Slenderness Effects in Circular RC Columns Strengthened with CFRP Sheets Using Different External Bonding Techniques

This study aims to investigate the behavior of slender RC columns retrofitted with fiber-reinforced polymer (FRP) composites by means of the grooving method (GM) in an attempt to lessen the slenderness effects observed in other retrofitting methods. For this purpose, nine circular concrete columns with slenderness ratios ranging from 15.4 to 27.7 were tested under constant eccentric loading. Six of the specimens were strengthened with longitudinal FRP composites by either externally bonded reinforcement (EBR) or externally bonded reinforcement on grooves (EBROG) methods. Results showed that with increasing slenderness, load-carrying capacity decreases. However, compared with the EBR and control columns, those strengthened through the EBROG method exhibited lower reductions; this was evidenced by the 12.4%, 12.9%, and 4.2% reduced load-carrying capacities in the control, EBR, and EBROG columns with increasing slenderness ratio. In addition, the EBROG method was observed to enhance the flexural stiffness of the columns and decrease the secondary moments compared with EBR and reference columns. Ductility was also observed to improve as a result of applying the EBROG method to strengthen the columns in the longitudinal direction compared with the EBR and control columns. Also, a semianalytical approach was used to evaluate the theoretical procedure for prediction of experimental results.