Seismic Response of Structures with Variable Friction Pendulum System

The dynamic response of a flexible multi-story structure isolated with the variable friction pendulum system (VFPS) under near-fault ground motions is investigated. The fault normal and parallel components are applied in two perpendicular horizontal directions of the isolated system. The frictional forces mobilized at the interface of the VFPS are assumed to be independent of the relative sliding velocity. The interaction between frictional forces of the VFPS in two horizontal directions is duly considered and the coupled differential equations of motion of the isolated system are solved in the incremental form by using a step-by-step method with iterations. The iterations are required due to the dependence of frictional forces on the response of the system. The response of the system with bi-directional interaction is compared with that without interaction (i.e., independent two-dimensional idealization in two directions) in order to investigate the effects of bi-directional interaction of the frictional forces. A parametric study is also carried out to critically examine the behavior of the structures isolated with the VFPS under bi-directional excitation. The various important parameters considered are: the superstructure time period, the initial time period, and the isolation period of the VFPS. From the above investigations, it is concluded that the VFPS is quite effective for controlling the seismic response of the structures under bi-directional near-fault ground motions. It is also found that the bi-directional interaction of frictional forces has noticeable effects and if these effects are neglected, the isolator displacements will be under predicted and the superstructure accelerations will be over predicted.

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