The Effects of Nonlinear Behavior of Soil and Foundation Uplift on Seismic Response of Inelastic SDOF Structures

In this research the simultaneously effects of foundation uplift and nolinear behavior of soil were investigated. Previous studies have showed that the effects of soil-structure interaction on seismic performance can be described through introducing a limited number of nondimensional parameters. In most studies it was assumed that the foundation is bonded to the soil and the behavior of the soil is considered to be linear or equivalent linear. In study it is showed that this concept can be extended to the nonlinear soil-structure systems by introducing number of new nondimensional parameters. The main goal of this investigation is to study the variations of nonlinear displacement and ductility of nonlinear soil-structure systems. To achieve this goal, the structure was considered as an nonlinear single degree of freedom with concentrated mass which mounted on rigid foundation rested on distributed dampers and springs. Then the variations of the response of nonlinear soil-structure systems are assessed by conducting nonlinear time history analyses for a wide range of nondimensional parameters. It was shown that the total displacement of soil-structure systems increases because of nonlinear soil behavior but the ductility of the structure as a part of soil-structure system decreases in comparison to the systems with linear soil behavior. So in this study, it was proposed to decrease the safety factor for the design of foundation. Since the permanent settlement of foundation is an important index in performance of soil-structure systems therefore it was calculated for some applicable systems and it is shown that although the permanent settlement of the foundation increases by decreasing safety factor of foundation but the value of permanent settlement is acceptable for ordinary systems.