Assessing wagon curve stability in heavy haul trains

The tradition of treating train dynamics and wagons dynamics as two separate problems continues to be supported by both software and standards. The assumption that coupler angles are so small that the consequential vertical and lateral force components can be ignored does not necessarily hold as trains become heavier and longer and coupler forces become larger. In the Australian AS7509 standard the wagon rollover risk from lateral forces is assessed only at slow speed and given an allowance of 100% wheel unloading. Conversely, wagon unloading, in response to curve geometry at speed, is given a limit 60% (excluding transients) and 80% maximum when including effects of the track geometry and typical irregularities. If wind loads are added the criteria is lifted to 90% wheel unloading. Lateral coupler forces, coupler misalignment due to empty wagons in loaded trains and wagon body and bogie pitch are examined. The effect of combining all of these issues is discussed. The results lead, logically, to a discussion of operational assessment verses wagon roadworthiness assessment.