Flexural and shear behaviour of high-strength SFRC beams without stirrups

This study investigates the effects of steel fibre content and reinforcement ratio on the flexural and shear behaviours of sustainable high-strength concrete (HSC) beams without stirrups. Five different volume fractions of hooked steel fibres, V_f, 0, 0·25, 0·5, 0·75, and 1%, and two different reinforcement ratios, ρ, 0·72 and 2·93%, were considered. Test results indicated that the minimum shear reinforcement of HSC beams was effectively eliminated by adding only a small amount of steel fibres (≥ 0·25 vol%). This amount was much smaller than the minimum requirement of the ACI 318 code. For the lightly reinforced HSC beams, the load-carrying capacity and post-cracking stiffness were improved by adding steel fibres and increasing their amount, whereas the ultimate deflection decreased with the addition of fibres because of the cracking localization phenomenon. For the heavily reinforced HSC beams, the first-cracking load, load-carrying capacity, and deflection capacity all increased with the addition of steel fibres and increasing their amount up to 0·75%. Finally, based on the comparison of experimental and predictive results, Craig's model and Narayanan's and Kwak's models were determined as the best predictive models for the factored flexural and shear strengths of reinforced HSC and steel-fibre-reinforced concrete beams without stirrups, respectively.