Coupling Effect Of Shear Failure Modes And Steel Corrosion On Shear Behavior Of RC Beams Shear-Strengthened With EB-CFRP

The mechanical behavior of reinforced concrete(RC)beams shear-strengthened with externally bonded(EB-)fiber reinforced polymer(FRP)is a hot research topic at present.However,most of the studies are based on fresh concrete beams,which lack of considering the effect of deterioration and degradation of these members due to steel corrosion.In existing structures,especially in the coastal environment,steel corrosion probably takes place as the passive film is broken down because of chloride penetration or concrete carbonation.Once corrosion occurs,the steel mechanical properties would be degraded,the interface bonding performance between the steel and concrete should decrease,and the concrete cover may be cracked and even spalled off.In addition,shear span ratio is one of the dominant factors governing shear failure mode of RC members,having significant effects on the mechanical properties of shear-strengthened beams.Therefore,based on the test results of the three-point bending test,coupling effect of shear span ratio and steel corrosion on shear behavior of RC beams strengthening in shear with externally bonded FRP is studied.Firstly,the experimental analysis of all specimens,such as distribution and propagation of shear cracks,shear failure mode,load-deflection relationship,development of stirrup strain,FRP strain and its ununiformed distribution,were carried out.Based on the above investigations,the thesis focuses on the variation of FRP shear contribution with different steel corrosion ratios under various shear failure modes,as well as the interaction among FRP,concrete and stirrup in the shear-strengthening system.Secondly,a series of mechanical equations are applied to evaluate the mean values of the shear contribution of FRP strips and steel stirrups intersected by the main shear crack at the ultimate limit state.Both of the differences between FRP testing contribution and calculating contribution,and the changes of stirrup contribution after externally bonding FRP strips were compared.Furthermore,the relationship in FRP-concrete-stirrup was deeply studied in order to give strongly support for the computational model establishment on FRP shear contribution under the condition of various shear span ratio and steel corrosion rate.Finally,after distinguishing the differences between the value calculated by existing design guidelines and the experimental value gained by test,evidence shows that without considering the effect of shear span ratio and steel corrosion rate,the predicted value won’t be so correct to some extent.In another word,the guidelines have a potential risk in application.For fixing the knowledge gap in this field,the shear span ratio correction factor f(λ)and the corrosion correction factor f(C)are proposed in the advanced shear-strengthening model.