Experimental study on effects of U-shape dampers on earthquake responses of a base-isolated LNG inner tank

•Behaviors of MFPB with U-shape dampers were evaluated by quasi-static cyclic tests.•A shaking table test on the inner tank of LNG storage tanks was conducted.•Responses of the tank under near-fault and near field earthquakes were compared.•Seismic-reduction effect of MFPB with U-shape dampers was analyzed.•Performances of U-shape dampers with different materials were investigated. Base-isolated liquefied natural gas (LNG) storage tanks are prone to violent liquid sloshing and large isolator displacements when subjected to near-fault earthquakes, which are characterized by long-period velocity pulses and large-amplitude displacements. Employing supplemental damping into isolation systems is an effective method to control the displacement of isolators. This paper aims to investigate effects of U-shape dampers on earthquake responses of an inner steel tank isolated by multiple friction pendulum bearings (MFPB). Two materials were selected to manufacture the U-shape dampers, i.e., Mg-Al alloy and mild steel. Hysteretic behaviors of MFPBs with and without U-shape dampers were first evaluated by quasi-static cyclic tests. Afterward, shaking table tests were conducted on a 1:25 scaled steel tank with different isolation systems. Results showed that the U-shape dampers could be used to effectively control the displacement of the isolators. Under the excitation of near-fault ground motions, the peak displacement of isolation bearings with Mg-Al alloy dampers decreased by 16 % ∼ 26 % and that with mild steel dampers decreased by 20 % ∼ 22 %. Meanwhile, adoption of U-shape dampers exhibited excellent reduction effects in both acceleration and hydrodynamic pressure of the tank. In comparison with MFPB, isolation bearings with U-shape dampers exhibited a more plumper hysteresis curve and higher energy dissipation capacity provided by sufficient slides of the bearings.