Experimental and Seismic Response Study of Laminated Rubber Bearings Considering Different Friction Interfaces

Unbonded LRBs (laminated rubber bearings) are commonly applied in small-to-medium-span bridges in China. The frictional sliding characteristics of LRBs have a vital influence on the seismic response of the bridge. Nine square LRBs were subjected to the quasi-static displacement loading test in this paper, and the differences in sliding characteristics of LRBs at the interface of steel and concrete test pad were investigated. The variation of the friction coefficient during sliding was then analyzed. Based on the experimental data, a three-fold mechanical constitutive model of LRBs that considers the breakaway-sliding friction characteristics is established. Further, the bridge seismic demands in longitudinal directions with different friction interfaces are compared by nonlinear dynamic analysis on a typical LRB-supported concrete bridge. The results show the causalities of the displacements and decreases of the friction coefficient of the LRB. The breakaway coefficient of friction of the concrete surface was generally greater than that of the steel in the pre-sliding stage, while the sliding coefficient of friction of the steel interface in the post-sliding stage was greater than that of the concrete. Moreover, the proposed three-fold constitutive model is able to simulate the frictional sliding behavior of LRBs accurately. Lastly, the seismic design of small-to-medium-span bridges should take into account the breakaway-sliding friction effect of the LRBs and the preference for steel as friction pads for LRBs is recommended.