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September 10, 2025Open Access

Soil-Structure Interaction in Nonlinear Pushover Analysis of RC Buildings

Key Points

Flexible soil conditions led to a drastic reduction in base shear, decreasing by over 80% in soft soil compared to fixed base conditions.
Roof displacements increased significantly under flexible soil, impacting the structural response of the RC building.
Nonlinear pushover analysis was performed using SAP2000 to evaluate the performance based on varying soil conditions.
Neglecting soil-structure interaction may lead to overestimation of seismic capacity, emphasizing the need for accurate modeling.

Abstract

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

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