Influence of concrete stress state on shear contribution of frp strips on rc beams

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.