Soil-Structure Interaction in Nonlinear Pushover Analysis of RC Buildings

The seismic performance of reinforced concrete (RC) buildings is significantly influenced by soil–structure interaction (SSI). Traditional pushover analysis, based on FEMA 356 and ATC-40, assumes a fixed base and neglects foundation flexibility, potentially leading to unsafe designs. This study presents a nonlinear pushover analysis incorporating SSI for a four-storey RC frame using SAP2000. Different soil conditions—soft, medium, and hard—were modeled using equivalent spring stiffness. Performance was evaluated in terms of base shear, roof displacement, hinge formation, and performance points. Results indicate that flexible soil drastically reduces base shear (by over 80% in soft soil compared to fixed base) and increases displacements, significantly altering hinge formation patterns. The study concludes that neglecting SSI may result in overestimation of seismic capacity. Recommendations for future work include torsional analysis, higher-mode effects, and experimental validation