The use of fiber-reinforced polymers (FRP) for retrofitting or strengthening deficient concrete columns noticeably increased in the past few decades. Plenty of research has been conducted on the behavior of FRP-strengthened circular concrete columns, but far less research has dealt with non-circular columns. In the current study, the focus was to investigate the behavior of square columns with low to medium grade concrete and low steel reinforcement that were strengthened using carbon fiber reinforced polymer (CFRP) wrap. In the experimental portion of this investigation, twelve short square reinforced concrete columns (5u22 x 5u22 in cross section and 12u22 high) were cast and tested under concentric axial loading. The specimens were divided evenly into two series, named C2 and C4. In the first series, C2, six column specimens were cast with 2000-psi concrete, representing low-grade concrete. One column was a u22control specimenu22 designed based on older non-seismic codes. A second column, another u22control specimenu22, was designed based on the current seismic design code, ACI 318-14. The four remaining columns were wrapped with CFRP sheets, but with a different number of CFRP wraps. The same scheme was followed for the specimens of the second series (C4), but they were cast with 4000-psi concrete, representing medium grade concrete. Thus, the main parameters considered in the current study were the concrete compressive strength and the thickness of the CFRP jacket (number of wraps). Those two parameters were utilized to investigate the effectiveness of the CFRP confinement in enhancing the axial load carrying capacity and ductility of the strengthened columns. Test results confirmed that the confinement produced by the CFRP jacket enhanced the axial load-carrying capacity, axial strain capacity, and energy absorption if compared to unwrapped columns. In addition, the results showed that there should be an effective thickness for the CFRP jacket in order to achieve a significant enhancement in the performance of the strengthened columns. Moreover, the test results demonstrated that the effectiveness of the CFRP confinement was more pronounced in the case of the low-grade concrete columns (Series C2).
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