Experimental and numerical study on shear behavior of shear pockets between ultra-high-performance and normal concrete for precast girder bridges

Ultra-high-performance concrete (UHPC) has been widely utilized in precast bridge girders as a new material to reduce structural self-weight and improve constructional efficiency. Typically, UHPC and normal concrete (NC) are implemented to construct precast girders and deck, respectively, and cast-in-place shear pockets are used to connect these two. However, these shear pockets are vulnerable components that affect the integrity of UHPC-NC bridge superstructure. Thus, to comprehensively and deeply investigate the shear performance of shear pockets, a push-off test on block specimens and a bending test on a scaled bridge superstructure are conducted in this study. In addition, A refined finite element model (FEM) is proposed for UHPC-NC interface, which incorporates the effects of cohesion, dowel action of reinforcement and frictional force. The accuracy of the proposed FEM is validated against experimental data. Besides, the code equations are evaluated by push-off test results. The push -off test results verify that reinforcement across the interface plays a critical role in enhancing the shear strength between UHPC and NC, and NC is a weak region for the UHPC-NC interface, which should be paid much attention when designing. The experimental and numerical results of the bending specimen indicate that NC deck and UHPC girder connected by shear pockets with shear reinforcement can satisfy the performance requirements of a bridge girder, showing satisfactory integrity for UHPC and NC members under flexure. Furthermore, design equations specified in ACI318R-19, AASHTO, MC-10 and Eurocode 4 can provide a satisfactory prediction of shear strength at UHPC-NC interface, as demonstrated by comparing with experimental results.