Research On Similarity Of Performance Degradation Of Concrete Structures Under The Coupling Effect Of Chloride And Load

Durability of concrete structures has caused enormous economic losses and social and environmental impacts to countries around the world.In today's world,there are many reasons for the lack of durability of concrete structures,and even the main causes of damage,such as corrosion of steel bars,frost damage and physical and chemical effects in erosion environment,and the most prominent problem is steel corrosion.Reinforcement corrosion not only reduces the effective cross-sectional area of steel bars and changes the performance of steel bars,but also leads to the degradation of the bond between steel and concrete,which seriously affects the bearing capacity of concrete structures.Therefore,it is of great theoretical and practical significance to study the performance degradation of corroded reinforced concrete structures and to evaluate the durability of active structures and the prediction of life expectancy.Based on the existing research results at home and abroad,the financial support from the National Natural Science Foundation?Grant No.51378241?is gratefully acknowledged.The similarity of performance degradation of concrete structures under the coupling of chloride and load is studied.The main research work is as follows:?1?Study on the law of chloride ion erosion in concrete under load.On the basis of Fick's second law,considering the influence of load and environment?temperature,relative humidity?on chloride ion diffusion law,the chloride ion diffusion equation in concrete under stress was obtained.The formula for calculating the initial rust time of steel in one-dimensional diffusion region of chloride ion was deduced.The method for calculating the initial rust time of the steel in the two-dimensional diffusion zone of chloride ion was obtained by modifying the formula of the initial rust time of the one-dimensional diffusion zone of chloride ion.?2?Similarity model of corrosion rate of reinforcement in concrete members under coupling of chloride and load was studied.Based on the law of Faraday's corrosion,the merits and demerits of the existing corrosion current density model were analyzed to determine the corrosion current density model used in this paper.When the corrosion rate in two kinds of chloride environment?natural environment and constant current power to accelerate the environment?and load coupling close to each other,assuming they were equal.Based on the reinforcement corrosion rate,the time similarity model was built up.The natural environmental test and the constant current power and accelerated test were carried out,with the constant current power to accelerate the electricity 160h component test case,the time similarity coefficient ?_t,?s of two kinds of chlorine salt environment and load coupling component reaching 4%steel corrosion rate were obtained as 0.025.The corrosion time of the natural environmental test component was calculated as 4a by using the value of?_t,?s,and the error between true value and the test?1400d?was 4.29%.The related content provided a theoretical reference for predicting the corrosion rate of steel bars in concrete structures under natural environment.?3?Similarity model of corrosion expansion of reinforcement in concrete members under coupling of chloride and load was studied.The model of the relationship between the rust and the corrosion time of the steel was deduced by using the thick-walled cylinder model and the polar coordinate method to calculate the uniformity of the steel and the model of the non-uniformity of the tension.When the steel rust force in two kinds of chloride environment?natural environment and constant current power to accelerate the environment?and load coupling close to each other,assuming the two were equal.Based on the reinforcement corrosion expansion force,the time similarity model was built up.The natural environmental test was carried out,with the constant current power to accelerate the electricity 12h component test case,the time similarity coefficient ?t,qr,of 5.42MPa was obtained as 0.178 by the two kinds of chlorine salt environment and the load coupling effect.The related content provided some theoretical reference for predicting the rust expansion of reinforced concrete in concrete structure and the time of crack initiation of protective layer in natural environment.?4?Similarity model of bond strength between corroded reinforcement and concrete in concrete structures coupled with chlorine and load was studied.Based on the Mohor-Coulomb strength failure criterion in multi-axial stress state,the bond strength of four critical states?internal fracture state,splitting state,limit state and residual state?during the bond slip failure of concrete members was obtained.When the two kinds of chloride environment?natural environment and constant current power to accelerate the environment?and load coupling under the bonding strength was close to the assumption that the two are equal to the bond strength as a link,based on the bond strength of the time similar model.When the bond strength in two kinds of chloride environment?natural environment and constant current power to accelerate the environment?and load coupling close to each other,assuming they were equal.Based on the bond strength,the time similarity model was built up.With the constant current acceleration power 12h component test case,time similarity coefficient was respectively 0.005,0.00511,0.00598 and 0.00545 when the tensile strength,splitting strength,ultimate strength and residual strength both reached 4.25MPa,7.98MPa,9.13MPa and 1.47MPa in two kinds of component chloride environment and load coupling effect,and similarity coefficient value between natural environmental test component corrosion time were 0.06a,0.0613a,0.0718a and 0.0654a.The related content provided some theoretical reference for predicting the bond strength in concrete structure under natural environment.