Maximum Shear Strength Limit for Reinforced Concrete Deep Beams

Although it is widely known that the shear strength of reinforced concrete (RC) deep beams is higher than that of general RC beams to which Bernoulli’s assumption can be applied, the maximum shear strength limit of deep beams is identical to that of general beams. Therefore, the shear strength of deep beams is limited to a low value due to the shear strength limit in many cases. Different codes currently in use have different limit values for the maximum shear strength of deep beams. The strength limit of deep beams in the ACI 318–19 code is a function of the square root of concrete compressive strength ( $$\sqrt{{{\varvec{f}}}_{{\varvec{c}}}\boldsymbol{^\prime}}$$ ), but that in the AASHTO-LRFD code is a linear function of $${{\varvec{f}}}_{{\varvec{c}}}\boldsymbol{^\prime}$$ . Therefore, the ACI 318–19 code tends to underestimate the shear strength of deep beams with high-strength concrete. In addition, because the strength limits of the two codes do not consider the influences of the shear span-to-depth ratio, they may overestimate the strength of large-size deep beams with a large shear span-to-depth ratio. In this study, an equation for evaluating the maximum shear strength limit of deep beams was developed and verified against the experimental results, considering the effective compressive strength of concrete, shear span-to-depth ratio. The proposed maximum strength limit of deep beams was compared with the shear strengths of 672 deep beams, and the results indicated that the prediction closely matched the measured strength limit. The coefficient of variation of the shear strength ratio of ACI318-19 code was 39.2%, while that of the proposed equation was 32.3%, which was the smallest among the three predictions.