Critical shear crack shapes in slender reinforced concrete beams with and without shear reinforcement

Abstract The accurate prediction of the shear capacity of reinforced concrete underpins the efficient and safe design of concrete buildings and infrastructure. Disagreement remains about shear mechanisms and the modeling of shear resistance. For slender beams without shear reinforcement, critical shear crack (CSC) models have attracted interest. In these models, the shear crack geometry informs the description of the crack kinematics and calculation of shear resistance. Hence, inaccuracies in the assumed crack geometry potentially have consequences for shear capacity prediction. In this paper, the importance of the shear crack geometry in slender reinforced concrete beams, and the parameters that influence the crack shape of a CSC, are discussed. An experimental program on slender shear critical beams with longitudinal steel ratios between and and with or without relatively modest shear reinforcement ratios (0.14%–0.18%) was undertaken. During testing, images of the CSC propagation were acquired and then analyzed using digital image correlation. It was found that the CSC typically had varying crack lengths, amplitudes, tensile delamination characteristics and compressive zone trajectories. While these features were not necessarily well captured with assumed linear, bi‐linear, or exponential crack shapes, they could be described using a fifth degree polynomial function. The ultimate shear capacities and crack shapes for the slender beams with or without shear reinforcement were quantified for the different longitudinal ratios. This new knowledge informs future shear designs.