Shear resistance of concrete reinforced with ultra-high strength steel fibres

In order to evaluate the performance of high strength concrete reinforced with Dramix 5D 65/60 BG fibres, with non-deformable hook and ultra-high tensile strength, 24 beams were subjected to shear, with different fibre content (0, 15, 30 and 50 kg/m³), with and without stirrups in the shear span. In a second test campaign, 18 of those beams were tested again in the opposite end, with a variable shear span/effective depth (a/d) ratio in order to evaluate the influence of this parameter in the shear crack pattern and shear resistance. A probabilistic approach was followed to derive the corresponding design value of the shear strength (a procedure herein named by Design Assisted by Testing, DAT), which was then compared with the design shear strength determined according to recommendations of RILEM, EHE and FIB. Test results of both campaigns showed a significant increase in shear strength in relation to beams without fibres. Besides that, the design values of the shear strength derived from test results (DAT) were considerably higher than the design shear resistance provided by design codes.