چكيده به لاتين
There are more than 600 Km of railway routes passing through the desert areas in Iran. The most prominent characteristic of these areas is the movement of loose and salty dunes that causes deterioration of railway components such as rails, connections, crossties, and fastening system. One of the problems of salty sand contamination around concrete crossties is the release of chloride ion that ingresses into the concrete, reaches to bars, and causes corrosion. Corrosion initiates the expansion of bars, which makes the surrounding concrete to crack and leads to failure of crosstie. In order to assess the effects of this phenomenon on the performance of crosstie, two crossties from the surveyed desert area are chosen for Half-cell potential and Liquid Penetration tests to determine corrosion initiation in concrete crossties. Afterward, a 3D FEM model of B70 crosstie is developed using the XFEM modulus of ABAQUS software to study the effect of cracking procedure through bar corrosion. In continue, the verification of numerical models is given and different parameters affecting crosstie failure like the location of ion invasion, length of bar corrosion, and the ballast fouling percentage are evaluated. According to these sensitivity analyses, with the increasing number of corroded bars, a reduction in bearing moment in the middle of crosstie happens in which corrosion in bottom bars and top bars show about 50% and 27% reduction in moment capacity, respectively. The amount of corrosion length has also a decreasing effect on bending moments and deflections in the middle of crosstie, especially happening in bottom bars. Accordingly, in severe conditions, top bars corrosion causes a 30% reduction and bottom bars corrosion causes about 50% reduction in moment capacity. Furthermore, by increasing the ballast fouling, moments decrease in the middle of crosstie. Regarding the fouling index, the fully polluted condition accompanied by bottom bars corrosion and top bars corrosion yields 50% and 34% decrease in moment capacity. Generally speaking, all evaluated factors lead to the reduction of bearing moment and deformation in the middle of crosstie.
