Influence of the lateral restoring force of isolation system to the seismic performance of isolated buildings in low-to-moderate seismicity regions

The decoupling effects of base-isolation systems significantly reduce the seismic damage to the superstructures throughout the elongation of their fundamental periods. Various seismic design codes generally require that isolation systems should be designed to possess the minimum restoring forces at the design displacements in order to limit the residual displacements after strong earthquake and, in turn, to reduce the probabilities of structural damage or collapse due to after-earthquake-shocks. However, such requirement on the minimum restoring forces developed in isolating systems might be harmful to their beneficial decoupling effects. This is pronounced for base-isolated buildings built in low seismic hazard regions. For this reason, the minimum restoring forces required for base-isolating systems at low seismicity regions needs to be deeply investigated. To do this, nonlinear time history analyses of prototype isolated buildings are performed in this study. Throughout comparative study on the seismic responses of the selected isolated buildings located at both high and low seismicity regions, it is observed that the existing criterion on the minimum lateral restoring forces of isolating systems at low seismicity regions would be modified to enhance the decoupling effects and to improve their acceleration response with assuring reasonable residual displacements.