Behaviour of circularized and FRP wrapped hollow concrete specimens under axial compressive load

Circularizing a square column by bonding concrete segments onto the sides of the column and then wrapping with fibre reinforced polymer (FRP) is considered an effective technique in strengthening square solid columns. This paper investigates the suitability of the circularization technique for strengthening square hollow concrete specimens. Eight specimens in two groups (four solid specimens and four hollow specimens) were cast and tested under axial compression. The first specimen from each group was the reference specimen. The corners of the second specimen were rounded to 20 mm radius and wrapped with two layers of carbon fibre reinforced polymer (CFRP). The third specimen was circularized with full length concrete segments and wrapped with two layers of CFRP. The fourth specimen was circularized with concrete segments shorter than the length of the specimen and wrapped with two layers of CFRP. The test results demonstrate that circularization of hollow specimens similar to the circularization of solid specimens reduces the stress concentration at the corners and enhances the ultimate load carrying capacity and ductility. The circularization with short concrete segments is more effective for hollow specimens than the circularization with full length concrete segments when the ductility is of main concern.