Critical shear displacement theory: on the way to extending the scope of shear design and assessment for members without shear reinforcement

This paper presents a new theory for the shear capacity of reinforced concrete members without shear reinforcement. While recognizing that there are multiple failure mechanisms, the theory attributes the opening of a critical flexural shear crack as the lower bound of the shear capacity. It proposes that the shear displacement of an existing flexural crack can be used as the criterion for the unstable opening of the critical flexural shear crack. Based on the theory, a simplified shear evaluation model is presented in the paper. Compare to the current shear provisions in the design codes, the model is characterized by good accuracy and a solid physical background. It shows great flexibility to deal with complex design conditions. As an example, the paper discusses the possibility of extending the theory to the shear resistance of higher strength concrete. The suggested method provides a more logic and fluent transition from normal strength to high strength concrete and shows good agreement with experimental observations.