Feed-forward control of active variable stiffness systems for mitigating seismic hazard in structures

In this paper we discuss a practical two-stage approach (design and operation) to the seismic control of structures equipped with active variable stiffness (AVS) systems, as a means to mitigate or eliminate resonance or near-resonance phenomena in structures due to seismic ground motion. During the design stage, past seismic events are processed to extract the characteristic frequency content against which the AVS-equipped structure is designed, using a conventional envelope spectrum approach. The motivation for the operation stage builds upon advances in early-warning systems that hold the promise of delivering the expected ground motion waveforms at sites equipped with AVS and at instances just prior to the first wave arrival. The working hypothesis for the operation stage is that notification of the incoming motion will be served to the AVS-equipped site so as to allow for a small but sufficient window for moving the hydraulics of the AVS system to compensate for the frequency content of the arriving seismic signal. Numerical results are presented for both design and operation stages of a prototype building under real past seismic events.