Semi-active building base isolation

Passive base isolation systems are one of the most successful and widely implemented technologies for seismic hazard mitigation. However, recent changes to the building codes have made the design requirements such that some of the potential gains of such systems may not be realized. This paper investigates the effects of using controllable semi-active dampers, such as magnetorheological fluid dampers, in a base isolation system. A two degree-of-freedom model of a base isolated building is used, with linear viscous, active, and semi-active supplemental damping devices in the isolation layer. Using an H/sub 2//LQG control design, semi-active and active devices are able to achieve a notable decrease in base drifts, compared to the optimal linear passive designs, with no accompanying increase in accelerations imparted into the superstructure.