Grooving methods in square RC columns strengthened with longitudinal CFRP under cyclic axial compression

The current research investigates the application of carbon-fiber reinforced polymer (CFRP) composites with longitudinally aligned fibers for enhancing the compressive strength and ductility of square reinforced concrete (RC) columns under cyclic axial compression. Global buckling of the composite described may result in the debonding of CFRP off the specimen surface, which hinders proper enhancement in the ductility and compressive strength of the strengthened specimens. To postpone the buckling of the longitudinal CFRP sheets under compression, the recently developed grooving method (GM) was employed in the current research and compared with the externally bonded reinforcement (EBR) technique using the conventional surface preparation technique. For this objective, 8 square RC columns were subjected to cyclic axial compression. The experimental parameters consisted technique employed for longitudinal strengthening of the columns and the presence (absence) of intermittent confining wraps. Two grooving techniques, the externally bonded reinforcement on grooves (EBROG) and the externally bonded reinforcement in grooves (EBRIG), were used. Experimental results indicated the considerably higher contribution of the grooving method, relative to that of the conventional EBR, to limiting the buckling of CFRP sheets and to enhancing the ductility and compressive strength of the columns. It was observed that when the GM is employed, the compressive strength of FRP is enhanced based on the exploitation of the compressive capacity of the carbon fibers in the longitudinal sheets. The results illustrated that in the specimens longitudinally strengthened using the EBROG or EBRIG techniques, fiber compressive capacity in the composite reached 43.9% and 69.3% of ultimate tensile strength of fibers in flat coupons; this amount was only 9.6% for the columns strengthened through the EBR technique.