Análisis de la capacidad de soporte sísmica de fundaciones superficiales apoyadas en suelos granulares :|bcomparativa entre formulaciones basadas en métodos de equilibrio y análsis límite y la práctica tradicional chilena
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2016
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es
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Universidad Andrés Bello (Chile)
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Licencia CC
Resumen
En el contexto de la práctica ingenieril, el problema de la capacidad de soporte
sísmica de fundaciones superficiales generalmente ha sido resuelto de modo
indirecto, ya sea por medio de un incremento en las tensiones admisibles
estáticas del suelo o bien utilizando un enfoque pseudoestático equivalente. Sin
embargo, durante las últimas décadas se han desarrollado una serie de
métodos analíticos que abordan el problema directamente desde el punto de
vista sísmico. Estos métodos han seguido dos líneas teóricas fundamentales: (i)
el Método de Equilibrio Límite (MEL), y (ii) la Teoría de Análisis Límite (TAL).
Mientras que el MEL es una herramienta aproximada comúnmente utilizada en
ingeniería geotécnica, la TAL entrega una aproximación más rigurosa a la
solución del problema; aun cuando su uso es comparativamente más complejo.
El desarrollo de modelos teóricos para estimar la capacidad de soporte sísmica
de fundaciones superficiales ha permitido obtener una serie soluciones de
referencia, y con ello establecer puntos de comparación entre las diferentes
teorías existentes. Sin embargo, este tipo de herramientas no han sido
completamente integradas en el ejercicio profesional estándar de los ingenieros
geotécnicos; en parte porque su desarrollo es relativamente incipiente, y
también debido a la costumbre que existe respecto del uso de las ecuaciones
tradicionales de capacidad de soporte derivadas para el caso estático.
En Chile, las normas de diseño sísmico no indican de forma explícita cómo
realizar el cálculo de la capacidad de soporte de fundaciones. Ante la ausencia
de disposiciones normativas específicas, la “práctica tradicional chilena” para el
diseño de fundaciones superficiales ante cargas sísmicas ha consistido en
permitir un incremento de un 33% en las tensiones de contacto admisibles del
suelo obtenidas para el caso estático. Si bien esta forma de abordar el
problema ha entregado resultados generales satisfactorios durante sismos
pasados, la disponibilidad de nuevos modelos analíticos para el cálculo de la
capacidad de carga sísmica pone de manifiesto la necesidad de establecer una
IV
medida de la confiabilidad asociada a su uso y evaluar posibles mejoras a los
procedimientos de diseño utilizados en la práctica.
Este trabajo presenta un análisis comparativo de tipo paramétrico entre
diferentes métodos existentes para la estimación de la capacidad de soporte
sísmica de fundaciones superficiales, desarrollados en el contexto del MEL y la
TAL. Se evalúan distintas razones de empotramiento, parámetros de resistencia
del suelo y coeficientes de aceleración pseudoestática horizontal. Los
resultados obtenidos muestran que existe un importante deterioro de la
capacidad de soporte de la fundación en la medida que la aceleración máxima
del sismo aumenta, lo cual refrenda la necesidad de revisar la pertinencia de la
denominada “práctica tradicional chilena” para el diseño de fundaciones
superficiales ante cargas sísmicas.
In the context of engineering practice, the problem of the seismic bearing capacity of shallow foundations have been solved indirectly, either due to an increase of the static allowable soil pressures or by adopting an equivalent pseudo-static approach. However, during last decades, a series of analytical methods that directly address the problem from the seismic point of view has been developed. These methods have followed two main theoretical lines: (i) the Limit-Equilibrium Method (LEM), and (ii) the Limit-Analysis Theory (LAT). While the LEM is an approximate tool commonly used in geotechnical engineering, the LAT give a more rigorous approach; although it use is comparatively more complex. The development of theoretical models for estimating the seismic bearing capacity of shallow foundations has made possible to obtain a series of reference solutions, and in consequence, establishing points of comparison between existing theories. Nevertheless, this type of tools has not been completely integrated into professional practice of geotechnical engineers; on one hand, because their development is relatively incipient and, on the other hand, due to the costume that exists regarding the use of traditional bearing capacity equations derived for static loading. In Chile, the standards for seismic design of structures does not indicate in an explicit way how to estimate the bearing capacity of foundations. Given this lack of specific standard provisions, the “Chilean traditional practice” for seismic design of shallow foundations have consisted in allowing an increase of 33% in static allowable soil pressures. Although this practice have given satisfactory general results in past earthquakes, the availability of new analytical methods for estimating the seismic bearing capacity of shallow foundations highlights the need to obtain a measure of the reliability associated with their use and evaluating possible improvements for the design procedures used in practice. VI This work presents a parametric comparative analysis between different existing methods for the estimation of the seismic bearing capacity of shallow foundations, developed in the context of LEM and LAT. Different embedment ratios, soil resistance parameters, and horizontal pseudo-static acceleration coefficients are considered. The results obtained show an important decrease of the bearing foundation capacity with increasing of the maximum earthquake acceleration, which suggest that the pertinence of the so-called “Chilean traditional practice” for design of shallow foundations under seismic loading has to be revised.
In the context of engineering practice, the problem of the seismic bearing capacity of shallow foundations have been solved indirectly, either due to an increase of the static allowable soil pressures or by adopting an equivalent pseudo-static approach. However, during last decades, a series of analytical methods that directly address the problem from the seismic point of view has been developed. These methods have followed two main theoretical lines: (i) the Limit-Equilibrium Method (LEM), and (ii) the Limit-Analysis Theory (LAT). While the LEM is an approximate tool commonly used in geotechnical engineering, the LAT give a more rigorous approach; although it use is comparatively more complex. The development of theoretical models for estimating the seismic bearing capacity of shallow foundations has made possible to obtain a series of reference solutions, and in consequence, establishing points of comparison between existing theories. Nevertheless, this type of tools has not been completely integrated into professional practice of geotechnical engineers; on one hand, because their development is relatively incipient and, on the other hand, due to the costume that exists regarding the use of traditional bearing capacity equations derived for static loading. In Chile, the standards for seismic design of structures does not indicate in an explicit way how to estimate the bearing capacity of foundations. Given this lack of specific standard provisions, the “Chilean traditional practice” for seismic design of shallow foundations have consisted in allowing an increase of 33% in static allowable soil pressures. Although this practice have given satisfactory general results in past earthquakes, the availability of new analytical methods for estimating the seismic bearing capacity of shallow foundations highlights the need to obtain a measure of the reliability associated with their use and evaluating possible improvements for the design procedures used in practice. VI This work presents a parametric comparative analysis between different existing methods for the estimation of the seismic bearing capacity of shallow foundations, developed in the context of LEM and LAT. Different embedment ratios, soil resistance parameters, and horizontal pseudo-static acceleration coefficients are considered. The results obtained show an important decrease of the bearing foundation capacity with increasing of the maximum earthquake acceleration, which suggest that the pertinence of the so-called “Chilean traditional practice” for design of shallow foundations under seismic loading has to be revised.
Notas
Tesis (Ingeniero Civil)
Palabras clave
Diseño Antisísmico, Suelos Arcillosos