Research On The Bond-slip Performance Of BFRP Bars And Concrete

FRP top replacement steel bar is one of the effective ways to solve the durability problem of concrete structure.FRP bar has the advantages of light weight,high strength,good durability,high temperature resistance,and wide selection of materials.As a structural bar,the county has many advantages.At present,the technology of applying FRP bars to concrete as the main bar material is not yet perfect,and the bonding performance of FRP bars to concrete is still to be studied.In this paper,through experiments,theoretical analysis and research on the bonding properties of FRP concrete.The main work completed is as follows:(1)Carry out a pull-out test study on the BFRP bar and concrete center pull-out test.The test results show that the BFRP bar and concrete center pull-out test specimens exhibit two failure modes: BFRP bar pull-out failure and concrete splitting failure;the loading rate is 0.025 mm/s-0.1mm/s range has no significant effect on bond strength;concrete strength is directly proportional to bond strength,but increasing concrete strength has no significant effect on bond strength;BFRP bars and concrete cyclic loading and unloading test results show that when loaded Within the range of 70%,the cyclic loading and unloading curve changes uniformly,and the bonding stiffness increases steadily.When the load exceeds 70%,the reloading curve deviates downward from the previous unloading curve,which can reduce the bonding stress at 70%.As the design bond strength of BFRP bars and concrete;(2)Through the pull-out test of BFRP bars and concrete,it was found that the bond slip curve of BFRP bars and concrete showed four-stage characteristics.The energy parameters and counting parameters of acoustic emission further revealed the development law of the four-stage bond slip curve;Based on the four-stage characteristic of the bond-slip curve between BFRP bars and concrete,a new four-stage bond-slip curve model is proposed,and the basic anchor length of BFRP bars is obtained according to the four-stage curve-slip model.(3)Acquire the acoustic emission signal during the pull-out test of the BFRP bar and concrete center by AE technology,and analyze the acoustic emission parameters.It is found that the amplitude parameter,energy-duration distribution and energy-amplitude distribution are in the bond slip curve The four phases have obvious distribution rules.By monitoring the parameter distribution in the drawing process,you can determine which stage is located;the acoustic emission b value of the specimen during the damage evolution process can be used to warn the drawing stage of the BFRP bar.The acoustic emission count level can represent the degree of damage of the specimen during the drawing process;the rate of cumulative count change can reveal the initial degree of damage of the specimen.