Comparative Study of Lead Rubber Bearing Base-Isolated and Fixed Base Buildings under IS 1893: 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

The construction of tall, slender high-rise buildings has increased, making them more vulnerable to lateral forces such as wind and earthquakes. Modern structural design now prioritizes resistance to these lateral loads to ensure strength, stability, and safety, especially during major seismic events. Unlike older designs focused mainly on vertical loads, current codes allow controlled inelastic behavior to dissipate seismic energy and minimize damage.

Seismic isolation, a technique to protect buildings by decoupling them from ground motion, has been developed since 1909 and widely adopted since the 1980s, especially for critical and heritage buildings globally. In India, base isolation has been applied notably after major earthquakes such as those in Killari (1993) and Bhuj (2001).

This research evaluates the seismic performance of a 15-story building using Lead Rubber Bearings (LRBs) for base isolation compared to a fixed-base system. The study involves field investigation, literature review, and modeling with ETABS 2021 software according to Indian seismic codes. Key parameters analyzed include fundamental period elongation, base shear reduction, storey displacement and drift, and diaphragm acceleration to assess structural response under seismic loads.

The modeled building complies with recent Indian standards, uses a dual RC structural system, and falls at the upper limit of base isolation applicability for mid-rise buildings. The isolation system design is based on linear mechanical properties: effective stiffness (which influences the building’s natural period) and hysteretic damping (energy dissipation through cyclic loading). Design parameters follow IS 1893 (Part 6): 2022, with seismic zone V, medium soil conditions, and specific response reduction factors.

Lead Rubber Bearings combine steel laminates and rubber with a lead core that yields under seismic loads, providing significant energy dissipation. The design process sets target natural periods around 2.5–3 seconds and calculates isolator stiffness and damping to reduce base shear and improve seismic resilience.

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

[1] R.S. Jangid, Optimum lead–rubber isolation bearings for near-fault motions, Engineering Structures 29 (2007) 2503–2513,ELSEVIER PUBLICATION-2007. [2] Mrudula Madhukumara, Helen Santhi M, Vasugi V, Performance analysis of lead rubber bearing isolation system for low, medium and high- rise RC buildings, Research on Engineering Structures & Materials 9(1) (2023) 263-276. [3] Pradeep Kumar Pandey, Comparision of Fixed Base and Base Isolation Reinforced Concrete Structure for Seismic Response, Volume 4, Issue 4, April -2017, International Journal of Advance Engineering and Research Development. [4] Sarvesh K. JAIN and Shashi K. THAKKAR, APPLICATION OF BASE ISOLATION FOR FLEXIBLE BUILDINGS, 13th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 1924. [5] M. Tamim Tanwer, Prof. Dr. Tanveer Ahmed Kazi, Prof. Dr. Mayank Desai, COMPARATIVE STUDY ON LEAD RUBBER BEARING (LRB) BASE ISOLATION SYSTEM ON G+12 & G+22 STORY RCC STRUCTURE OVER FIXED BASED FOR INDIAN SUBCONTINENT, Volume 10, Issue 11, November 2019, pp. 423-433, Article ID: IJCIET_10_11_043. International Journal of Civil Engineering and Technology (IJCIET) . [6] Anas M. Fares, Comparison between fixed base and isolated base in seismic response of high-rise buildings: a case study, CHALLENGE JOURNAL OF STRUCTURAL MECHANICS 6 (4) (2020) 204–214, 3 June 2020. [7] Swapnil Ambasta, Dushyant sahu, G.P. Khare, ANALYSIS OF THE BASE ISOLATED BUILDING (LEAD PLUG BEARING) IN ETABS, Volume: 05 Issue: 01 | Jan-2018, International Research Journal of Engineering and Technology (IRJET). [8] SANKET VIJAY MUNOT, P.B.AUTADE, Design of Lead Rubber Bearing Base Isolator system for High Rise Structure, ISSN: 2320-2882 Volume 9, Issue 7, International Journal of Creative Research Thoughts (IJCRT)-JULY 2021. [9] Dhruv V. Jain, Dr.(Major). Chaitanya S. Sanghvi, Comparative study of IS: 1893 part-6 (draft code) Base Isolated buildings with International codes, Volume 8, Issue 5, Journal of Emerging Technologies and Innovative Research (JETIR)-MAY 2021. [10] A. Paul, “Base Isolation System: Outline on Principles, Types, Advantages & Applications,” [Online]. Available: https://civildigital.com/base-isolation-system-outline-on-principles-types-advantages-applications/. [11] M. N. a. M. Ziyaeifar, “Vertical Seismic Isolation of structures,” Journal of Applied Sciences, p. 7, 2008. [12] Z. Q. L. F. I. T. Yun-Peng Zhu, “Analysis and design of non-linear seismic isolation systems for building structures—An overview,” Front. Built Environ, p. 14, 2023. [13] “Different Types of Base Isolators Used in Buildings,” [Online]. Available: https://theconstructor.org/earthquake/different-types-base-isolators-structures/36177/#google_vignette. [14] F. N. a. J. M. Kelly, “Code Provisions For Seismic Isolation,” John Wiley & Sons, Inc., p. 30, 1999. [15] I. Systems, “Dynamic Isolation Systems,” 2010. [Online]. Available: https://dis-inc.com/pdf_files/DIS_Terms_Symbols.pdf. [16] FipMec, “fipmec.it,” [Online]. Available: https://www.fipmec.it/en/download-area/catalogues/#category-53. [17] Major Sandeep Shah (Retd) FIAStructE, ETABs Commands/Procedure for Defining Dampers , Taylor Devices inc. [18] “What are the Effects of Earthquake on Structures?,” [Online]. Available: https://theconstructor.org/structural-engg/earthquake-effects-structures/2704/. [19] C.V.R.Murty, “IITK- Earthquake Tip 5,” [Online]. Available: https://www.iitk.ac.in/nicee/EQTips/EQTip05.pdf. [20] “Seismic Dampers – Types, Working Mechanism, and Components,” [Online]. Available: https://theconstructor.org/earthquake/seismic-dampers/8332/. [21] E. I. M. &. C. Ozer, “Seismic Performance Comparison of Fixed and Base-Isolated Models,” Iranian Journal of Science and Technology, Transactions of Civil Engineering, vol. 47, p. 16, 2022. [22] IS 456:2000 – Plain and Reinforced Concrete – Code of Practice [23] IS 875:1987 – Code of Practice for Design Loads (Other than Earthquake) for Buildings and Structures [24] Part 1: Dead Loads [25] Part 2: Imposed Loads [26] Part 3: Wind Loads [27] IS 1893:2016 (Part 1) – Criteria for Earthquake Resistant Design of Structures – General Provisions and Buildings [28] IS 1893:2022 (Part 6) – Criteria for Earthquake Resistant Design of Structures – Base-Isolated Buildings [29] IS 16700:2017 – Criteria for Structural Safety of Tall Concrete Buildings [30] NBC 2016 – National Building Code of India 2016

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.