Size effect of square concrete columns confined with CFRP wraps

Most of the previous research conducted on concrete columns confined with fiber- reinforced polymer (FRP) composites has been based on small sized specimens. Such sizes can result in the FRP confinement relative to the concrete component to be significantly stiffer than practical retrofit applications. In addition, few investigations have confirmed the validity of extrapolating small-scale specimen results to large-scale specimen results. In this study, nine square concrete columns wrapped with carbon fiber-reinforced polymer (CFRP) composites were divided into five groups and tested under concentric axial monotonic compressive loading. In each group, the specimens consisted of two different cross-sectional dimensions but the same lateral confinement pressure according to ACI.440-2R Code. The experimental results showed that for specimens with different cross-sectional dimensions but same lateral confinement, there were significant differences in the compressive strength and axial stress-strain responses. The confinement of CFRP wraps resulted in significant increases in both the axial strain and stress capacity of confined small-sized columns, while significant enhancement in axial strain but only slightly increases in axial stress for large-sized square columns were observed. All axial stress-strain responses exhibited the same bilinear ascending trend, however, the slope of the second linear portion of the large-sized columns was smaller than that of the small-sized columns.