SSI ANALYSIS OF G+6 RCC BUILDING ON STIFF SOIL USING ETABS AND SAFE

Abstract: Soil-Structure Interaction (SSI) changes the seismic response of reinforced concrete buildings because the soil, foundation, and superstructure act together as one system. This paper studies a G+6 RCC moment-resisting frame building resting on stiff soil using ETABS for the building model and SAFE for the raft foundation model. Two cases were compared: a conventional fixed-base model and a flexible-base SSI model. The analysis was carried out according to IS 1893 (Part 1): 2016 for Seismic Zone III, with load details taken from IS 875 and material properties from IS 456:2000. The results show that considering SSI increases the fundamental time period by about 18–24% and the lateral displacement by about 28–35%, while reducing the base shear by about 12–18% compared to the fixed-base case. The SAFE results also show non-uniform soil pressure beneath the raft and noticeable settlement variation, which means the foundation flexibility affects the building response even on stiff soil. Overall, the study shows that fixed-base analysis can miss important serviceability effects such as drift and settlement, and that combined ETABS-SAFE modelling gives a more realistic way to assess mid-rise RCC buildings.

Keywords: Soil-Structure Interaction, ETABS, SAFE, G+6 RCC Building, Stiff Soil, Raft Foundation.