Study On Bonding Properties Of Rusted Steel Bars And Concrete

Corrosion of steel bars is the main cause of structural concrete degradation.The effect of this deterioration on residual strength is the key to ensuring the safe operation of the concrete structure.Although a large number of studies have been carried out in recent years to develop and predict the model of the service life of reinforced concrete structures,they are mainly concentrated in the initial stage of new construction and service life until the corrosion of steel bars begins.There are few studies on the impact of the strength of the subsequent life stages of the structure.In this paper,a detailed experimental study and theoretical analysis are carried out on the influence of steel bar rust on the bond properties of concrete.The evolution law of bond properties under steel bar rust is revealed,and the relationship between the degree of corrosion and the relative ultimate bond strength,bond-slip constitutive model is obtained.After different corrosion cycles of reinforcing bars,the relationship between corrosion cycle and mass loss rate and the relative corrosion area of reinforcing bars based on MATLAB image processing is analyzed.It is found that the corrosion degree of ribbed reinforcing bars is higher than that of round reinforcing bars.The maximum relative corrosion area of both reinforcing bars reaches 90%,and the reinforcing bars are totally corroded.The pull-out failure modes of different relative rust areas of various test pieces and the load-slip curves of the free end and the load end of the test piece are analyzed.It shows that there is no rust expansion force between the rusted steel and the concrete.This is the research of this subject.The difference in research is important.The average ultimate bond stress of the test piece is analyzed.At the same time,due to the complexity of the calculation of the bond stress between steel and concrete,this paper proposes a new method for calculating the bond stress based on the previous research: through the balance of the micro end of the steel bar.Conditions,establish the balance equation of the steel micro-segment.According to the measured strain at each point,the strain is fitted with the anchor depth distribution function,and after deriving it into the equilibrium condition,the distribution of the bond stress with the anchor depth can be obtained.The peak position and size of the bond stress of the specimens with different degrees of corrosion were analyzed.It was found that the peak of the bond stress of the ribbed steel specimens was stable at the anchorage position of 0.1la and 0.9la.The stress transfer speed between the steel and the concrete was gradually changed.Small is the reason for the large change in the bond stress curve.The average limit slip value of the test piece was analyzed.At the same time,the force of the concrete of the light-round steel bar specimen was analyzed by ABAQUS simulation.The bond stress distribution function of the anchor section obtained by the test was input at the interface to establish the pull-out test piece model.The strain of the interface concrete is obtained,and the relative slippage of the steel bar and the concrete at each point of the interface is calculated.The distribution law of the slip curve of different relative rust areas is obtained,and the reason for the discreteness of the curve is analyzed.By analyzing the influence of the shape of different test pieces on the average ultimate bond stress and the average limit slip value,it is found that the average limit strength data of the cylindrical test piece shape is relatively uniform;the multi-axis force range and the symmetry of the test piece are discussed.The effect of the average limit slip value and the uneven coefficient of the light round steel test piece.Based on the ABAQUS simulation,the influence of the shape of the test piece on the interface concrete strain and the interface concrete unevenness coefficient is analyzed.The causes of the stress state of the concrete of the light-reinforced steel specimens under different shapes and the length of the compression part along the anchorage length are analyzed.The relationship between the γc value and the anchoring depth of the light-circumferential specimens under different load levels is studied.The relationship between the variation of the unevenness coefficient and the shape of the test piece.