The effects of cross-sectional shape and loading condition on performance of reinforced concrete members confined with Carbon Fiber-Reinforced Polymers

This paper presents results of an experimental study to investigate the effect of the cross-sectional shape on the structural performance of reinforced concrete (RC) members confined with Carbon Fiber-Reinforced Polymers (CFRP) under various loading conditions. A total of 32 specimens were tested. Test parameters included the cross-sectional shape: circular, square, and rectangular with two different aspect ratios, and the loading condition. The loading condition included concentric loading, eccentric loading with two different eccentricity-to-section-height ratios of 0.46 and 0.6, and pure bending. The level of the CFRP-confinement in the strengthened specimens and the slenderness ratio of the eccentrically loaded members were kept constant. Test results indicated that the CFRP-confinement effectively improved the load capacity and ductility under concentric loading. The gains in load capacity and ductility of the concentrically loaded members were greatly affected by the cross-sectional shape, ranging from 23% to 44% increase in load capacity and 250% to 350% increase in axial deformation for the rectangular and circular cross-sections, respectively. The CFRP-confinement also improved the performance of the eccentrically loaded members but to a lower extent with an increase in load capacity ranging from 18% to 28%, and in ductility, measured by the lateral displacement capacity, ranging from 43% to 120%. For the level of confinement and eccentricity ratios used in this study, the cross-sectional shape had a slight effect on the ductility of the eccentrically loaded members where rectangular cross-sections exhibited lower gain in ductility relative to the square and circular cross-sections, but it had no noticeable effect on the gain in load capacity under eccentric loading. For the members of pure bending, the CFRP-confinement had no significant effect on the flexural capacity but resulted in a remarkable improvement in the member ductility, ranging from 340% to 460% increase in deflection capacity of the members with the rectangular and square cross-sections, respectively.