INTRODUCTION

More than 65% of the land area of India isprone to moderate to severe earthquake shaking, and there are several important infrastructures built in these areas. To safeguard these structures, earthquake resistant design is essential. In contrast to conventional approach of earthquake resistant design, wherein damage is expected to occur in select structural members, the approach adopted in critical infrastructure and important buildings is to eliminate damage to a considerable extent through the use of base isolators. The concept of base isolation is to use base isolators between the foundation and the superstructure, such that the superstructure is isolated from the ground. (This concept is similar to the provision of neoprene bearings at the supports below the bridge decks).

Buildings resting on such base isolators are called base isolated buildings. It has been observed from past experience that base isolation systems are more effective for buildings with following conditions: a) stiff superstructure, b) rigid foundation on stiff soil, c) ground motions that do not have sharp pulse-like motions, and d) ductile detailing of the whole structure [IS 1893-Part 6 (2022)]. 

Seismic isolation systems prevent seismic energy from entering buildings by using devices made from rubber or steel plates coated with a friction-generating material that slide over one another to minimize the effect of an earthquake.These isolation devices are installed between the building’s foundation and the building (See Fig. 1). Alternatively, seismic dampers, installed in each story of a building, could absorb earthquake energy the way shock absorbers work in a car and convert it into heat energy to minimize damage.

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