Strengthening of RC beams with externally bonded and anchored thick CFRP laminate

Abstract

Premature debonding of externally bonded FRP laminate from retrofitted reinforced concrete (RC) members can lead to inefficient use of FRP and can limit the level of strength increase that can be achieved. In this investigation, π-CFRP anchors are used in an attempt to delay the onset of premature debonding and to achieve higher strength in beams retrofitted with a 1.2 mm thick and 50 mm wide CFRP laminate. This investigation consisted of testing six large scale T-beams with a 4500 mm span, 400 mm height and 500 mm flange width under four-point bending. Two beams were tested without retrofit as control beams, one beam with the laminate epoxy bonded to the beam and the remaining three beams with the laminate epoxy bonded and anchored using CFRP π-anchors. One of the beams with 30 anchors exhibited a 46% increase in the debonding load over the beam without anchors while the laminate attained a maximum strain equal to 80% of its ultimate strain capacity, a 94% increase compared to the maximum strain reached in the companion beam strengthened with only the epoxy bonded laminate. The displacement ductility ratio of the latter beam at debonding exceeded 4. The results demonstrate the π-anchoring system effectiveness and a feasible way for efficiently utilizing strong and thick laminates in strengthening RC members.