generated through finite element simulations of a typical graphite reflector.
CONCRETE BASED ON MODIFIED DISPERSE CEMENT SYSTEM
Directory of Open Access Journals (Sweden)
D. V. Rudenko
2016-08-01
Full Text Available Purpose. The article considers definition of the bond types occurring in a modified cement concrete matrix, and the evaluation of the quality of these links in a non-uniform material to determine the geometrical and physical relationships between the structure and the cement matrix modifiers. Methodology. To achieve this purpose the studies covered the microstructure of dispersed modified concrete cement matrix, the structure formation mechanism of the modified cement concrete system of natural hardening; as well as identification of the methods of sound concrete strength assessment. Findings. The author proposed a model of the spatial structure of the concrete cement matrix, modified by particulate reinforcement crystal hydrates. The initial object of study is a set of volume elements (cells of the cement matrix and the system of the spatial distribution of reinforcing crystallohydrates in these volume elements. It is found that the most dangerous defects such as cracks in the concrete volume during hardening are formed as a result of internal stresses, mainly in the zone of cement matrix-filler contact or in the area bordering with the largest pores of the concrete. Originality. The result of the study is the defined mechanism of the process of formation of the initial strength and stiffness of the modified cement matrix due to the rapid growth of crystallohydrates in the space among the dispersed reinforcing modifier particles. Since the lack of space prevents from the free growth of crystals, the latter cross-penetrate, forming a dense structure, which contributes to the growth of strength. Practical value. Dispersed modifying cement matrix provides a durable concrete for special purposes with the design performance characteristics. The developed technology of dispersed cement system modification, the defined features of its structure formation mechanism and the use of congruence principle for the complex of technological impacts of physical
Effect of adhesive thickness and concrete strength on FRP-Concrete Bonds
López González, Julio César; Fernandez Gomez, Jaime Antonio; González Valle, Enrique
2012-01-01
The use of fiber-reinforced polymer (FRP) composites for strengthening, repairing, or rehabilitating concrete structures has become more and more popular in the last 10 years. Irrespective of the type of strengthening used, design is conditioned, among others, by concrete-composite bond failure, normally attributed to stress at the interface between these two materials. Single shear, double shear, and notched beam tests are the bond tests most commonly used by the scientific community to esti...
Initial rheological description of high performance concretes
Directory of Open Access Journals (Sweden)
Alessandra Lorenzetti de Castro
2006-12-01
Full Text Available Concrete is defined as a composite material and, in rheological terms, it can be understood as a concentrated suspension of solid particles (aggregates in a viscous liquid (cement paste. On a macroscopic scale, concrete flows as a liquid. It is known that the rheological behavior of the concrete is close to that of a Bingham fluid and two rheological parameters regarding its description are needed: yield stress and plastic viscosity. The aim of this paper is to present the initial rheological description of high performance concretes using the modified slump test. According to the results, an increase of yield stress was observed over time, while a slight variation in plastic viscosity was noticed. The incorporation of silica fume showed changes in the rheological properties of fresh concrete. The behavior of these materials also varied with the mixing procedure employed in their production. The addition of superplasticizer meant that there was a large reduction in the mixture's yield stress, while plastic viscosity remained practically constant.
Askari, Amir R.; Tahani, Masoud
2017-02-01
This paper focuses on the size-dependent dynamic pull-in instability in rectangular micro-plates actuated by step-input DC voltage. The present model accounts for the effects of in-plane displacements and their non-classical higher-order boundary conditions, von Kármán geometric non-linearity, non-classical couple stress components and the inherent non-linearity of distributed electrostatic pressure on the micro-plate motion. The governing equations of motion, which are clearly derived using Hamilton's principle, are solved through a novel computationally very efficient Galerkin-based reduced order model (ROM) in which all higher-order non-classical boundary conditions are completely satisfied. The present findings are compared and successfully validated by available results in the literature as well as those obtained by three-dimensional finite element simulations carried out using COMSOL Multyphysics. A detailed parametric study is also conducted to illustrate the effects of in-plane displacements, plate aspect ratio, couple stress components and geometric non-linearity on the dynamic instability threshold of the system.
Institute of Scientific and Technical Information of China (English)
2015-01-01
利用有限元软件ANSYS研究分析了温度变化对于外贴碳纤维材料加固的钢筋混凝土梁的应力影响，具体讨论了碳纤维布的弹性模量、粘贴厚度、热膨胀系数等参数的影响，得出了一些有实用价值的结论。%Applying finite element software ANSYS,the paper analyzes the stress impact of temperature change upon external carbon fiber reinfor-cing steel reinforced concrete,specifically discusses the influence of carbon fiber elastic modulus,cohesive thickness,heat expanding coefficient and other parameters,and finally draws some practical valuable conclusions.
Dynamic response of concrete pavement structure with asphalt isolating layer under moving loads
Directory of Open Access Journals (Sweden)
Jianmin Wu
2014-12-01
Full Text Available A three-dimensional finite element model (3D FEM is built using ABAQUS to analyze the dynamic response of a concrete pavement structure with an asphalt isolating layer under moving loads. The 3D model is prepared and validated in the state of no asphalt isolating layer. Stress and deflection at the critical load position are calculated by changing thickness, modulus of isolating layer and the combination between the isolating layer and concrete slab. Analysis result shows that the stress and deflection of the concrete slab increase with the increase of thickness. The stress and deflection of the concrete slab decrease with the increase of combination between the isolating layer and concrete slab. The influence of changing the isolating layer modulus to the stress and deflection of the concrete slab is not significant. From the results, asphalt isolating layer design is suggested in concrete pavement.
Institute of Scientific and Technical Information of China (English)
严少华; 钱七虎; 孙伟; 尹放林
2001-01-01
在实际工程中推广应用钢纤维高强混凝土,要了解其基本力学性能.采用MTS815.03型液压伺服刚性压力试验机,对钢纤维含量为0～6%、抗压强度在65～120MPa范围的4种钢纤维高强混凝土,进行单轴压缩荷载作用下的应力应变全过程试验.结合试验给出全曲线的方程,并分析钢纤维对抗压强度、弹性模量、韧度、泊松比等的影响.试验表明,当钢纤维长度大于或接近于最大集料尺寸时,钢纤维高强混凝土具有较高的抗压强度和韧度,是一种优良的新型建筑材料.%It is necessary to research the basic mechanical performance inorder to use high-strength steel fiber reinforced concrete (HSFC) in practical engineering. Tests are conducted to characterize the stress-strain relationship of HSFC in compression by MTS815.03 rock testing machine. The concrete strength investigated ranges from 65 to 120 MPa and the volume fraction of steel fiber ranges from 0 to 6%. Based on the test data, an analytical model is proposed to generate the complete stress-strain curve for HSFC. The elastic modulus and toughness and Poisson’s ration of HSFC are also calculated in this paper. It is also proved by tests that HSFC is a good building material with high strength and high toughness when steel fibers are longer than the size of aggregate in concrete.
Institute of Scientific and Technical Information of China (English)
李新凯; 侯相深; 马松林
2012-01-01
水泥混凝土在强度形成过程中，水泥砂浆体积变形受到约束后将导致水泥混凝土内产生残余应力。对水泥混凝土路面板而言，板表层水泥砂浆的体积变形受外部环境影响更严重，因此板表面存在较大的残余应力，超过其抗弯拉强度时将导致微观裂缝的出现。目前，根据金属工程中测量表面残余应力的钻孔法，相关学者提出了钻环测量水泥混凝土表面残余应力的方法，并对其可行性进行了分析。该文将在该方法可行性分析的基础上，建立有限元模型对钻环过程进行模拟，确定室内试验时钻环法的相关技术参数，然后浇注水泥混凝土板，考虑加载和不加载两种工况进行室内试验，试验结果表明：钻环能够释放板表面的残余应力，该方法可以用于水泥混凝土表面残余应力测量。%In the procedure of concrete strength development, the changes in cementitious material volume results in the production of internal residual stress. Because the volume changes of cement pasted on the surface are influnced more obviously by environmental factors, the residual stress on the surface of rigid pavement slab will develop quickly and may lead to the appearance of micro crackings. According to the hole drilling strain gage （HDSG） method which is often used to measure residual stress in metal structure, some researchers developed the core ring strain gage （CRSG） method for concrete structures and the feasibility of this method was studied. In this paper a finite element model （FEM） is developed to simulate the process of core ring drilling in concrete slab. The parameters in CRSG method are selected based on FEM＇s results for different cases. Large scale slabs are casted in laboratory and tests using CRSG method to measure residual stress are conducted. The test results of two cases （loading on slab comer and no loading） indicate that CRSG method can release
Nanostructured silicate polymer concrete
Directory of Open Access Journals (Sweden)
Figovskiy Oleg L'vovich
2014-03-01
Full Text Available It has been known that acid-resistant concretes on the liquid glass basis have high porosity (up to 18~20 %, low strength and insufficient water resistance. Significant increasing of silicate matrix strength and density was carried out by incorporation of special liquid organic alkali-soluble silicate additives, which block superficial pores and reduce concrete shrinkage deformation. It was demonstrated that introduction of tetrafurfuryloxisilane additive sharply increases strength, durability and shock resistance of silicate polymer concrete in aggressive media. The experiments showed, that the strength and density of silicate polymer concrete increase in case of decreasing liquid glass content. The authors obtained optimal content of silicate polymer concrete, which possesses increased strength, durability, density and crack-resistance. Diffusive permeability of concrete and its chemical resistance has been investigated in various corroding media.
Properties of Refractory Concrete in Tension and Compression
Sampson, Jeffrey
2009-01-01
Refractory concrete on the LC-39A Flame Deflector has been damaged during multiple Space Shuttle launches (e.g. STS-124, STS-126, STS-119, and STS-125, STS-127). These events have prompted a better understanding of the system via an analytical model of the Flame Deflector assembly to include the Fondu Fyre refractory concrete. This model requires test data inputs of the refractory concrete's mechanical properties, which include stress versus strain curves in tension and compression, modulus of elasticity, and Poisson's ratio. Sections of Fondu Fyre refractory concrete removed from the LC-39A Flame Deflector were provided for this testing.
Analysis of reinforced concrete building according to the EC 8
Dimec, Andrej
2009-01-01
In the Thesis the analysis and the software based design of the six-storey reinforced concrete wall building according to the European Standard Eurocode is presented. The structural system of the building consists of reinforced concrete walls. First the calculation of the self weight, variable actions, snow and the wind loads has been examined. The major part of the thesis deals with seismic analysis, which was performed by the modal analysis and simplified non-linear seismic a...
An Incursion on Punching of Reinforced Concrete Flat Slabs
2009-01-01
Starting from the early 60s continuous studies have been made regarding punching of concrete flat slabs. The evolution of technology and calculus systems influenced this engineering branch. Nowadays is possible to account in structural analysis all the non-linear behaviour of reinforced and prestressed concrete and to get the most close structural response in comparison with the real behaviour. As a controversy matter, several tests and theories have been developed. Nowadays researchers try t...
Behaviour of concrete filled steel tubular columns under fire
Institute of Scientific and Technical Information of China (English)
查晓雄; 钟善桐
2002-01-01
A three dimensional nonlinear FE program is used to calculate the fire resistances of concrete filledsteel tubular columns under fire. The temperature distributions in the circular section fire are decided by solvingthe Fourier Transfer Equation , and the mechanical behaviour and failure of concrete filled steel tubular columnsunder fire are thus investigated, and the effects of several parameters on the fire resistance are analysed. Theresults obtained are in good agreement with the Eurocode.
Parametric resonance in concrete beam-columns
Sharma,Mamta R.; Singh,Arbind K; Benipal,Gurmail S
2014-01-01
A dynamic instability, called parametric resonance, is exhibited by undampedelastic beam-columns when under the action of pulsating axial force. The scope of the existing theory of parametric resonance is restricted to physically linear beam-columns undergoing finite lateral displacements. In this Paper, the dynamic behaviour of physically nonlinear elastic cracked concrete beam-columns under pulsating axial force and constant lateral force is investigated. The constitutive equations derived ...
Energy Technology Data Exchange (ETDEWEB)
Sadiq, Muhammad, E-mail: muhammad.sadiq@pnra.org [Center for Nuclear Safety (CNS), Pakistan Nuclear Regulatory Authority (PNRA), PO Box 1912, Islamabad (Pakistan); Xiu Yun, Zhu, E-mail: lyzhuxiuyun@163.com [Nuclear and Radiation Safety Center (NSC), Ministry of Environmental Protection (MEP), Beijing (China); Rong, Pan, E-mail: panrong@chinansc.cn [Nuclear and Radiation Safety Center (NSC), Ministry of Environmental Protection (MEP), Beijing (China)
2014-07-01
Highlights: • Simulation analysis is carried out with two constitutive concrete models. • Winfrith model can better simulate nonlinear response of concrete than CSCM model. • Performance of steel plate concrete is better than reinforced concrete. • Thickness of safety related structures can be reduced by adopting steel plates. • Analysis results, mainly concrete material models should be validated. - Abstract: The steel plate reinforced concrete and reinforced concrete structures are used in nuclear power plants for protection against impact of an aircraft. In order to compare the impact resistance performance of steel plate reinforced concrete and reinforced concrete slabs panels, simulation analysis of 1/7.5 scale model impact tests is carried out by using finite element code ANSYS/LS-DYNA. The damage modes of all finite element models, velocity time history curves of the aircraft engine and damage to aircraft model are compared with the impact test results of steel plate reinforced concrete and reinforced concrete slab panels. The results indicate that finite element simulation results correlate well with the experimental results especially for constitutive winfrith concrete model. Also, the impact resistance performance of steel plate reinforced concrete slab panels is better than reinforced concrete slab panels, particularly the rear face steel plate is very effective in preventing the perforation and scabbing of concrete than conventional reinforced concrete structures. In this way, the thickness of steel plate reinforced concrete structures can be reduced in important structures like nuclear power plants against impact of aircraft. It also demonstrates the methodology to validate the analysis procedure with experimental and analytical studies. It may be effectively employed to predict the precise response of safety related structures against aircraft impact.
Woodson, R Dodge
2011-01-01
Whether or not, you are on the job site or back in the office, this book will help you to avoid mistakes, code violations, and wasted time and money. The book's four part treatment begins with constituent materials followed by self contained parts on Concrete Properties, Processes, and Concrete Repair and Rehabilitation. Designed to be an ""all in one"" reference, the author includes a wealth information for the most popular types of testing. This includes: Analysis of Fresh Concrete; Testing Machines; Accelerated Testing Methods; Analysis of Hardened Concrete and Mortar; Core Sampl
Response of structural concrete elements to severe impulsive loads
Krauthammer, T.; Shanaa, H. M.; Assadi, A.
1994-10-01
The behavior and response of structural concrete elements under severe short duration dynamic loads was investigated numerically. The analytical approach utilized the Timoshenko beam theory for the analysis of reinforced concrete beams and one-way slabs. Nonlinear material models were used to derive the flexural and shear resistances, and the differential equations of the Timoshenko beam theory were solved numerically by applying the finite difference technique. A simplified approach was developed for estimating the strain rate in structural concrete members, and the corresponding strain rate effects on the strength of the steel and concrete were incorporated into the analysis. Detailed failure criteria were established for predicting the collapse of structural concrete members. Five cases subjected to localized impact loads and eleven cases subjected to distributed explosive loads were analyzed, and the results were compared to experimental data obtained by other investigators.
Investigation of basalt plastic reinforcement and its Adhesion with Concrete
Directory of Open Access Journals (Sweden)
Kustikova Yulia Olegovna
2014-03-01
Full Text Available The load-bearing capacity and durability of concrete structures with metal or other reinforcement depends on their physical and mechanical properties and adhesion values with concrete. In this regard, there is an urgent need in the definition of adhesion of basalt reinforcement and concrete of various compositions and classes. One of the main problems with the use of basalt rods in concrete structures is - providing a high degree of load-carrying capacity in different conditions of stress-strain state of the structure, and the related amount of its adhesion with concrete. Meeting these requirements can be achieved with load-bearing capacity of individual rods, adhesion value, in general, of basalt reinforcement with concrete.
Uniaxial Tension Test of Slender Reinforced Early Age Concrete Members
Directory of Open Access Journals (Sweden)
Wenbo Zhang
2011-08-01
Full Text Available The present study aims to obtain the tensile properties of early age concrete based on a uniaxial tension test employing RC slender members. First, the paper shows that concrete strain is equal to the strain of rebar at the mid-span of the RC member. The tensile Young’s modulus and the strain capacity of early age concrete are estimated using strain measurements. The experiment indicated that the tensile Young’s modulus at an early age is higher than the compressive modulus. This observation was similar to one found in a previous investigation which used a direct tension test of early age concrete. Moreover, the paper describes how an empirical equation for mature concrete can be applied to the relation between uniaxial tensile strength and splitting tensile strength even in early age concrete. Based on a uniaxial tension test, the paper proposes an empirical equation for the relationship between standard bond stresses and relative slip.
Lifetime Reliability Assessment of Concrete Slab Bridges
DEFF Research Database (Denmark)
Thoft-Christensen, Palle
A procedure for lifetime assesment of the reliability of short concrete slab bridges is presented in the paper. Corrosion of the reinforcement is the deterioration mechanism used for estimating the reliability profiles for such bridges. The importance of using sensitivity measures is stressed. Fi...
Application of Bond-Slip in the Finite Element Analyses of Reinforced Concrete Shear Walls
Directory of Open Access Journals (Sweden)
İlker Kazaz
2012-03-01
Full Text Available Transfer of tensile forces from reinforcing steel into the surrounding concrete affects the behavior of reinforced concrete members. This transfer relies on the bond action between the steel and the concrete. Under monotonic loading the part of bond strength due to chemical adhesion is easily exhausted and bearing against the lugs is the primary load-transfer mechanism at loads near the ultimate. These stresses cause internal cracking of concrete at the steel-concrete interface. This paper deals with the finite element modeling of the bond-slip and its application due to internal cracking of the first layer of concrete surrounding the bar and the bending and/ or cracking of the small concrete teeth near the bar lugs. A previously proposed constitutive steel stress-bond slip relation by Mirza and Houde (1979 was used in finite element analysis of reinforced concrete shear wall specimens and the results were presented.
Analytical Solutions for Corrosion-Induced Cohesive Concrete Cracking
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Hua-Peng Chen
2012-01-01
Full Text Available The paper presents a new analytical model to study the evolution of radial cracking around a corroding steel reinforcement bar embedded in concrete. The concrete cover for the corroding rebar is modelled as a thick-walled cylinder subject to axisymmetrical displacement constraint at the internal boundary generated by expansive corrosion products. A bilinear softening curve reflecting realistic concrete property, together with the crack band theory for concrete fracture, is applied to model the residual tensile stress in the cracked concrete. A governing equation for directly solving the crack width in cover concrete is established for the proposed analytical model. Closed-form solutions for crack width are then obtained at various stages during the evolution of cracking in cover concrete. The propagation of crack front with corrosion progress is studied, and the time to cracking on concrete cover surface is predicted. Mechanical parameters of the model including residual tensile strength, reduced tensile stiffness, and radial pressure at the bond interface are investigated during the evolution of cover concrete cracking. Finally, the analytical predictions are examined by comparing with the published experimental data, and mechanical parameters are analysed with the progress of reinforcement corrosion and through the concrete cover.
LIGHTWEIGHT CONCRETE BASED GRANSHLAK
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NETESA M. I.
2016-02-01
Full Text Available Raising of problem. Concrete advisable to obtain a low strength with local secondary resources for recycling and reduce the environmental burden on the environment. But it is important to design such concrete compositions with a reduced flow of cement. It is known that the coefficient of efficiency of use of cement in the concrete of the heavy and B10 is less than about 0.5, which is almost two times smaller than in class B15 concrete and above. Even lower coefficient of efficiency in light concrete cement low strength. Therefore, it is important to find patterns determining the composition of lightweight concrete based on local-products industry with more efficient use of cement in them. Purpose.. Based on the analysis of earlier research results, including with the use of methods of mathematical planning of experiments to determine the concrete contents, which can provide the requirements for the underlying layers of the floor, the compressive strength of which should correspond to the class B5. It is important to provide the required strength at minimum flow of the cement, which is the most expensive and energy-intensive part of concrete. Conclusion. Analysis of the test results of control samples of concrete in 28-day-old, the following laws. The required tensile strength of concrete compressive strength of 7.0 MPa can be obtained in the test range when used in formulations as a filler as the Dnieper hydroelectric power station fly ash and tailings Krivoy Rog iron ore YuGOK. To ensure providing the required characteristic strength of the concrete in the underlying layers of the floor is advisable to use a nominal composition per cubic meter of concrete: cement 160 kg granshlaka Plant named after Petrovsky, 675 kg of fly ash Dnieper HPP 390 kg, 400 kg of sand, 230 liters of water. Thus, while ensuring rational grain composition components can obtain the desired strength lightweight concrete based granshlaka plant Petrovsky, using as fillers
Constitutive Modeling and Numerical Simulation of Frp Confined Concrete Specimens
Smitha, Gopinath; Ramachandramurthy, Avadhanam; Nagesh, Ranganatha Iyer; Shahulhameed, Eduvammal Kunhimoideen
2014-09-01
Fiber-reinforced polymer (FRP) composites are generally used for the seismic retrofit of concrete members to enhance their strength and ductility. In the present work, the confining effect of Carbon Fiber-Reinforced Polymer (CFRP) composite layers has been investigated by numerical simulation. The numerical simulation has been carried out using nonlinear finite element analysis (FEA) to predict the response behaviour of CFRP-wrapped concrete cylinders. The nonlinear behaviour of concrete in compression and the linear elastic behaviour of CFRP has been modeled using an appropriate constitutive relationship. A cohesive model has been developed for modeling the interface between the concrete and CFRP. The interaction and damage failure criteria between the concrete to the cohesive element and the cohesive element to the CFRP has also been accounted for in the modeling. The response behaviour of the wrapped concrete specimen has been compared with the proposed interface model and with a perfectly bonded condition. The results obtained from the present study showed good agreement with the experimental load-displacement response and the failure pattern in the literature. Further, a sensitivity analysis has been carried out to study the effect of the number of layers of CFRP on the concrete specimens. It has been observed that wrapping with two layers was found to be the optimum, beyond which the response becomes flexible but with a higher load-carrying capacity
Characteristics and applications of high-performance fiber reinforced asphalt concrete
Park, Philip
Steel fiber reinforced asphalt concrete (SFRAC) is suggested in this research as a multifunctional high performance material that can potentially lead to a breakthrough in developing a sustainable transportation system. The innovative use of steel fibers in asphalt concrete is expected to improve mechanical performance and electrical conductivity of asphalt concrete that is used for paving 94% of U. S. roadways. In an effort to understand the fiber reinforcing mechanisms in SFRAC, the interaction between a single straight steel fiber and the surrounding asphalt matrix is investigated through single fiber pull-out tests and detailed numerical simulations. It is shown that pull-out failure modes can be classified into three types: matrix, interface, and mixed failure modes and that there is a critical shear stress, independent of temperature and loading rate, beyond which interfacial debonding will occur. The reinforcing effects of SFRAC with various fiber sizes and shapes are investigated through indirect tension tests at low temperature. Compared to unreinforced specimens, fiber reinforced specimens exhibit up to 62.5% increase in indirect tensile strength and 895% improvements in toughness. The documented improvements are the highest attributed to fiber reinforcement in asphalt concrete to date. The use of steel fibers and other conductive additives provides an opportunity to make asphalt pavement electrically conductive, which opens up the possibility for multifunctional applications. Various asphalt mixtures and mastics are tested and the results indicate that the electrical resistivity of asphaltic materials can be manipulated over a wide range by replacing a part of traditional fillers with a specific type of graphite powder. Another important achievement of this study is development and validation of a three dimensional nonlinear viscoelastic constitutive model that is capable of simulating both linear and nonlinear viscoelasticity of asphaltic materials. The
Strain rate effects for spallation of concrete
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Häussler-Combe Ulrich
2015-01-01
Full Text Available Appropriate triaxial constitutive laws are the key for a realistic simulation of high speed dynamics of concrete. The strain rate effect is still an open issue within this context. In particular the question whether it is a material property – which can be covered by rate dependent stress strain relations – or mainly an effect of inertia is still under discussion. Experimental and theoretical investigations of spallation of concrete specimen in a Hopkinson Bar setup may bring some evidence into this question. For this purpose the paper describes the VERD model, a newly developed constitutive law for concrete based on a damage approach with included strain rate effects [1]. In contrast to other approaches the dynamic strength increase is not directly coupled to strain rate values but related to physical mechanisms like the retarded movement of water in capillary systems and delayed microcracking. The constitutive law is fully triaxial and implemented into explicit finite element codes for the investigation of a wide range of concrete structures exposed to impact and explosions. The current setup models spallation experiments with concrete specimen [2]. The results of such experiments are mainly related to the dynamic tensile strength and the crack energy of concrete which may be derived from, e.g., the velocity of spalled concrete fragments. The experimental results are compared to the VERD model and two further constitutive laws implemented in LS-Dyna. The results indicate that both viscosity and retarded damage are required for a realistic description of the material behaviour of concrete exposed to high strain effects [3].
Combined Transverse Steel-External FRP Confinement Model for Rectangular Reinforced Concrete Columns
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Ahmed Al-Rahmani
2016-02-01
Full Text Available Recently, the need to increase the strength of reinforced concrete members has become a subject that civil engineers are interested in tackling. Of the many proposed solutions, fiber-reinforced polymer (FRP materials have attracted attention due to their superior properties, such as high strength-to-weight ratio, high energy absorption and excellent corrosion resistance. FRP wrapping of concrete columns is done to enhance the ultimate strength due to the confinement effect, which is normally induced by steel ties. The existence of the two confinement systems changes the nature of the problem, thus necessitating specialized nonlinear analysis to obtain the column’s ultimate capacity. Existing research focused on a single confinement system. Furthermore, very limited research on rectangular sections was found in the literature. In this work, a model to estimate the combined behavior of the two systems in rectangular columns is proposed. The calculation of the effective lateral pressure is based on the Lam and Teng model and the Mander model for FRP wraps and steel ties, respectively. The model then generates stress-strain diagrams for both the concrete core and the cover. The model was developed for the analysis in extreme load events, where all possible contributions to the column’s ultimate capacity should be accounted for without any margin of safety. The model was validated against experiments, and the results obtained showed good agreement with almost all of the available experimental data.
Concrete, hardened: Self desiccation
DEFF Research Database (Denmark)
Hansen, Ernst Jan De Place; Hansen, Kurt Kielsgaard; Persson, Bertil
1999-01-01
The test method covers the determination of internal relative humidity (RH) in hardened concrete and cement mortar using RH instruments. The determination of RH is done on crushed samples of concrete or cement motar. This test method is only for measuring equipment which gives off or takes up...
Directory of Open Access Journals (Sweden)
Leczovics Péter
2014-12-01
Full Text Available Present paper introduces a new interpretation of concrete, demonstrating some extreme possibilities of this rigid material such as a design element. In the first part a brief overview of the previous achievements are shown. The second part of this paper focuses on the relationship between concrete and fashion.
Laubacher, Remo
2011-01-01
This book is part of Packt's Beginner's Guide series. You will be guided through the set up of a Concrete5 site with step-by-step practical examples. This book is ideal for developers who would like to build their first site with Concrete5. Some k
Řehoř, Martin; Pr&oring; ša, Vít; T&oring; ma, Karel
2016-10-01
Rigorous analysis of the response of nonlinear materials to step inputs requires one to simultaneously handle the discontinuity, differentiation, and nonlinearity. This task is however beyond the reach of the standard theories such as the classical theory of distributions and presents a considerable mathematical difficulty. New advanced mathematical tools are necessary to handle the challenge. An elegant and relatively easy-to-use framework capable of accomplishing the task is provided by the Colombeau algebra, which is a generalisation of the classical theory of distributions to the nonlinear setting. We use the Colombeau algebra formalism and derive explicit formulae describing the response of incompressible Maxwell viscoelastic fluid subject to step load/deformation in the lubricated squeeze flow setting.
Amann, C. P.; Siebenbürger, M.; Ballauff, M.; Fuchs, M.
2015-05-01
Transient stress-strain relations close to the colloidal glass transition are obtained within the integration through transients framework generalizing mode coupling theory to flow driven systems. Results from large-scale numerical calculations are quantitatively compared to experiments on thermosensitive microgels, which reveals that theory captures the magnitudes of stresses semi-quantitatively even in the nonlinear regime, but overestimates the characteristic strain where plastic events set in. The former conclusion can also be drawn from flow curves, while the latter conclusion is supported by a comparison to single particle motion measured by confocal microscopy. The qualitative picture, as previously obtained from simplifications of the theory in schematic models, is recovered by the quantitative solutions of the theory for Brownian hard spheres.
Amann, C M; Siebenbürger, M; Ballauff, M; Fuchs, M
2015-05-20
Transient stress-strain relations close to the colloidal glass transition are obtained within the integration through transients framework generalizing mode coupling theory to flow driven systems. Results from large-scale numerical calculations are quantitatively compared to experiments on thermosensitive microgels, which reveals that theory captures the magnitudes of stresses semi-quantitatively even in the nonlinear regime, but overestimates the characteristic strain where plastic events set in. The former conclusion can also be drawn from flow curves, while the latter conclusion is supported by a comparison to single particle motion measured by confocal microscopy. The qualitative picture, as previously obtained from simplifications of the theory in schematic models, is recovered by the quantitative solutions of the theory for Brownian hard spheres.
Institute of Scientific and Technical Information of China (English)
刁志明; 邓文杰; 刘良军; 王俊杰
2013-01-01
以重庆市金佛山混凝土面板堆石坝为例,采用邓肯—张E-B非线性弹性模型对其进行了静力三维有限元应力一应变分析.结果表明,施工期和蓄水期坝体沉降量分别为71.55、73.75 cm,占最大坝高的0.65％和0.67％；面板和趾板的压应力和拉应力均小于混凝土的抗压与抗拉强度；面板最大沉降量分别为0.38、0.64 cm,且位于面板中部；施工期面板顺河向水平位移朝向上游,最大值仅为0.14 cm；蓄水后面板顺河向水平位移朝向下游,最大值为1.09 cm；垂直缝和周边缝的变形量较小,均能满足设计要求.%Taking Jinfoshan Concrete Facing Rockfill Dam(CFRD)in Chongqing city for an example, the E-B model is applied to 3D finite element analysis of stress-strain. The results indicate that the dam settlements in construction and storage periods are 71. 55 cm and 73. 75 cm respectively, which accounts for 0. 65% and 0. 67% of the dam height; the compressive stress and tensile stress in the face slab and toe slab are smaller than the compressive and tensile strength of the concrete; the maximum face slab settlements are 0. 38 cm and 0. 64 cm respectively, which lie in the middle of the face slab; in the construction period, the horizontal displacement along river is toward the upstream side, which the maximum value is 0. 14 cm; while in the storage period, the displacement is toward downstream side, which the maximum value is 1. 09 cm; the vertical joints and perimeter joints are small, and they are both meet the design requirement.
Institute of Scientific and Technical Information of China (English)
李继兰; 李国芬; 陈耀章
2012-01-01
The decking on the top of bridge pier of the continuous steel-concrete composite beam is easily cracked by the action of non-load factors. The support forced displacement method is one of the effective methods to control or slow down the crack. To discuss the pre-compressed stress effect of the forced displacement method in the negative bending moment area of the decking of the composite beam bridge, taken the 6 x90 m continuous steel-concrete composite beam bridge at Hankou side of Erqi Changjiang River Bridge as research object, the improvement on traditional support forced displacement method was conducted. Besides, a local simulation analysis was accomplished on the basis of a hybrid finite element model of large "beam-shell-solid" which was established through APDL of ANSYS. A conclusion drawn from the theoretical and measured values shows that enough pre-compressed stress reserves, the maximum compressive stress of which was 18. 5 MPa, was produced in the decking of the negative moment area by the improved support forced displacement method. On this basis, the pre-compressed stress reserves by the improved method gained more than 0. 41 - 0. 46 times in the negative moment area on bridge decks. This study provided a reference for design and construction of super long-span continuous steel-concrete composite beam bridge.%针对连续钢-混叠合梁桥墩项区桥面板,在非荷载因素作用下受拉易产生裂缝,采用支座强迫位移法解决上述问题.为研究支座强迫位移法对叠合梁桥负弯矩区桥面板产生的预压应力效应,以武汉二七长江大桥汉口侧6×90m连续钢-混叠合梁桥为研究对象,对传统的支座强迫位移法进行了改进,同时利用ANSYS的APDL语言建立大型“梁-壳-实”有限元混合模型,并对其进行局部仿真分析和实测.理论和实测值均表明,改进的支座强迫位移在负弯矩区桥面板中产生了足够的预压应力储备,最大压应力大小为18.5 MPa.在
Directory of Open Access Journals (Sweden)
Chan-Gi Park
2016-01-01
Full Text Available Hybrid glass/jute fiber reinforced polymer (HGJFRP composite bars were manufactured for concrete structures, and their interlaminar shear stress and tensile performance were evaluated. HGJFRP composite bars were manufactured using a combination of pultrusion and braiding processes. Jute fiber was surface-treated with a silane coupling agent. The mixing ratio of the fiber to the vinyl ester used in the HGJFRP composite bars was 7 : 3. Jute fiber was used to replace glass fiber in proportions of 0, 30, 50, 70, and 100%. The interlaminar shear stress decreased as the proportion of jute fiber increased. Fractures appeared due to delamination between the surface-treated component and the main part of the HGJFRP composite bar. Tensile load-strain curves with 50% jute fiber exhibited linear behavior. With a jute fiber volume fraction of 70%, some plastic deformation occurred. A jute fiber mixing ratio of 100% resulted in a display of linear elastic brittle behavior from the fiber; however, when the surface of the fiber was coated with poly(vinyl acetate, following failure, the jute fiber exhibited partial load resistance. The tensile strength decreased as the jute fiber content increased; however, the tensile strength did not vary linearly with jute fiber content.
Institute of Scientific and Technical Information of China (English)
王军玺; 徐聪
2011-01-01
The theoretical practicability of simulating the concrete temperature field on software ANSYS is discussed The principal problems and the corresponding key technologies of simulating the concrete temperature field and temperature stress field are studied- Based on the general service flatbase of the finite element software ANSYS,a flow chart of simulation analysis is designed. By running some modules interactively, and using APDL and built-in functions of the software ANSYS,the control program is developed to control software ANSYS, thus it is possible to describe the analysis process, which is from modeling and numerical calculation to post-treatment by parameter, greatly increasing the efficiency of solving the engineering problems by the large universal software ANSYS.%探讨了ANSYS软件模拟混凝土瞬态温度场理论上的可行性，研究了施工期及运行期温度场、温度应力场仿真计算的主要问题及相应的关键技术，基于通用有限元软件ANSYS平台，设计了仿真分析流程图，通过各模块的交互运用，利用参数设计语言(APDL)以及多种内部函数，编制了宏命令以控制ANSYS程序，成功实现了仿真分析过程从建模、求解及后处理的参数化，提高了利用ANSYS软件解决工程实际问题的效率.
Chiumenti, M.; Cervera, M.; Agelet de Saracibar, C.; Dialami, N.
2013-05-01
In this work a novel finite element technology based on a three-field mixed formulation is presented. The Variational Multi Scale (VMS) method is used to circumvent the LBB stability condition allowing the use of linear piece-wise interpolations for displacement, stress and pressure fields, respectively. The result is an enhanced stress field approximation which enables for stress-accurate results in nonlinear computational mechanics. The use of an independent nodal variable for the pressure field allows for an adhoc treatment of the incompressibility constraint. This is a mandatory requirement due to the isochoric nature of the plastic strain in metal forming processes. The highly non-linear stress field typically encountered in the Friction Stir Welding (FSW) process is used as an example to show the performance of this new FE technology. The numerical simulation of the FSW process is tackled by means of an Arbitrary-Lagrangian-Eulerian (ALE) formulation. The computational domain is split into three different zones: the work.piece (defined by a rigid visco-plastic behaviour in the Eulerian framework), the pin (within the Lagrangian framework) and finally the stirzone (ALE formulation). A fully coupled thermo-mechanical analysis is introduced showing the heat fluxes generated by the plastic dissipation in the stir-zone (Sheppard rigid-viscoplastic constitutive model) as well as the frictional dissipation at the contact interface (Norton frictional contact model). Finally, tracers have been implemented to show the material flow around the pin allowing a better understanding of the welding mechanism. Numerical results are compared with experimental evidence.
Institute of Scientific and Technical Information of China (English)
张旭伟
2012-01-01
从钢筋混凝土本构关系入手,基于有限元分析软件,建立钢筋混凝土梁有限元分析模型,分析计算出锈蚀段处梁的裂缝宽度及挠度,并与我国现行规范计算公式的计算结果对比,表明有限元软件模拟局部锈蚀钢筋混凝土梁挠度是可行的。%To begin with constitutive structure relationship of steel reinforced concrete, based on finite element analysis software, the paper establishes finite element analysis model of steel reinforced concrete beam, analyzes and calculates the cracking length and deflection of corrosion section, compares it with domestic calculation formula, and finally shows that is feasible to simulate partial corrosion steel reinforced concrete deflection with finite element software.
Energy Technology Data Exchange (ETDEWEB)
Yepes, V.; Alcala, J.; Diaz, J.; Gonzalez-Vidosa, F.
2011-07-01
In the work a study to statistically characterise 82 prestressed concrete bridge decks of real flyovers of constant depth are treated. The main objective of the study is to find design formulae with the least number of data so as to improve the preliminary design of this type of structures. The study performs an exploratory analysis and a multivariate analysis of the geometrical variables, the amount of materials and the cost for voided decks. The regression models have allowed predicting the depth of the deck as function of the span and the external void. The depth is the variable that better explains (51,9%) the cost per unit surface of the deck in road bridges, while for railway decks this variable only explains in the order of 23,4%, what implies more independent variables. The main spans and the total length in the case of the railway deck are enough to find the preliminary design of the slab with reasonable accuracy for the economic assessment of the design. (Author) 17 refs.
Axisymmetric finite element (FE) method was developed using a commercial computer program to simulate cone penetration process in layered granular soil. Soil was considered as a non-linear elastic plastic material which was modeled using variable elastic parameters of Young’s Modulus and Poisson’s r...
Dynamic Response of Concrete and Concrete Structures.
1986-05-30
Strain Rate Effects on Fracture (ed. S. Mindess and S. P. Shah), Symposium ’- S, Boston, Dec. 1985, Materials Research Society Symp. Proceedings, ". Vol...Reinforced Concrete Subjected to Impact Loading," in Cement-Based Composites: Strain-Rate Effects on Fracture (ed. S. Mindess and S.P. Shah) Materials
Concrete sample point: 304 Concretion Facility
Energy Technology Data Exchange (ETDEWEB)
Rollison, M.D.
1995-03-10
This report contains information concerning the analysis of concretes for volatile organic compounds. Included are the raw data for these analysis and the quality control data, the standards data, and all of the accompanying chains-of-custody records and requests for special analysis.
Neural Network Model for Moment-Curvature Relationship of Reinforced Concrete Sections
Bağcı, Muhiddin
2010-01-01
The analysis of moment-curvature relationship of reinforced concrete sections is complex due to large number of variables as well as non-linear material behavior involved. Artificial Neural Networks (ANNs) are found to be a tool capable of solving such problems. This has led to increasing use of ANN for analyzing the behavior of reinforced concrete sections. This paper reports the details of a study conducted using ANN for predicting moment-curvature relationship of a reinforced concrete sect...
Institute of Scientific and Technical Information of China (English)
屠永清; 刘林林; 叶英华
2012-01-01
The confinement that the concrete core is subjected to in multi-cell T-shaped concrete-filled steel tubular （MT-CFST） columns is characterized by defining the equivalent square section and the angle of boundary between effectively confined area and ineffectively confined area of the concrete core. According to experimental results, the constitutive relationship of the concrete core is suggested by means of modifying the expressions of effective lateral pressure and the descending stage in Mander＇s confined concrete model. Numerical simulation of 8 MT-CFST stub columns under axial load is accomplished based on ABAQUS. The comparisons between calculated results and experimental data demonstrate that the suggested concrete constitutive relationship is applicable for the finite element analysis of MT-CFST columns. Subsequent discussion on the cooperative properties of two materials shows the similarity on mechanism between the MT-CFST columns and other types of CFST columns. Considering the MT-CFST columns as a combination of three rectangular concrete-filled steel tubular units with two extra steel plates removed, the formula for their bearing capacities is proposed based on superposition principle, which may provide some references for engineering practice.%通过定义等效方形截面和改变混凝土强约束区、弱约束区界线底角来衡量多室式T形截面内钢材对混凝土的整体约束作用，依据轴压试验结果修正了Mander约束混凝土模型中有效侧向约束力及下降段的表达式，建立了核心混凝土的本构关系。应用ABAQUS对8个多室式钢管混凝土T形短柱试件的轴压性能进行了模拟，模拟结果与试验数据的对比表明，该本构关系能较好地适用于对构件性能的非线性分析。在此基础上探讨了构件中钢材和混凝土的共同工作情况，发现其工作机理与其它截面形式的钢管混凝土柱较为一致。将多室式
Seismic performance evaluation of concrete gravity dams
Energy Technology Data Exchange (ETDEWEB)
Yamaguchi, Y.; Sasaki, T.; Kanenawa, K. [Public Works Research Institute, Tsukuba City (Japan); Hall, R.; Yule, D. [United States Army Engineer Research and Development Center, Vicksburg, MS (United States); Matheu, E. [Louisiana State Univ., Baton Rouge, LA (United States); Chudgar, A. [United States Army Corps of Engineers, Washington, DC (United States)
2004-07-01
This paper addresses technical issues related to seismic design practices and current evaluation methods in Japan and the United States. Nonlinear analysis procedures can identify the ultimate capacity of existing concrete dams, taking into account the most critical nonlinear phenomena controlling the response. A numerical model of a non-overflow monolith of Koyna Dam, subject to earthquake motion, is used as a case study to compare the different approaches for seismic evaluation of concrete gravity dams currently employed in the two countries. The complexity of nonlinear analysis procedures and the scarcity of appropriate calibration strategies force analysts to frequently interpret results using their own judgment. It was concluded that the influence of the input parameters and ground excitation on the nonlinear dynamic response should be investigated in order to identify the most critical conditions. It was also suggested that methodologies for qualitative damage estimation based on results from linear analyses could be used to develop a systematic assessment tool and reference framework for the adequate interpretation of results. 14 refs., 2 tabs., 13 figs.
Energy Technology Data Exchange (ETDEWEB)
Vind, H P; Mathews, C W
1980-07-01
Various toxic agents were evaluated as to their capability to prevent or inhibit the attachment of marine fouling organisms to concrete for OTEC plants. Creosote and bis-(tri-n-butyltin) oxide (TBTO) were impregnated into porous aggregate which was used in making concrete. Cuprous oxide, triphenyltin hydroxide (TPTH), and 2-2-bis-(p-methoxyphenyl)-1,1,1-trichloroethane (methoxychlor) were used as dry additives. Two proprietary formulations were applied as coatings on untreated concrete. Test specimens were exposed at Port Hueneme, CA, and Key Biscayne, FL. The efficacy of toxicants was determined by periodically weighing the adhering fouling organisms. Concrete prepared with an aggregate impregnated with a TBTO/creosote mixture has demonstrated the best antifouling performance of those specimens exposed for more than one year. The two proprietary coatings and the concrete containing methoxychlor, TPTH, and cuprous oxide as dry additives have exhibited good antifouling properties, but they have been exposed for a shorter time. The strength of concrete containing the toxicants was acceptable, and the toxicants did not increase the corrosion rate of reinforcing rods. Organotin compounds were essentially unchanged in concrete specimens exposed 6-1/2 years in seawater.
Energy Technology Data Exchange (ETDEWEB)
Vind, H P; Mathews, C W
1980-07-01
Various toxic agents were evaluated as the their capability to prevent or inhibit the attachment of marine fouling organisms to concrete. Creosote and bis-(tri-n-butyltin) oxide (TBTO) were impregnated into porous aggregate which was used in making concrete. Cuprous oxide, triphenyltin hydroxide (TPTH), and 2-2-bis-(p-methoxyphenyl)-1,1,1-trichloroethane (methoxychlor) were used as dry additives. Two proprietary formulations were applied as coatings on untreated concrete. Test specimens were exposed at Port Hueneme, CA, and Key Biscayne, FL. The efficacy of toxicants was determined by periodically weighing the adhering fouling organisms. Concrete prepared with an aggregate impregnated with a TBTO/creosote mixture has demonstrated the best antifouling performance of those specimens exposed for more than one year. The two proprietary coatings and the concrete containing methoxychlor, TPTH, and cuprous oxide as dry additives have exhibited good antifouling properties, but they have been exposed for a shorter time. The strength of concrete containing the toxicants was acceptable, and the toxicants did not increase the corrosion rate of reinforcing rods. Organotin compounds were essentially unchanged in concrete specimens exposed 6 1/2 years in seawater.
Performance of Waterless Concrete
Toutanji, Houssam; Evans, Steve; Grugel, Richard N.
2010-01-01
The development of permanent lunar bases is constrained by performance of construction materials and availability of in-situ resources. Concrete seems a suitable construction material for the lunar environment, but water, one of its major components, is an extremely scarce resource on the Moon. This study explores an alternative to hydraulic concrete by replacing the binding mix of concrete (cement and water) with sulfur. Sulfur is a volatile element on the lunar surface that can be extracted from lunar soils by heating. Sulfur concrete mixes were prepared to investigate the effect of extreme environmental conditions on the properties of sulfur concrete. A hypervelocity impact test was conducted, having as its target a 5-cm cubic sample of sulfur concrete. This item consisted of JSC-1 lunar regolith simulant (65%) and sulfur (35%). The sample was placed in the MSFC Impact Test Facility s Micro Light Gas Gun target chamber, and was struck by a 1-mm diameter (1.4e-03 g) aluminum projectile at 5.85 km/s. In addition, HZTERN code, provided by NASA was used to study the effectiveness of sulfur concrete when subjected to space radiation.
Limit analysis of solid reinforced concrete structures
DEFF Research Database (Denmark)
Larsen, Kasper Paaske
2009-01-01
element for lower bound analysis of reinforced concrete structures is presented. The method defines the stress state at a point within the solid as a combination of concrete- and reinforcement stresses and yield criterions are applied to the stress components separately. This method allows for orthotropic......Recent studies have shown that Semidefinite Programming (SDP) can be used effectively for limit analysis of isotropic cohesive-frictional continuums using the classical Mohr-Coulomb yield criterion. In this paper we expand on this previous research by adding reinforcement to the model and a solid...... reinforcement and it is therefore possible to analyze structures with complex reinforcement layouts. Tests are conducted to validate the method against well-known analytical solutions....
Strack, David
2013-01-01
The Cookbook-style recipes allow you to go both directly to your topic of interest or follow topics throughout a chapter to gain in-depth knowledge. This practical Cookbook will cater to the needs of both intermediate and advanced concrete5 developers.This book is geared towards intermediate to advanced PHP developers who would like to learn more about the concrete5 content management system. Developers already familiar with concrete5 will learn new time-saving tricks and will find the book to be a great reference tool.
Analytical and Numerical Modelling of FRP Debonding from Concrete Substrate under Pure Shearing
Institute of Scientific and Technical Information of China (English)
PAN Jinlong; XU Zhun; C K Y Leung; LI Zongjin
2012-01-01
External bonding of fiber reinforced polymer (FRP) composites on the concrete structures has been proved to be an effective and efficient way to strengthen concrete structures.For a FRP strengthened concrete beam,it is usually observed that the failure occurs in the concrete and a thin layer of concrete is attached on the surface of the debonded FRP plate.To study the debond behavior between concrete and FRP composites,an analytical model based on the three-parameter model is developed to study the debonding behavior for the FRP-to-concrete joint under pure shearing.Then,nonlinear FEM analysis is conducted to verify the proposed analytical model.The FEM results shows good agreement with the results from the model.Finally,with the analytical model,sensitivity analyses are performed to study the effect of the interfacial parameters or the geometric parameters on the debonding behavior.
Electrokenitic Corrosion Treatment of Concrete
Cardenas, Henry E (Inventor)
2015-01-01
A method and apparatus for strengthening cementitious concrete by placing a nanoparticle carrier liquid in contact with a first surface of a concrete section and inducing a current across the concrete section at sufficient magnitude and for sufficient time that nanoparticles in the nanoparticle carrier liquid migrate through a significant depth of the concrete section.
Thermal analysis of reinforced concrete beams and frames
Directory of Open Access Journals (Sweden)
Essam H. El-Tayeb
2017-04-01
The obtained results of the studied cases reveal that material modeling of reinforced concrete beams and frames plays a major role in how these structures react to temperature variation. Cracking contributes to the release of significant portion of temperature restrain and in some cases this restrain is almost eliminated. The response of beams and frames deviates significantly based on the temperature gradient, linear or nonlinear; hence, the nonlinear temperature gradient which is the realistic profile is important to implement in the analysis.
Institute of Scientific and Technical Information of China (English)
无
2001-01-01
With the combination of electrochemical corrosion due to straycurrent in running tunnels of metro, the formula to determine the corrosion products of rebars in reinforced concrete subjected to externally applied direct current is proposed, and the influence of corrosion on stress in concrete is also discussed. Meanwhile, the concept of corrosion stress field and its mathematical formula are presented in the paper. Finally the failure mode of concrete and its shortest breaking time are also analyzed.
Corrosion-resistant sulfur concretes
McBee, W. C.; Sullivan, T. A.; Jong, B. W.
1983-04-01
Sulfur concretes have been developed by the Bureau of Mines as construction materials with physical and mechanical properties that suit them for use in acid and salt corrosive environments where conventional concretes fail. Mixture design methods were established for preparing sulfur concretes using different types of aggregates and recently developed mixed-modified sulfur cements. Bench-scale testing of the sulfur concretes has shown their potential value. Corrosion resistance, strength, and durability of sulfur concrete are superior to those of conventional materials. Field in situ evaluation tests of the sulfur concretes as replacement for conventional concrete materials are in progress in corrosive areas of 24 commercial chemical, fertilizer, and metallurgical plants.
Will Nonlinear Backcalculation Help?
DEFF Research Database (Denmark)
Ullidtz, Per
2000-01-01
demonstrates, that treating the subgrade as a nonlinear elastic material, can result in more realistic moduli and a much better agreement between measured and calculated stresses and strains.The response of nonlinear elastic materials can be calculated using the Finite Element Method (FEM). A much simpler...... approach is to use the Method of Equivalent Thicknesses (MET), modified for a nonlinear subgrade. The paper includes an example where moduli backcalculated using FEM, linear elastic theory and MET are compared. Stresses and strains predicted by the three methods are also compared to measured values...
Anchorage in concrete construction
Eligehausen, Rolf; Silva, John F
2013-01-01
A comprehensive treatment of current fastening technology using inserts (anchor channels, headed stud), anchors (metal expansion anchor, undercut anchor, bonded anchor, concrete screw and plastic anchor) as well as power actuated fasteners in concrete. It describes in detail the fastening elements as well as their effects and load-bearing capacities in cracked and non-cracked concrete. It further focuses on corrosion behaviour, fire resistance and characteristics with earthquakes and shocks. It finishes off with the design of fastenings according to the European Technical Approval Guideline (ETAG 001), the Final Draft of the CEN Technical Specification 'Design of fastenings for use in concrete' and the American Standards ACI 318-05, Appendix D and ACI 349-01, Appendix B.
CSIR Research Space (South Africa)
Dlamini, MN
2014-03-01
Full Text Available are manufactured from raw clay as their primary ingredient. However concrete brick has also become a favoured material in recent times. This review will adumbrate the impact of these building materials on energy use and the environment....
Federal Laboratory Consortium — This is a 20,000-sq ft laboratory that supports research on all aspects of concrete and materials technology. The staff of this facility offer wide-ranging expertise...
Wassink, J.
2014-01-01
A polymer prepared from waste water extends the useful life of concrete. It also appears to be suitable as a protective coating for offshore applications. Chemistry professor Stephen Picken predicts that this ‘alginate’ could become huge.
Hurst, MK
1998-01-01
This edition provides up-to-date guidance on the detailed design of prestressed concrete structures. All major topics are dealt with, including prestressed flat slabs, an important and growing application in the design of buildings.
Moghaddasi B., Nasim S.; Zhang, Yunfeng; Hu, Xiaobin
2012-03-01
This paper presents a new type of structural bracing intended for seismic retrofitting use in framed structures. This special composite brace, termed glass-fiber-reinforced-polymer (GFRP)-tube-confined-concrete composite brace, is comprised of concrete confined by a GFRP tube and an inner steel core for energy dissipation. Together with a contribution from the GFRP-tube confined concrete, the composite brace shows a substantially increased stiffness to control story drift, which is often a preferred feature in seismic retrofitting. An analysis model is established and implemented in a general finite element analysis program — OpenSees, for simulating the load-displacement behavior of the composite brace. Using this model, a parametric study of the hysteretic behavior (energy dissipation, stiffness, ductility and strength) of the composite brace was conducted under static cyclic loading and it was found that the area ratio of steel core to concrete has the greatest influence among all the parameters considered. To demonstrate the application of the composite brace in seismic retrofitting, a three-story nonductile reinforced concrete (RC) frame structure was retrofitted with the composite braces. Pushover analysis and nonlinear time-history analyses of the retrofitted RC frame structure was performed by employing a suite of 20 strong ground motion earthquake records. The analysis results show that the composite braces can effectively reduce the peak seismic responses of the RC frame structure without significantly increasing the base shear demand.
Performance of "Waterless Concrete"
Toutanji, H. A.; Grugel, R. N.
2009-01-01
Waterless concrete consists of molten elementary sulfur and aggregate. The aggregates in a lunar environment will be lunar rocks and soil. Sulfur is present on the Moon in Troilite soil (FeS) and, by oxidation of the soil, iron and sulfur can be produced. Sulfur concrete specimens were cycled between liquid nitrogen (approx.]91 C) and room temperature (^21 C) to simulate exposure to a lunar environment. Cycled and control specimens were subsequently tested in compression at room temperatures (^21 C) and ^-101 C. Test results showed that due to temperature cycling, the compressive strength of cycled specimens was 20% of those non-cycled. This reduction in strength can be attributed to the large differences in thermal coefficients of expansion of the materials constituting the concrete which promoted cracking. Similar sulfur concrete mixtures were strengthened with short and long glass fibres. The lunar regolith simulant was melted in a 25 cc Pt- Rh crucible in a Sybron Thermoline high temperature MoSi2 furnace at melting temperatures of 1450 to 1600 C for times of 30 min to i hour. Glass fibres and small rods were pulled from the melt. The glass fibres were used to reinforce sulfur concrete plated to improve the flexural strength of the sulfur concrete. Beams strengthened with glass fibres showed to exhibit an increase in the flexural strength by as much as 45%.
Directory of Open Access Journals (Sweden)
José Julio de Cerqueira Pituba
2010-07-01
Full Text Available O artigo apresenta uma discussão sobre a aplicabilidade de modelos de dano na análise não-linear física de estruturas em concreto armado, procurando, particularmente, validar a proposta de um modelo formulado recentemente por Pituba que compara as respostas numéricas obtidas com as respostas de modelos já testados, além de respostasexperimentais encontradas na literatura. O modelo proposto admite o concreto como meio inicialmente isótropo e que passa a apresentar deformações plásticas, bimodularidade e anisotropia induzidas pelo dano. Já o modelo proposto por Mazars considera o concreto como meio elástico e isótropo. Em seguida, apresenta-se a formulação do modelo proposto por La Borderie, que leva em conta deformações plásticas induzidas pelo dano e mantém a característica de isotropia do material. Na segunda parte do trabalho, os modelos são empregados na análise de vigas e pórtico em concreto armado, e as respostas numéricas são confrontadas com medidas experimentais. Os resultados evidenciam o bom desempenho dos modelos de dano e, em particular, valida-se o emprego do modelo proposto por Pituba nas situações estudadas. Observa-se ainda que formulações simples de modelos de danopara o concreto podem apresentar resultados bastante satisfatórios, dando margem para possíveis aplicações na prática da Engenharia de Estruturas.This work presents a discussion on the employment of a damage model recently proposed for concrete and other damage models in the non-linear analysis of reinforced concrete structures. The validation of the model is obtained by the comparison between numerical responses and experimental ones. The model proposed by Pituba regards concrete as an initially isotropic medium that starts to present plastic deformations, bimodularity and anisotropy induced by the damage. The model proposed by Mazars considers concrete to be an elastic and isotropic medium. Next, the model proposed by La Borderie is
New generation concretes including reactive powder concretes
Directory of Open Access Journals (Sweden)
Stefania Grzeszczyk
2015-09-01
Full Text Available Based on a broad literature review, this paper presents characteristics of new generation composites on the basis of cements which are applied in engineering structures and in rehabilitation of structures. The role of cement, microfillers, superplasticizers and fibers in the above stated composites i.e. factors which allow for the maximum packing of particles in the cement matrix and a minimum pore volume, and the increase in composite bending strength, have been discussed. Special attention was paid to Reactive Powder Concrete in which coarse aggregate was replaced by ground quartz and sand. Such composites contain active microfillers and the applied new-generation superplasticizers allow us to decrease the water-cement ratio in the composite up to 0.2. Whereas, steel fibre additive allows us to significantly improve the bending strength.The paper presents the properties of the excellent Ductal — a composite from Reactive Powder Concrete, which at compressive strength from 180 to 230 MPa achieves the tensile strength of 30 to 50 MPa. Its application allows us to create slim profiles and tall light and slender, and simultaneously durable and corrosion-resistant structural elements of considerable span. This paper gives a few examples of Ductal application in practice.[b]Keywords[/b]: civil engineering, composite materials, reactive powder concrete
Advanced modelling of concrete deterioration due to reinforcement corrosion
Energy Technology Data Exchange (ETDEWEB)
Isgor, O.B. [Carleton Univ., Dept. of Civil and Environmental Engineering, Ottawa, Ontario (Canada); Razaqpur, A.G. [McMaster Univ., Dept. of Civil Engineering, Hamilton, Ontario (Canada)
2006-06-15
A comprehensive model is presented for predicting the rate of steel corrosion in concrete structures and the consequent formation and propagation of cracks around the steel reinforcement. The corrosion model considers both the initiation and the propagation stages of corrosion. Processes commencing in the initiation stage, such as the transport of chloride ions and oxygen within the concrete and variation in temperature and moisture, are assumed to continue in the propagation stage while active corrosion is occurring contemporaneously. This allows the model to include the effects of changes in exposure conditions on the corrosion rate and the effects of the corrosion reactions on the transport properties of concrete. The corrosion rates are calculated by applying the finite-element solution of the Laplace equation for electrochemical potential, with appropriate boundary conditions. Because these boundary conditions are nonlinear, a nonlinear solution algorithm is used. The results of the analysis are compared with available test data, and the comparison is found to be satisfactory. (author)
Institute of Scientific and Technical Information of China (English)
李红豫; 滕军; 李祚华
2016-01-01
The traditional serial computation platform has some disadvantages such as low accuracy and dramatically high time consuming,which have hindered the development of structural nonlinear dynamics analysis.In order to achieve a higher computing accuracy and save calculation time in the process of nonlinear dynamic analysis of reinforced concrete (RC)frames,a simulation platform HSNAS(GPU)based on the graphics processing unit (GPU)was developed.For static analysis,a GPU-based incremental displacement algorithm was introduced to deal with negative stiffness problems,and a parallel preconditioned conjugate gradients (PCG)solver was developed.For dynamic analysis, the GPU-based Newmark-beta algorithm was presented.The fiber beam model was improved by considering the effects of shear and torsion.In addition,the constitutive models of steel and concrete were developed.The results of numerical examples illustrate that the developed platform HSNAS(GPU)could improve the efficiency of nonlinear static and dynamic analysis besides satisfying the accuracy requirement.%基于传统串行计算平台的有限元分析面临精度不足、耗时巨大的问题成为目前高层钢筋混凝土框架结构非线性动力时程分析面临的瓶颈，利用 GPU 强大的并行计算能力，开发了一种结构非线性有限元静力、动力分析的高精度和高效率分析平台 HSNAS（GPU）。针对静力问题提出了适用于 GPU 计算，且能有效解决结构负刚度问题的位移增量迭代算法，开发了相应的 GPU 线性方程组并行求解器；针对动力问题，开发了 GPU 基于 Newmark 时间积分算法的动力分析软件平台，结合纤维模型单元技术，引入扭转、剪切变形以及材料非线性。算例模型表明，HSNAS（GPU）平台在满足精度条件下能有效地提高结构非线性静、动力分析的计算效率。
Earthquake safety assessment of concrete arch and gravity dams
Institute of Scientific and Technical Information of China (English)
Lin Gao; Hu Zhiqiang
2005-01-01
Based on research studies currently being carried out at Dalian University of Technology, some important aspects for the earthquake safety assessment of concrete dams are reviewed and discussed. First, the rate-dependent behavior of concrete subjected to earthquake loading is examined, emphasizing the properties of concrete under cyclic and biaxial loading conditions. Second, a modified four-parameter Hsieh-Ting-Chen viscoplastic consistency model is developed to simulate the rate-dependent behavior of concrete. The earthquake response of a 278m high arch dam is analyzed, and the results show that the strain-rate effects become noticeable in the inelastic range. Third, a more accurate non-smooth Newton algorithm for the solution of three-dimensional frictional contact problems is developed to study the joint opening effects of arch dams during strong earthquakes. Such effects on two nearly 300m high arch dams have been studied. It was found that the canyon shape has great influence on the magnitude and distribution of the joint opening along the dam axis. Fourth, the scaled boundary finite element method presented by Song and Wolf is employed to study the dam-reservoir-foundation interaction effects of concrete dams. Particular emphases were placed on the variation of foundation stiffness and the anisotropic behavior of the foundation material on the dynamic response of concrete dams. Finally, nonlinear modeling of concrete to study the damage evolution of concrete dams during strong earthquakes is discussed. An elastic-damage mechanics approach for damage prediction of concrete gravity dams is described as an example. These findings are helpful in understanding the dynamic behavior of concrete dams and promoting the improvement of seismic safety assessment methods.
Dynamic Elasto-Plastic Model for Reinforced Concrete Members
Van der Veen, C.; Blaauwendraad. J.
1983-01-01
It is becoming increasingly necessary to investigate the strength of reinforced concrete structures subjected to dynamic loading. Experience and knowledge relating to the non-linear dynamic behaviour of such structures is still limited, however. Attempts to solve this type of problems with the aid o
Development of Advanced Constitutive Models for Plain and Reinforced Concrete.
1985-04-08
appreciation to Dr. D. H. Brownell and ir. R. G. Herrmann , who provided excellent computational support throughout the course of the research...above studies, wniicnh are .11rected towarI nonlinear steel-concrete interaction ef’ecti, severa’ test r~oiems nave been exami ned wich were intended to
Recycled Concrete as Aggregate for Structural Concrete Production
Directory of Open Access Journals (Sweden)
Mirjana Malešev
2010-04-01
Full Text Available A comparative analysis of the experimental results of the properties of fresh and hardened concrete with different replacement ratios of natural with recycled coarse aggregate is presented in the paper. Recycled aggregate was made by crushing the waste concrete of laboratory test cubes and precast concrete columns. Three types of concrete mixtures were tested: concrete made entirely with natural aggregate (NAC as a control concrete and two types of concrete made with natural fine and recycled coarse aggregate (50% and 100% replacement of coarse recycled aggregate. Ninety-nine specimens were made for the testing of the basic properties of hardened concrete. Load testing of reinforced concrete beams made of the investigated concrete types is also presented in the paper. Regardless of the replacement ratio, recycled aggregate concrete (RAC had a satisfactory performance, which did not differ significantly from the performance of control concrete in this experimental research. However, for this to be fulfilled, it is necessary to use quality recycled concrete coarse aggregate and to follow the specific rules for design and production of this new concrete type.
Fracture characteristics of concrete subjected to impact loading
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
This paper takes concrete as a four-phase composite made of the intact matrix and three mutually perpendicular groups of penny-shaped micro-cracks. The intact matrix is assumed to be elastic,homogeneous and isotropic,and the micro-cracks are penny-shaped. Combined with the failure mechanism of concrete subjected to impact loading,a dynamic constitutive model for concrete is developed based on Mori-Tanaka’s average stress concept and Eshelby’s equivalent inclusion theory. Experimental results show that concrete is rate-dependent. The model predictions are in good agreement with the experimental results. The model may be used to simulate the mechanical behavior of concrete under impact loadings.
Chloride permeability of concrete under static and repeated compressive loading
Energy Technology Data Exchange (ETDEWEB)
Saito, Mitsuru; Ishimori, Hiroshi [Kanazawa Inst. of Technology, Ishikawa (Japan)
1995-05-01
The chloride permeability of normal weight concrete subjected to static and repeated compressive loading was evaluated by using the AASHTO T277 test method. The results of concrete under static loading showed that the application of loads up to 90% of the ultimate strength had little effect on the chloride permeability. It was found from the results of concrete under repeated loading that load repetitions at the maximum stress levels of 60% or more caused the chloride permeability to increase significantly. The test results also indicated that the chloride permeability of concrete subjected to static and repeated loading increased at an increasing rate with its residual strain. The relation between the chloride permeability obtained and the cracking behavior of concrete previously reported was discussed.
Lithuanian Quarry Aggregates Concrete Effects of Alkaline Corrosion Tests
Directory of Open Access Journals (Sweden)
Aurimas Rutkauskas
2016-02-01
Full Text Available Aggregate alkaline corrosion of cement in concrete is going to respond in sodium and potassium hydroxide (lye with active SiO2 found in some aggregates. During this reaction, the concrete has resulted in significant internal stresses which cause deformation of the concrete, cracking and disintegration. The reaction is slow and concrete signs of decomposition appear only after a few months or years. The study used two different aggregates quarries. Studies show that Lithuania gravel contaminated with reactive particles having amorphous silicon dioxide reacting with cement in sodium and potassium hydroxide and the resulting alkaline concrete corrosion. It was found that, according to AAR 2 large aggregates include Group II – potentially reactive because of their expansion after 14 days, higher than 0.1%.
Experimental studies of fiber concrete creep
Directory of Open Access Journals (Sweden)
Korneeva Irina
2017-01-01
Full Text Available The results of two-stage experimental studies of the strength and deformation characteristics of fibrous concrete reinforced with steel fiber. In the experiments we used steel fiber with bent ends, which practically does not form "hedgehogs", which allows to achieve an even distribution of the fiber by volume. At the first stage, the cube and prismatic strength, deformability at central compression, a number of special characteristics are determined: water absorption, frost resistance, abrasion; the optimal percentage of fiber reinforcement and the maximum size of the coarse aggregate fraction were selected. Fiber reinforcement led to an increase in the strength of concrete at compression by 1,35 times and an increase in the tensile strength at bending by 3,4 times. At the second stage, the creep of fibrous concrete and plain concrete of similar composition at different stress levels was researched. Creep curves are plotted. It is shown that the use of fiber reinforcement leads to a decrease in creep strain by 21 to 30 percent, depending on the stress level.
Percolation Model of Graphite-modified Asphalt Concrete
Institute of Scientific and Technical Information of China (English)
MO Liantong; WU Shaopeng; LIU Xiaoming; CHEN Zheng
2005-01-01
The addition of graphite powder in conventional asphalt mixture can produced asphalt concrete with excellent electrical performance. Percolation theory was employed to discuss the relation between the conductivity and graphite content of graphite-modified asphalt concrete. It was found that the results of percolation model are consistent with experimental values. The percolation threshold of graphite-modified asphalt concrete is 10.94% graphite content account for the total volume of the binder phase consisting of asphalt and graphite. The critical exponent is 3.16, beyond the range of 1.6-2.1 for the standard lattice continuous percolation problem. Its reason is that the tunnel conduction mechanism originates near the critical percent content, which causes this system to be not universal. Tunnel mechanism is demonstrated by the nonlinear voltage-current characteristic near percolation threshold.The percolation model is able to well predict the formation and development of conductive network in graphite-modified asphalt concrete.
Heidari, Mohammad; Heidari, Ali; Homaei, Hadi
2014-01-01
The static pull-in instability of beam-type microelectromechanical systems (MEMS) is theoretically investigated. Two engineering cases including cantilever and double cantilever microbeam are considered. Considering the midplane stretching as the source of the nonlinearity in the beam behavior, a nonlinear size-dependent Euler-Bernoulli beam model is used based on a modified couple stress theory, capable of capturing the size effect. By selecting a range of geometric parameters such as beam lengths, width, thickness, gaps, and size effect, we identify the static pull-in instability voltage. A MAPLE package is employed to solve the nonlinear differential governing equations to obtain the static pull-in instability voltage of microbeams. Radial basis function artificial neural network with two functions has been used for modeling the static pull-in instability of microcantilever beam. The network has four inputs of length, width, gap, and the ratio of height to scale parameter of beam as the independent process variables, and the output is static pull-in voltage of microbeam. Numerical data, employed for training the network, and capabilities of the model have been verified in predicting the pull-in instability behavior. The output obtained from neural network model is compared with numerical results, and the amount of relative error has been calculated. Based on this verification error, it is shown that the radial basis function of neural network has the average error of 4.55% in predicting pull-in voltage of cantilever microbeam. Further analysis of pull-in instability of beam under different input conditions has been investigated and comparison results of modeling with numerical considerations shows a good agreement, which also proves the feasibility and effectiveness of the adopted approach. The results reveal significant influences of size effect and geometric parameters on the static pull-in instability voltage of MEMS.
Reliable evaluation method of quality control for compressive strength of concrete
Institute of Scientific and Technical Information of China (English)
CHEN Kuen-suan; SUNG Wen-pei; SHIH Ming-hsiang
2005-01-01
Concrete in reinforced concrete structure (RC) is generally under significant compressive stress load. To guarantee required quality and ductility, various tests have to be conducted to measure the concrete's compressive strength based on ACI(American Concrete Institute) code. Investigations of recent devastating collapses of structures around the world showed that some of the collapses directly resulted from the poor quality of the concrete. The lesson learned from these tragedies is that guaranteeing high quality of concrete is one of the most important factors ensuring the safety of the reinforced concrete structure.In order to ensure high quality of concrete, a new method for analyzing and evaluating the concrete production process is called for.In this paper, the indices of fit and stable degree are proposed as basis to evaluate the fitness and stability of concrete's compressive strength. These two indices are combined to define and evaluate the quality index of the compressive strength of concrete. Principles of statistics are used to derive the best estimators of these indices. Based on the outcome of the study, a concrete compressive strength quality control chart is proposed as a tool to help the evaluation process. Finally, a new evaluation procedure to assess the quality control capability of the individual concrete manufacturer is also proposed.
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Directory of Open Access Journals (Sweden)
Mohammad Heidari
2013-01-01
Full Text Available In this study, the static pull-in instability of beam-type micro-electromechanical system (MEMS is theoretically investigated. Considering the mid-plane stretching as the source of the nonlinearity in the beam behavior, a nonlinear size dependent Euler-Bernoulli beam model is used based on a modified couple stress theory, capable of capturing the size effect. Two supervised neural networks, namely, back propagation (BP and radial basis function (RBF, have been used for modeling the static pull-in instability of microcantilever beam. These networks have four inputs of length, width, gap, and the ratio of height to scale parameter of beam as the independent process variables, and the output is static pull-in voltage of microbeam. Numerical data employed for training the networks and capabilities of the models in predicting the pull-in instability behavior has been verified. Based on verification errors, it is shown that the radial basis function of neural network is superior in this particular case and has the average errors of 4.55% in predicting pull-in voltage of cantilever microbeam. Further analysis of pull-in instability of beam under different input conditions has been investigated and comparison results of modeling with numerical considerations show a good agreement, which also proves the feasibility and effectiveness of the adopted approach.
DEFF Research Database (Denmark)
Burcharth, Hans F.
The following types of forces contribute to the stresses in a Dolos in a pack exposed to waves: 1)Gravity forces Compaction forces (mainly due to settlements, gravity and flow forces) 2) Flow forces 3) Impact forces (impacts between moving concrete blocks)......The following types of forces contribute to the stresses in a Dolos in a pack exposed to waves: 1)Gravity forces Compaction forces (mainly due to settlements, gravity and flow forces) 2) Flow forces 3) Impact forces (impacts between moving concrete blocks)...
Analysis on concrete segment stress in shielding tunnel%盾构隧道混凝土管片受力分析
Institute of Scientific and Technical Information of China (English)
李建平
2012-01-01
以杭州地铁一号线下沙开发区某区间隧道工程成环管片为研究对象,利用ANSYS软件建立成环管片数值模型,分析了管片在土中的受力情况,同时结合在本工程实际施工中管片出现的一些情况,得到较可靠的结论。%Taking Hangzhou subway line No.1 interaction tunnel engineering circular segment in Xiasha development region as the research target,the paper establishes the circular segment numerical model by using ANSYS software,analyzes the stress conditions of segments in the earth,and obtains rather reliable conclusions by integrating with some actual segment conditions occurring in the engineering construction.
Computational Model for Internal Relative Humidity Distributions in Concrete
Directory of Open Access Journals (Sweden)
Wondwosen Ali
2014-01-01
Full Text Available A computational model is developed for predicting nonuniform internal relative humidity distribution in concrete. Internal relative humidity distribution is known to have a direct effect on the nonuniform drying shrinkage strains. These nonuniform drying shrinkage strains result in the buildup of internal stresses, which may lead to cracking of concrete. This may be particularly true at early ages of concrete since the concrete is relatively weak while the difference in internal relative humidity is probably high. The results obtained from this model can be used by structural and construction engineers to predict critical drying shrinkage stresses induced due to differential internal humidity distribution. The model uses finite elment-finite difference numerical methods. The finite element is used to space discretization while the finite difference is used to obtain transient solutions of the model. The numerical formulations are then programmed in Matlab. The numerical results were compared with experimental results found in the literature and demonstrated very good agreement.
Institute of Scientific and Technical Information of China (English)
苏尔好; 袁捷; 黄崇伟
2015-01-01
为深入研究机场道面接缝缝槽的水平和竖向位移对于嵌缝材料黏附性失效和嵌缝材料挤出的影响,采用有限元分析的手段,计算机场水泥道面接缝缝槽在环境温度和湿度变化下引起的缝槽水平位移量,以及飞机荷载作用引起的缝槽竖向位移量,并与实际观测数据进行对比分析.计算表明,机场水泥道面接缝缝槽水平位移量为2．2 mm左右,拉伸应变量可取为25％,与公路水泥路面基本相当；接缝缝槽的竖向位移量处于0．25~0．61 mm,剪切应变量处于3．1％~7．7％,较公路水泥路面大一些.选择包含弹簧单元及Kelvin模型的三参数固体模型描述嵌缝材料的流变特性,通过拉伸松弛实验实际测定3种典型嵌缝材料的弹簧系数和黏壶系数,利用缝槽内嵌缝材料拉伸应力和剪切应力的简化计算公式,计算3种典型嵌缝材料极限状态下的结构应力,结果表明,嵌缝材料的结构应力主要来自于接缝水平位移所引起的拉伸应力,剪切应力与接缝传荷能力的变化密切相关.%To study the influence of horizontal and vertical displacements of j oint on the cohesion failure and extrusion of the sealants in rigid pavement of airports,the displacement of the j oint and structural stress of the sealants were researched.Horizontal displacement caused by environmental temperature & humidity and vertical displancement caused by airplane loads were calculated separately by the finite element meth-ods,and the data of in-situ were compared with these calculation results.It is suggested that about 2.2 mm (corresponding to 25% tensile strain)of the horizontal displacement and 0.25—0.61 mm (corresponding to 3.1%—7.7% shear strain)of the vertical displacement are reasonable as the parameters for calculating the structural stress of sealants in concrete pavement j oints.The model containing of a spring element and a Kelvin model was used for depicting the sealants
Mortar constituent of concrete under cyclic compression
Maher, A.; Darwin, D.
1980-10-01
The behavior of the mortar constituent of concrete under cyclic compression was studied and a simple analytic model was developed to represent its cyclic behavior. Experimental work consisted of monotonic and cyclic compressive loading of mortar. Two mixes were used, with proportions corresponding to concretes having water cement ratios of 0.5 and 0.6. Forty-four groups of specimens were tested at ages ranging from 5 to 70 days. complete monotonic and cyclic stress strain envelopes were obtained. A number of loading regimes were investigated, including cycles to a constant maximum strain. Major emphasis was placed on tests using relatively high stress cycles. Degradation was shown to be a continuous process and a function of both total strain and load history. No stability or fatigue limit was apparent.
DEFF Research Database (Denmark)
Tanev, George; Saadi, Dorthe Bodholt; Hoppe, Karsten
2014-01-01
features from electrocardiograms (ECG) acquired by the wireless wearable ePatch® recorder. The highest recognition rates were acquired for the neutral stage (90%), the acute stress stage (80%) and the baseline stage (80%) by sample entropy, detrended fluctuation analysis and normalized high frequency...
Effects of Voids on Concrete Tensile Fracturing: A Mesoscale Study
Directory of Open Access Journals (Sweden)
Lei Xu
2017-01-01
Full Text Available A two-dimensional mesoscale modeling framework, which considers concrete as a four-phase material including voids, is developed for studying the effects of voids on concrete tensile fracturing under the plane stress condition. Aggregate is assumed to behave elastically, while a continuum damaged plasticity model is employed to describe the mechanical behaviors of mortar and ITZ. The effects of voids on the fracture mechanism of concrete under uniaxial tension are first detailed, followed by an extensive investigation of the effects of void volume fraction on concrete tensile fracturing. It is found that both the prepeak and postpeak mesoscale cracking in concrete are highly affected by voids, and there is not a straightforward relation between void volume fraction and the postpeak behavior due to the randomness of void distribution. The fracture pattern of concrete specimen with voids is controlled by both the aggregate arrangement and the distribution of voids, and two types of failure modes are identified for concrete specimens under uniaxial tension. It is suggested that voids should be explicitly modeled for the accurate fracturing simulation of concrete on the mesoscale.
The Effect of Steel Corrosion on Bond Strength in Concrete Structures
Institute of Scientific and Technical Information of China (English)
FANG Cong-qi; KOU Xin-jian
2005-01-01
The effect of steel corrosion on the behavior of bond between steel and the surrounding concrete was in vestigated. Pullout tests were carried out to demonstrate bond stress-slip response for reinforcing steel bars of a series of corrosion level. Specimens either confined or unconfined were investigated for evaluation of the effect of confinement on bond strength and failure mode. Also, the tests were analyzed using nonlinear finite element analysis. It was shown that for both confined and unconfined steel bars, bond strength generally decreases as the corrosion level increases when corrosion level is relatively high. Confinement was demonstrated to provide excellent means to conteract bond loss for corroded reinforcing steel bars. It was shown that unconfined specimens generally split at a small slip with a large crack width and result in splitting failure while confined specimens contribute to a small crack width and generally cause a pullout failure. The analysis results agree reasonably well with the experiments.
Fracture Mechanics of an Elastic Softening Material like Concrete
Reinhardt, H.W.
1984-01-01
Concrete is modelled as a linear elastic softening material and introduced into fracture mechanics. A discrete crack is considered with softening zones at the crack tips. Following the approach of Dugdale/Barenblatt, closing stresses are applied to the crack faces in the softening zone. The stresses
Magnesium oxychloride cement concrete
Indian Academy of Sciences (India)
A K Misra; Renu Mathur
2007-06-01
The scope of magnesium oxychloride (MOC) cement in concrete works has been evaluated. MOC cement concrete compositions of varying strengths having good placing and finishing characteristics were prepared and investigated for their compressive and flexural strengths, -values, abrasion resistance etc. The durability of MOC concrete compositions against extreme environmental conditions viz. heating–cooling, freezing–thawing, wetting–drying and penetration and deposition of salts etc were investigated. The results reveal that MOC concrete has high compressive strength associated with high flexural strength and the ratio of compressive to flexural strength varies between 6 and 8. The elastic moduli of the compositions studied are found to be 23–85 GPa and the abrasion losses between 0.11 and 0.20%. While alternate heating–cooling cycles have no adverse effect on MOC concrete, it can be made durable against freezing–thawing and the excessive exposure to water and salt attack by replacing 10% magnesium chloride solution by magnesium sulphate solution of the same concentration.
Crack Identification in Reinforced Concrete Beams Using Ansys Software
2014-01-01
Analytical determination of displacements and stresses in reinforced concrete material was difficult task and engineers had to rely on empirical formulas because concrete consists of heterogeneous material and creep and shrinkage influenced deformations in it. Due to these complexities engineers in past had been facing difficulties in coping such problems, but with the advancement of digital computerization and modern numerical methods for analysis such as finite element metho...
Measuring autogenous strain of concrete with corrugated moulds
DEFF Research Database (Denmark)
Tian, Qian; Jensen, Ole Mejlhede
2008-01-01
A reliable technique to quantify autogenous strain is a prerequisite to numerical modeling in stress calculations for high performance concrete. The introducing of a special kind of corrugated tube mould helps to transforming volume strain measurement into liner strain measurement in horizontal...... direction for fluid concrete, which not only realizes the continuous monitoring of the autogenous shrinkage since casting, but also effectively eliminates the disturbance resulting from gravity, temperature variation and mould restraint on measuring results. Based on this measuring technique, this paper...
Directory of Open Access Journals (Sweden)
Richard Ottermanns
Full Text Available In this study we present evidence that anthropogenic stressors can reduce the resilience of age-structured populations. Enhancement of disturbance in a model-based Daphnia population lead to a repression of chaotic population dynamics at the same time increasing the degree of synchrony between the population's age classes. Based on the theory of chaos-mediated survival an increased risk of extinction was revealed for this population exposed to high concentrations of a chemical stressor. The Lyapunov coefficient was supposed to be a useful indicator to detect disturbance thresholds leading to alterations in population dynamics. One possible explanation could be a discrete change in attractor orientation due to external disturbance. The statistical analysis of Lyapunov coefficient distribution is proposed as a methodology to test for significant non-linear effects of general disturbance on populations. Although many new questions arose, this study forms a theoretical basis for a dynamical definition of population recovery.
Nonlinear Ultrasonic Diagnosis and Prognosis of ASR Damage in Dry Cask Storage
Energy Technology Data Exchange (ETDEWEB)
Qu, Jianmin [Northwestern Univ., Evanston, IL (United States); Bazant, Zdenek [Northwestern Univ., Evanston, IL (United States); Jacobs, Laurence [Georgia Inst. of Technology, Atlanta, GA (United States); Guimaraes, Maria [Electrical Power Research Institute, Palo Alto, CA (United States)
2015-11-30
Alkali-silica reaction (ASR) is a deleterious chemical process that may occur in cement-based materials such as mortars and concretes, where the hydroxyl ions in the highly alkaline pore solution attack the siloxane groups in the siliceous minerals in the aggregates. The reaction produces a cross-linked alkali-silica gel. The ASR gel swells in the presence of water. Expansion of the gel results in cracking when the swelling-induced stress exceeds the fracture toughness of the concrete. As the ASR continues, cracks may grow and eventually coalesce, which results in reduced service life and a decrease safety of concrete structures. Since concrete is widely used as a critical structural component in dry cask storage of used nuclear fuels, ASR damage poses a significant threat to the sustainability of long term dry cask storage systems. Therefore, techniques for effectively detecting, managing and mitigating ASR damage are needed. Currently, there are no nondestructive methods to accurately detect ASR damage in existing concrete structures. The only current way of accurately assessing ASR damage is to drill a core from an existing structure, and conduct microscopy on this drilled cylindrical core. Clearly, such a practice is not applicable to dry cask storage systems. To meet these needs, this research is aimed at developing (1) a suite of nonlinear ultrasonic quantitative nondestructive evaluation (QNDE) techniques to characterize ASR damage, and (2) a physics-based model for ASR damage evolution using the QNDE data. Outcomes of this research will provide a nondestructive diagnostic tool to evaluate the extent of the ASR damage, and a prognostic tool to estimate the future reliability and safety of the concrete structures in dry cask storage systems
DEFF Research Database (Denmark)
Hansen, Kurt Kielsgaard; Geiker, Mette Rica; Nygaard, Peter Vagn;
2002-01-01
Estimated and measured relative humidity (RH) change during drying are compared for two concretes, 1: w/c=0.46 and 2: w/(c+0.5fa+2sf)=0.50. The estimations were undertaken by means of the Swedish program TorkaS 1.0. Measurements were performed by RH-sensors type Humi-Guard. Drying of 150 mm thick...... samples from sides at 60% RH and 22 °C took place from 4 to 56 days after casting. At the end of the drying period the measured RH was about 4% lower than the estimated RH at 1/5th depth from the exposed surface for both concretes. In the middle of the samples, the measured RH of concretes 1 and 2 were 2...
DEFF Research Database (Denmark)
Hansen, Kurt Kielsgaard; Geiker, Mette Rica; Nygaard, Peter Vagn
2002-01-01
Estimated and measured relative humidity (RH) change during drying are compared for two concretes, 1: w/c=0.46 and 2: w/(c+0.5fa+2sf)=0.50. The estimations were undertaken by means of the Swedish program TorkaS 1.0. Measurements were performed by RH-sensors type Humi-Guard. Drying of 150 mm thick...... samples from sides at 60% RH and 22 °C took place from 4 to 56 days after casting. At the end of the drying period the measured RH was about 4% lower than the estimated RH at 1/5th depth from the exposed surface for both concretes. In the middle of the samples, the measured RH of concretes 1 and 2 were 2...
DEFF Research Database (Denmark)
Jensen, Ole Mejlhede; Hansen, Per Freiesleben
This report gives a survey of different techniques for incorporation of designed, water-filled cavities in concrete: Water entrainment. Also an estimate of the optimum size of the water inclusions is given. Water entrainment can be used to avoid self-desiccation and self-desiccation shrinkage...... during hydration [1,26]. What is needed is some sort of container which retains the shape of the water when mixed into the concrete. The container may function based on several different physical or chemical principles. Cells and gels are examples of containers found in nature. A cell membrane provides...... a boundary to water, whereas a polymer network incorporates water in its intersticious space with its affinity due to interaction energy and polymer entropy. Such containers allow water to be stored as an entity. In relation to concrete the water encapsulation may be accomplished either before or after start...
Gurbatov, S N; Saichev, A I
2012-01-01
"Waves and Structures in Nonlinear Nondispersive Media: General Theory and Applications to Nonlinear Acoustics” is devoted completely to nonlinear structures. The general theory is given here in parallel with mathematical models. Many concrete examples illustrate the general analysis of Part I. Part II is devoted to applications to nonlinear acoustics, including specific nonlinear models and exact solutions, physical mechanisms of nonlinearity, sawtooth-shaped wave propagation, self-action phenomena, nonlinear resonances and engineering application (medicine, nondestructive testing, geophysics, etc.). This book is designed for graduate and postgraduate students studying the theory of nonlinear waves of various physical nature. It may also be useful as a handbook for engineers and researchers who encounter the necessity of taking nonlinear wave effects into account of their work. Dr. Gurbatov S.N. is the head of Department, and Vice Rector for Research of Nizhny Novgorod State University. Dr. Rudenko O.V. is...
Coupled elasto-plasticity damage constitutive models for concrete
Institute of Scientific and Technical Information of China (English)
Qiang XU; Jian-yun CHEN; Jing LI; Gang XU
2013-01-01
The paper is to design and construct a coupled elasto-plasticity damage constitutive model for concrete.Based on the energy dissipation principle,the Hsieh-Ting-Chen four-parameter yield function is used.The model can reflect different strength characteristics of concrete in tension and compression,and reduce the limitation and lacuna of the traditional damage constitutive models for concrete.Furthermore,numerical test for concrete stress-strain relation under uniaxial tension and compression is given.Moreover,the damage process of concrete gravity dam is calculated and analyzed in seismic load.Compared with other damage constitutive models,the proposed model contains only one unknown parameter and the other parameters can be found in the Hsieh-Ting-Chen four-parameter yield function.The same damage evolution law,which is used for tension and compression,is good for determining stress-strain constitutive and damage characteristics in complex stress state.This coupled damage constitutive models can be applied in analyzing damage of concrete gravity dam and arch dam.
Institute of Scientific and Technical Information of China (English)
阎石; 陈鑫; 季保建
2011-01-01
研究配有高强钢筋的高强混凝土框架结构的抗震性能.采用OpenSees开放式软件对配有高强钢筋的高强混凝土框架结构进行了地震作用下的非线性有限元分析,并将计算结果与同等参数条件下的结构拟动力试验进行了对比.得到不同峰值加速度情况下的结构层间反应时程曲线,层间位移滞回曲线,以及破坏模式等,数值计算结果与试验吻合程度较好.研究结果表明利用基于OpenSees的有限元分析方法,能够有效地分析配有高强钢筋的高强混凝土框架结构的地震响应,可以辅助研究该结构的抗震性能.%The nonlinear seismic response analysis of a two-story high-strength concrete frame structure is completed by using OpenSees software, which installed high-strength transverse and partly longitudinal reinforcement. The placement of the high-strength bars is to increase the ductility of the frame by effectively confining the core concrete to a three dimensional compression state. The results of the FEM simulation are compared with those of pseudo-dynamic model test with the same parameters, so the relative time history responses for the stories, hysteretic loops and failure modes of the frame under different peak acceleration are obtained, results between numerical computation and test are matched well. The FEM based on OpenSees software can effectively analyze the seismic responses of the high-strength concrete frame structure reinforced with high-strength bars and can additionally study the seismic performance of the kind of structures.
Investigation on Cracking of Concrete Shear Wall under Exceeded Temperature Differences Rate
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
In situ, the changes of temperature, deformation, and stressing of steel bar of C40 reinforced concrete shear wall were measured, respectively. The results are obvious that the temperature change of climate is one of the most effective factors which could lead the concrete shear wall to cracking at earlier age. The temperature differences between inside and outside concrete shear wall are so large that the concrete will gain larger shrinkage. This larger shrinkage which is caused by the temperature reducing ratio will gain the strained action of head, end and reinforced steel bar of concrete shear wall. This action can lead to tensile stress on the surface and inside concrete shear wall. If the tensile stress would exceed the pull strength of concrete, the concrete shear wall would crack and cause deterioration. Thus, the enhancing curing of concrete shear wall in suit at earlier age, and controlling temperature reducing ratio and deform caused by shrinkage, will be available treatments which control occurring and developing of cracking on concrete shear wall.
Electrokinetic decontamination of concrete
Energy Technology Data Exchange (ETDEWEB)
Lomasney, H. [ISOTRON Corp., New Orleans, LA (United States)
1995-10-01
The U.S. Department of Energy has assigned a priority to the advancement of technology for decontaminating concrete surfaces which have become contaminated with radionuclides, heavy metals, and toxic organics. This agency is responsible for decontamination and decommissioning of thousands of buildings. Electrokinetic extraction is one of the several innovative technologies which emerged in response to this initiative. This technique utilizes an electropotential gradient and the subsequent electrical transport mechanism to cause the controlled movement of ionics species, whereby the contaminants exit the recesses deep within the concrete. This report discusses the technology and use at the Oak Ridge k-25 plant.
Concentrated loads on concrete
DEFF Research Database (Denmark)
Lorenzen, Karen Grøndahl; Nielsen, Mogens Peter
1997-01-01
This report deals with concentrated loads on concrete.A new upper bound solution in the axisymmetrical case of a point load in the center of the end face of a cylinder is developed.Based on previous work dealing with failure mechanisms and upper bound solutions, new approximate formulas are devel......This report deals with concentrated loads on concrete.A new upper bound solution in the axisymmetrical case of a point load in the center of the end face of a cylinder is developed.Based on previous work dealing with failure mechanisms and upper bound solutions, new approximate formulas...
Sparavigna, Amelia Carolina
2011-01-01
It is commonly believed that the ancient Romans were the first to create and use concrete. This is not true, as we can easily learn from the Latin literature itself. For sure, Romans were able to prepare high-quality hydraulic cements, comparable with the modern Portland cements. In this paper, we will see that the use of concrete is quite older, ranging back to the Homeric times. For instance, it was used for the floors of some courts and galleries of the Mycenaean palace at Tiryns
Concentrated loads on concrete
DEFF Research Database (Denmark)
Lorenzen, Karen Grøndahl; Nielsen, Mogens Peter
1997-01-01
This report deals with concentrated loads on concrete.A new upper bound solution in the axisymmetrical case of a point load in the center of the end face of a cylinder is developed.Based on previous work dealing with failure mechanisms and upper bound solutions, new approximate formulas are devel......This report deals with concentrated loads on concrete.A new upper bound solution in the axisymmetrical case of a point load in the center of the end face of a cylinder is developed.Based on previous work dealing with failure mechanisms and upper bound solutions, new approximate formulas...
2007-11-02
Reinforcement Ratios 84 8-5 Ductility Indices 86 5 LIST OF FIGURES FIGURE PAGE 2-1 Failure Modes of Concrete Beams 17 2-2 Composite Jacket Installation...20 2-3 Composite Jacket Application 20 2-4 Four Point Bending Configuration 21 3-1 Stress-Strain Relationship for Concrete 27 3-2 Standard Rebar 28 3...researchers around the world, such as reinforcing and prestressing concrete structures, seismic retrofitting of concrete and unreinforced masonry
Nonlinear parallel momentum transport in strong turbulence
Wang, Lu; Diamond, P H
2015-01-01
Most existing theoretical studies of momentum transport focus on calculating the Reynolds stress based on quasilinear theory, without considering the \\emph{nonlinear} momentum flux-$$. However, a recent experiment on TORPEX found that the nonlinear toroidal momentum flux induced by blobs makes a significant contribution as compared to the Reynolds stress [Labit et al., Phys. Plasmas {\\bf 18}, 032308 (2011)]. In this work, the nonlinear parallel momentum flux in strong turbulence is calculated by using three dimensional Hasegawa-Mima equation. It is shown that nonlinear diffusivity is smaller than quasilinear diffusivity from Reynolds stress. However, the leading order nonlinear residual stress can be comparable to the quasilinear residual stress, and so could be important to intrinsic rotation in tokamak edge plasmas. A key difference from the quasilinear residual stress is that parallel fluctuation spectrum asymmetry is not required for nonlinear residual stress.
Tendons Arrangement Effects on Reinforced Concrete Frames
Directory of Open Access Journals (Sweden)
Ayad B. Bahnam
2013-05-01
Full Text Available The tendons arrangement effects on the response of reinforced concrete frame experiencing blast loads is investigated in this paper. The structure is modeled using nonlinear finite elements employing a bilinear hysteretic model. So that elements are used so that yielding of the structures could be accurately modeled and captured. The frame is analyzed using a non-linear, elastic-plastic finite element program written in code MATLAB. Six tendon architectures were investigated. A single tendon was placed between different floors and its effects investigated. From the obtained results, the ideal case which causes a reduction in the maximum displacement and the amount of permanent deflection without increase in the maximum structural shear forces greatly is obtained.
Corrosion Inhibitors for Reinforced Concrete
ECT Team, Purdue
2007-01-01
Steel corrosion in reinforced concrete structures has been a major problem across the U.S. Steel-reinforced concrete structures are continually subject to attack by corrosion brought on by naturally occurring environmental conditions. FerroGard, a corrosion inhibitor, developed by Sika Corporation, penetrates hardened concrete to dramatically reduce corrosion by 65% and extend the structure's service life.
Danish High Performance Concretes
DEFF Research Database (Denmark)
Nielsen, M. P.; Christoffersen, J.; Frederiksen, J.
1994-01-01
In this paper the main results obtained in the research program High Performance Concretes in the 90's are presented. This program was financed by the Danish government and was carried out in cooperation between The Technical University of Denmark, several private companies, and Aalborg University...
Designing concrete for durability
Directory of Open Access Journals (Sweden)
Boyd, A. J.
2001-12-01
Full Text Available Some of the factors affecting the durability of modern concrete structures are discussed, with an emphasis on the problems caused by modern portland cements. This is followed by a description of some concrete durability issues of current interest, such as plastic shrinkage, seawater attack, and sulfate attack. The strategies for testing for durability are also discussed. It is concluded that, to produce durable concretes, a holistic approach to concrete construction must be adopted.
Se discuten algunos de los factores que influyen en la durabilidad de las estructuras de hormigón modernas, haciendo énfasis en los problemas causados por el cemento Portland. A esto sigue una descripción de algunas cuestiones de interés general de la durabilidad del hormigón tales como la retracción plástica, el ataque por agua de mar y el ataque por sulfatos. Se discuten también las estrategias de los ensayos de durabilidad. Se concluye que para producir hormigones durables se debe adoptar un enfoque holístico de la construcción con hormigón.
DEFF Research Database (Denmark)
Goltermann, Per
2014-01-01
The teaching of concrete structures has been revised and a number of new approaches have been developed, implemented and evaluated. Inductive teaching, E-learning and “patches” have been found to be improvements and may be an inspiration and help for others development of the teaching and learning...
1988-01-25
reflects the dispersion of the coarse aggregates on the mesoscale. Specifically, the experimental measure- ments indicate ( Mindess and Young 1981, Zaitsev...Mecanique des Materiaux Solides, Dunod, Paris. Mindess , S. and J. Young (1981), Concrete, Prentice-Hall Inc., Englewood Cliffs, NJ. Mura, T. (1982
1990-10-18
Mindess (1981) also agrees with the first of the two reactions but allows for transformation of the ettringite to monosulphate in the case when all...Comp. Materials, 23, pp. 163-194. 3 Mindess , S. and J. F. Young (1981), Concrete, Prentice Hall, Englewood Clifs, N.J. * 74 I Moavenzadeh, F.(1971
Structural concrete and sustainability
CSIR Research Space (South Africa)
Grieve, G
2010-04-01
Full Text Available the typical specific CO2 per ton of cementitious binder is about 765 kg. However, the effect of this is significantly diluted by the addition of aggregates (around 80% of the mass of a cubic meter of concrete) and cement extenders, of which many are industrial...
Forterra Concrete Products, Inc.
The EPA is providing notice of a proposed Administrative Penalty Assessment against Forterra Concrete Products, Inc., a business located at 511 E. John Carpenter Freeway, Irving, TX, 75062, for alleged violations at its facility located at 23600 W. 40th St
Electrical pulses protect concrete
Van Kasteren, J.
2006-01-01
Even concrete is not as hard as it looks. Sea water, salt on icy roads, and indirectly even carbon dioxide from the air can corrode the steel of the reinforcing bars and so threaten the strength and integrity of a bridge pier, jetty, or viaduct. Dessi Koleva, a chemical engineer from Bulgaria, spent
1983-03-01
1967, Cedergren 1974, Federal Highway .’,U .. V,47 -’":: 37 Administration 1980). Block pavements have essentially the same prob- lems with moisture...Vicksburg, Miss. Cedergren , H. R. 1974. Drainage of Highway and Airfield Pavements, John Wiley and Sons, New VOk. I Cement and Concrete Association
Contaminated soil concrete blocks
Korte, de A.C.J.; Brouwers, H.J.H.; Limbachiya, Mukesh C.; Kew, Hsein Y.
2009-01-01
According to Dutch law the contaminated soil needs to be remediated or immobilised. The main focus in this article is the design of concrete blocks, containing contaminated soil, that are suitable for large production, financial feasible and meets all technical and environmental requirements. In ord
Hydrophobic treatment of concrete
Vries, J. de; Polder, R.B.
1996-01-01
As part of the maintenance policy of the Dutch Ministry of Transport, Civil Engineering Division, hydrophobic treatment of concrete was considered as an additional protective measure against penetration of aggressive substances, for instance deicing salts in bridge decks. A set of tests was designed
Hydrophobic treatment of concrete
Vries, J.de; Polder, R.B.
1997-01-01
As part of the maintenance policy of the dutch Ministry of Transport, Civil Engineering Division, hydrophobic treatment of concrete was considered as an additional protective measure against penetration of aggressive substances, for instance deicing salts in bridge decks. A set of tests was designed
Fracture Mechanics of Concrete
DEFF Research Database (Denmark)
Ulfkjær, Jens Peder
Chapter 1 Chapter l contains the introduction to this thesis. The scope of the thesis is partly to investigate different numerical and analytical models based on fracture mechanical ideas, which are able to predict size effects, and partly to perform an experimental investigation on high-strength......Chapter 1 Chapter l contains the introduction to this thesis. The scope of the thesis is partly to investigate different numerical and analytical models based on fracture mechanical ideas, which are able to predict size effects, and partly to perform an experimental investigation on high......-strength concrete. Chapter 2 A description of the factors which influence the strength and cracking of concrete and high strength concrete is made. Then basic linear fracture mechanics is outlined followed by a description and evaluation of the models used to describe concrete fracture in tension. The chapter ends...... with a description of the different types of size effects. Three examples which discuss the two terms 'size effect' and 'brittleness' and the importance of a stiff test rig. Finally some brittleness numbers are defined. Chapter 3 In chapter 3 the most well-known numerical methods which use the fictitious crack...
1981-11-01
Gorsuch 1962, Kruse 1966, Jacoby 1967, and Hargett 1970). The final slab design used in construction is shown in Figure 2. These slabs were 6 ft wide, 24...Experiment Station, CE, Vicksburg, Miss. Gorsuch , R. F. 1962. "Preliminary Investigation of Precast Prestressed Concrete Pavements," MS Thesis, South Dakota
Comparative analysis of results from experimental and numerical studies on concrete strength
Directory of Open Access Journals (Sweden)
Mkrtychev Oleg
2017-01-01
Full Text Available Some results of numerical experiments of testing concrete cubes and prisms on unconfined compression, and the comparison of results obtained with experimental and specified data, are presented in the article. When performing calculations of structures in a nonlinear setting, it is very important to choose adequate deformation diagrams or material models. Because of the fact that there are no instructions how to use the diagrams of concrete and armature deformation in collaboration of steel and concrete, the simulation of reinforced concrete structures by finite elements of the same type without any assumptions is impossible. Numerical experiments have been performed in the LS-DYNA software package. This software package allows simulating the collaboration of concrete and steeling with the help of three-dimensional (for concrete and rod (for the reinforcement finite elements. As samples, a cube and a prism with dimensions of 150×150×150 mm and 150×150×600 mm, respectively, have been taken. The samples are simulated by solid finite elements. For the simulation of concrete, the non-linear CSCM (Continuous Surface Cap Model material is used. The tests were carried out with samples of the following classes of concrete as for cylinder compressive strength: C12, C16, C20, C25, C30, C35. This corresponds to the following classes of cube compression strength: B15, B20, B25, B30, B37, B45. The tests have been carried out considering the friction coefficients between the plates of a testing machine, and a sample. The performed researches have shown that the destruction nature of the samples in a numerical experiment corresponds to the failure nature in real tests. The investigated model of CSCM concrete can be used in the calculation of concrete and reinforced concrete structures with acceptable accuracy for main classes of concrete.
Heinemann, H.A.; Zijlstra, H.; Hees, R.P.J. van; Nijland, T.G.
2012-01-01
The conservation of historic concrete is an increasing task, challenging both concrete repair specialists and conservation specialists. In practice, too often repair strategies are followed where conservation strategies would have been necessary. The application of repair techniques poses two threat
Analysis of steel-concrete composite structure with overlap slab of Xingguang bridge
Institute of Scientific and Technical Information of China (English)
YE Mei-xin; HUANG Qiong; WU Qin-qin
2007-01-01
Finire element modeling methods of steel-concrete composire structure with overlap slab were investigated.A two-step finite element method wag presented.It was applied to analyze an extra long span composite bridge.The conversion of structure system and the mechanical behavior of the bridge were analyzed with two different construction methods.The stresses of steel beams, precast slabs and in-situ-place concrete under the total load were compared. The results show that steel-concrete composite structure with overlap slab has many advantages, the construction method that the top in-situ concrete and the concrete in construction joints are cast respectively is rather reasonable than the one that the top in-situ concrete and the concrete in construction joints are cast at the same time, and the two-step finite element method is affective to such large-scale structures.
Effects of Temperature and Strain Rate on Dynamic Properties of Concrete
Institute of Scientific and Technical Information of China (English)
JIA Bin; TAO Junlin; LI Zhengliang; WANG Ruheng; ZHANG Yu
2008-01-01
To study the dynamic properties of the concrete subjected to impulsive loading,stress-time curves of concrete in different velocities were measured using split Hopkinson pressure bar (SHPB).Effects of temperature and strain rate on the dynamic yield strength and constitutive relation of the concrete were analyzed.The dynamic mechanical properties of the reinforced concrete are subjected to high strain rates when it is at a relatively low temperature.But with temperature increasing,the temperature softening effect makes the strength of the concrete weaken and the impact toughness of the concrete is saliently relative to strain rate effect.So,strain rate effect,strain hardening and temperature softening work together on the dynamic mechanical capability of concrete and the relation between them is relatively corn plex.
Directory of Open Access Journals (Sweden)
Aleš Florian
2016-01-01
Full Text Available Complex statistical and sensitivity analysis of principal stresses in concrete slabs of the real type of rigid pavement made from recycled materials is performed. The pavement is dominantly loaded by the temperature field acting on the upper and lower surface of concrete slabs. The computational model of the pavement is designed as a spatial (3D model, is based on a nonlinear variant of the finite element method that respects the structural nonlinearity, enables to model different arrangement of joints, and the entire model can be loaded by thermal load. Four concrete slabs separated by transverse and longitudinal joints and the additional structural layers including soil to the depth of about 3 m are modeled. The thickness of individual layers, physical and mechanical properties of materials, characteristics of joints, and the temperature of the upper and lower surface of slabs are supposed to be random variables. The simulation technique Updated Latin Hypercube Sampling with 20 simulations is used for the reliability analysis. As results of statistical analysis, the estimates of basic statistics of the principal stresses σ1 and σ3 in 106 points on the upper and lower surface of slabs are obtained. For sensitivity analysis the sensitivity coefficient based on the Spearman rank correlation coefficient is used. As results of sensitivity analysis, the estimates of influence of random variability of individual input variables on the random variability of principal stresses σ1 and σ3 are obtained.
Survey of four damage models for concrete.
Energy Technology Data Exchange (ETDEWEB)
Leelavanichkul, Seubpong (University of Utah, Salt Lake City, UT); Brannon, Rebecca Moss (University of Utah, Salt Lake City, UT)
2009-08-01
Four conventional damage plasticity models for concrete, the Karagozian and Case model (K&C), the Riedel-Hiermaier-Thoma model (RHT), the Brannon-Fossum model (BF1), and the Continuous Surface Cap Model (CSCM) are compared. The K&C and RHT models have been used in commercial finite element programs many years, whereas the BF1 and CSCM models are relatively new. All four models are essentially isotropic plasticity models for which 'plasticity' is regarded as any form of inelasticity. All of the models support nonlinear elasticity, but with different formulations. All four models employ three shear strength surfaces. The 'yield surface' bounds an evolving set of elastically obtainable stress states. The 'limit surface' bounds stress states that can be reached by any means (elastic or plastic). To model softening, it is recognized that some stress states might be reached once, but, because of irreversible damage, might not be achievable again. In other words, softening is the process of collapse of the limit surface, ultimately down to a final 'residual surface' for fully failed material. The four models being compared differ in their softening evolution equations, as well as in their equations used to degrade the elastic stiffness. For all four models, the strength surfaces are cast in stress space. For all four models, it is recognized that scale effects are important for softening, but the models differ significantly in their approaches. The K&C documentation, for example, mentions that a particular material parameter affecting the damage evolution rate must be set by the user according to the mesh size to preserve energy to failure. Similarly, the BF1 model presumes that all material parameters are set to values appropriate to the scale of the element, and automated assignment of scale-appropriate values is available only through an enhanced implementation of BF1 (called BFS) that regards scale effects to be coupled to
Self-compacting concrete (SCC)
DEFF Research Database (Denmark)
Geiker, Mette Rica
2008-01-01
In many aspects Self-Compacting Concrete (SCC, “Self-Consolidating Concrete” in North America) can be considered the concrete of the future. SCC is a family of tailored concretes with special engineered properties in the fresh state. SCC flows into the formwork and around even complicated...... reinforcement arrangements under its own weight. Thus, SCC is not vibrated like conventional concrete. This drastically improves the working environment during construction, the productivity, and potentially improves the homogeneity and quality of the concrete. In addition SCC provides larger architectural...
Early Property Development in Concrete
DEFF Research Database (Denmark)
Normann, Gitte; Munch-Petersen, Christian
2014-01-01
The Freiesleben Maturity function is widely used for planning of execution. We tested if for concrete with and without fly ash. The test showed surprisingly that the maturity function in general is not valid. We found that curing at high temperature gave a significant decrease in strength. Fly ash...... appears to reduce this decrease somewhat. We also examined the resistance against chloride penetration for the different concrete types. The resistance was reduced at high temperatures for concrete without fly ash. For concrete with fly ash, it was the opposite; concrete with fly ash obtained higher...
Experimental and finite element analysis of bond-slip in reinforced concrete
Directory of Open Access Journals (Sweden)
A. R. V. WOLENSKI
Full Text Available Abstract The modeling of reinforced concrete structures has taken advantage of the increasing progress on Computational Mechanics, in such way that complex phenomena, such as cracking and crushing, creep, reinforcement yielding, steel-concrete bond loss, can be modeled in a reasonable realistic way, using the proper set of numerical and computational resources. Among several options, the ones based on the Finite Element Method (FEM allow complex analysis simulations of reinforced concrete structures, including the interaction of different nonlinear effects. This paper deals with the nonlinear finite element analysis of the bond-slip between reinforcing steel and concrete, taking into account an experimental study previously performed. The FEM analysis presented uses a combination of resources where the material behavior of concrete is described by the Microplane Constitutive Model, and an embedded reinforcement model is used to represent steel inside the concrete and take into account the effect of bond-slip. The FEM models were created using the INSANE (INteractive Structural ANalysis Environment computational system, open source software that has a set of FEM tools for nonlinear analysis of reinforced concrete structures. The correlations between numerical-experimentals results and several parameters validate the proposed combination of resources and identifies the significance of various effects on the response.
Very high cycle fatigue testing of concrete using ultrasonic cycling
Energy Technology Data Exchange (ETDEWEB)
Karr, Ulrike; Schuller, Reinhard; Fitzka, Michael; Mayer, Herwig [Univ. of Natural Resources and Life Sciences, Vienna (Austria). Inst. of Physics and Materials Science; Denk, Andreas; Strauss, Alfred [Univ. of Natural Resources and Life Sciences, Vienna (Austria)
2017-06-01
The ultrasonic fatigue testing method has been further developed to perform cyclic compression tests with concrete. Cylindrical specimens vibrate in resonance at a frequency of approximately 20 kHz with superimposed compressive static loads. The high testing frequency allows time-saving investigations in the very high cycle fatigue regime. Fatigue tests were carried out on ''Concrete 1'' (compressive strength f{sub c} = 80 MPa) and ''Concrete 2'' (f{sub c} = 107 MPa) under purely compressive loading conditions. Experiments at maximum compressive stresses of 0.44 f{sub c} (Concrete 1) and 0.38 f{sub c} (Concrete 2) delivered specimen failures above 109 cycles, indicating that no fatigue limit exists for concrete below one billion load cycles. Resonance frequency, power required to resonate the specimen and second order harmonics of the vibration are used to monitor fatigue damage in situ. Specimens were scanned by X-ray computed tomography prior to and after testing. Fatigue cracks were produced by ultrasonic cycling in the very high cycle fatigue regime at interfaces of grains as well as in cement. The possibilities as well as limitations of ultrasonic fatigue testing of concrete are discussed.
Innovative process routes for a high-quality concrete recycling.
Menard, Y; Bru, K; Touze, S; Lemoign, A; Poirier, J E; Ruffie, G; Bonnaudin, F; Von Der Weid, F
2013-06-01
This study presents alternative methods for the processing of concrete waste. The mechanical stresses needed for the embrittlement of the mortar matrix and further selective crushing of concrete were generated by either electric impulses or microwaves heating. Tests were carried out on lab-made concrete samples representative of concrete waste from concrete mixer trucks and on concrete waste collected on a French demolition site. The results obtained so far show that both techniques can be used to weaken concrete samples and to enhance aggregate selective liberation (that is the production of cement paste-free aggregates) during crushing and grinding. Electric pulses treatment seems to appear more efficient, more robust and less energy consuming (1-3 kWh t(-1)) than microwave treatment (10-40 kWh t(-1)) but it can only be applied on samples in water leading to a major drawback for recycling aggregates or cement paste in the cement production process. Copyright © 2013 Elsevier Ltd. All rights reserved.
Life Cycle Assessment of Concrete
Energy Technology Data Exchange (ETDEWEB)
Sjunnesson, Jeannette
2005-09-15
This is an environmental study on concrete that follows the standard protocol of life cycle assessment (LCA). The study is done for two types of concrete, ordinary and frost-resistant concrete, and has an extra focus on the superplasticizers used as admixtures. The utilization phase is not included in this study since the type of construction for which the concrete is used is not defined and the concrete is assumed to be inert during this phase. The results show that it is the production of the raw material and the transports involved in the life cycle of concrete that are the main contributors to the total environmental load. The one single step in the raw material production that has the highest impact is the production of cement. Within the transportation operations the transportation of concrete is the largest contributor, followed by the transportation of the cement. The environmental impact of frost-resistant concrete is between 24-41 % higher than that of ordinary concrete due to its higher content of cement. Superplasticizers contribute with approximately 0.4-10.4 % of the total environmental impact of concrete, the least to the global warming potential (GWP) and the most to the photochemical ozone creation potential (POCP). Also the toxicity of the superplasticizers is investigated and the conclusion is that the low amount of leakage of superplasticizers from concrete leads to a low risk for the environment and for humans.
DEFF Research Database (Denmark)
Keller, Hanne Dauer
2015-01-01
Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....
DEFF Research Database (Denmark)
Keller, Hanne Dauer
2015-01-01
Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb.......Kapitlet handler om stress som følelse, og det trækker primært på de få kvalitative undersøgelser, der er lavet af stressforløb....
Research advance in safety analysis methods for high concrete dam
Institute of Scientific and Technical Information of China (English)
REN; QingWen; XU; LanYu; WAN; YunHui
2007-01-01
High tensile stresses occurred in high concrete dams and in their foundation lead to the growing importance of their safety with the increase of concrete dam height.Without any exiting specification or successful experiences of concrete dams up to 300 m at home and abroad for reference,experts feel obliged to figure out how to perform safety analysis on high concrete dam.This paper involves the main contents and mechanical features of the safety analysis on high concrete dam and shows the current state and progress of the analysis methods.For the insufficiency and problems existing in normative methods,study on modern numerical method such as finite element method must be strengthened to find out the stress control criterion which is in accordance with the methods.Two aspects of the safety analysis of high dam--local damage from material level and integral destruction from structure level--should be considered.For the local damage,we should consider the non-homogeneity of material and strengthen the research of meso-damage mechanics.While for integral destruction of the system of high dam and its foundation,a study on non-strength theory should receive enough concerns.Further,attention should be paid to the research on the failure modes and criterions of high concrete dam failure analysis and safety evaluation,and the effect of uncertainty and classification of safety should be considered too.
Importance of dowels in transversal joints in concrete pavements
Grosek, Jiri; Chupik, Vladimir; Stryk, Josef; Brezina, Ilja
2017-09-01
Concrete pavements are designed for heavy loaded road structures. Their usage brings a number of specific issues. It is necessary to solve them all to ensure that concrete pavements will fulfil their function along the whole design period. One of these issues concerns dowels, which are located in transversal joints. Modelling of load, caused by heavy vehicles, with the use of the finite element method, provides valuable information about the stress condition of concrete pavement. The results of modelling can be verified by measurements or experiments in practice. Dowels and tie bars in jointed unreinforced concrete pavements and the importance of their correct placement, dimensions and material quality on pavement behaviour and lifespan were studied as a part of R&D projects of Technology Agency of the Czech Republic Nos. TA02031195 and TE01020168. The paper presents the experience from the modelling and performed experiments and makes conclusions which are important for the use in practice.
Lattice Modeling of Early-Age Behavior of Structural Concrete
Pan, Yaming; Prado, Armando; Porras, Rocío; Hafez, Omar M.; Bolander, John E.
2017-01-01
The susceptibility of structural concrete to early-age cracking depends on material composition, methods of processing, structural boundary conditions, and a variety of environmental factors. Computational modeling offers a means for identifying primary factors and strategies for reducing cracking potential. Herein, lattice models are shown to be adept at simulating the thermal-hygral-mechanical phenomena that influence early-age cracking. In particular, this paper presents a lattice-based approach that utilizes a model of cementitious materials hydration to control the development of concrete properties, including stiffness, strength, and creep resistance. The approach is validated and used to simulate early-age cracking in concrete bridge decks. Structural configuration plays a key role in determining the magnitude and distribution of stresses caused by volume instabilities of the concrete material. Under restrained conditions, both thermal and hygral effects are found to be primary contributors to cracking potential. PMID:28772590