No abstract

Cut spike fasteners, used with conventional AREMA rolled tie plates and solid sawn timber ties, are the most common tie and fastener system used on North American freight railroads. Cut spikes are also used to restrain tie plates that incorporate an elastic rail fastener — that is, an elastic clip that fastens the rail to the tie plate. Elastic fasteners have been shown to reduce gage widening and decrease the potential for rail roll compared to cut spike-only systems. For this reason, elastic fastener systems have been installed in high degree curves on many railroads. Recent observations on one Class I railroad have noted broken cut spikes when used with these types of tie plates in mountainous, high degree curve territory. Broken screw spikes and drive spikes on similar style plates have also been observed. In this paper, a simulation method that integrates a vehicle-track system dynamics model, NUCARS®, with a finite element analysis model is used to investigate the root causes of the broken spikes. The NUCARS model consists of a detailed multibody train, wheel-rail contact parameters, and track model that can estimate the dynamic loading environment of the fastening system. For operating conditions in tangent and curve track, this loading environment is then replicated in a finite element model of the track structure — ties, tie plates, and cut spikes. The stress contours of the cut spikes generated in these simulations are compared to how cut spikes have failed in revenue service. The tuning and characterization of both the vehicle dynamics multibody model and the finite element models are presented. Additionally, the application of this approach to other types of fastening systems and spike types is discussed. Preliminary results have identified a mechanism involving the dynamic unloading of the tie plate-to-tie interface due to rail uplift ahead of the wheel and the resulting transfer of net longitudinal and lateral forces into the cut spikes. Continued analysis will attempt to confirm this mechanism and will focus on the severity of these stresses, the effect of increased grade, longitudinal train dynamics, braking forces, and curvature.

Recent rail rollover derailments motivated this investigation. The wheel/rail forces under seven track/rail conditions were measured at a curve of a heavy haul line. The investigation indicated that combinations of reverse rail cant, weak rail restraint, poor truck steering and poor wheel/rail contact can increase the risk of a rail rollover derailment. This investigation reaffirms the findings from previous rail roll studies and further stresses three important issues related to track maintenance practice. First, track maintenance tasks that involve changing track gage or rail orientation can have the unintended consequence of causing adverse wheel/rail contact, resulting in large lateral forces. Rail grinding should be coordinated with the restoration of rail cant to correct wheel/rail contact patterns. Second, restoring and restraining only the high rail has a high risk of causing a rollover derailment from the low rail. Third, rail grinding cannot be properly conducted on a track that has weak rail restraint and variable levels of reverse rail cant.