Performance and reliability of semi-active equipment isolation

This study examines the performance and reliability of passive and semi-active damping in equipment isolation systems for earthquake protection. Performance and reliability measures are the peak accelerations sustained by the equipment and the peak displacements of the isolation system. A new hybridization of two previously studied semi-active control rules regulates the damping in the semi-active isolation system. A parameter study identifies suitable values for the stiffness and damping parameters of the passive isolation system, and feedback control constants for the semi-active equipment isolation and compares the performance for a set of historical earthquakes and for a set of different building models. The reliability of passive and semi-active equipment isolation systems is assessed separately for four historic earthquakes and in regards to uncertainties in the isolation system. The reliability assessment makes use of a polynomial metamodel of the responses as a function of the relevant random variables. Results illustrate the performance limitations of passive isolation systems in protecting shock- and vibration-sensitive equipment from near-fault ground motions and show the improvements associated with semi-active equipment isolation in terms of the mean and variability of the peak responses. Correlations between the isolation system variables and the responses provide guidance for improved behavior.