Study On Failure Mechanics Of Shear Strengthened Beam With U-jacket FRP

Currently, the research on shear strengthening for RC beams with FRP, which still lags behind the one on flexural strengthening with FRP, mainly inculdes the computing of shear capacity and debonding mechanics of FRP. In the last decade, many scholars at home and abroad have done extensive experiment studies and finite elements analysis on shear strengthened beam with FRP, formulates of shear capacity were presented and relevant codes were built. However, the mechanism of debonding propagation process of FRP haven't been further studied due to its complexity. Recent studies show that the bond behaviour between FRP and concrete in RC beams shear strengthened with FRP may be closely represented by simple shear tests. Therefore, the FRP-concrete interfacial bond-slip relationship which obtained from the shear tests can be applied to the analysis of the debonding failure of shear strengthening with bonded FRP.Compared with side-bonded FRP, bonded with U-jacket FRP can increase the shear capacity of RC beam more effectively. This paper establishes the mechanical model of shear strengthened RC beam with U-jacket FRP, in which the bilinear local bond-slip law given by H. Yuan is employed and the unloading is taken into account: within the elastic stage unloading path is like the original, but within the softening stage unloading path is parallel to the initial stiffness. Then theoretical solution which is capable of predicting the entire debonding propagation process is presented and expressions for normal stress of FRP, interfacial shear stress and the load-displacement relationship at the crack are derived for different loading stages.Through analysing critical lengths of FRP above principal inclined crack for different debonding failure process in each section, the flowchart for the debonding failure process of FRP, the relationship between normal stress of FRP and shear crack width in the section of different critical lengths, the normal stress of FRP distribution and FRP-to-concrete interfacial shear stress distribution are presented. Using the program of MATLAB language, the relationship between shear capacity and uniform crack width and the normal stress distribution of FRP in shear strengthened beam with U-jacket FRP are abtained by employing different simplified principal inclined crack, and the results are compared with that shear strengthed with side-bonded FRP.Finally, the shear strengthening effect and debonding failure process of FRP are studied by a test of shear strengthened RC beam of different corrosion grade with U-jacket FRP.