Bending performance of reactive powder concrete frame beams reinforced with steel-FRP composite Bars

To investigate the bending behavior of Steel-FRP Composite Bars (SFCBs) reinforced Reactive Powder Concrete (RPC) frame beams, both experimental and theoretical study were conducted on five concrete frame beams with different reinforcement ratio, types of concrete and reinforcement. The results indicate that the bending behavior of SFCBs-RPC frame beams progresses through three distinct stages: from loading to the cracking of tensile RPC, from cracking to the yielding of tensile SFCBs, and from yielding to failure. Compared with steel-reinforced RPC frames, the load of SFCBs-RPC frame beam continues to increase with the increase of deformation after the yielding of SFCBs, demonstrating good bearing capacity and ductility. Furthermore, the deformation and crack width of RPC frame beams are obviously lower than those of ordinary concrete frame beams, indicating the excellent deformation control and crack resistance ability of RPC beams. In addition, formulae for flexural stiffness at each stage were derived using the effective moment of inertia method. Taking the design code of reinforced concrete structure for reference and the tensile contribution of steel fibers and the mechanical performance of SFCBs into consideration, and the formulae for crack width of SFCBs-RPC flexural beam were developed. Formulae for the bearing capacity of SFCBs-RPC frame beams were also proposed on the base of simplified materials constitutive models and reasonable basic assumptions. The values predicted by these proposed formulae aligned well with the results tested. The research provides a theoretical support for the design and application of SFCBs-RPC frame beams.