Assessing seismic fragility on direct displacement-based designed RC frame considering SSI effect

The study delves into direct displacement-based design (DDBD), an approach rooted in performance-based design, operating within predetermined response limits. The approach’s positive influence on diverse structural typologies is evident, emphasising the soil beneath reinforced concrete (RC) frame structures, particularly those designed using DDBD. The present research scrutinises the performance of a 15-storey RC frame building, considering the intricate interplay of soil-structure interaction (SSI). Employing a fiber modelling approach for frame elements and adopting a pile-raft foundation model, incorporating soil stiffness and nonlinearity through soil springs, the RC frame is meticulously designed to meet rigorous life safety performance criteria under DDBD principles. Various ground motions of varying intensities are applied to the RC frame to conduct incremental dynamic analysis (IDA), offering a comprehensive assessment of nonlinear structural behaviour in terms of displacements and inter-storey drift ratios. Ground motions are judiciously selected and scaled following the comprehensive calculative procedure outlined in FEMA P695 (Quantification of building seismic performance factors, FEMA P695. Prepared by Applied Technology Council For the Federal Emergency Management Agency, Washington, 2009). The resulting responses are leveraged to predict collapse probabilities, employing diverse approaches in the construction of seismic fragility curves. The research significantly contributes to the advancement of seismic design methodologies, ensuring structures adhere to robust resilience standards against seismic hazards. The RC frame design incorporating SSI demonstrates an 11.25% reduction in the inter-storey drift ratio and a lower probability of collapse at higher intensities compared to a fixed-based RC frame, indicating improved structural flexibility.