Study On The Bond-slip Properties Of Corroded Anchor Bar

The bonding behavior of anchor bar to concrete interface is an important property of anchor bar concrete structure,and it is also the focus and difficulty of structural durability research.The changes of physical,chemical properties and geometric dimensions of concrete or anchor bar will lead to the appearance changes of concrete members,so that they can’t meet the normal use requirements,which even cause the degradation of bearing capacity.Ultimately the safety of the whole structure will be affected.The corrosion caused by chloride erosion is the most common and important reason for durability failure of concrete structures.The change of bonding property between corroded anchor bar and concrete is the basis of studying the mechanical properties of concrete members,the main methods of which are test and finite element analysis.In previous studies,the corrosion rate of anchor bar varying with mass was obtained through experiments,and then the pullout test or numerical simulation of the corroded anchor bar were carried out.In this paper,COMSOL and ABAQUS software will be used to simulate the corrosion process of anchor bar and the pull-out of corroded anchor bar respectively.The advantages of this method are: to simulate the longitudinal non-uniform corrosion state of anchor bar according to the actual corrosion characteristics of anchor bar;the corrosion rate of anchor bar changes with time,so the bearing capacity change of anchor bar with different corrosion degree can be simulated.Specific research contents include:(1)Correlative parameters of chloride-induced corrosion are determined according to specific environmental conditions.The processes of chloride ion diffusion,temperature transfer,water transport and electrochemical reaction were coupled,and the corresponding partial differential equations were established.The process of chloride ion erosion and corrosion of anchor bar was simulated by using COMSOL software.The depassivation time,corrosion current density,corrosion depth and the loss rate of anchor bar section in different time were determined.(2)Based on the corrosion results of anchor bar,ABAQUS software was used to simulate the bond-slip behavior between corroded anchor bar and concrete.The change law of bearing capacity,bond stress and slip of anchor bar under different corrosion rates varying with time are obtained.The rationality and accuracy of the model are confirmed by comparing them with the theoretical model and the experimental results in literature.(3)The bearing capacity,bond properties of the anchor bar concrete component under different parameters(corrosion rate of anchor bar,diameter of anchor bar,anchoring length,distance between anchor bar and member edge,load types and combination of multiple anchor bars)are further studied.Through the analysis of the simulation results,the influence rule of the parameter variation on the bond performance of anchor bar concrete component is obtained,which can be used to guide the engineering design and durability prediction.(4)The failure modes of anchor bar concrete members under different parameters are studied.The influence law of chloride-induced corrosion of anchor bar on anchorage length is analyzed,and suggestions for ductility design of concrete structures under corrosion environment are put forward.The results show that: with the increase of corrosion time,non-uniform corrosion occurred around the anchor bar near the chloride erosion surface of member,and the corrosion rate was positively correlated with chloride concentration.The established bond-slip model can be used to study the bond property degradation law of non-uniform corroded anchor bar concrete member,while the model still has some shortcomings.When the anchor bar has not yielded yet,the bearing capacity of the corroded anchor bar will decline to different degrees,and the slip will increase.Also the bonding force will shift to the uncorroded section.With the increase of corrosion time,the bond-slip properties of anchor bar don’t alter qualitatively.Under the same conditions,the failure modes of corroded anchor bar concrete members do not change.In order to increase the bearing capacity of corroded anchor bar concrete members,it is suggested that additional anchoring length should be considered in the design of corroded anchor bars when the adhesive failure occurs.The corresponding fitting formula is proposed for reference.