Study On The Bond Performance Between GFRP Rebars And Concrete Under Repeated Loading

In the strong corrosive environment such as the ocean,the steel bars in reinforced concrete(RC)structures are vulnerable to corrosion,which has a great negative impact on the performance of RC structures.As a new type of rebars,GFRP rebar has the advantages of high corrosion resistance and light weight.It can be used to replace reinforcement in some projects to solve the problem of structural premature failure caused by reinforcement corrosion.The bond performance between GFRP rebar and concrete is the basis of their excellent performance of concrete structure,and in the service process,they will inevitably be subjected to long-term repeated load.With the accumulation of fatigue damage,the bond performance between GFRP rebar and concrete structures may be greatly affected.Therefore,in order to study the effect of repeated load on the bond performance of GFRP reinforced concrete,4 groups,with size of 550 mm × 150 mm × 100 mm beam specimen is designed and made.The change rule of the sliding amount of beam specimen with the increase of loading times was tested and analyzed,and the calculation model of the sliding amount with the change of loading times was established;Through bending bond test,study the bond performance between GFRP rebar and concrete,and establish the bond stress-slip constitutive relationship between GFRP rebar and concrete under repeated load;In addition,through the central pull-out test,the results obtained from the beam test and the central pull-out test are compared and analyzed.The main research work and conclusions are as follows:(1)The following conclusions can be obtained through repeated load test: with the increase of repeated load level,the initial slip and final slip between GFRP rebar and concrete will increase;The greater the final slip;The residual slip and total slip between GFRP rebar and concrete increased rapidly in the early stage of loading(before the 8th loading),and then the growth rate gradually slowed down and tended to be stable;The more times of loading,the greater the total slip and the smaller the slip recovery value;The calculation model of the residual slip value changing with the loading times is established by using the subsection function and the Boxlucas1 stress transfer model respectively.(2)Through the bending bond test,it was found that each group of specimens has pull-out failure,and the failure occurs on a half of the beam;After breaking the concrete and taking out the GFRP rebars in the bonding section,it is found that the surface of the bonding section has obvious wear phenomenon,and the surface rib is obviously weakened;There is a linear relationship between the ultimate bond strength and the level of repeated load.The higher the level of repeated load,the lower the ultimate bond strength;The residual bond strength decreases with the increase of the repeated load,and the reduction is most obvious when the repeated load level is 45% Pu(Pu is the ultimate load of beam specimen).(3)Through the central pull-out test,it is found that the larger the diameter of GFRP rebars,the lower the ultimate bond strength;The ultimate bond strength measured by the beam specimen is slightly lower than the bond strength measured by the central pull-out specimen,which is related to the different stress of the two types of specimens.It can be seen from the comparison that the direction and shape of the bond-slip curve obtained from the beam test and the central pull-out test are similar,but the failure of the beam test is earlier than that of the central pull-out test.(4)The shape of bond stress-slip curve between GFRP rebar and concrete is basically similar under different levels of repeated load;The repeated load reduces the nominal bond stiffness and effective bond stiffness between GFRP rebar and concrete.At the same time,the bond toughness also decreases with the increase of the repeated load level,reflecting the deterioration of the bond performance of GFRP rebar and concrete under repeated load.Considering the effect of repeated load,the three-segment model is used to fit the relevant test data of bond stress and slip between GFRP rebar and concrete under repeated load.From the fitting results,it can be seen that the test data is in good agreement with the model.