Stiffness Degradation Of Concrete Beams Under Sulfate Corrosion Condition Law Analysis And Model Test Research

Our northwest region is broad,geology and climate types are various,generally,the climate is dry,the temperature difference between day and night is big,all kinds of salt corrosion especially in the deicing salt environment sulfate corrosion problem is more serious,how to according to the unique environmental conditions to optimize the durability of the structure design,is an engineering practical problem.In this kind of environment,reinforced concrete Bridges usually suffer from excessive deformation,stiffness degradation and other diseases,which seriously affect the durability of Bridges.According to the special environmental characteristics in northwest China,the stiffness degradation law analysis and model test of concrete beam under sulfate corrosion condition were carried out,which could provide reference for the construction of similar bridge projects in western China.Based on the major science and technology project "The Whole Life Design and Application Technology Research of Highway Concrete Bridge in Gansu Province(Science and Technology Project 2020-05)" set up by Gansu Provincial Department of Transportation,this paper carried out a model test study of sulfate corroded reinforced concrete beam based on the actual salt environment in the province and the requirements of relevant test codes.The cracking load,bearing capacity,crack development law,stiffness and other performance indexes of the test beam were analyzed respectively,and the variation law of mechanical properties of the reinforced concrete test beam at different corrosion times was studied.The main research results are as follows:(1)With the increase of corrosion time,the white crystals precipitated from the surface of the test beam are increasing,and the deterioration degree of the concrete on the surface of the test beam is higher.It is found that the test beam with initial damage has a more serious corrosion degree than the intact section beam at the same corrosion time.(2)With the increasing corrosion time,the cracking load of the test beam increases first and then decreases.This is because the corrosion degree of the concrete beam will directly affect the size of the cracking load.With the increase of the corrosion degree of concrete,the expansion products are generated continuously to make the concrete structure become dense,and the cracking resistance of concrete is enhanced.However,as the corrosion degree continues to deepen,the mechanical properties of concrete gradually decline,leading to the decline of concrete crack resistance,resulting in concrete cracking.(3)Study the influence of sulfate corrosion on mechanical properties of reinforced concrete with intact section.The intact section test beam was immersed in the erosion solution,and the static bending test was carried out on the test beam with corrosion time of 0d,60 d,360d and 600 d.The test results show that the ultimate bending moment of the intact beam increases by 1.6% after 60 days of corrosion.After 360 d of corrosion,the ultimate bending moment decreases by 4% compared with B-0 test beam.After the corrosion time reaches 600 d,the ultimate bending moment decreases by 14.2%.The ultimate bending moment of the intact section test beam increases first and then decreases with the corrosion time,but its decreasing speed is slower than that of the damaged beam.After 600 days of corrosion,the reduction rate of the ultimate bending moment of the damaged beam is twice that of the intact beam.(4)Influence of sulfate corrosion on crack development of reinforced concrete beams.The average crack spacing of reinforced concrete beams after sulfate corrosion tends to increase.According to the test data and the existing norms,the calculation formula of the average crack spacing under corrosion environment is obtained.The maximum crack width of reinforced concrete beam first increases linearly with the increase of the standard bending moment ratio.When the standard bending moment ratio reaches the range of 0.6～0.8,the critical point of crack width increases sharply,and the longer the corrosion time,the earlier the critical point appears,and then the crack width increases sharply,and the longer the corrosion time under the same load,the greater the crack width.(5)Study the stiffness degradation law of sulfate corroded concrete beams.The measured stiffness of the beam after sulfate corrosion test is higher than the predicted value calculated by the code.Taking FB-360 test beam as an example,the measured stiffness is about 25% higher than the predicted value.Therefore,a reasonable correction coefficient is introduced to modify the calculation formula of the short-term stiffness of the test beam with intact section and the test beam with initial damage respectively.The calculation error of the corrected stiffness model is controlled within 10%.The test results show that the stiffness of each test beam increases first and then decreases with the increase of corrosion time,but the stiffness of the test beam with initial crack decreases faster,mainly because the crack provides a convenient channel for the corrosive medium to enter the structure,accelerates the corrosion process,and shortens the service life of the structure rapidly.(6)Combined with the actual size,reinforcement and loading mode of the test beam,the numerical model was established by ABAQUS nonlinear finite element software.The loaddisplacement curve obtained by numerical simulation is similar to that of the test beam,and the cracking load errors are 3.9%,4.8%,5.8% and 6.2%,respectively.The reliability of the numerical model is proved.The variation of crack propagation,reinforcement stress and midspan deflection with corrosion time is analyzed.