Variable friction pendulum system for near-fault ground motions

The seismic response of a flexible multi-storey building isolated with variable friction pendulum system (VFPS) is investigated under normal component of six near-fault ground motions. The VFPS. an advanced friction base isolator, is proposed in this study. The variation of the friction coefficient in VFPS is such that up to a certain value of displacement the frictional force increases and then it decreases with further increase in displacement. Such variation is selected with the criterion that the isolator displacement and building base shear decrease significantly without much alteration to superstructure acceleration under near-fault ground motions. The governing equations of motion of building isolated with VFPS are derived and solved in the incremental form by using Newmark's step-by-step method assuming linear variation of acceleration over small time interval. In order to verify the effectiveness of VFPS, the seismic responses are compared with that of the same building isolated by conventional friction pendulum system (FPS). A parametric Study is also carried out to critically examine the behaviour of building isolated with VFPS. The important parameters considered are the number of stories of superstructure. initial time period and isolation period of the VFPS. In addition, the seismic response of building isolated with VFPS under simple cycloidal Pulses is also investigated. From the above investigations, it was concluded that the VFPS is quite effective for controlling the seismic response Of buildings under near-fault ground motions. Copyright (C) 2007 John Wiley & Sons, Ltd.