Experimental study on shear transfer across interfaces with post-installed shear reinforcement

To address the fit-up issues arising from reinforcement congestion and limited seating area over precast beams, an improved joint detail characterized by post-installed interface shear reinforcement has been developed. The incorporation of post-installed narrower looped bars as an alternative to conventional protruding stirrups significantly expedites the erection of precast flooring systems. Moreover, direct shear tests are performed on 30 Z-shaped specimens to investigate the influence of joint details, surface roughness, looped bar ratio, and embedment length of post-installed bars on the interface shear behavior. Experimental results indicate that employing post-installed narrower looped bars not only ensures adequate seating length for precast flooring systems, but also prevents the splitting failure of concrete cover which can induce the degradation of dowel action. Sufficient anchorage is the prerequisite for post-installed looped bars to impose clamping stress on concrete interface, and a shallow embedment length may trigger the occurrence of pull-out failure. Surface roughness is another factor determining the interface shear resistance and stiffness. Untreated surfaces, in contrast to intentionally roughened surfaces, are susceptible to the cohesion fracture and may hinder the development of shear-friction action. Furthermore, a linear correlation exists between looped bar ratio and the shear resistance of concrete interface. Based on the experimental results, design recommendations, including the minimum required anchorage length for post-installed looped bars, are proposed for the novel joint detail.