STUDY ON LAMINATED RUBBER BEARING BASE ISOLATORS FOR SEISMIC PROTECTION OF STRUCTURES

Ganga Warrier A, Balamonica K, Sathish Kumar K, Dhanalakshmi

Abstract: Base isolation or seismic base isolation is an effective means for protection of structures, its contents and its occupants during the event of an earthquake. The principle of base isolation is vibration isolation. It decouples the building from damaging action of the earthquake. The isolator partially reflects and partially absorbs input seismic energy before it gets transmitted to the superstructure. Laminated Rubber Bearing Isolators are placed between the superstructure and foundation, which reduces the horizontal stiffness of the system. It thereby increases the time period of the structure and decreases the spectral acceleration of the structure. The superstructure acts like a rigid body, thus inter storey drift is reduced. Such type of isolators are used in practice in India, yet a proper design procedure based on IS code is unavailable. The paper presents design procedure for LRB adopting the procedure of IS 1893:2002 (Part-1) for earthquake resistant design of buildings. Design charts have been developed and presented in this paper which gives isolator diameter and rubber thickness as design outputs. The design procedure requires different input parameters like fundamental period and damping of the fixed base structure, axial load on the column, seismic zone, type of soil and shore hardness of rubber. These design charts enable the designer to easily arrive at the isolator parameters to achieve seismic isolation. Using the charts, case study has been done using SAP2000. Building displacement and acceleration are compared for model with and without base isolator. Comparative study of linear and non-linear base isolators has also been carried out. Linear and non-linear time history analysis has been done using El Centro earthquake

Keywords: base isolation, laminated rubber bearing, IS Code, seismic protection, design charts, time history analysis, SAP2000

DOI: https://doi.org/10.15623/ijret.2015.0402064