Punching shear tests and design of UHTCC-enhanced RC slab-column joints with shear reinforcements

Reinforced concrete (RC) flat slab structure may suffer progressive collapse, which is usually caused by the punching shear failure of slab-column joints. Existing research has shown that the utilization of shear reinforcements or ultra-high toughness cementitious composite (UHTCC) in slab-column joints is efficient in improving their punching shear performance. In this study, shear reinforcement was introduced into UHTCC-enhanced RC slab-column joints. Specimens of UHTCC-enhanced slab-column joints considering the effect of shear reinforcements were tested. The cracking development process, bearing capacity, and ductility were analyzed. Yield line theory and critical shear crack theory were adopted to predict flexural and punching shear capacities, respectively. Finally, the failure patterns of the specimens were discriminated by comparing the predicted punching shear and flexural capacities, taking the ductile coefficient into account. The theoretical results combined with test results show the effect of shear reinforcement on the behavior of UHTCC-enhanced joints. Significant improvement in the bearing capacity and ductility of joints is achieved by applying shear reinforcement. The failure pattern of a joint varies from premature punching shear failure to flexural-triggered punching shear failure with the application of UHTCC, and this transform is more pronounced with shear reinforcement applied into the UHTCC-enhanced joint.