Nonlinear Soil-Structure Interaction Effects on Building Frames: A Discussion on the Seismic Codes

Recent seismic codes include design requirements in order to take soil-structure interaction (SSI) into account for realistic modelling of structures. The paper investigates the performance of multi-story building-foundation systems through a Winkler-based approach. A set of 4-, 8-, 12- and 16-story steel moment resisting frame buildings on three soil types with shear wave velocities less than 600m/s subjected to actual earthquake records with a probability of exceedance of 10% in 50 years are modeled with and without SSI. It is observed that the performance level of frames supported by flexible foundation, particularly at soft soil sites, may alter significantly in comparison to fixed-base structures. Moreover, the nonlinear foundation is found to have a significant effect on the force and displacement demands. A comparison and brief discussion on the design guidelines for consideration of flexible foundation behavior is also included.