Design Of Base Isolation Systems for an R.C.C. Building

Abstract

Conventional seismic design attempts to make buildings that do not collapse under strong earthquake shaking, but may sustain damage to non-structural elements and to some structural members in the building. This may render the building non-functional after the earthquake, which is not acceptable for important buildings, like hospitals, fire stations, etc. Special techniques are required to design buildings such that they remain practically undamaged even in a severe earthquake. Buildings with such improved seismic performance usually cost more than normal buildings do. However, this cost is justified through improved earthquake performance. One of the technologies used to protect buildings from damaging earthquake effects is “Base Isolation”. The idea behind base isolation is to detach (isolate) the building from the ground in such a way that earthquake motions are not transmitted up through the building, or at least greatly reduced. The work undertaken is an attempt to understand the fundamentals of Base Isolation, its design & behavior under seismic loading. A RCC building of Basement + GF +4 has been considered with basement constructed of RCC wall at its periphery. As, no specific guidelines are available for design of building with base isolators in Indian code IS 1893-2002 (Part I), IBC 2000 recommendations were used. Three basic types of base isolators namely Lead Rubber Bearing (LRB), High Damping Rubber Bearing (HDR) & Friction Pendulum System (FPS) were designed. The base isolated RCC building was exposed to Design Spectrum seismic loading of IS 1893-2002 (Part I) to compute its response. The conclusions were drawn on the basis of analysis and design of base isolator along with comparison of displacement, storey drift and base shear for fixed base with RCC isolated building. A commonly available, widely used software SAP2000 v 8.08 was utilized as it is available at Computer centre of Civil Engineering Department, Institute of Technology, Nirma University.