Experimental and numerical study on the consequence of seismic-induced transversal poundings for a simply-supported bridge

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Shear keys bolted at the underside of bridge girders are expected to act as restrainers to prevent girder dislocation in the transversal direction when experiencing a strong earthquake. However, the impact forces generated at the restrainers will be transferred to adjacent structures and may cause damage to the bridge. Previous research on this topic was scarce as shear keys are usually regarded as secondary structures due to their relatively small dimensions compared to the main components, e.g., girders and piers. This study investigates the pounding effect on the transmission of seismic force in a simply-supported bridge with spherical steel bearings. Shake table tests are carried out on 1:6 scaled models with and without shear keys. To incorporate the effect of excitation characteristics, three ground motions with different peak accelerations are considered. The result indicates that in the absence of shear keys (i.e., no pounding), the bearings can partially isolate the girder from piers. Consequently, the table acceleration transferred to the girder is much smaller than to the pier top. In the case of installing shear keys, the seismic behavior of bearings would significantly influence the pounding occurrence and thus the subsequent bridge response. When involving poundings, the generated impact loads will dramatically increase the acceleration of the girder and the bending moment at the pier base compared to the counterpart without shear keys. Based on the experimental result, a numerical model is established and validated. The model is then used to determine a proper gap size between the participating impact components for obtaining a good overall bridge performance.