Strengthening of RC columns by longitudinal CFRP sheets: Effect of strengthening technique

• Ten RC column specimens were strengthened with longitudinal CFRP sheets.
• Four different methods were used for strengthening of RC column specimens.
• Grooving method (GM) significantly increased the load capacity compared to EBR.
• PIV technique was used to investigate the bond behavior of CFRP-to-concrete under compression.
• PIV measurements verified that GM improves the bond of CFRP-to-concrete compared to EBR method.

In the present study, the effect of utilizing longitudinal carbon fiber reinforced polymer (CFRP), as external compression reinforcement, on the behavior of strengthened RC columns is investigated. To do so, 10 RC columns including 5 circular columns with diameter of 150 mm and 5 square columns with dimension of 133 mm were cast. Four different methods including conventional externally bonded reinforcement (EBR) and near surface mounted (NSM) techniques, as well as the recently introduced grooving method (GM) in the forms of externally bonded reinforcement on grooves (EBROG, to be pronounced as /ebrΛg/) and externally bonded reinforcement in grooves (EBRIG, to be pronounced as /ebrIg/) techniques were used to strengthen the specimens in compression with CFRP. The specimens were tested under monotonic uniaxial compression, and different effects of the strengthening techniques were comprehensively discussed. Furthermore, an image-based deformation measurement technique, i.e. particle image velocimetry (PIV) was used to further investigate the stress transfer between longitudinal CFRP sheet and concrete substrate. Experimental results demonstrated that utilizing grooving method (GM) for bonding CFRP to concrete surface postpones the CFRP buckling, and subsequently, a significant increase in load carrying capacity of strengthened RC columns by compression CFRP sheets was observed.