Shear Behaviour of UHPC Beams with Varying Degrees of Fibre and Shear Reinforcement

An experimental campaign was conducted to investigate the behaviour of I-shaped single span beams made of Ultra-High Performance Concrete (UHPC) subjected to shear loading. The main parameters were the fibre content (up to 2% by volume) and the degree of stirrup reinforcement (no stirrups or with stirrups diameter 10 mm, spacing 125 to 300 mm). A total of 18 tests were performed, all of them ending up in typical shear failure: Pronounced shear cracks formed along the web between support and load introduction at around a level of 60-70% of the ultimate load. Close to the maximum load level, the formation of a critical main shear crack with an average inclination of about 30 degrees to 35 degrees was observed, finally propagating into the compressed upper flange sections. The effect of the fibres as well as the stirrup contribution are assessed and quantified. Thereby a decisive effect of the fibres was observed: The addition of 1% to 2% fibres by volume led to a more distributed crack pattern as well as a significant increase of the ultimate load, rather proportional to the residual tensile strength than to the fibre content. The effect of adding fibres was larger for non shear-reinforced beams than for beams provided with stirrups.