Unified shear strength model for reinforced concrete beams - Part I: Development

A theoretical model was developed to predict the shear strength of reinforced concrete (RC) beams with and without shear reinforcement. It was assumed that the shear strength of concrete beams can be determined from the failure of the compression zone of a beam cross section. The shear strength of the compression zone was evaluated, considering the interaction between the shear strength and normal stresses developed by the flexural moment. The failure mechanism of the compression zone changes from a tension failure to a compression failure as the shear span-to-depth ratio (a/d) decreases. The transition of the failure mechanism was properly addressed by considering the geometry of the beam and using material failure criteria of concrete. Therefore, the proposed strength model can describe the failure mechanisms of both slender beams and deep beams with and without shear reinforcement.