An experimental study on seismic isolation using a leverage-type stiffness controllable system

The technique of semi-active isolation with variable-stiffness property has been proven theoretically to be an effective means for seismic protection of equipment or structural systems. To demonstrate the feasibility of this technique, a shaking table test is conducted in this study. The seismic response of a novel isolation system called the leverage-type stiffness controllable isolation system (LSCIS) controlled by a newly developed controller called the least input energy method (LIEC) and some traditional control laws are investigated. The LSCIS is able to vary its isolation stiffness in real time by adjusting the position of the pivot point on its lever arm. The LIEC controller, which is designed particularly for variable stiffness systems, reduces the transmitted seismic motion of the LSCIS by minimizing the input seismic energy of the system. As demonstrated by the test, the acceleration response and seismic input energy of the LSCIS can be significantly reduced by properly adjusting the isolation stiffness which is controlled by the LIEC controller. As compared to traditional control strategies, the LIEC is able to achieve the best acceleration reduction rate for the LSCIS, and meanwhile requires the least demands on control energy and control force.