Experimental study on precast concrete columns reinforced with bundled SFCBs under horizontal cyclic loading

The poor corrosion resistance of steel bars limits the potential application of precast concrete structures. A promising solution is the use of steel-fiber reinforced polymer (FRP) composite bars (SFCBs) as reinforcements. SFCBs consist of an inner steel bar and an outer layer of FRP, providing excellent durability and customizable post-yield stiffness. The fabrication process of precast concrete structures can be more efficient by the utilization of bundled reinforcement and the deformation capacity can be enhanced by the weakening of the bond behavior. This paper describes a quasi-static test conducted on five precast concrete columns reinforced with bundled SFCBs (PCC-B-SF), as well as one conventional reinforced concrete column. The variables of the experiment contained the number of bars in each bundle (one (SF-1-P), two (SF-2-P), and three (SF-3-P)) and the construction method used (cast-in-place, partial grouting assembly, or fulllength grouting assembly). The failure modes, hysteretic behavior, energy dissipation, residual deformation, and plastic hinge length were investigated. The results show that increasing the number of bars in each bundle of PCC-B-SFs leads to higher deformation capacity, energy ductility and self-centering ability. The ultimate deformation of SF-3-P was approximately 43.8% higher compared to the single-bar reinforced concrete column. Furthermore, the energy ductility of SF-2P, SF-3-P, and SF-3-PL (with full-length grouting) was 16.1%, 20.7%, and 79.2% higher compared to SF-1-P. However, increasing the number of bars in each bundle may have a negative impact on energy dissipation. With full-length grouting, the highly bundled PCC-B-SF (consisting of three or more bars in one bundle) was found to enhance the bearing capacity and prolong plastic hinge regions. These findings suggest that the performance of PCC-B-SFs can exceed that of cast-in-place concrete columns.