Implications of Field Loading Patterns on Different Tie Support Conditions using Discrete Element Modeling: Dynamic Responses

With increasing demands for rail passenger and freight operations, sharing a line or track is an economical solution if operational efficiency and track reliability challenges can be accommodated properly. This paper presents findings of ballast layer dynamic responses related to four different freight and passenger car loading patterns studied for four different tie support conditions using the Discrete Element Method (DEM). With the DEM model setup being identical for each support condition, ballast particle contact force networks were visualized first under one dynamic load cycle. Certain load transfer chains were observed associated with all four support conditions. Next, crosstie dynamic velocities were analyzed for all sixteen combinations of the different loading patterns and support conditions. The freight car loads traveling at 50 mph could induce higher crosstie vibration velocities than the lighter passenger car loads traveling at 110 mph and 150 mph in three support conditions: lack of center support, high center binding, and lack of rail seat support. Dynamic movements of ballast particles were visualized in velocity vector plots based on their initial and final centroid coordinates. Results reveal that for the same axle load, higher speeds will cause larger ballast particle movements. However, with higher load magnitudes, larger particle movements can be observed even at lower speeds. Generally, high center binding results in the smallest particle movement while lack of center support presents the largest particle movement. Dynamic load responses of the ballast layer simulations provide insights into evaluating and optimizing tracks to be shared by passenger and freight trains.