Effect of CFRP strip width, spacing, and anchors on the axial and flexural performance of RC columns

This study experimentally investigates the effectiveness of strengthening reinforced concrete (RC) columns with carbon fiber-reinforced polymer (CFRP) strips to enhance their axial load capacity and nonlinear deformation behavior under both concentric and eccentric axial loading. A total of eighteen half-scale RC column specimens, including two unstrengthened references, were fabricated and tested under monotonic axial loads until failure. The experimental program systematically examined the influence of CFRP strip width, spacing, the incorporation of fan-type anchors, and the eccentricity of the applied loads on key structural performance parameters. The results revealed that CFRP strip strengthening significantly improved the load-bearing and energy dissipation capacities of RC columns. Under concentric axial loading, strengthened columns exhibited an average increase of approximately 40% in ultimate load capacity and 14% in initial stiffness, along with a 35% improvement in energy dissipation capacity. However, axial displacement at ultimate load decreased by 39%, indicating that enhanced confinement reduced deformation demands. Under eccentric axial loading, strengthening was even more effective, increasing ultimate load capacity by about 71%, doubling the initial stiffness, and improving the displacement ductility ratio by 25%, thereby enhancing both strength and post-peak deformation capacity. Additionally, the use of fan-type anchors further amplified these benefits. Concentrically loaded specimens with anchors demonstrated increases of 32% in load capacity and 8% in ductility compared to unanchored specimens, while eccentrically loaded anchored columns achieved improvements of 18% in load capacity and 32% in stiffness. These findings highlight the potential of CFRP strip systems combined with anchorage techniques to substantially enhance the load-carrying, stiffness, and energy absorption characteristics of RC columns, which is critical for the seismic retrofit of existing structures subjected to combined axial and bending demands.