Research On Bond Behavior Of Steel Fiber Reinforced Self-stressing And Self-compacting Concrete Filled Steel Tube

Based on concrete-filled steel tube(CFST)structure,this paper advanced a new structure model,called steel fiber reinforced self-stressing and self-compacting concrete filled steel tube.The new structure not only retain the advantages of CFST,but also use self-compacting concrete to improve the fluidity of concrete,and self-stressing concrete can produce self-stress to improve the interaction between steel tube and concrete,and steel fiber to improve the tensile,compressive strength of concrete,the working performance of CFST structure is improved.Based on the project on research on design theory of fiber reinforced self-stressing and self-compacting high strength concrete filled steel tube columns by the National Natural Science Foundation of China(51678456),this paper mainly study on bond behavior of steel fiber reinforced self-stressing and self-compacting concrete filled steel tube,this paper carried out the following works:(1)Research on proportioning design of steel fiber reinforced self-stressing and self-compacting concrete,and compounded the concrete successfully.The mixtures were cast into the cubes,then this paper investigated the expansive capacity of concrete under constraint conditions of steel tube.The test results showed that:steel fiber reinforced self-stressing and self-compacting concrete under the limit of the steel tube can produce self-stress.The values of self-stress increases with the steel ratio,and reduces with the increasing of the steel fiber volume percentage.(2)The first push-out tests were conducted on 8 groups of self-compacting CFST,8 groups of self-stressing and self-compacting CFST and 9 groups of steel fiber reinforced self-stressing and self-compacting CFST,and the second reversed push-out tests were conducted after 2.5years.The tested parameters include self-stress,concrete strength,steel fiber volume percentage and steel ratio.The test results showed that the bond strengths of self-compacting CFST specimens in first push-out tests are higher than that in second reversed push-out tests.However,the bond strengths of self-stressing and self-compacting CFST specimens and steel fiber reinforced self-stressing self-compacting CFST specimens in first tests are smaller than that in second tests.Self-stress improves the bond strengths of specimens in two tests.The bond strengths in two tests increase with the increasing of concrete strength,steel ratio.the steel fiber volume percentage increased,the bond strength enhancement rate increased.Moreover,formulas were proposed to predict the bond strength of steel fiber reinforced self-stressing and self-compacting CFST specimens,and the predictions agreed well with the test results.(3)Research the bond slip constitutive relation of steel fiber reinforced self-stressing and self-compacting concrete filled steel tube,according to the results of the push-out tests,steel fiber reinforced self-stressing and self-compacting concrete filled steel tube bond-slip constitutive relation were proposed.The mathematical description of the average bond stress-slip curve is divided into three sections.(4)In order to study the bonding performance degradation of steel fiber reinforced self-stressing self-compacting CFST specimens,the quartic push-out tests were conducted on 3 groups of self-stressing self-compacting CFST and 3 groups of steel fiber reinforced self-stressing self-compacting CFST after the curing period of 2.5years.The test results showed that the bond strengths at 2.5 curing years are higher than that at 28 curing days.The bond strengths decrease with the increasing of test number.Steel fibers can alleviate the bonding performance degradation of CFST specimens.