THE EFFECT OF SOIL-STRUCTURE INTERACTION ON NON-LINEAR STRUCTURAL ANALYSIS

Abstract

Soil–structure interaction (SSI) plays a crucial role in influencing the seismic response of buildings, particularly those supported by deep foundations on soft soil deposits. Although previous studies have reported that SSI may reduce seismic forces while increasing structural deformation, comparative evaluations considering different building heights under identical soil conditions remain limited. This study investigates the influence of SSI on 5-story and 10-story buildings, comparing mid- and high-rise buildings with significant differences in structural periods, reinforced concrete moment-resisting frame structures using response spectrum and nonlinear pushover analyses. The pile foundation is modeled using distributed spring elements along the pile depth to represent soil stiffness. The results indicate that incorporating SSI increases the natural period of the structures and reduces the seismic base shear by 10% for the 5-story model and 9% for the 10-story model. However, displacement increases by 40% and 26%, while inter-story drift rises by 32% and 38% for the 5-story and 10-story structures, respectively. Nonlinear analysis further shows reduced plastic hinge formation and improved structural performance index under SSI conditions. These findings highlight the importance of incorporating SSI into seismic design, where drift increases even as base shear decreases. This makes performance-based structural assessment even more realistic.