Axial compression behavior of concrete columns with mixed reinforcement of GFRP bars and steel bars

Concrete columns reinforced with GFRP bars, partially or fully replacing steel, can effectively meet the durability requirements of structures in corrosive environments. Axial compression tests were conducted on four groups of concrete columns with hybrid (mixed) reinforcement and single-type reinforcement. The results show that all specimens failed by concrete splitting, with several longitudinal bars buckling and extensive the concrete cover spalling at failure. In terms of ductility, specimens with hybrid longitudinal reinforcement and GFRP stirrups exhibited the highest value. Under conventional steel stirrup conditions, variations in longitudinal reinforcement configuration minimally affected ductility, whereas specimens reinforced entirely with GFRP bars exhibited the lowest ductility. The ultimate load capacity formula, which comprehensively accounts for the contributions of both longitudinal and transverse reinforcement, yielded theoretical values in close agreement with the experimental results. The test results indicate that the utilization rate of stirrups at the mid-height of hybrid reinforcement columns is greater than that in columns with only ordinary steel or only GFRP reinforcement. The reinforcement configuration showed little influence on the mechanical performance of the concrete itself in the columns. In terms of longitudinal reinforcement utilization, the hybrid steel-GFRP-reinforced columns performed better than those reinforced with GFRP bars alone.