The Stripping Behavior Of Frp Shear Strengthening Of Concrete Beams

A number of failure modes in reinforced concrete (RC) members shear strengthened with U-fiber reinforced polymer (FRP) sheets are directly caused by debonding of the FRP from the concrete, therefore, the performance of the FRP-concrete interface in providing an effective stress transfer is of crucial importance. In this thesis, a systematic investigation is carried out on shear behavior and debonding mechanism of RC beams strengthened with U-FRP sheets based on the existing test data and the FEM results. The proposed models represent substantial improvements to existing models as verified by compared to existing test data.The major contributions of the work in this thesis are listed as follows:1) By means of finite element analysis software ANSYS, the shear behaviors of RC beams strengthened with U-FRP are simulated and analyzed, including ultimate shear capacity, load-deflection relationship, stress and strain distributions of concrete, stirrups and FRP, and slippage of glue. The factors, such as shear span ratio, FRP pattern and amount, are all considered in this approach. Furthermore, the influence factors on shear capacity and debonding mechanism are discussed.2) The element of COMBIN39 could be better modeled with the glue slippage. The numerical result shows that the maximum glue slippage is at the top of beam and the minimum is at the bottom of beam. And it also shows the excessive glue slippage is the key reason to debonding fracture of U-FRP.3) The FEM results of shear capacity distribution indicated that the U-FRP works as stirrups and shares the capacity of strengthened beam as tension bars of truss-arch model.4) Based on the detailed understanding of the debonding failure mechanism and the effect of the previous factors on the shear capacity, new formulae of debonding capacity are deduced for U-FRP- strengthened RC beams by modified truss-arch model. A parameter D_f is used to describe the non-uniform strain of FRP. The predictions of the proposed formulae are shown to be in close agreement with the test data, and have higher calculation precision.5) Considering the influence of U-FRP-debonding on shear capacity, a suitable design method and calculation procedure is put forward for designer. And some measures of anchoring system and quality control of processing are proposed to avoid the debonding failure.