A comparative study of models for shear strength of reinforced concrete deep beams

The shear behaviour of deep reinforced concrete beams has been a focus of experimental and analytical studies since the early 1950s, resulting in different approaches for predicting the shear strength of deep beams. This paper compares the main modelling assumptions of these approaches and summarizes the results from validation studies available in the literature. Based on these comparisons, a twoparameter kinematic theory (2PKT) and a mechanical model by Zararis are selected for further evaluation with the help of test series with different experimental variables. It is shown that both approaches predict the trends in beam series with varying shear-span-to-depth ratios, even though the mechanical model overestimates the shear strength of beams without web reinforcement. It is also shown that the two models differ significantly in capturing the effect of transverse reinforcement and the size effect in shear. While the 2PKT accounts for sliding shear failures which limit the effectiveness of transverse reinforcement beyond a certain reinforcement ratio, the mechanical model predicts a monotonic increase of shear strength with the ratio. The 2PKT is also shown to capture the size effect in shear observed in two series of tests well, while the mechanical model neglects this effect.