Detailing of shear reinforcement for deep beams

Abstract

This study aims to assess the effectiveness of inclined shear reinforcement in controlling shear crack propagation in deep reinforced concrete beams having depths of 600 mm or greater, as defined within the scope of this study. Although such members may not be classified as deep members in the traditional sense, their behaviour is dominated by non-linear stress distributions and cannot be addressed by conventional methods of designing for vertical stirrups. An analytical modelling of the behaviour of deep beams is performed through the application of the Variable Strut Inclination Method (VSIM) and the Strut-and-Tie Model (STM). The influence of the orientation of shear reinforcement is also addressed by considering vertical stirrups and inclined reinforcement at angles of 45°, 60°, and 75° to the beam longitudinal axis. The effectiveness of inclined shear reinforcement is clearly illustrated and is shown to be highly beneficial in achieving good alignment with the principal tensile stresses. Of the orientations considered in this investigation, an inclination of 60° is shown to be the optimum compromise between the concrete's compression capacity and the reinforcement's tensile capacity. Additionally, the critical region of the beam is identified as spanning over one-quarter of the span length from the support (L/4). A detailing procedure for the reinforcement of such members is proposed and is presented as a means of addressing the issue of shear crack control in deep reinforced concrete beams. Such a procedure is also compatible with conventional methods of design and is therefore a rational solution to the problem of shear behaviour in such members. As such, this study bridges the gap between analytical modelling and practical detailing and provides a solution to the problem of shear behaviour in deep reinforced concrete beams.