Shear enhancement in reinforced concrete cantilevers with multiple point loads

The shear resistance of reinforced concrete beams is enhanced by arching action when loads are applied to their top face within around twice the beam effective depth (d) of the supports. Previous experimental investigations into shear enhancement have almost exclusively considered simply supported beams with a single point load applied within 2d of supports. Such academic tests are unrepresentative of practice, where loading and support conditions are usually more complex. For example, balanced cantilever cross-head girders of bridges and continuous beams can have multiple point loads applied to the flexural tension face within 2d of supports. Such cases have not previously been investigated experimentally. An experimental programme was thus carried out to investigate shear enhancement in balanced cantilever beams subjected to pairs of concentrated loads within the failing shear span. The shear resistance of the cantilever beams was found to be slightly less than matching simply supported beams, with the difference greatest for beams without shear reinforcement. A strut and tie model was developed for cantilever beams with pairs of concentrated loads applied to the tension face within 2d of the supports. Measured beam strengths were also compared with the predictions of various codes and non-linear finite-element analysis.