Experimental evaluation of supplemental viscous dampingfor a sliding isolation system under pulse-likebase excitations

Abstract

Near-fault earthquakes that usually contain a long-period pulse component may causeexcessive responses to a base-isolated structure, especially with regard to its peakisolator displacement. Viscous-type dampers, whose damping force is proportional to theexcitation velocity, can be used to mitigate the excessive responses of the isolatedstructure. In this study, the effect of viscous-type supplemental damping on a slidingisolation system subjected to pulse-like ground excitations is evaluated experimentallyby a shaking table test. The test program involves a relatively rigid structure isolated bysliding-type isolators and a fluid viscous damper installed within the isolation layer.Seismic excitations with and without a long-period pulse component were imposed onthe isolated system, and the experimental responses of the system with and withoutinstallation of the fluid damper were compared. The test results demonstrate that, for arigid superstructure, the viscous damper is able to effectively suppress the peak isolatordisplacement induced by the long-period pulse component without increasing theacceleration level of the superstructure; however, it also slightly increases the structuralacceleration in the seismic excitation without the pulse component. The results alsoshow that a pulse-like ground motion is able to induce resonance-like behavior for theisolator displacement of a sliding system when the pulse period is close to the isolationperiod. However, this resonance-like behavior can be effectively mitigated by addingviscous damping to the isolation system. Finally, by using linear and nonlinear viscousmodels to simulate the experimental responses, the influence of the damper nonlinearityon the test results was also investigated