Study On Bond Slip Behavior Between GFRP Reinforcement And Concrete And Its Related Applications

The corrosion of steel reinforcement will reduce the service performance and service life of reinforced concrete structures.Many countries spend a lot of manpower and money on structural maintenance and reinforcement every year.FRP(Fiber reinforced Polymer)reinforcement is one kind of corrosion-resistant reinforcement,which can be used in concrete structures instead of steel reinforcement.The reliable bond property between them is one of the foundations of cooperative work,and it is also closely related to nonlinear finite element analysis.In order to evaluate bond property between FRP reinforcement and concrete and discuss the influence of various parameters on the bond performance,relevant experiments and theoretical research were carried out in this paper.The bond theory was applied to analyze the flexural behavior of GFRP reinforced concrete beams.In this paper,16 specimens were made for beam end test.The effects of loading sequence,concrete strength,surface form of reinforcement,diameter of reinforcement,thickness of protective layer and stirrup on failure mode,characteristic value of bond stress,slip amount and bond-slip curve were discussed.Test results showed that the loading sequence affected the characteristic value of bond stress,but basically did not affect the slip.Bond strength was roughly proportional to the 0.75 th power of cube compressive strength of concrete and approximately proportional to the relative thickness of protective layer.The bonding performance of GFRP bars with surface fiber helical wrapped and concrete was better than that of shallow ribbed and sand coated or ribbed GFRP bars.Bond strength decreased with the increase of the diameter of the reinforcement,and the configuration of stirrups increased the bond stress,but had little effect on the slip.Through the pull-out test database,the calculation formulas of bond strength proposed by Liu Huajie,CSA S6-06,CSA S806-12 and ACI440.1R-15 were checked and revised.Based on the beam-end test results,the calculation formulas of bond strength,residual strength and basic anchorage length were proposed.The suggested formula for calculating anchorage length was more conservative than the formulas specified in CSA S6-06 and CSA S806-12,and was comparable to the requirements for anchorage length in ACI440.1R-15.A three-stage bond-slip constitutive model which can truly reflect the test process and stress state was raised.The bending behavior of GFRP reinforced concrete beams considering bond slip was analyzed by ABAQUS software.The results showed that the simulation results were closer to the test values after considering bond slip.Under monotonic static load,small slip occured between GFRP reinforcement and concrete.Bond strength,slip amount or bond-slip constitutive law affected the flexural behavior of GFRP reinforced concrete beams.The test data showed that the ratio of the maximum service load to the bearing capacity of most GFRP reinforced concrete beams was 0.3～ 0.6.Compared with the concrete strength and reinforcement ratio,increasing the elastic modulus of GFRP reinforcement can not only improve the maximum service load,but also make full use of the tensile strength of GFRP reinforcement.Replacing GFRP reinforcement with equal area steel reinforcement and equal strength steel reinforcement could effectively improve the service load.The effect of the latter was more significant,and the service load could be nearly doubled.