NON-LINEAR PERFORMANCE EVALUATION OF - BASE ISOLATED RC FRAMED BUILDINGS

Abstract

There has been a great loss of life and property due to the occurrence of earthquakes in the past. The poorly constructed buildings are likely to collapse during earthquakes. There is a need to reduce the seismic demand on these buildings so that they can perform better during future earthquakes. This need can be fulfilled using the concept of base isolation. In seismic base isolation, the superstructure is decoupled from the potentially damaging ground motion. In order to predict the response of the structure during earthquake, accurate evaluation of structural properties and precise modeling of the isolation devices has to be done. The most common type of isolation system is Laminated Lead Rubber Bearing (LLRB). They not only isolate the building but also serve the purpose of energy dissipation, giving structural support, horizontal flexibility, damping and re-centering. In the present study, the design of LLRB has been discussed in detail. A case study has been taken up to compare the response of base isolated building with that of a conventionally designed earthquake resistant building. The finite element software SAP2000 v17.I.1 has been used for modeling and analysis. Non-linear static pushover analysis and non-linear time history analysis have been performed to study the response of base isolated building as well as fixed base conventionally designed building. An alternative cost effective approach has been proposed in which number of isolators to be used has been reduced gradually to find out the best combination on the basis of isolator cost only. It has been shown that the performance of the building has not been * compromised. The effective horizontal stiffness is a very important parameter in the isolator design. In this study, the total effective horizontal stiffness has been varied by gradually - removing some of the isolators and its effect on the performance has been studied