Performance and reliability of passive and controllable seismic isolation systems

Passive base isolation systems protect buildings from earthquakes by mechanically de-coupling the building from the ground. These systems are placed in the building foundation and consist of bearings that provide little resistance to lateral motions of the ground. Controllable or "semi-active" isolation systems, in which the stiffness, damping, or friction of the isolation system can be controlled, represent an emerging enhancement to passive isolation systems.; This dissertation addresses the robustness of semi-active base isolation systems with respect to time lags among the controllable devices, investigates the drawbacks of heavy isolation damping in both linear and nonlinear passive isolation systems, compares the performances of structural systems equipped with controllable damping and controllable stiffness devices, analyzes the effects of device and system parameters such as isolation level stiffness, maximum and minimum device damping and device stiffness on the performance of semi-active systems in terms of reduction in transmissibilities, and examines the reliability requirement of isolation system components to effectively protect vibration-sensitive equipment located in critical facilities.; Findings from this research show that appropriate combinations of passive isolation systems can sufficiently limit the base isolation drift without increasing interstory drifts and floor accelerations for many situations. Better performance may be obtained by semi-active isolation and this dissertation provides guidelines for designing such systems in order to meet certain performance criteria, including low base drift, interstory drifts, floor accelerations, and device forces. Results also reveal that use of seismic isolation significantly increases the reliability of secondary systems such as vibration sensitive equipment placed in critical facilities.