Control strategy for liquid spring-mr damper for vertical isolation

Seismic isolation is an effective technique used to mitigate effects of horizontal shaking and helps to achieve higher seismic performance objectives, such as continued operation or immediate occupancy following a design earthquake event. In this study, combined horizontal and vertical isolation is provided by combining an elastomeric bearing to resist horizontal shaking in series with a bilinear liquid spring (BLS)-controllable magnetorheological fluid damper (CMRD) for vertical ground shaking. The controllable damping allows the BLS-CMRD capacity to be adjusted according to the intensity of the applied earthquake, which helps the BLS-CMRD sustain a range of earthquake intensities including larger than anticipated in design. A numerical model of a simplified rigid 2D block is developed to predict the BLS-CMRD response under earthquake loading. The BLS-CMRD resisting force is determined by four components; spring, friction, viscous damping and MR damping force. Theoretical equations are applied to implement the first three component forces, while a Bouc-wen model is used to calculate MR force. A new conceptually simple control strategy is developed and implemented to simulate the semi-active response, wherein the applied current is determined by a combination of displacement and velocity response feedback values. Finally, the results of the proposed control strategy are presented. Preliminary results show that the proposed control strategy helps reduce vertical bearing displacement and drift ratio compared to the passive-OFF case and achieve lower vertical acceleration at the bearing and reduced operating time relative to the passive-ON case. The semiactive behavior enhances energy dissipation with low power requirements by adjusting the amount and duration of current needed to activate MR damping.