Experimental and numerical study on seismic sliding mechanism of laminated-rubber bearings

Typical laminated rubber bearings are widely used in small to medium-span highway bridges in China. These bearings are economical, and are proved to perform well at service-level conditions. However, damage investigation after the 2008 Wenchuan earthquake revealed that sliding between the laminated rubber bearing and the bridge girder was a common phenomenon, which could actually act as fuses and protect the substructures from severe damage. Thus no damage or only minor damage of substructures was reported in the Wenchuan earthquake for those bridges with bearing sliding. In this paper, an experimental program was carried out to investigate the sliding behavior of laminated rubber bearings with typical configurations in China. The bearing was placed directly on a steel plate representing the embedded steel plate at the bottom of bridge girders, to create an elastomer-steel sliding surface. Experiment results showed that the behavior of bearings before obvious sliding could be approximated as a linear elastic response, with an effective shear modulus in the range of 610-1100 kPa. The sliding coefficients of friction were observed to be inversely related to the normal force, and positively related to the sliding velocity. An analytical model considering the sliding response of laminated-rubber bearings on steel plates was developed and calibrated. Numerical simulations were also conducted to compare the proposed model to the model with typical Coulomb's friction. Results from the numerical simulations indicated that the vertical earthquake caused differences of bearing displacement response between these two models. And this difference would be more significant as the intensity of vertical earthquake increased.