Effects of UHPC shear key on strengthening shear performances of wet joint in prefabricated composite beams

Ultra-high-performance concrete (UHPC) has excellent mechanical properties, which could be used in the connecting region between different prefabricated members to improve the continuity and integrity of prefabricated composite structures. In this paper, a novel kind of wet joint with UHPC shear key was proposed to connect different prefabricated components for assembled steel-concrete composite beams, and the effects of different parameters for UHPC shear key on strengthening shear performances of wet joints were evaluated via a series of push-out tests. Results indicated that the specimens with wet joints mainly failed and slipped in the precast and post-cast concrete interface under the longitudinal force. The application of the UHPC shear key could significantly increase the ultimate shear strength of the interface compared to the single layer of extended reinforcements, and the UHPC shear key with embedded short reinforcements could further improve the shear resistance and ductility to ensure the composite action between the precast slab and wet joint. Compared with the dual layers of extended reinforcements, the combination of the UHPC shear key and short straight steel bar presented a better performance in strength under a relatively lower slip level. In addition, the increase in width was helpful for enhancing the shear strength of the UHPC shear key, but the shear keys with the larger width might cause the failure of the precast part between two UHPC shear keys prior to the UHPC shear keys so limiting the strength development of interface, thus the reasonable design size of the shear key should be selected depending on the precast and post-cast concrete strength. Furthermore, an equation for the wet joint with UHPC shear key was proposed, which considered the proportion of effects of different factors such as the interface bonding strength, interface friction, extended reinforcement, negative bending moment, UHPC shear key and embedded short straight steel bar on the longitudinal shear behavior of UHPC wet joints.