Interface - The Journal of Wheel/Rail Interaction

RAIL CANT

Rail Cant Measurement of Concrete Crossties
(Part 1 of 2)
By Arthur Clouse • October, 2008

In response to accidents, unregulated causal factors and the National Transportation Safety Board’s recommendation (NTSB R-06-19), the Federal Railroad Administration (FRA) Office of Safety together with the Office of Research and Development initiated a study to identify and evaluate the safety of concrete crossties. The FRA established a task force to develop recommendations and provide guidance to the Railroad Safety Advisory Committee (RSAC) Working Group on concrete crossties.

A rail profile measurement system capable of accurately measuring rail cant was installed onboard FRA’s Automated Track Inspection Program (ATIP) track geometry cars (see Figure 1) in order to collect valuable data regarding concrete crosstie rail seat deterioration. The intent of this collaborative effort is to provide practical guidance for manual and automated inspections of concrete crossties, and to reduce the number of track geometry-caused derailments that occur when the rail seat pad material deteriorates and exposes the rail base to the concrete (see Figure 2). The deterioration, or abrasion, is the result of a compressive load and/or the mechanical effects of deterioration from repeated, concentrated wheel loading, which typically develops a triangular void on the field side of the tie and allows the rail to tilt or roll outward under load, increasing track gauge (see Figure 3).

Between April 2006 and March 2007 a task force made up of government and railroad personnel studied the problem and addressed the need for a concrete crosstie safety advisory and the potential need for new regulations in the Federal Track Safety Standards. The recommended guidance would primarily promote widespread adoption of a concrete crosstie performance specification in FRA Class 2, 3, 4, and 5 track. The guidance would address (at a minimum) missing, broken, or wear limits for rail seat “abrasion” and tie pad failure; and rail fastener integrity (fatigue failure), including the loss of appropriate toe load pressure, improper fastener configurations, and excessive lateral rail base movement.

The concrete crosstie performance specifications would take into account the data and analytical information associated with the high-profile Amtrak derailments at Stevenson and Sprague, Wash. This includes information relating to track and operating conditions; truck rotation and car and locomotive and car suspension characteristics; the design specifications and research history of concrete crossties; track maintenance practices; and preventive automated and manual track inspection procedures.

Recommendations would also take into account the mechanism (mechanical and compression) of or basis for rail seat failure. They would utilize computer simulation data to compare the truck side L/V, gauge-widening and rail rollover forces associated with the P42-type Amtrak locomotives (versus the freight locomotives operating in the accident area) and why the lightweight passenger locomotives derailed when the more frequent and heavier freight locomotives didn’t.

The effort would also examine the combination of FRA-compliant but irregular track geometry conditions such as gauge, profile, crosslevel and alignment that contribute to excessive lateral wheel / rail forces, which may impose greater wheel force than a singular noncompliant geometry condition.

The study was designed to lead to a method of detecting rail seat failure through automated inspections such as the FRA’s ATIP geometry cars and R&D geometry and Gauge Restraint Measurement System (GRMS) test cars, railway-operated geometry cars, and hi-rail-based geometry / GRMS cars.

Data from these vehicles would be used to develop performance-based rail cant and base gauge requirements that are specific to concrete crosstie or comparable construction specifications and tolerances focused on establishing, identifying and locating excessive individual or combined values relating to inward / outward rail cant and base gauge measurements. Measurements would be used to establish a basis for automated performance-based thresholds relating to, or caused by, missing, worn, and damaged fasteners (sprung clips); worn or missing tie pads; failed crossties (due to mechanical wear or compression on the surface or underneath); center broken or visible reinforcing strands (in the gauge, crossties rail seat area, and shoulder areas); and worn, or damaged concrete rail seat deterioration.

This effort would enable the industry to develop automated procedures and on-the-ground confirmation of rail cant and base gauge measurement values. It would also help the industry to develop and implement the tools and procedures to manually inspect, measure and identify concrete crosstie rail seat deterioration under load. These tools include a toe load (torque or resistance force) gauge and a void (feeler) depth gauge. (Note: 1/8 inch void in the rail seat area equates to one degree of inward or outward rail cant and correspondingly affects track gauge about 1/8 inch.) This effort would also examine the crosstie support required to support typical loadings and to maintain track geometry safety limits, according to track classification.

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