On the Nondestructive In Track Measuring the Longitudinal Force

A conventional railroad track consists of two long steel rails resting on and fastened to discretely spaced crossties, which in turn are embedded in a layer of crushed stone ballast. The ends of the rails either are connected by joint bars to form an expandable joint or are welded together to form long length of continuously welded rail (CWR). The track structure, when subjected to sufficiently high longitudinal compressive forces in the rail, can exhibit sudden and rapid lateral or vertical movement over a relatively short length. This lateral movement, or buckling of the track, results in a severe misalignment condition that may not permit the safe negotiation of train traffic (Figure 1). If buckling occurs under the train, a derailment is likely to occur. If it occurs between trains, traffic must either be stopped of slowed down until the buckled track condition is corrected. The magnitude of this problem can be seen in the fact that, during 1977, there were 109 train derailments attributed to buckling of the track. The reported damage for these derailments amounted to over $5.5 million. Furthermore, for every track buckle that resulted in a derailment, there were three to four instances of buckled track where the railroad maintenance forces were able to correct the problem before a derailment occurred. Consequently, countless hours of maintenance time are devoted to inspecting for and correcting buckled track. When the track structure is subjected to longitudinal tensile forces, pull-apart of the rail can occur. In CWR track, these , these pull-aparts, which generally occur at the welded joints, result in the appearance of a gap or separation in the rails. Such a gap, which can result in derailment or at the very least rail batter, requires the slowing down or halting of traffic until appropriate corrective action is taken. Although the detection of pull-aparts is signaled territory is facilitated by the interruption of the traffic signals, the maintenance cost of pull-aparts is appreciable. One of the greatest difficulties associated with the detection and prevention of track buckling or rail pull-apart is that it often occurs without real warning. This is because the buildup of longitudinal forces in track that is in good condition, particularly continuously welded rail track, will not be evident until it reaches the point where the track will fail. That can be too late. Yet, there is presently no practical method available for measuring the longitudinal force in the track without disturbing the track structure itself. Railroads currently rely on the subjective judgment of the maintenance-of-way man on the scene. It is the purpose of this paper to explore the various techniques used to date to measure longitudinal rail force and to lay the ground work for the continuing research effort aimed at developing a practical technique for the non-destructive in-track measurement of longitudinal force in rail.
Zarembski, A. M., “On the Nondestructive In Track Measuring the Longitudinal Force”, Conference on Nondestructive Techniques for Measuring the Longitudinal Force in Rails, Washington, D.C., February 1979.