Chloride Diffusion Characteristics Of Prestressed Beam Box Under Coupled Salt Fog-fatigue Effects

Prestressed box beams of cross-sea railway bridge are usually located in harsh environment. Chloride corrosion and fatigue loads make a dual effect on prestressed box beam all the year round. The coupling of fatigue and chloride corrosion will accelarate the speed of reinforcement corrosion, and crack and deterioration of concrete will be more severe as well. These damages will make the railway bridges work in a high-risk situation. This paper mainly foucses on the chloride duffusion characteristics of prestressed box beam when the coupling effect of chloride corrosion and fatigue loads is considered at the same time. The purpose of this paper is to give some useful advice to durability design of prestressed box beam of railway bridge.Firstly, the thermal-structure coupling module of ANSYS was used to caculate the chloride distribution. As the module has limitation, volumetric strain and porosity are used as intermediate variable to link static load and chloride transfer coefficient. Meanwhile, through fatigue anlysis module, ANSYS can give the damage degree(D) of fatigue load. Residual strain and total volumetric strain can be caculated through the damage theory based on strain. Then the relationship between total volumetric strain and chloride transfer coefficient of fatigue-corrosion coupling can be established as well. The results of numerical simulation are compared with the test data.Secondly, the finite element modeling of prestressed box beam was established. Static load from specification and fatigue load spectrum from statistical data are applied to the FE model, seperately. And chloride distribution of both coupling situations are caculated. Furthermore, in order to study how load form influences coupling effect, the chloride distribution of both coupling situations are compared.Finally, to investigate whether the chloride ion penetration will be affected by prestress, the prestress level of FE model is changed. And results of different coupling situations with different prestress levels were compared. As the fatigue stress level can make great contributions to chloride diffusion, different fatigue stress levels are choosed to investigate the influnce of chloride diffusion in prestressed box beam. At last, accoding to the method of single coupling, multiple coupling analysis method is proposed. Results of these two coupling methods are compared and discussed.