Tests For A SMA-laminated Rubber Bearing Under Low-cycle Reversed Loading And Its Application Into Isolated Bridges Subjected To Near-Fault Ground Motions

The near-fault ground motions indicate significantly different special effects from what far-field ground motions do, such as impulsive effect. Owing to the effect of long period velocity pulse, bridges near the fault area are more prone to severe earthquake damage coMPared with the one in far-field ground motion. Damage of bridge in Wenchuan earthquake shows that highway bridges in small to medium span which use the pot rubber bearings and plate rubber bearings are less capable of protecting bridges from near fault ground motions. In order to improve the seismic isolation performance of the bearings in the near fault earthquake, a novel SMA-laminated isolation rubber bearing is proposed utilizing energy dissipation capacity and self-centering ability of shape memory alloy wire.. In order to study the seismic isolation performance of these bearings, both the hysteretic behavior of SMA bearing and its seismic isolation performance in bridges are studied. The main research contents and conclusions are as follows:(1) Experiment on material property characterization of SMA wireThe material properties of SMA were tested, and the effects of different strain rate, strain amplitude and cyclic loading on the hysteretic behavior of SMA were studied both in elastic range and plastic range of SMA wires. The limit recoverable strain of SMA wire was defined. The experimental results show that the super elastic SMA wire has a strong energy dissipation capacity and self-centering ability. After plastic yielding, the energy dissipation capacity of SMA wire decreases by about 40%, while the peak stress increases by about 90%. The plastic yield effect does not affect the ultimate stress of SMA wire, and can weaken its ultimate strain is. The recverable strain of SMA wire can reach 10%.(2) Quasi-static experiment study of SMA-rubber bearingThe quasi-static experiment of SMA-laminated rubber bearing was completed, and the difference of hysteresis characteristics between the ordinary rubber bearing and SMA rubber bearing under different shear amplitude, vertical load and load frequency was studied. The test results show that the hysteretic behavior of the two kinds of bearings under different vertical loads is more stable. CoMPared to the ordinary rubber bearings, the energy dissipation capacity, the stiffness and the equivalent damping ratio of SMA rubber bearing are increased with varying degrees.(3)Study on hysteresis model of SMA-rubber bearingThe feasibility of the numerical calculation model of K-layout SMA wire was verified by the test data, and the linear equivalence of the rubber bearing model was also carried out. Based on the numerical calculation model of rubber bearing and SMA wire, a double-flag shape self-centering hysteresis model of SMA rubber bearing is proposed. Based on the hysteresis model, the hysteretic behavior of SMA-rubber bearing under different configuration of SMA filament was studied. Results show that with the increasing of SMA filament configuration, The energy dissipation and stiflhess of the SMA rubber bearing increases linearly, and the equivalent damping ratio increases obviously.(4) Seismic damage evaluation of continuous beam bridges with SMA-rubber bearing under near fault ground motionTo study the effectiveness of seismic isolation of SMA-rubber bearing, a finite element model of four span continuous girder bridge was established based on OpenSees. In this paper, SMA-rubber bearings, pot rubber bearings and plate rubber bearings are applied to the bridge, respectively. Two sets of near fault ground motion records were selected, and the elastic-plastic time history analysis was carried out. The seismic response and structural damage state of continuous beam bridge under near fault ground motions are also studied for both records. Results show that the pulse-like near fault ground motions are more serious than that of the non pulse-like near fault earthquake. Pot rubber bearings can cause more damage to the bridge piers, while the isolation effect of plate rubber bearing is obvious, but the substructure displacement is too large. SMA-rubber bearing makes the isolated bridge achieve the bi-objective of isolation and displacement control. The amount of SMA wire has a considerable influence on the performance of the bearings In this paper, SMA-rubber bearing which uses of cross section ratio of 0.19% can achieve the best isolation performance.