Shear-friction behavior of concrete-to-concrete interface under direct shear load

Shear transfer at concrete-to-concrete interfaces under direct shear is of great significance to the performance of concrete structures. In this study, a series of direct shear specimens with concrete-to-concrete interfaces were designed by considering the normal pressure, longitudinal reinforcement, and coupling effects. Adding reinforcement or normal pressure increased the interface cracking stress, ultimate shear strength, and residual shear strength, and changed the brittle behavior of the bonding interface to a gradual strength degradation mode. However, an increase in the normal pressure from 4 to 8 MPa only slightly improved the elastic stiffness and plastic ductility of the direct shear specimens. Furthermore, comparing the observed ultimate strengths with the calculated ultimate strengths of three models in main codes, it was shown that all calculated strengths were conservative. During the shear-slip process, among cohesion, friction, and dowel action, the friction was the most affected property during the direct shear process. In the final residual stage, the ratios of cohesion, friction, and dowel action were found to be similar, and no significant relationship was observed between the longitudinal reinforcement and normal pressure before the ultimate shear stress was reached. However, after the ultimate shear stress was reached, the interaction was found to improve the shear resistance at the concrete-to-concrete interface, thereby improving the ductility and interface shear performance.

Automated summary

The study found that increasing reinforcement or normal pressure can enhance the bonding strength, ultimate shear strength, and residual shear strength of concrete-to-concrete interfaces, while also modifying their brittle behavior. However, increasing normal pressure has minimal impact on the elastic stiffness and plastic ductility of the specimens. The calculated ultimate strengths from different models were all conservative, with friction being the most affected property during the shear-slip process.