SEISMIC ANALYSIS OF LOW TO MEDIUM RISE BUILDING FOR BASE ISOLATION

Abstract

Seismic isolation is an alternative to conventional design methods for dealing with earthquake loading s in relatively high frequency structures, especially in low to medium rise buildi ngs. One of the goals of seismic isolation is to sh ift the fundamental frequency of the structure away from the dominant frequencies of sei smic excitations and fundamental frequency of the f ixed base structure. This innovative design approach aims mainly at the isola tion of a structure from the supporting ground, usu ally in the horizontal directions in order to reduce the transmission of the earthqua ke motion to the super structure. In this paper seismic analysis performed for a low to medium rise fixed base building and it was obser ved that the fundamental time period of the fixed system are typically in the res onance range of 0.1 sec. to 2.0 sec. This results iamplification of the ground acceleration causing severe damage to structures an d their contents. To avoid such a situation, the pe riod must be lengthened, by increasing the flexibility of the structure by introducing seismic base isolators between the foundati on and super structures. A six storey structure under both fixed base and seismica lly isolated boundary conditions is studied to demo nstrate the effectiveness of seismic isolation. The comparative result shows tha t maximum floor acceleration, inter-storey drifts a nd storey shear forces are reduced substantially for seismically isolated stru cture.