Shear behavior of RC beams with CFRP-steel strip hybrid stirrups

This study proposes a novel carbon fiber reinforced polymer (CFRP)-steel strip hybrid stirrup to enhance the ductility of reinforced concrete (RC) beams. To investigate its effectiveness, three-point bending tests on 11 RC beams were conducted, comparing the proposed hybrid stirrups with conventional steel and CFRP strip stirrups. The effects of stirrup spacing and number of CFRP layers were also examined. Results showed obvious advantages of the proposed hybrid stirrups. Compared to the beam reinforced with only CFRP strip stirrups, the inner steel strip of the hybrid stirrups enhanced the rigidity and crack control, enhancing the reinforcing efficiency by up to 45%. In comparison with the beam reinforced with only steel strip stirrups, the outer CFRP strip of the hybrid stirrups can maintain the load in the later loading stages, thereby effectively improving the ultimate deflection by 1.7 times. For beams with CFRP strip stirrups, neither decreasing the stirrup spacing nor increasing the layers of CFRP contributed obviously to the shear capacity and ductility. However, for beams with hybrid stirrups, while the ductility increased significantly as the layers of CFRP, both shear capacity and ductility decreased with the stirrup spacing. Finally, a formula to calculate the shear capacity of the beams with hybrid stirrups was proposed and the calculated results agreed well with the experimental findings, which validated its applicability.