Strength and Ductility of RC Beams Repaired with Bonded CFRP Laminates

The objective of this study is to investigate the strength and ductility aspects of reinforced concrete (Re) beams strengthened with an externally bonded carbon fiber reinforced polymer (CFRP) laminate and to examine how such retrofitting affects strength, deflection, curvature, and energy, as exemplified by the area under the load-deflection curve of the strengthened composite beam. Three series of tests on eleven RC beams were carried out and their ultimate load capacities and ductilities evaluated. The variables in the experimental program were longitudinal steel ratio, volume of internal stirrups, and the location and configuration of external anchorages. The results show that both deflection and energy absorption are drastically reduced when beams are strengthened with bonded CFRP plates without external anchorages. Suitably designed and positioned external anchorages allow much of this lost ductility to be regained; however, even then the ductility of the strengthened beam cannot be restored to its original level. It is shown that definitions of ductility based on deflection and energy are able to give a good and rational representation of the physical aspects of ductility of RC beams strengthened with bonded CFRP laminates with or without external anchorages. The results show that the effects on ductility arising from strengthening existing RC beams with CFRP laminates cannot be ignored, even if it is not clear at this stage how to apply the concept of ductility indices and ductility ratios developed in this paper in design practice.