Experimental Study On Bond Performance Of Steel-carbon Fiber Reinforced Concrete Under Unidirectional And Repeated Loads

In offshore engineering construction,due to the erosion of chlorine salt,the corrosion of steel bars in reinforced concrete is more serious,which brings a series of safety problems in structural use.The steel-FRP composite reinforcement(SFCB),which is prepared by using FRP as the outer material and wrapping steel bars,can be used as a substitute material for steel bars in concrete structures to solve such problems.At the same time,SFCB integrates the advantages of high elastic modulus,good ductility,strong FRP corrosion resistance and high ultimate strength of ordinary steel bars,and has high research value.In reinforced concrete,bond performance has important influence on cracking,internal force distribution and hysteretic behavior under earthquake.Similarly,in SFCB concrete,good bonding is the key to ensure that SFCB and concrete give full play to mechanical properties and ensure durability of the structure.In addition to being a static bearing structure,reinforced concrete structures are also subjected to periodic loads,such as transport vehicle loads,ocean wave impact loads and wind loads.Therefore,it is of great significance to study the bond performance and fatigue performance of SCFCB concrete in engineering practice.In order to understand the bond performance between SCFCB and concrete under unidirectional loading and different repeated loading modes,considering the factors such as concrete strength,bond length and reinforcement type,36 central pull-out specimens were tested,and the failure mode,stress process,bond slip curve and bond stress distribution law of SCFCB were analyzed.The main contents and research results of this paper are as follows:1.Based on 24 central pull-out specimens,the unidirectional pull-out tests of reinforced concrete,CFRP reinforced concrete and SCFCB concrete with different strength grades and bond lengths are carried out,and the bond failure modes,load-slip curves and bond-slip curves of SCFCB concrete are systematically analyzed.the results show that the bond failure modes of SCFCB concrete are similar to those of CFRP reinforced concrete,and there are two kinds of situations of steel core yielding and non-yielding.There are four stages in the load-slip curve and bond-slip curve of SCFCB concrete,showing secondary bond stiffness at the yield point of SCFCB steel core.2.Equal-order repeated drawing and variable-order repeated drawing tests were carried out based on 12 central drawing specimens.The results show that the failure mode of SCFCB concrete under repeated loading is mostly SCFCB pull-out failure,and the bond-slip curve forms hysteresis loop due to residual deformation during unloading.With the loading moving to the right,there are differences in the recovery ability of different reinforcement materials in residual deformation,which are mainly manifested in the different recovery degree of residual slip during the first unloading and the different increase amplitude of residual slip under the same loading times.3.Based on the central drawing specimen with embedded fiber Bragg grating,the distribution law of SCFCB strain and bond stress at bond interface of SCFCB concrete in unidirectional drawing and repeated drawing tests is analyzed.The results show that the strain distribution of SCFCB decreases step by step to the free end under uniaxial and repeated drawing tests,and the bond stress is transferred from the loading end to the free end.Under repeated pull-out tests,the distribution of bond stress is concentrated near the free end.