Mechanical Properties of Steel-FRP Composite Bars (SFCBs) and Performance of SFCB Reinforced Concrete Structures

A steel-fiber reinforced polymer (FRP) composite bar (SFCB) is a novel reinforcing rebar made of an inner steel bar and outer FRP integrated in a pultrusion process. To promote the application of this new reinforcing rebar, this paper explores the mechanical properties of SFCBs and the performance of SFCB-reinforced concrete structures. Test results of SFCBs under uniaxial and cyclic tensile loading show that SFCB has a high elastic modulus, a stable post-yield modulus and a high ultimate strength. The tensile characteristics of SFCBs calculated according to the mixture law are found to be in good agreement with test results. A direct pullout test between SFCBs and concrete was conducted. The failure modes included SFCB pullout before or after inner steel bar yielded, which depended on factors like the steel/FRP ratio, effective bond length, and concrete strength. With its high-performance, especially with regard to anti-corrosion, and low cost, SFCBs are an ideal near-surface mounted (NSM) material to strengthen concrete beams. Experimental results show that NSM-SFCB strengthening can significantly increase both the section stiffness of the flexural members in the service stage and the bearing capacity in the ultimate stage. Concrete columns reinforced by SFCBs under horizontal cyclic loading were also tested, and the results show that concrete columns reinforced by SFCBs possess high initial stiffness, acceptable bearing capacity and good ductility. More importantly, SFCB columns had an obvious post-yield stiffness, which resulted in smaller residual displacement and, therefore, better post-earthquake reparability.