Optimization Of Concrete Sleepers Subjected To Static And Impact Loadings

Prestressed concrete sleepers (PCSs) play an essential role in the track‟s performance and safety responses. PCS‟s most important function is to transfer and distribute loading from the track‟s superstructure to ballast bed. Loadings on sleeper are static and impact. Impact loadings originating from wheel or rail abnormalities is one of the main causes of cracks on the PCS‟s thus the excessive railway track maintenance cost. Previously, the effect, behavior and optimization of different prestressed sleeper shape subjected to static and impact loadings and the effect of prestressing steel horizontal spacing on sleeper loading capacity, has not been well investigated. The objective of this research was to optimize concrete sleeper shape subjected to static and impact loadings. Finite element package, ANSYS 16 was used in PCSs to analyze the static and impact loading responses on sleepers. A three-dimensional solid element, SOLID 65 was used to model concrete part of the sleeper. To simulate the behavior of pre-stressing wires, truss elements, LINK180, were used to withstand the initial strain attributed to pre-stressing forces. Validation of FE results was done using existing experimental data with a comparison of force-deflection diagrams of the experimental and FEM results. It was found that the quality of FE results is good. Conclusions to this research revealed that irregular hexagon sleeper shapes were safe as far as static and impact loadings are concerned. The sleeper SVII3 (sleeper 40), was found to be the best geometrical sleeper shape in terms of sleeper safety and volume. Furthermore, the best geometrical sleeper shape has a 1.75% volume reduction compare to the existing sleeper (in Addis-Djibouti railway track). In terms of the best geometrical irregular shaped sleeper safety, upon application of impact loading, 60% of sleepers were safe as compared to 40% of trapezoidal sections. However, in the case of rectangular shaped sleepers, none was safe. Static analysis of all modelled sleepers showed that all the three shapes used, were safe. Horizontal prestressing wire spacing had no effect on the sleeper loading capacity and deformation. Recommendations from this research thus points out to irregular hexagonal shape sleepers are economical and safe. Therefore, sleeper model SVII3 that has an irregular hexagon shape is proposed for use on future extension of the line or in the construction of new lines in Ethiopia.

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