An external rotary friction device for displacement mitigation in base isolation systems

Abstract

An analysis of the effect of recently observed near-fault and anticipated long-period ground motions indicates that conventional base isolation systems need an immediate retrofitting for improving their performance against earthquakes. In particular, the large displacement response of isolators, which might exceed the displacement limits, is of outmost importance. This study proposes a new external device for mitigating the displacement in conventional base isolation systems. The device consists of a rotary friction system with a wire wound on a shaft connected to a coil spring. The efficacy of the rotary friction is controlled by attaching a so-called ‘ratchet switch’ to the isolated object, which works in accordance with the changes in the direction of the movement at the end of the wire. Through computations, this study verifies the improvement in the performance of base isolation systems by using the rotary friction device. The results show that the proposed device markedly reduces the lateral displacement response of the systems against both near-fault and long-period ground motions. Furthermore, the robustness of the system with respect to the mechanical properties of the friction device is also verified for practical use. Copyright © 2013 John Wiley & Sons, Ltd.