Study On Bond-slip Performance And Damage Evaluation Of Bond Interface Between BFRP And Fiber Reinforced Concrete

FRP material has become one of the most potential materials to effectively solve the durability problem of reinforced concrete structures because of its excellent corrosion resistance and high tensile strength.The research shows that adding fiber into concrete can improve the bond strength between FRP reinforcement and concrete.In order to explore the influence of fiber types on the bond strength of FRP bars,predict and analyze the development of bond strength,and deduce the constitutive model fitting the bond slip relationship between FRP bars and fiber reinforced concrete,the main research contents and conclusions of this paper are as follows:1.The basic mechanical properties of concrete mixed with different fiber types are experimentally studied.The results show that the addition of fiber improves the connectivity of internal components of concrete.With the increase of fiber content,the splitting tensile strength and flexural strength of concrete increase accordingly.The improvement of splitting tensile strength of concrete by carbon fiber is the highest,up to83.27%,and the improvement of splitting tensile strength by polypropylene fiber is low,up to 5.76%.Through the microscopic observation of the damaged pattern by scanning electron microscope(SEM),it is found that the fiber plays a bridging role in the concrete,which hinders the generation and development of micro cracks in the concrete,so as to enhance the tensile and crack resistance of the concrete.2.The central pull-out test of concrete and reinforcement and BFRP reinforcement mixed with different fiber types is carried out,and the bond strength between concrete and reinforcement and BFRP reinforcement mixed with different fiber types is analyzed.The results show that different types of fibers in concrete have different effects on the bond strength between reinforcement and BFRP reinforcement.Basalt fiber,carbon fiber and glass fiber increase the bond strength;Polypropylene fiber and polyvinyl alcohol fiber are used to reduce the bond strength,and the influence trend of steel fiber on the bond strength of the two kinds of reinforcement is different.3.The bond strength calculation formula and peak slip calculation formula for reinforcement and BFRP reinforcement considering fiber influence coefficient are proposed.Using the test data in this paper and the data in other literature to verify the calculation formula,it is found that the ratio of the calculated value to the test value is concentrated near "1",and the calculation result is ideal.Based on the calculation formulas of bond strength and peak slip and referring to the existing constitutive models,a bond slip curve constitutive model with low dependence on the test results is proposed for reinforcement and BFRP reinforcement.It is verified that the goodness of fit of the model is more than 0.97,which can provide reference and basis for the calculation of BFRP reinforced concrete structure.4.The ANSYS finite element analysis model of central drawing specimen is established.The results show that the constitutive model proposed in this paper can describe the bond slip relationship between BFRP reinforcement and concrete,and can improve the finite element analysis efficiency of BFRP reinforced concrete structures.By outputting the stress distribution characteristics of the bonding interface between BFRP reinforcement and concrete,the bonding mechanism between BFRP reinforcement and concrete is deeply analyzed,and the variation characteristics of the bonding interface are explained.It lays a foundation for finite element parameter analysis.5.During the central pull-out test,the damage of the internal bonding interface of the specimen was monitored by acoustic emission equipment.By analyzing the characteristic parameters of acoustic emission signal,the corresponding relationship between the development process of bond strength and the characteristic parameters of acoustic emission is established.Using fractal theory,the acoustic emission energy sequence is reconstructed in phase space.It is found that the bond slip damage between reinforcement and concrete has fractal characteristics,and the correlation dimension can better evaluate the damage of the bond interface.