Seismic Performance Evaluation of Vertically Regular and Irregular High-Rise Structures with Base Isolation Using Response Spectrum Analysis

This study investigates the seismic performance of vertically regular and irregular high-rise structures using response spectrum analysis. Four structural configurations are considered: regular fixed-base, regular base-isolated, irregular fixed-base, and irregular base-isolated models using Lead Rubber Bearings (LRB). The buildings are modeled in ETABS with identical geometry, material properties, and loading conditions, and seismic analysis is carried out in accordance with IS 1893 (Part 1): 2016. Vertical irregularity is introduced in the form of setback geometry along the height of the structure. Key response parameters such as base shear, storey displacement, storey drift, and overturning moment are evaluated. The results indicate that vertically irregular structures exhibit different seismic behavior compared to regular structures due to uneven distribution of stiffness and mass, leading to localized effects such as drift concentration. The introduction of base isolation significantly reduces seismic forces and improves overall structural performance. Composite structures demonstrate better response compared to RCC structures due to reduced mass and enhanced ductility. Among all configurations, the base-isolated composite structure shows the most efficient seismic performance, achieving significant reduction in base shear and overturning moment while maintaining acceptable deformation limits.