Design and analysis of Base Isolated Structure

Abstract

Base isolation is a method used to decouple the super structure from the ground by installing a flexible link
between them to make the structure safe from the damaging effects of ground motion. There are various methods to make the
structure flexible. Using High Damping Rubber Bearing (HDR) is one of the ways to increase flexibility of the structure and
increase its time period. HDR is made up of alternate layers of high damping rubber laminated with steel shims. This paper
presents a design procedure to proportion the diameter and thickness of layers of rubber and steel shims. Fixed base and
base isolated structures were modelled in ETABS. After seismic analysis of both structures, a comparative study was
conducted between the response of the two structures. Inter storey drifts and shear forces were seen to be greatly reduced in
base isolated structure. Displacement of the base isolated structure, however, was increased. Most of the deformation
occurred in the flexible HDR installed at the base. Moreover, time period of the base isolated structure greatly increased
(upto 2.5sec) which decreased the probability of resonance of the structure with common time period of the earthquake on
hard soil i.e in the range 0.03-0.33 sec.