Repairing or strengthening of structural members is required in many cases to prevent damages caused by seismic loading. The application of fiber reinforced polymer (FRP) composites has been successfully promoted for external strengthening of reinforced concrete (RC) members such as RC columns. These jackets are commonly formed in a wet layup process for confinement of columns. It has been well established in recent studies that the rupture strains (or strengths) of FRP measured in tests on such FRP-confined RC columns fall substantially below those from flat coupon tensile tests. Furthermore, this problem is more important in rectilinear columns because of premature rupture of FRP at corners due to stress concentration at these parts. Up to now, numerous studies have been conducted on FRP confined rectangular columns to improve the efficiency of composite in confinement; such as rounding corners or using vertical strips as a local reinforcement at corners. In this study, a new method was investigated as using CFRP strips at corners and CFRP battens at sides. In the method, FRP composite does not experience any curvature in confining section and the behavior of FRP is very close to flat coupons in tensile tests. For this purpose, twenty-five RC columns with 133 mm x 133 mm cross section for square columns and 110 mm x 160 mm cross section for rectangular columns were tested experimentally under uniaxial compression. All of the column specimens were 500 mm high. The experimental results clearly demonstrate that the new method of corner strip-batten makes more uniform confinement pressure distribution on section and eliminates the stress concentration at corners; so improves the performance of FRP in confinement significantly. In this case, the compressive strength and ductility of column specimens were respectively increased 10.3% and 32.3% compared to the column confined using usual wrap. Based on results obtained from the current study, local reinforcement at the corners of rectilinear columns with CFRP strips, before horizontal wrapping in the method of corner strip-wrap, avoids premature rupture of FRP wrap at the corners and improves the confinement effectiveness of horizontal CFRP layers. In this method, the compressive strength and ductility of column were increased 11.6% and 36.8%, respectively compared to specimen without corner strip. Key Words Confinement, CFRP composite, Rectilinear RC column, Corner strip, FRP batten, Uniaxial compression.
