Pushover Analysis of Multi Story Building with and Without Lead Rubber Bearing

Abstract

This study investigates the seismic performance of multi-story reinforced concrete (RC) buildings with and without base isolation using Lead Rubber Bearings (LRB). Nonlinear static (pushover) analysis is Implemented to evaluate and compare the structural response under seismic loading conditions. Analytical models of G+9-storey and G+14-storey RC buildings are developed and analyzed using ETABS. Key performance parameters such as base shear, roof displacement, and fundamental time period are assessed to understand the influence of base isolation on overall structural behavior.

Introduction

The study investigates the effectiveness of Lead Rubber Bearing (LRB) base isolation systems in improving the seismic performance of reinforced concrete (RCC) buildings. The results show that LRB isolation significantly enhances earthquake resistance by increasing the natural period of the building, thereby reducing the impact of earthquake forces. For instance, in a G+9 building, the natural period increased from 1.71 seconds to 2.81 seconds after introducing LRB isolation. This increase helps reduce seismic response and improves structural safety.

The study also observed a reduction in base shear forces in isolated buildings. In the G+14 building, the base shear reduced from 5,349.85 kN to 4,373.61 kN with the use of LRBs. Although roof displacement slightly increased, the seismic forces became concentrated at the isolation interface rather than being transferred directly to the superstructure. As a result, beams and columns experienced less damage, improving the overall safety and stability of the building during earthquakes.

Two RCC building models, G+9 and G+14, were considered for the study. Both buildings had a plan size of 12 m × 12 m and were located in Seismic Zone V on medium soil conditions. The buildings were designed using M25 grade concrete and Fe500 reinforcement steel. Structural elements included beams of sizes 230 mm × 450 mm and 300 mm × 500 mm, columns of various dimensions, slab thickness of 150 mm, and floor height of 3 m. Pushover analysis was used for seismic evaluation. The zone factor was taken as 0.36, the importance factor as 1.2, and the response reduction factor was considered as 3 for fixed-base buildings and 1 for isolated buildings.

The buildings were modeled and analyzed using ETABS software. Beams and columns were modeled as line elements with four degrees of freedom per node. Material properties for M25 concrete and HYSD500 steel reinforcement were defined according to Indian Standard codes. The study included both plan and 3D modeling of the structures.

The analysis procedure involved several steps. First, detailed building models were created by defining grid systems, story heights, slabs, beams, columns, and material properties. Second, different types of loads such as dead load, live load, and earthquake load were assigned according to IS 875 and IS 1893 standards. Two structural models were prepared: one with a fixed base and another with LRB base isolation.

In the third step, the LRB system was modeled by assigning appropriate stiffness and damping properties to simulate its seismic isolation behavior. Finally, nonlinear hinge properties were assigned to beams and columns to capture their inelastic behavior during earthquakes, allowing a realistic assessment of structural performance under seismic loading.

Conclusion

1) Seismic Energy Dissipation: The LRB system enhances structural resilience by providing lateral flexibility and high levels of hysteretic damping. The lead core undergoes plastic deformation during seismic loading, effectively dissipating kinetic energy and reducing the impact of ground motion. 2) Superstructure Decoupling: By implementing base isolation, the system decouples the superstructure from the horizontal components of ground acceleration. This significant reduction in seismic demand ensures that structural members, such as beams and columns, remain within the elastic range. Consequently, the building maintains structural integrity and achieves \"Immediate Occupancy\" performance levels with negligible residual damage. 3) Displacement Control and Rigid-Body Response: Although the isolation layer increases the fundamental period and overall lateral displacement, these movements are concentrated at the isolation interface. This reduces inter-story drift and promotes a rigid-body response in the upper floors, protecting both the structural frame and sensitive non-structural components from high-frequency vibrations.

References

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Copyright

Copyright © 2026 Mr. Dipak P. Patil, Mr. Aniket S. Chavan, Mr. Pruthviraj D. Chougule, Mr. Harshwardhan S. Desai. 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.