Abstract: FRP (fibre reinforced polymer) debonding is one of the major failure modes for reinforced concrete beams shear-strengthened with external FRP strips. Currently, the properties of the FRP-concrete interface based on pull-off tests are adopted in the capacity prediction of FRP shear-strengthened reinforced concrete beams. However, the concrete layers underneath FRP strips in these two cases are in different stress states, and so are the behaviours of the FRP-concrete interfaces. As a result, the FRP shear contribution may be over-estimated. This effect is examined in this paper, and a reduction factor accounting for the effect of the complex stress state in U jacketed RC beams is proposed based on test results from literature. A comparison with test results shows that better agreement is achieved using the proposed factor to modify FRP shear contribution.