Assessment of Structural Behaviour in Lead Rubber Bearing Base-Isolated and Fixed Base Building under IS 1893 (Part 6): 2022 Guidelines

Abstract

Base isolation is recognized as an effective strategy in earthquake-resistant design, significantly reducing floor accelerations and inter-storey drifts. This enhances the safety of both structural and non-structural components, ensuring continued functionality of buildings even after major seismic events. The performance of base isolation systems largely depends on the linear and bilinear properties of the isolators used. This study investigates the seismic performance of a base-isolated structure in comparison to a conventional fixed-base building. A G+15 storey building model was developed and analysed using ETABS 21 software, employing Lead Rubber Bearings (LRB) for base isolation. A comparative evaluation was conducted based on key response parameters, including displacement, inter-storey drift, storey shear, and storey acceleration. The isolators were modelled using linear properties and analysed using the Response Spectrum Method in accordance with IS 1893 (Part 6): 2022. A comprehensive literature review was conducted to support the research framework, followed by model validation to align the methodology with established studies in the field. The concluding section summarizes the findings from the comparative analysis, highlighting the effectiveness of base isolation systems in enhancing seismic performance and providing insights for future research and design improvements in seismic isolation technology.

Introduction

There has been a significant rise in constructing taller, slender high-rise buildings, which are more vulnerable to lateral forces such as wind, earthquakes, and blasts. Modern structural design now prioritizes resisting these lateral loads to ensure safety and stability, especially during seismic events where buildings must endure inelastic deformations. Contemporary building codes permit controlled structural damage to dissipate earthquake energy, enhancing resilience.

Base isolation—a technique that protects buildings by decoupling them from ground motion—has been used since the early 20th century and gained popularity globally from the 1980s. It is widely applied to safeguard critical and heritage structures, with over a thousand buildings worldwide employing this technology. In India, base isolation has been used notably after major earthquakes, such as the 1993 Killari and 2001 Bhuj quakes.

The research focuses on evaluating seismic performance of a 15-storey building with and without base isolation using Lead Rubber Bearings (LRBs). The study includes field investigations, literature reviews, and structural modeling. Using ETABS 2021 software, two models (fixed-base and isolated-base) are analyzed through response spectrum analysis to compare parameters like fundamental period, base shear, storey displacement, storey drift, and diaphragm accelerations.

Model parameters comply with recent Indian standards (IS 1893, IS 875, IS 16700) and include detailed material specifications, loading conditions, and a dual structural system with RC walls and frames. The chosen building height is at the upper limit of typical base isolation applicability.

The linear isolation system is designed considering key properties such as effective stiffness (which affects the building’s natural period) and hysteretic damping (which dissipates seismic energy), both critical to reducing seismic demands and improving structural safety and occupant comfort.

Conclusion

This study presents a comparative seismic performance evaluation of a fixed-base and a base-isolated (Lead Rubber Bearing) multi-storey building as per IS 1893 (Part 6)-2022 using linear isolation modeling and response spectrum analysis in ETAB21. The findings highlight the substantial advantages offered by base isolation systems across various critical structural parameters, affirming their effectiveness in seismic mitigation. The results demonstrate a remarkable reduction in displacement, storey drift, storey shear, and storey acceleration when linear base isolation is implemented. Specifically, the top-storey displacements were reduced by approximately 56–61% in both X and Y directions. Similarly, storey drifts were lowered by 55–60%, reinforcing the role of base isolators in limiting inter-storey deformation and enhancing structural and non-structural safety. In terms of storey shear, a consistent reduction of 50–65% was observed across all levels, significantly reducing the lateral force demands on structural members. Furthermore, the modal time periods of the isolated structure increased by an average of 110%, effectively shifting the building\'s dynamic response out of the range of dominant ground motion frequencies, which contributes to a substantial reduction in seismic forces. A key finding is the reduction in storey accelerations above the isolation layer, where values decreased by 38–41% in both directions. This drop plays a critical role in safeguarding internal contents, sensitive equipment, and ensuring post-earthquake functionality—vital for hospitals, heritage buildings, and other critical infrastructure. Overall, the linear base isolation system, particularly using Lead Rubber Bearings, exhibits enhanced seismic performance by reducing structural responses, increasing energy dissipation, and improving occupant safety. The significant improvements observed across all seismic response parameters strongly support the adoption of base isolation as a reliable and effective strategy in performance-based seismic design, especially for buildings located in high seismic zones.

References

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Copyright

Copyright © 2025 Pruthvirajsingh Pramod Bokey, Dr. V. R. Patel. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.