Steel fibres as minimum shear reinforcement in reinforced concrete beams

The results of an experimental appraisal of the ACI Building Code provisions allowing the use of deformed steel fibres as minimum shear reinforcement in reinforced concrete beams are presented. Two types of hooked-end steel fibres of lengths 35 mm and 60 mm were used in the fibrous concretes at volume fractions in the range of 0.75 to 1.5% and 0.5 to 1%, respectively. The performance of the fibrous concrete beams was compared to that of beams detailed with code-specified minimum web reinforcement. The results indicate that the use of hooked-end steel fibres even at a volume fraction (0.5%) lower than the ACI Code-specified minimum of 0.75% led to multiple diagonal cracking with crack widths significantly smaller than permissible values. The measured shear strengths across all fibre aspect ratios and volume fractions were higher than a lower bound limit for fibrous concrete beams reported in the literature as well as predicted values of the beams with code-specified conventional minimum web reinforcement. The results of this investigation support the use of the steel fibres used in the experiments as minimum shear reinforcement in normal-strength reinforced concrete beams with depths equal to those of the tested beams.