Fuzzy Logic Controllers for a Seismic Isolation System with Variable Friction Damper

Protecting a seismic isolated building from the attack of near-fault earthquakes is a challenge, because a near-fault earthquake usually contains strong long-period components, which are significantly different from a regular earthquake. Conventional seismic isolation systems, such as sliding or elastomeric bearing systems, may induce excessive isolator drift in a near-fault earthquake. To overcome this problem, current practice usually adopts supplementary passive damping in the isolation system. Nevertheless, due to its passive nature, the parameters of a passive damper can not be adjusted online, so the damper may not perform well when it is subjected to an earthquake significantly different from the one that the damper is designed for. In order to improve the performance of seismic isolation in near-fault areas, this study investigates the possible use of a fuzzy logic controlled variable friction damper (VFD) in a sliding isolation system. Four types of fuzzy controllers were studied numerically for the control of the VFD, and their resulting isolation performances in both near-fault and far-field earthquakes with various earthquake intensities are compared and highlighted. It is demonstrated that by properly selecting the fuzzy control law, the isolator drift induced by a near-fault earthquake can be significantly suppressed, without sacrificing the isolation efficiency.