Absolute-energy-based active control strategies for linear seismic isolation systems

The general purpose of seismic isolation systems is to reduce the ground acceleration transmitted onto the isolated object down to a minimum possible level within an allowable isolator displacement. Therefore, the efficiency of an isolation system can usually be quantified by the acceleration level transmitted onto the isolated object. In order to improve the performance of active isolation systems (AISs) for acceleration-sensitive equipment or structures, two optimal control laws that utilize performance indices associated with system absolute energy are proposed in this study. The first control law, which requires the measurement of the ground velocity in deciding the control force, is derived based on the concept of instantaneous optimal control. The second one is based on the concept of discrete-time optimal control, in which the feedback gain can be obtained by solving the discrete-time algebraic Riccati equation. The numerical simulation results of this study demonstrate that the isolation performance of an AIS system using the proposed absolute-energy-based control laws is much superior to the conventional optimal control in reducing the super-structural acceleration response for either near-fault or far-field earthquake. In addition, a comparison between the two proposed control laws reveals that the first control law has a lower acceleration response, whereas the second one results in less isolator displacement.