CFRP- confined square RC columns. I: experimental investigation

The majority of experimental studies investigating the stress-strain behavior of square concrete columns confined with carbon fiber-reinforced polymer (CFRP) composites have focused largely on unreinforced columns of small size. Research on the influence of larger cross section, height, internal steel reinforcement, and initial damage on the axial strength and compressive behavior of CFRP-confined square reinforced concrete (RC) columns is, however, limited. To address such knowledge gaps, this paper presents the results of an experimental investigation on the axial stress-strain behavior of 34 larger-sized square-sectioned RC columns confined with CFRP composite wraps. The primary test variables were (1) cross-sectional dimensions, (2) volumetric ratio of internal hoop steel reinforcement, (3) number of layers of CFRP wrap, (4) nature of loading (i.e., monotonic and cyclic), and (5) damage level before CFRP wrapping. The experiments showed the CFRP wrap to considerably enhance the axial strain capacity but to only slightly increase the axial stress capacity. The experiments also showed the internal reinforcement to influence the shape of the axial stress-strain envelope curve and unloading path and the ultimate axial strain and plastic strain values. Predamage was, however, found to have a small influence. A new confinement pressure model for fiber-reinforced polymer (FRP) confined square RC columns is finally proposed.