Three‐Dimensional Nonlinear Dynamic Analysis of Soil–Pile–Structure Interaction in Clay: Insights Into the Role of Mode Shapes on Seismic Response

ABSTRACT Both kinematic and inertial interactions of piles under seismic loading play important roles in the various aspects of seismic responses in soil‐pile‐structure systems. In this paper, the seismic responses of the soil–pile–structure system were investigated through a set of nonlinear three‐dimensional numerical analyses in the time domain simulating soil nonlinear hysteresis behavior under cyclic loading. The lateral displacements of the superstructure, along with the bending moment and lateral displacement of the pile, have been investigated to determine the effect of different parameters on the seismic responses of the soil–pile–structure systems. The results of this study showed that it is necessary to examine the soil–structure oscillation shape and clarify the effect of inertial forces on the soil–pile–structure systems' seismic responses, considering the motion direction of both the superstructure and soil domain. In addition, it was concluded that the piled raft lateral stiffness affects the lateral displacement of the superstructure, which impacts the response of soil–pile–structure systems. Moreover, it was found that the inertial interaction does not necessarily increase by increasing the number of stories. Furthermore, it was specified that more amplification in the seismic responses of a system with a shorter superstructure (a smaller number of stories) causes more devastating responses, which shows the importance of the loading frequency. Additionally, it was concluded that the effect of soil properties on the pile response at the mid‐range loading frequency (2 Hz) is more than the effect of soil properties on the pile response at the high‐range loading frequency (5 Hz).