Bond Performance Of Steel-CFRP Bar Reinforced Concrete

In marine engineering construction,a large number of chloride ions and the marine environment accelerate steel corrosion,lead to early degradation of the bonding interface of traditional reinforced concrete structures,reduce the bearing capacity of the structure,and seriously affect the service life of reinforced concrete structures.In order to improve the corrosion resistance of reinforcing bars,the fiber reinforced polymer(FRP),which has the characteristics of corrosion resistance and high tensile strength,is used instead of steel reinforcing bars,which can effectively solve the engineering failure caused by the corrosion of reinforcing bars.However,FRP bars are brittle materials,they have shortcomings such as low modulus of elasticity,poor ductility and high price.Finally,FRP-concrete members cannot provide early warning in structures fail,which limits their application in construction.Existing studies have showns that steel-carbon fiber reinforced polymer(SCFRP)is a new material with obvious secondary stiffness.It can effectively solve the durability problem caused by steel corrosion and the brittle failure caused by the low elastic modulus of FRP bars.However,reliable bond behavior between SCFRP and concrete is a fundamental issue for reinforced concrete as the same as common steel and FRP bars.Therefore,study on bond behavior between SCFRP and concrete is an important issue.In order to understand the bond performance between SCFRP bars and concrete,48 pull-out tests of SCFRP reinforced concrete is performed.Different parameters such as the types,bond lengths and concrete strength of SCFRP reinforcements were investigated.The failure modes,failure mechanism,stress process,bond-slip relationship,transfering regulation on SCFRP stress and transfering regulation on bond stress of the specimens were analyzed.1.Based on 24 pull-out specimens,this paper studies the bond properties of SCFRP concrete under monotonic loading.The results showed that the bonding performance between SCFRP and concrete is close to that of FRP reinforced concrete,but its bond slip failure mode and failure mechanism are more complicated than a single material reinforcement.The failure modes of steel bar pull-out can be divided into steel core pull-out before yielding and steel core pull-out after yielding.The concrete splitting failure modes can be divided into concrete splitting before steel core yielding and concrete splits after steel core yielding.There are four characteristic points in the bond slip curve: elastic slip point,yield slip point,peak slip point and residual slip point.2.Based on 24 pull-out specimens,this paper studies the bond properties of SCFRP concrete under repeated loading.The results showed that the bond failure modes of SCFRP and concrete under repeated loading is close to that of SCFRP and concrete under monotonic loading.Duringloading and unloading,due to the irreversible residual deformation at the SCFRP and concrete interface,the bond-slip curve forms are hysteresis loops.As the number of loadings increases,the hysteresis loops gradually moves to the right,and the moving rate gradually decreases.This phenomenon is roughly the same as the development of the basic relationship of the reinforced concrete bond slip under repeated loads.3.Based on the pull-out test specimen of the embedded fiber bragg grating,transfering regulation on SCFRP stress and transfering regulation on bond stress of SCFRP and concrete under monotonic load and repeated load are studied in this paper.The results showed that regardless of monotonic loading or repeated loading,the growth rate and growth trend of SCFRP's steel core stress distribution curve and fiber layer stress distribution curve are basically the same.As the distance between the test point and the loading side increases,the stress gradient of the steel bars decreases gradually.At the same time,the growth rate and growth trend of the bond stress distribution curve of the fiber-steel core interface and the fiber-concrete interface bond stress distribution curve of SCFRP are also roughly the same.As the distance between the test point and the loading end increases,the interfacial bonding stress gradient of most specimens have double-peak characteristic.