Numerical Simulation Study On Shear Capacity Degradation Of Stud Considering Corrosion Environment

Steel-concrete composite structure bridge can give full play to the performance of steel and concrete,and has the advantages of both steel structure and concrete structure.As a new type of bridge structure,it has a great application prospect.Existing application experience has shown that the corrosive medium environment invasion will cause composite structure durability degradation,which results in the decrease of structure capacity.The diffusion of chloride ions in concrete will lead to the surface of steel depassivation in concrete,resulting in corrosion of steel.For composite structure,chloride ion will cause stud corrosion,and it is very difficult to detect stud corrosion of composite structure bridge in service.Therefore,it is very important for the durability design of composite structure to establish a simulation method for the corrosion process of studs in composite structure bridges and to provide a time-varying stud bearing capacity curve under the action of corrosion.In this paper,the electrochemical reaction coupling analysis of chloride ion diffusion and stud corrosion in concrete,considering the influence of aggregate,studied the corrosion form and bearing capacity degradation law of stud under the action of chloride ion.The main research contents of this paper are as follows:1.The ratio of chloride ion to hydroxide was used as the depassivation threshold to establish the coupling analysis method of chloride ion diffusion and steel corrosion.Based on Fick’s second law and Butler-Volmer equation,a quantitative simulation method for material transport and electrochemical reaction in concrete was established.The initial PH value of concrete and the migration of hydroxide under the action of electric field were considered to reflect the depassivation law of steel bar surface in the actual corrosion process.By setting regular aggregate,the influence of aggregate on the distribution of chloride ion in concrete and the position of depassivation reinforcement were studied.In reference to the corrosion law of steel exposed to atmospheric environment,the microcell reaction was introduced as a supplement to the macro-cell reaction of steel corrosion,and the corrosion rate of micro-cell reaction was controlled by calculating oxygen transmission and consumption.The results of corrosion form and accumulated corrosion amount of reinforcement in concrete are obtained.2.The coupling calculation method of chloride ion diffusion and steel corrosion is adopted to simulate the corrosion process of studs in steel-concrete composite beams.By analyzing the structural characteristics of steel-concrete composite beam,two kinds of chloride ion exposure surfaces were set,and random round aggregate was put into the concrete area,and the uneven corrosion morphology of studs was calculated.When the concrete bottom plate is the exposed surface,the corrosion position of the stud develops from the root to the top,from the face to the back,and is deep on the bottom and shallow on the top,and the section is approximately elliptical.When the concrete roof is exposed surface,the corrosion position of studs develops from the top to the root on the whole,and the corrosion development of the nail head is slow in a certain range,showing shallow upper and lower,deep in the middle,and the section is round.In the local area,due to the hindrance of chloride ion diffusion by aggregate,the local area lag reaches the depassivation threshold,and the local uneven corrosion is formed.3.By setting the longitudinal control section and using the method of cross-sectional area equivalent,the non-uniform corroded studs are simplified.The mechanical properties of the studs exposed to two kinds of chloride ions at different corrosion times were calculated by using finite element numerical simulation of the pull-out experiment,and the degradation curves of the mechanical properties with time were obtained.