Cyclic Experimental Behavior of Nonseismic Elastomeric Bearings with Stiffened Angle Side Retainer Fuses for Quasi-Isolated Seismic Bridge Response

Abstract

Laminated elastomeric bridge bearings are commonly employed at bridges as expansion bearings to accommodate thermal displacements. In regions of low to moderate seismicity, these bearings can also be used as fusing components to effectively isolate the superstructure from the substructure during earthquakes. Stiffened angle retainers provide lateral restraint against transverse construction and service demands on a bridge but can also be used as fuses to establish a threshold of maximum inertial force transfer to the substructure. An experimental program has been carried out to evaluate the overall performance and key behavioral characteristics for assemblies of steel-reinforced, laminated elastomeric bridge bearings with stiffened angle retainers subjected to transverse bridge movement. The testing program demonstrated that the retainer-and-bearing assemblies possess significant force capacity, which should be calibrated to maximize the effectiveness of the fuse for protection of the substructure. The experimental configurations exhibited lateral force capacities as much as 100% of the applied vertical load. The structural response of the bearings depended strongly on the bearing type and the base width of the retainer in the direction of the load relative to bearing height. Bearings comprising only a reinforced elastomer block and a thick top plate achieved distinct pre- and postfusing response ranges if the retainer base width was sufficiently large, with a pinched, stiff hysteresis up to a maximum shear strain of 50–100%, followed by a sharp reduction in force capacity after retainer fusing. Elastomer-on-concrete sliding response diminished during initial cycles but stabilized at a consistent sliding friction coefficient. If the retainer base width was not sufficiently large, the behavior was complex, with concrete crushing at the retainer toe and interaction of the retainer heel with the elastomer block. Bearings with a polytetrafluoroethylene (PTFE) sliding layer were fabricated with bottom steel plates, which permitted a more reliable fusing mechanism without the complications of concrete interaction at the retainer toe.