Flexural strengthening of concrete beams with near-surface mounted steel–fiber-reinforced polymer composite bars

This article presents an experimental study on concrete beams strengthened with NSM reinforcements under monotonic static loading. The NSM reinforcements include commonly used steel bars, CFRP bars, and four different types of SFCBs. The main parameters of SFCBs considered in this study have been the types of FRP used (CFRP and basalt FRP) and steel/FRP ratio. The results show that (1) the stiffness during the elastic stage and the load capacity at the ultimate state of concrete beams strengthened with NSM–SFCB could be enhanced significantly; (2) the failure modes of the two concrete beams were as follows: the concrete beam strengthened with ordinary steel bar crushed after the steel bar yielded, while the beam strengthened with CFRP bar demonstrated a debonding of concrete cover on the beam soffit without any crushing of the concrete in the compression zone; (3) the steel/FRP ratio is of vital importance for the performance of beams strengthened with NSM–SFCBs. For SFCB with a high FRP/steel ratio, debonding of the concrete cover occurred after the yielding of the SFCB inner steel bars, while for beams strengthened with NSM SFCB with lower FRP/steel ratio, concrete crushing occurred after the rupture of the SFCB outer FRP; (4) compared with NSM–CFRP bars, NSM–SFCB can achieve the same anticorrosion properties at a much lower cost, which makes SFCB a competitive material for NSM strengthening of concrete structures.