Experimental investigation and mechanical modelling of shear failure in reinforced concrete members with plain and ribbed bent-up bars

Abstract

Using bent-up bars as shear reinforcement was state of the art in reinforced concrete (RC) construction until the 1970s. Since the approach to shear reinforcement design has changed since then, the structural assessment according of structural members to current structural codes often yield insufficient theoretical shear capacities. In this paper, a series of twelve shear tests on members with plain and ribbed bent-up bars is presented. Despite the beams only containing plain bars or widely spaced bent-up bars, the test results show higher shear capacity compared to reference beams without any shear reinforcement, and the formation of pronounced localised shear cracks. The contribution of the bent-up bars to the shear strength is evaluated by combining the constitutive laws of various shear transfer mechanisms along an idealised shear crack. The model approach is validated by a comparison with detailed test measurements. It is shown that the interaction of the bent-up reinforcing bars with other shear mechanisms in a localised shear crack is highly dependent on the bond behaviour of bent-up and longitudinal bars. The great potential of this approach for the refined assessment of existing structures with bent-up bars is confirmed by the accuracy of its predictions.