The Performance Assessment of Lead Rubber Bearing-Isolated High-Rise Reinforced Concrete Buildings in Indian Seismic Zones

Abstract

Seismic isolation can modify the dynamic response of reinforced-concrete (RC) buildings by partially decoupling the superstructure from ground motion. However, comparative evidence for tall RC buildings integrating direct structural response measures with probabilistic fragility assessment across all Indian seismic zones remains limited. This study investigates a 20-storey RC Special Moment Resisting Frame (SMRF) in two configurations: a conventional fixed-base model and an otherwise identical model supported on Lead Rubber Bearings (LRBs). The models were developed in ETABS in accordance with IS 1893 (Part 1):2016, IS 456:2000, and IS 875. Modal, response-spectrum, and dynamic analyses were combined with a fragility framework to evaluate changes in fundamental period, base shear, roof displacement, inter-storey drift, and damage-state exceedance. The LRB configuration substantially reduced superstructure demands. Base shear decreased by about 66.7%, while roof displacement decreased by about 37–43% across the investigated seismic zones. Maximum inter-storey drift decreased by more than 92%. The first-mode period increased from 2.681 s for the fixed-base model to 3.421 s for the isolated model, representing a 27.6% increase. Fragility analysis indicated a shift toward higher PGA levels for complete damage, with median PGA increasing from approximately 0.80 g to 1.60 g. Overall, the results demonstrate the potential of LRB isolation to enhance seismic performance while acknowledging numerical and modelling limitations.