Performance evaluation of FPS and LRB isolated frames under main and aftershocks of an earthquake

Abstract

The seismic behaviour of a 10-storey building frame isolated with the Friction Pendulum System (FPS) and Lead Rubber Bearing (LRB) is investigated under the mainshock and a single aftershock of (i) far-field earthquakes with narrow and broadband characteristics; (ii) near field earthquake with directivity effect; and (iii) near field earthquake with the fling step effect. In order to make the investigation, a realistic one, the FPS and LRB are so designed that their dynamic characteristics are quite comparable. The difference in seismic responses (maximum and residual values) between the FPS and LRB isolated frames is calculated to assess the relative performances of the two systems. A non-linear time history analysis is performed to determine the response parameters which include base shear, peak top storey displacement, absolute acceleration, isolator displacement and the number of hinges formed. The effect of µslow (Friction coefficient at low sliding velocity) which controls the re-centring capability of the FPS and earthquake intensity parameter (PGA) of earthquakes on the difference in responses is demonstrated. It is concluded that better re-centring capability of the FPS isolated frame is observed for lower values of µslow (friction parameter) and higher values of PGA as compared to the LRB isolated frame. Further, less number of plastic hinges are formed in the FPS isolated frame for lower values of µslow.