Numerical Investigation of Soil Plasticity Effects on the Seismic Response of RC Moment Resisting Frames

Abstract Soil-Structure Interaction (SSI) represents an interdisciplinary issue characterized by complex material and geometrical nonlinearities affecting mutually the supporting soil and the superstructure of the system during a seismic event that can compromise serviceability. In this study the following objectives are developed: i) to evaluate the effects of the inelastic supporting soil behavior on the interaction of soil-structure systems; ii) to investigate the changes in the dynamic behavior of archetype low and mid-rise moment resisting building frames when inelastic soil deformation develops. To reach these goals, numerical models of linear-elastic and nonlinear-inelastic underlain soil of buildings on shallow foundations are subjected to earthquake time histories with different frequency content. By employing the finite difference software FLAC2D, the direct method which is capable to tackle SSI issues is used to accounting for soil nonlinearities. A succession of parametric analyses is performed. The slenderness of the superstructure as well as the frequency content of input excitations are important parameters. Nonlinear analyses show a significant increase in deformability and damping of the soil-structure system, implying a consequent reduction of the seismic forces on the structure. As a result, the base shear values dropped by approximately 57.56%, 44.46%, and 69% in the 3, 6, and 9-story frames, respectively.