Effect of soil flexibility on seismic response of setback RC buildings considering raft foundation

Buildings with an irregular distribution of mass, stiffness, and strength throughout their height may have dramatically different seismic performance than regular buildings. Vertically uneven buildings are commonly constructed around the world for both functional and aesthetic reasons. The seismic response of multi-story constructions is influenced by soil-structure interaction (SSI). For multi-story buildings subjected to earthquake loading combinations, SSI can have a substantial impact on the computed in-structure reaction spectra and the derived seismic design demand forces. The seismic response of a vertical irregular (setback) building is investigated in this research, which includes soil-structure interaction (SSI). The study focuses mostly on three different soil conditions, i.e. soft, medium, and hard soil. A point spring element and a fixed support condition are used to account for the SSI effect. Setback G + 10 story structure with basement with L-shape (L-SW) and T-shape (T-SW) shear walls resting on raft foundation is considered for the study. All of the building models have been analyzed as per IS1893:2016. The responses of several parameters such as story drift, story displacement, story shear, story stiffness, time period, and base shear are obtained to understand the diverse circumstances of the soil on the structure for comparative study. The findings of the study emphasize the critical importance of incorporating Soil-Structure Interaction (SSI) effects into the seismic design of multi-storey buildings. By doing so, a notable reduction in regulating design forces can be achieved, while ensuring the safety of the structure. Shear walls serve as highly effective lateral load resisting structures, effectively mitigating displacement and drift. Additionally, it is essential to avoid assuming a fixed base, as this may lead to a significant overestimation of design stresses and seismic response of the structure.