Axial strengthening of CFST members using CFRP composites

Abstract

The upgrading of metallic structures is not as widespread compared to upgrading or retrofitting of reinforced concrete (RC) structures as it posses a different and more difficult set of problems. It has already been proved that fibre reinforced polymer (FRP) composites significantly improved the strength of RC structures. The main objective of this study is to experimentally investigate the structural improvements of concrete filled steel tubular (CFST) sections with normal strength concrete using unidirectional carbon fibre reinforced polymer (CFRP) fabrics under axial compression. The size and height of the specimens used in this study were 91.5 x 91.5 x 3.6mm and 600 mm respectively. Out of seven columns, six were externally bonded by CFRP strips having a constant width of 30mm with the spacing of 20mm, 40mm and 60mm and the remaining one was used as reference column. Experiments were undertaken until column failure to fully understand the influence of FRP characteristics on the compressive behaviour of square CFST sections including their failure modes, axial stress-strain behaviour, and load carrying capapcity. From the test results, it was found that the external bonding of CFRP strips provides external confinement pressure effectively and delays the local buckling of steel tube and also improves the load carrying capacity further.