Comparative Seismic Analysis of a G+40 RCC High-Rise Building with and without Lead Rubber Bearing Base Isolation Using ETABS

Abstract

This study presents a comparative seismic analysis of a G+40 reinforced concrete high-rise building with varying aspect ratios, analyzed with and without Lead Rubber Bearing (LRB) base isolation using ETABS. The structure is modeled under Seismic Zone V conditions with medium soil, as per IS 1893 (Part 1): 2002 provisions. Five different aspect ratios ranging from 0.25 to 2.0 are evaluated to investigate their influence on seismic performance. Response Spectrum analysis is performed to assess key structural parameters including storey displacement, storey drift, base shear, natural time period, and frequency. The results demonstrate that the incorporation of LRB base isolation significantly enhances seismic performance. Storey displacement is reduced by approximately 35–45%, storey drift decreases by 35–50%, and base shear is lowered by 40–60% compared to the fixed-base models. Additionally, the natural time period increases while the natural frequency decreases, indicating improved flexibility and reduced seismic force transmission to the superstructure. The study confirms that LRB base isolation is highly effective for tall buildings in Zone V and that aspect ratio plays a critical role in seismic response behavior.

Introduction

Earthquakes are among the most destructive natural disasters, causing severe damage to buildings and human life. Since earthquakes occur with little or no warning, earthquake engineering plays a crucial role in designing structures that can resist seismic forces. High-rise buildings face major challenges such as overturning moments and torsional effects caused by ground motion. To reduce earthquake damage, various structural protection techniques have been developed, among which base isolation is one of the most effective.

Base isolation works by introducing flexibility and damping at the foundation level, preventing strong ground motions from directly transferring into the structure. This reduces seismic forces, storey drift, base shear, and floor acceleration while improving structural safety and protecting occupants and building contents. Lead Rubber Bearings (LRB), developed by Dr. Bill Robinson in the 1970s, are widely used isolation devices that allow buildings to move independently from ground motion.

Another important factor influencing seismic performance is the aspect ratio of a building, defined as the ratio of building height to base width. High aspect ratio (tall and slender) buildings tend to have longer vibration periods and greater lateral displacement during earthquakes, while low aspect ratio (short and wide) buildings are more rigid but may experience higher base shear. Therefore, understanding the relationship between aspect ratio and base isolation effectiveness is essential for designing earthquake-resistant structures.

Previous research shows that optimized aspect ratios, proper shear wall placement, and base isolation systems can significantly reduce seismic forces, structural drift, and displacement, improving building stability and safety. However, most studies focus on low- to mid-rise buildings, and limited research exists on very tall G+40 RCC buildings with varying aspect ratios under Seismic Zone V conditions.

To address this research gap, this study models a G+40 storey RCC building using ETABS 2016 and evaluates its seismic performance using both fixed-base and Lead Rubber Bearing (LRB) base-isolated systems. Six different building configurations with aspect ratios ranging from 0.25 to 2.5 are analyzed under Zone V earthquake conditions using Equivalent Static Analysis and Response Spectrum Analysis as per Indian Standard codes. Key parameters such as storey displacement, storey drift, base shear, natural time period, and natural frequency are compared to determine the most efficient structural configuration for high seismic zones.

Conclusion

The study concludes that the incorporation of Lead Rubber Bearing (LRB) base isolation in a G+40 high-rise RCC building significantly enhances seismic performance under Seismic Zone V conditions. The isolated models exhibited a reduction in lateral displacement of approximately 35–40%, indicating improved overall structural stability. Storey drift values decreased by nearly 40–45%, demonstrating effective control of inter-storey deformation during seismic excitation. Additionally, base shear forces were reduced by approximately 40–55%, confirming that base isolation substantially minimizes seismic force transmission to the superstructure. The increase in fundamental time period and corresponding reduction in spectral acceleration demand contributed to improved damping behavior and reduced structural and non-structural damage potential. Due to the reduced seismic demand, the structural reliability and expected service life of the building are likely to improve, making base isolation a highly effective strategy for tall buildings in high seismic regions. However, one limitation of the present study is that the analysis is based on linear response spectrum methods and assumes idealized isolator behavior, which may not fully capture complex nonlinear seismic responses under severe ground motions. Therefore, future research is recommended to incorporate nonlinear time history analysis and soil–structure interaction effects to obtain a more realistic assessment of isolated high-rise buildings. Further investigation into long-term performance and maintenance considerations of isolation systems may also enhance practical implementation strategies. Overall, the study establishes that LRB base isolation provides significantly improved seismic resilience compared to conventional fixed-base systems and is a viable solution for high-rise structures in severe seismic zones. The findings are particularly beneficial for tall buildings in high seismic zones where conventional fixed-base systems may experience excessive lateral demand.

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Copyright

Copyright © 2026 Mr. Sanket Shivanand Nandarge, Mr. Keshav Raghunath Kale. 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.