Flexural behaviour of steel–basalt fibre composite bar-reinforced concrete beams

The utilisation of steel–basalt fibre composite bars (SBFCBs) can effectively solve the corrosion problem of steel-reinforced concrete beams and avoid the poor ductility problem of pure FRP-reinforced concrete beams. However, the research on flexural performance of SBFCB-reinforced concrete beams is still rare. Eleven beams with different reinforcement methods were tested to study the flexural behaviour of SBFCB-reinforced concrete beams and provide reference for its design and application. The failure mode, ultimate bearing capacity and strain of concrete and reinforcement, as well as the crack distribution during loading, were studied. The effects of different reinforcement methods and equivalent reinforcement ratios on the flexural performance of the beams was discussed. In addition, the equivalent reinforcement ratio range of under-reinforced failure was determined, and the theoretical calculation formulas of the yield load and ultimate bearing capacity of the beams were deduced. Results demonstrated that the failure mode of SBFCB-reinforced concrete beams was affected by the equivalent reinforcement ratio; the cracking load values of the beams were close to each other, and the yield load and ultimate load increased with the increase in equivalent reinforcement ratio. The SBFCB-reinforced concrete beams have obvious secondary stiffness. Furthermore, the deflection of the beams at the late loading stage increased faster than that before the yield of the steel bar, which indicates that the beams have good ductility. Moreover, increasing the equivalent reinforcement ratio increased the crack number in the pure bending section of beams, reduced the average crack spacing and reduced the maximum crack width. The ultimate bearing capacity calculated by the deduced formulas were in good agreement with the measured values. The maximum strain of SBFCBs is recommended to be limited to 0.75 times the ultimate strain to prevent sudden brittle failure.