Seismic assessment of irregular RC frames with tall ground story incorporating nonlinear soil-structure interaction

This paper is dedicated to evaluate the nonlinear Soil-Structure Interaction (SSI) impact on the earthquake-based response of vertically irregular reinforced concrete (RC) moment resisting frames. The main contribution of this paper is to evaluate the seismic performance of RC structures with 5 and 10 stories considering a number of key parameters including irregularity ratio, soil type and the vertical safety factor (FSv) of the foundation. In this regard, the beam on nonlinear Winkler foundation (BNWF) scheme is used for the modeling of shallow foundations resting on a semi-infinite sandy medium. Vertical irregularity is considered by using a tall ground story in the RC frames. The models are subjected to 15 earthquake ground motions for conducting nonlinear dynamic time-history analyses to capture the seismic demands of soil-structure systems. The results demonstrate that considering SSI influence reduces the seismic demands in the lower stories, which is more evident in the case of soft soils (site class E). Moreover, a rational relationship between the maximum inter-story drifts and the response of the foundations is observed. It is also concluded that for both regular and irregular structures, lower values of the FSv lead to a considerable decrease in the structural demands (story drifts) and an impressive growth in transient and residual foundation settlements.