Interfacial stress analysis of beams strengthened with a prestressed CFRP plate

The debonding failure caused by the interfacial stress concentrations at the cut-off ends of the CFRP plate is one of the main failure modes of the retrofitted beams. This paper presents an analytical solution to calculate the interfacial stresses in the beams strengthened with a CFRP plate under mechanical loads, thermal loads and prestressing actions. Two simplified equations for the maximum interfacial stresses are given as well. The prestressed FRP strengthening scheme and load-relief jacking scheme are employed to apply prestress to the CFRP plate. An example and the parametric study are employed to investigate the development of interfacial stresses and longitudinal stresses in the CFRP plate under different load cases, including mechanical loads, thermal loads and prestressing actions, etc. Results show the interfacial stress concentrations caused by the load-release jacking scheme is far less than those introduced by prestessed FRP strengthening scheme and thermal change. In addition, the length of the CFRP plate has no influencence on the maximum interfacial stresses caused by prestressed FRP strengthening scheme, but the stresses caused by load-relief jacking scheme decreases with the plate length. Moreover, for all the loading cases the maximum interfacial stresses increase with the plate thickness.