Sample records for displacements seismic
from WorldWideScience.org

Sample records 1 - 5 shown.



1

Investigación de respuestas sísmicas críticas incorporando la torsión accidental/ Investigation of critical seismic responses including accidental torsion

Hernández, Julio J; López, Oscar A
2007-11-01

Resumen en español Se presenta una investigación de las respuestas sísmicas críticas, es decir las más desfavorables, que se presentan en los sistemas estructurales cuando se incluyen las acciones que conducen a la torsión accidental: componente sísmica rotacional y variaciones de las excentricidades entre los centros de masa y de rigidez, considerando diversas propiedades del sistema estructural. Se estudian sistemas de un piso en el rango elástico de respuesta, sujetos a la acción (mas) de un espectro rotacional y espectros traslacionales principales en dos direcciones horizontales, considerando las respuestas máximas ante la variación del ángulo de incidencia. Se consideran excentricidades nominales y accidentales según las dos direcciones principales de la planta. El trabajo atiende a los desplazamientos máximos en los extremos de la planta, los cuales sobrellevan las mayores solicitaciones sísmicas, identificando los casos críticos. Los efectos accidentales estudiados cubren la respuesta a sismos moderados y son una referencia de la respuesta posible a sismos severos y de la respuesta de edificios de varios pisos, indicando situaciones peligrosas posibles. En función de los resultados obtenidos, se revisa la relativa precisión de las prescripciones torsionales contenidas en las normas sísmicas de Venezuela, México y Estados Unidos, así como del procedimiento de De La Llera y Chopra Resumen en inglés This paper presents a research of the critical, i.e. the more unfavorable, seismic responses of structural systems when actions leading to accidental torsion are included: rotational seismic component and variation of the eccentricities between the stiffness and mass centers, considering several structural system properties. Elastic one-story systems are studied, subjected to rotational spectrum and principal translational spectra along two horizontal directions, consider (mas) ing the maximum responses due to the variation of the incident angle. Nominal and accidental eccentricities along the two plan directions are included. This work looks at the peak displacements at plan edges, which withstand the larger seismic forces, identifying the critical cases. The studied accidental effects cover the response to moderate seismic motions, and are a reference of the possible response to severe seismic motions and of the response of multi-storey buildings, pointing out possible hazardous situations. The obtained results allow an evaluation of the relative accuracy of several torsional specifications incorporated in the seismic codes of Venezuela, Mexico and USA, as well as that of De La Llera and Chopra procedure

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2

Experimental behaviour of RC interior wide beam-column joint subject seismic actions and axial load/ Comportamiento experimental de uniones interiores viga plana-columna de concreto armado bajo acciones sísmicas y carga axial

Hurtado-Alvarado, Marcial; Picón-Rodríguez, Ricardo
2009-04-01

Resumen en español Este trabajo presenta un modelo experimental que muestra la influencia de la carga axial en las juntas interiores viga plana-columna de concreto armado sometida a desplazamientos laterales simulando su comportamiento ante un sismo. Existe una parte numérica donde se simula el ensayo experimental usando el Modelo de Daño con Deslizamiento en las Juntas viga plana-columna. Los resultados numéricos y experimentales son muy parecidos. Los ensayos experimentales se realizar (mas) on sin carga axial de compresión en la columna y con carga axial aplicando el método de post-tensado para incorporar y mantener la carga axial en la columna de la junta. Los fenómenos analizados de los resultados experimentales son el estrangulamiento en las curvas de comportamiento histerético, la disipación de energía y la comparación entre las curvas de comportamiento experimentales y las simulaciones numéricas. Como resultado se reportan el aumento de resistencia al desplazamiento lateral de la probeta con carga axial aplicada, la mayor energía disipada de la probeta sin carga axial aplicada. Los niveles de daño obtenidos en la simulación con carga axial de compresión en la columna de la junta son mayores que sin carga axial, estando estos resultados numéricos acordes a los experimentales. Resumen en inglés This paper presents experimental tests that show the influence of axial load of the RC wide beam-column interior joint subjected to lateral displacements. A numerical part where the numerical results of the experimental tests is included. A damage model with slip in the wide beam-column joints is used. The numerical results and experimental tests were similar. Experimental tests with and without axial load application were performed. The axial load on the interior joint c (mas) olumn was applied using the post-tension technique. The pinching phenomenon and energy dissipation from experimental curves were analyzed. The lateral stress increased with the compression axial load application on the joint column is reported. The energy dissipation increases when the axial load on the column of interior joint decrease. The damage levels of the simulations in the wide beam-column joints increased with low axial load on the column. The numerical results are accord with experimental tests.

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3

Paleo and historical seismicity in Mallorca (Baleares, Spain): a preliminary approach

Goy, José Luis; Zazo, Caridad; Silva, P. G.; Carrasco, P.; González-Hernández, F. M.
2001-01-01

Digital.CSIC (Spain)

4

Estructuras de deformación (¿sismitas?) en la Formación Río Negro, provincia de Río Negro, Argentina

Schillizzi, Roberto; Luna, Liliana; Falco, Juan Ignacio
2010-07-01

Resumen en español A Las estructuras de deformación (ED) en sedimentos blandos comprenden las alteraciones que se producen casi simultáneamente con la sedimentación. Estos procesos se hallan en relación directa con las características internas de los materiales sedimentarios y de los factores externos que actúan sobre ellos. Sus resultados incluyen deformaciones como inyecciones, fracturas, volcanes y laminaciones convolutas que afectan total o parcialmente la estratificación. Los se (mas) dimentos blandos deformados por sismos se incluyen bajo la denominación general de sismitas (seismites). Como objetivo de esta investigación se plantea reconocer, por primera vez, estructuras de deformación ubicadas en la Formación Río Negro presentes en el sector norte del Golfo San Matías, en inmediaciones del Faro Río Negro. La metodología empleada consistió en el reconocimiento y descripción de las estructuras, para lo cual se extrajeron muestras para determinar granulometría, mineralogía y contenido de materia orgánica. Se fotografiaron los distintos sectores con deformaciones con el fin de establecer modelos comparativos. El sector estudiado, de 4 km de extensión, se ubica entre el faro de Río Negro y el inicio del Banco Verde y morfológicamente corresponde a un frente acantilado con orientación ENE-OSO. En él se determinaron las siguientes ED: a- de carga simple, pseudonódulos contiguos y aislados, y estructuras complejas; b- de escape de fluidos y c- estructuras de deslizamiento basal y por presión dirigida. El origen de las deformaciones se debe a las características de las sedimentitas y a los procesos que las afectan tales como los efectos por carga, escapes de fluidos y las presiones dirigidas. Como origen de estos procesos se señalan: la presión de la columna litológica, las olas de tormentas y los terremotos. Por los rasgos hallados las deformaciones del litoral rionegrino tendrían un origen sísmico, proceso ocurrido en un único evento durante el ciclo Andino cuyos inicios se fijan hace aproximadamente 45 Ma. Por otra parte sus techos y bases no se hallan asociados a otros procesos de deformación y sus espesores no exceden el metro de potencia. Además se hallan acotadas a la zona de transición entre los miembros medio y superior de la Formación Río Negro descansando en algunos casos sobre arcilitas y en otros sobre limolitas, originadas en un paleorelieve de interdunas. Resumen en inglés Soft-sediment deformation structures (SSD) are alterations produced almost simultaneously with sedimentation. They are directly related to internal characteristics of sedimentary materials as well as to external factors acting on them. Results derived from such alterations are evidenced as injections, fractures, volcanoes and convolute laminations, among other forms, affecting stratification either totally or partially. Soft-sediment deformation structures resulting from (mas) seisms are known as seismites. The present study aims at determining for the first time the presence of SSD structures in the Río Negro Formation, located in the northern area of San Matías Gulf, near Río Negro Lighthouse, Argentina (Fig. 1). To this end, structures were firstly identified and further described. Samples were subsequently collected for the determination of grain-size, mineralogy and organic matter content. Photographs of the different sectors evidencing deformations were taken in order to determine further comparative models. Morphology in the study area is associated to cliffs with vertical, fractured fronts and with an average height of 70 m in whose base torn-down blocks are accumulated. The geological structure of the study area is related to the Cuenca del Colorado and the Comarca Nordpatagónica, whose basement is mainly composed of Paleozoic and Mesozoic crystalline rocks. The sedimentary tertiary cover from the Miocene-Pliocene is represented by light-blue sandstones of the Río Negro Formation (Andreis, 1965). This unit was formed in an aeolian environment with intercalations of clay-silt shallow lagoons and a marine episode located in the mid area of the Río Negro Formation. At the top of the Río Negro Formation there are Pleistocene-Holocene sedimentites having a thickness of up to 5 m. Within the local structural framework of our study area there are fractures with a NE-SW and a NW-SE direction, which are related with fractures N55º, N90º and N350º azimuth located in the abrasion platform. According to Dzulinsky and Walton (1965), Lowe (1975), Brencley and Newall (1977), Clauss (1993), van Loon (2002), Owen (2003), Neuwerth et al. (2006), Alfaro et al. (2006), Montenat et al. (2007), among others (Table 1), and, taking into account the geometry of deformations, laboratory reconstructions and field observations from our study area, it can be concluded that the classifications of SSD structures tend to establish morphologic and genetic systematizations. The following characteristics were identified in our study area: limited deformations among stratigraphic horizons; a lateral continuity of SSD structures at considerable distances; and a confinement between non-deformed strata and its lithological association with psamitic-pelitic sediments. The study area, which is 4 km long and is located between Río Negro Lighthouse and the beginning of Banco Verde, is from the morphological point of view, a cliffed front with an ENE-WSW orientation. Different types of SSD structures were identified in this area. For example, from the morphological point of view and according to the loading mechanisms observed, simple-load structures (Fig. 2), attached and detached pseudonodules (Figs. 3, 4 and 5) and complex structures (Fig. 6) were identified. Furthermore, from the genetic point of view and according to the intrusion processes observed in soft sediments, water-scape structures (Fig. 7) and plate- or fountain-like deformations (Fig. 8) were found. From the genetic point of view, and based on the collapse and pressure mechanisms observed, basal slumping (Fig. 9) and directed-pressure structures (Fig. 11) were also found. The above-mentioned SSD structures were analyzed and interpreted following Strachan´s model (2002) (Fig. 10) and Laird´s model (1968) (Fig. 12). The origin of SSD structures depends on the characteristics of sedimentites and on the mechanisms that produce them. In the study area, the materials susceptible to deformation come from an interdune environment that is characterized by granulometric variations derived from the fluctuating and restrictive climatic conditions (Cojan and Thiry, 1992) that typify the Río Negro Formation. Fine-grained materials having low cohesion and poor sorting such as the sediments of deformed strata (Fig. 13) produced SSD structures as a result of high pore pressure and liquefaction effects (Tsuchida and Hayashi, 1971; Obermeier, 1996). Grain packing with a porous value as that allows intercommunication among grains and saturated material, is also crucial to the formation of SSD structures. The mineralogic content of deformed levels is composed of i) quartz, chalcedony, orthose, plagioclase, pyroxenes and biotite, opaques (magnetite and ilmenite, autigenic pyrite) in crystalline aggregates; ii) undetermined Fe oxides; and iii) colorless and light-brown unaltered volcanic glass shards, clays identified as smectite-illite interstratified and scarce kaolinite. Grains are mainly subangular and, to a lesser extent, sub-round and round. The surface of the majority of grains in the study area was found clean and with some marks. The percentage of CaCO3 was found to vary from 0.5 to 3% and that of total organic carbon (TOC) was found to reach 1.5%. Deformations may be produced as a result of load deformation mechanisms, fluid escape, basal slumping or pressure-directed displacements. Due to load deformation mechanisms, structures are linked to gravity-related movements occurring during the initial stages of deposition. For these deformations to occur, grain-size at the overlaying levels should be thicker than at the underlying levels, for example, sandstones rather than silstones or claystones. These deformations are related to water saturation at the deformed level (fluidization-liquefaction). Therefore, deformation mechanisms, which involve both expulsion and rotation of fragments as well as fluid escape, are characterized by the action of lithostatic pressure which produces movement (deformation) and by the action of the underlying sedimentary levels. Deformations may also result from a fluid escape mechanism, i.e., from a mechanism associated to i) the spatial arrangement of grains (packing), ii) their shape, iii) their tendency to inequigranularity, and iv) the communication among macro- and micro- pores as well as the high or low sinuosity connection among themselves (Net and Limarino, 2000). Further requirements for deformations to occur include particular thixotrophic conditions, especially the presence of colloids among grains. The rupture of unions of particles either by hitting or by shearing is, among others, a cause which produces an unbalance between hydrostatic pressure and lithostatic pressure. If the latter is altered, the energetic unbalance makes fine sediments flow among the weakly lithified sandstones whose extrusion will occur via both vertical and horizontal pore ducts (Lopez Gamundi, 1986; Clauss, 1993). Basal slumping produces deformations that are associated not only to soft sediments deposited in natural slopes but also to interbedded sand- and mud-levels. Layers tend to have a prismatic-shaped geometry whose materials are under ductile-to-fragile conditions, in which antique layers support younger ones. Once horizontality is affected, movement, which is marked by a rupture of the original slope, begins. The lower levels are expected to transport the upper ones without affecting the original succession of layers. At the delay of movement derived from the compressive effect of the displacement front, fluids extrude forming cones or cut dikes (Fig. 10). Several deformations of this type initiate movement as result of differences in the hydrostatic gradient (Strachan, 2002). Deformations may be also produced as a result of pressure-directed displacements which are conditioned by the compaction level, thickness and ability of materials to deform. Thus, deformations occur because the original level is saturated in water as a result of the ductile behavior of materials (Bracco et al., 2005). Laird (1968) claims that SSD structures should meet some of the following requirements to be considered of seismic origin: slightly curved strata walls and floors to follow the original stratification and interruption of continuity of the stratum that is marked by a scar in which the sedimentary fillings keep their characteristics both above and below stratification. There could be rotated sediment clasts below the discontinuity as a result of a thrust-induced drag of the upper sedimentary packing. These processes could be, in turn, triggered either by the charge or pressure of the lithologic column, storm waves and seismicity. Storm-wave impact may also produce deformation in soft sediments. Nonetheless, no high energy structures such as cross-beddings or tsunami-type chaotic sedimentation were observed in our study area. Noteworthingly, for stormwave-derived liquefaction to occur, waves should reach magnitudes higher than 6 m (Alfaro et al., 2002), this being a phenomenon that was not recorded in our study area. Taken together, findings from the present study indicate that SSD structures in our study area are seismic alterations that occurred in an event during the Andean cycle whose beginnings are traced approximately 45 My ago. The fact that i) both the roofs and bottoms of these structures are not associated to other processes of deformation, ii) their thickness does not exceed one meter, and iii) they are confined to a transitional area between the middle and top members of the Río Negro Formation, lying in some cases on claystones and in some other cases, on siltstones, originated in an interdune paleorelief, confirms their seismic origin.

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5

Deficiencias, limitaciones, ventajas y desventajas de las metodologías de análisis sísmico no lineal

Mora, Mauricio Alexander; Villalba, Jesús Daniel; Maldonado, Esperanza
2006-07-01

Resumen en español El presente trabajo está dirigido a la comparación de las metodologías de análisis sísmico: dinámico cronológico no lineal, pushover tradicional, y dos procedimientos modales. La comparación se realizó a partir del estudio de un edificio de mediana altura, aporticado, de concreto reforzado, representativo de las edificaciones típicamente construidas en Bucaramanga. La estructura fue sometida a uno de los sismos definidos por el estudio de microzonificación de l (mas) a ciudad, escalado a diferentes valores de aceleración pico efectiva. Los resultados obtenidos fueron comparados en términos de desplazamientos y derivas, con lo cual se pudieron detectar algunas deficiencias, limitaciones, ventajas y desventajas de las metodologías utilizadas, concluyendo que las metodologías modales son una buena aproximación para la determinación del comportamiento sísmico de estructuras de concreto reforzado. Resumen en inglés This research presents the comparison of different non linear analysis methodologies: the non linear response history analysis, the traditional pushover methodology, and two modal pushover methodologies. A medium rise reinforced concrete building, with moment resisting space frame, representative of the typical buildings in Bucaramanga, is examined using one of the earthquakes in the microzonation study of the city, which was scaled to different values of effective peak a (mas) cceleration. The comparison of the results (floor displacements and interstory drifts) permitted to find deficiencies, limitations, advantages and disadvantages of the methodologies used. It was found that Modal Methodologies are a good approach to assess the seismic performance of reinforced concrete buildings

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