Effect of Soil-Structure Interaction on the Torsional Behavior of L-Shaped RC Buildings under Bi-Directional Ground Motions

Abstract

This study investigates the seismic torsional response of a nine-story L-shaped reinforced concrete (RC) building, with particular emphasis on the effects of soil-structure interaction (SSI). Using three-dimensional nonlinear dynamic analyses in SAP2000, the building’s performance was evaluated under 30 pairs of scaled bidirectional ground motion records. SSI effects were modeled using the substructure method, with soil properties corresponding to ZC soil class as defined by the Turkish Seismic Code (TBEC-2018). Torsional behavior coefficients (ηbi) were computed from the displacement differentials obtained, and fragility curves were developed using ηbi as the engineering demand parameter. The results showed that SSI increased the fundamental periods by approximately 8% and torsional irregularity by up to 30% compared to fixed-base conditions. Fragility analysis indicated that the probability of exceeding the critical ηbi value of 1.2 was approximately 10% under fixed-base conditions and about 40% when SSI was considered. These findings highlight the significant impact of SSI on the torsional response of irregular structures and emphasize the importance of accounting for SSI effects in the seismic design and performance assessment of RC buildings.

Keywords

• Torsional irregularity
• Soil-structure interaction
• Nonlinear dynamic analysis
• Fragility curve
• L-shaped building

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