Seismic performance of short concrete columns reinforced with steel-FRP composite bars and GFRP stirrups

The steel-FRP composite bar (SFCB) is an ideal reinforcement choice for structures aimed at enhancing durability and resilience. However, research on the seismic applications of SFCBs has primarily focused on flexure-dominated concrete columns, with limited experimental investigation into columns subjected to axial-shear-flexure interaction. To address this gap, quasi-static tests were conducted on six short concrete columns to evaluate their seismic performance. The study examined the effects of key variables, including longitudinal reinforcement type, the spacing of GFRP stirrups, and shear span-to-depth ratios. The results show that all specimens exhibited a shear-flexure failure mode. Compared to the steel-reinforced short column, SFCB-reinforced short columns with an equal stiffness design method demonstrate better seismic performance, including reduced shear-flexure damage, similar initial stiffness, higher load-bearing capacity, and increased resilience. Reducing the GFRP stirrup spacing enhances the shear capacity of SFCB-reinforced columns, thereby reducing shear deformation and improving ductility. A decrease in the shear span-to-depth ratio significantly increases the stiffness and overall load-displacement curves of SFCB-reinforced columns, with a slight improvement in resilience. An analytical model incorporating axial-shear-flexure interaction was developed using the uniaxial-shear-flexure model (USFM) approach and validated by comparing the predicted envelope curves with the experimental results.