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° to 35° 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.
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