Abstract: At present, ultra-high performance concrete (UHPC) is widely used for reinforcement of composite members and normal concrete (NC) structures. After reinforcement, the interface between UHPC and NC becomes the most vulnerable part due to the combined effect of interface normal tensile stress and interface tangential shear stress. Reinforcement planting treatment is a common method to connect the interface between old concrete and new concrete. In this study, the shear strength of UHPC-NC specimens with and without reinforcement planting and the effect of reinforcement rate on shear performance were comprehensively analyzed by straight shear test and finite element simulation. The results show that the shear strength of specimens without reinforcement planting is only 20% of that of integrally cast specimens, while the shear strength of the reinforcement planting specimens could reach 40% to 80%. In specimens without reinforcement planting, the damage form is brittle damage. In reinforcement planting specimens, the development of interface cracks is controlled, the interface shear strength is improved, the slip of interface slip is increased, and the interface is ductile failure.

Key words: UHPC, new and old concrete, reinforcing bar reinforcement, bond surface, shear property, reinforcement rate