Experimental study on the effect of nonlinear viscous dampers on base-isolated structures under near-fault earthquakes

Abstract

Base isolation is an effective way to protect structures from earthquake-induced damage. However, near-fault (NF) earthquakes may seriously damage base isolation structures. Viscous dampers can control the isolation displacement and enhance the energy dissipation of base isolators. Therefore, a series of shaking table tests were conducted to investigate the influence of nonlinear viscous dampers (VDs) on the seismic performance of base-isolated structures under NF ground motion. A 1/4 scaled frame model structure with four base isolation systems was designed for the shaking table tests. Laminated natural rubber bearings (LNRB) or lead rubber bearings (LRB) were selected as two base isolation systems. Additional nonlinear viscous dampers (NLVDs) were installed at the base-isolation level of the LNRB- and LRB-isolated structures to add two additional base-isolated systems. Three ground motions, including one far-fault (FF) and two NF, provide seismic inputs to the base-isolated structures. The effects of supplemental NLVDs on the dynamic properties and seismic performance of the superstructures were investigated. The floor acceleration spectrum and energy dissipation of the isolation level were considered to evaluate the ground motion characteristics on the seismic performance of the base-isolated structures. The test results show that the pulse-like NF ground motion caused the greatest deformation and shear force in the isolation bearings while inducing the largest drift and floor acceleration. The NLVDs were effective when the base-isolated structure experienced pulse-like NF ground motion. The supplemental NLVDs amplified the inter-story drift and floor acceleration response of the superstructure under FF ground motion, especially for the LRB-isolated structure.