Confinement effect of FRP and transverse steel on retrofitting square concrete columns

Abstract

© 2013 International Institute for FRP in Construction. This study presents an experimental investigation into strain distribution of Fibre-Reinforced Polymer (FRP) in FRP-confined concrete columns with internal steel reinforcement under concentric and eccentric loading conditions. A total of nine reinforced concrete columns were cast and tested. Three of them were square in cross-section while the others were originally square but were shape-modified into circular columns with four pieces of segmental circular concrete covers and confined with three layers of CFRP. The nominal compressive strength of the segmental concrete covers was 40 MPa and 80 MPa. All columns were tested under concentric load, 25 mm or 50 mm eccentric load. Strain distribution was obtained by a number of strain gauges located symmetrically around the circumference of the columns. The CFRP strain distribution in the hoop direction and the hoop rupture strain of the shape-modified reinforced concrete columns under different load eccentricity was examined. Moreover, the load-carrying capacity and ductility were compared with columns with different volumetric ratio of transverse steel reinforcement from a previous study to discover the effect of transverse steel confinement on the ductility of FRP-confined columns under both concentric and eccentric load. Results showed that the hoop strain distribution for eccentrically loaded columns was not uniform with the maximum strain that occurred at the extreme compression fibre while the minimum strain occurred at the extreme tension fibre of the columns. The variation of the CFRP hoop strain increased when the eccentricity increased. In addition, columns with different volumetric ratio of transverse steel reinforcement had similar normalised stress and ductility, suggesting that transverse steel reinforcement is insignificant effect on the load-carrying capacity and ductility of FRP-confined columns.