Many track-related derailments are caused by gage widening, a track safety factor that develops primarily as a result of degradation of the ties and fastenings. Gage degradation of a wooden-tie track is examined from a mechanistic point of view. A finite element model is used to simulate the lateral rail deflection under load and to investigate the growth mechanism of bad tie clusters. The ties are assumed to be in new condition at the beginning. Because the degradation of individual ties is not uniform, one tie is assumed to degrade first, which leads to load redistribution to the adjacent ties. Several different configurations and degradation patterns of tie clusters are examined, and rail deflections at each degrading stage are simulated for several scenarios. Results of the analysis indicate that rail deflection with different tie lateral-strength levels is not linear but follows a third-order polynomial trend. Rail deflection increases much more quickly when the lateral strength of a tie degrades below 50% of its capacity. The gage-restraint capacity of a track is determined not solely by the absolute number of defective ties in the track but mainly by bad tie clusters and the configuration of those clusters.
Samenvatting