Influence of nonlinear SSI on the seismic response of low-to-mid-rise steel moment resisting frame buildings

The nonlinear behavior of a soil–foundation interface due to mobilization of the ultimate capacity and the consequent energy dissipation may be utilized to alter seismic demands of a structure. However, current design practice does not account for the nonlinear behavior of soil–foundation interface primarily due to the absence of reliable nonlinear soil–structure interaction (SSI) modeling techniques. The objective of this study is to simulate the performance of multi-story building-foundation systems through a Winkler-based approach. Opensees finite element framework is employed for simulation. Four typical 4, 8, 12 and 16-story steel moment resisting frame (MRF) buildings on three hypothetically soft, medium and hard soil sites with shear wave velocities less than 600m/s subjected to actual ground motion records of varied hazard levels are modeled with and without SSI. It is observed that the performance level of models supported by flexible foundation, particularly in an intense earthquake event, may alter significantly in comparison to fixed-base structures. Moreover, for MRFs on soft soil, the nonlinear foundation is found to have a significant effect on the force and displacement demands. This is indicating the necessity for consideration of flexible foundation behavior in the modern design codes in order to accomplish an economic yet safe structural design.