Axial compression performance of circular concrete columns with steel, BFRP, and Steel–FRP composite bar cages: Experimental and numerical evaluation

Durable reinforcement systems are increasingly needed for concrete infrastructure exposed to aggressive environments, where conventional steel reinforcement is vulnerable to corrosion and pure FRP reinforcement may show limited post-peak load resistance. This study experimentally and numerically evaluates complete reinforcement cage systems made of conventional steel, basalt FRP (BFRP), and steel–FRP composite bars (SFCBs) for circular concrete columns. Thirty-six large-scale specimens with a diameter of 250 mm and a height of 1000 mm were tested under concentric axial compression. The investigated variables were cage material, transverse reinforcement configuration (helical spirals or rectilinear ties), and transverse spacing of 58, 76, and 95 mm. The results showed that steel cages provided the highest peak-load envelope, whereas BFRP cages exhibited more brittle post-peak degradation. SFCB cages combined the mechanical contribution of the internal steel core with the potential corrosion-protection benefit of an external FRP layer. At 58 mm spiral spacing, the nominal peak axial stress of the SFCB-reinforced column exceeded those of the corresponding steel- and BFRP-reinforced specimens by approximately 11.9% and 16.0%, respectively. Among tie-confined columns, the SFCB specimen with 76 mm spacing achieved the highest ductility index owing to its extended near-peak deformation range, exceeding the steel and BFRP counterparts by 39.0% and 33.6%, respectively. At 95 mm tie spacing, the SFCB column also showed the largest post-peak energy absorption among the three corresponding specimens. Numerical parametric analyses further indicated enhanced residual load-carrying capacity for the modeled SFCB cages at increased reinforcement ratios. Within the concentric axial-compression conditions investigated, SFCB cages therefore showed a promising balance of peak resistance and post-peak load retention.