Comparative Seismic Performance Assessment of Fixed-base and base-Isolated Multi-Storey Structures

Seismic design of multi-story buildings aims to ensure safety, serviceability, and stable structural performance during earthquake events. Conventional fixed-base buildings are designed to resist seismic forces through strength and ductility. However, during strong ground motion, such structures often experience high base shear and excessive inter-story drift, which causes significant damage to the structures. To overcome these limitations, base isolation has emerged as an effective seismic protection technique that reduces the earthquake forces to the superstructure of a building and decreases the overall seismic demand. In this study, a comparative seismic evaluation of base-isolated reinforced concrete multi-story buildings and fixed-base buildings was performed using advanced analytical techniques. Two building models were considered for the seismic analysis using the STAAD Pro software. Model one is a conventional fixed-base system, and model two is a base-isolated system. Lead rubber bearings are introduced at the base of the isolated model and idealized using equivalent linear spring damper elements. According to IS1893:2016(Part-1) for seismic Zone V, both model’s seismic responses are assessed using response spectrum analysis. Key response factors, such as base shear act at foundation level, inter story, and roof displacement were analyzed and compared. The results give that the base-isolated structure shows a rise in the fundamental time period, which leads to a considerably lower the seismic forces acting on the superstructure. Compared to the fixed-base building, the base-isolated model exhibits less base shear and reduces the interstory drift. However, the roof displacement remained within the permissible limits. The study concluded that the base isolation system is a more effective and reliable method than the fixed base to improve the seismic resistance and resilience of multistory buildings in high-seismic regions.