Fatigue and Dynamic Behavior of Prestressed Concrete Sleepers

In ballasted railway tracks, one of the important components that supports the rails and distributes wheel/rail loading onto the ballast supporting formation is a railway sleeper. In this paper, the dynamic and fatigue response of prestressed concrete sleepers used along the Ethiopian National Railway lines (Chinese Type II sleeper) is presented. For simulation, a finite element modelling package, ANSYS was employed. Concrete was modelled using a three-dimensional solid element (SOLID 65) and the behavior of prestressing wires was simulated using truss elements (LINK 180). Validation of simulation results was done using existing experimental data of Rikard’s model. To obtain resonance conditions; the harmonic response of the sleeper for the excitation in the range of 0-2000Hz and variation of stress and displacement amplitudes with respect to frequency were studied. It’s observed that the most resonant frequency corresponds to the third bending mode shape. From fatigue life assessment in this study, it is observed that the sleeper fails before attaining its design life of 40 years (11,300,400 cycles). This is due to the development of cracks which are likely to limit the sleeper’s ability to hold the geometry of the line. As a result, the sleeper cannot attain the main technical standards of speed of 120 km/h and axle load of 25 tons. The minimum life of the sleeper is equivalent to about 31.8% of its design life. Moreover, it was observed that at a speed of 80km/h and an axle load of 25 tons, the life of the sleeper was found to be 85%. Thus, to attain the design life of the sleeper, during operational phase, it is recommended to limit the speed of the train to 80km/h.