Experimental investigation on the shear performance of UHPC large-keyed epoxy joints subjected to direct shear loading

The joints between precast segments in prefabricated ultra-high performance concrete (UHPC) segmental bridges are of great concern since reinforcements and fibers are disconnected at the interface of joints. To investigate the shear performance of UHPC large-keyed epoxy joints, a series of direct shear specimens were tested to consider three parameters, that is, the confining stress, the depth-height ratio of the shear key, and the steel fiber volume ratio. The cracking patterns, failure modes, and shear capacities of all the UHPC epoxy joints were systematically analyzed to explore the effect of the three parameters. Experimental results showed that the three parameters have significant impacts on the direct shear performance of UHPC large-keyed epoxy joints. Specimens with a depth-height ratio of 0.35 are more beneficial to the shear strength than those of the specimens of 0.2 and 0.5. This phenomenon is quite significant in the situations of low confining stress states. The increase of the confining stress and volume ratio of steel fiber substantially improved the shear strength and the ductility of UHPC epoxy joints, especially when the volume ratio of steel fiber increases from 1% to 2%. The initial crack occurred at 42% similar to 84% of the ultimate shear load, and the initial stiffness and the residual strength increased greatly with the increase of the confining stress. In addition, a modified theoretical model was proposed to predict the shear strength of the UHPC large-keyed epoxy joint, which exhibited a relatively good agreement with the test data.