Elastic fasteners have been shown to reduce gage widening and decrease the potential for rail roll compared to conventional cut-spike-only systems. For this reason, elastic fastening systems have been installed in high-degree curves on many North American heavy-haul railroads. Field observations in the United States, however, have noted broken cut spikes and screw/drive spikes on this type of fastening system, especially in steep-grade, high-degree curve territories. It was found that spikes typically fracture between 1 to 1.5 inches below the top surface of the ties, making them difficult to detect by visual inspection alone. Notable recent derailments have been attributed to broken spikes as reported by Class I railroads.
Transportation Technology Center, Inc. (TTCI), as part of a joint program between the Federal Railroad Administration (FRA) and the Association of American Railroads (AAR), completed the initial phase of a study investigating the root cause of these broken cut and screw/drive spikes. Previous research under this joint program has confirmed through metallurgical investigation that material fatigue was the failure mechanism, and subsequent numerical simulation has shown that the bending stress in spikes can exceed the fatigue limit of the spike material. To further investigate the in-track loading environment of spikes, cut spikes instrumented with strain gages were installed in the high-tonnage test loop of the Facility for Accelerated Service Testing (FAST) at FRA’s Transportation Technology Center The test investigated the loading environment of spikes by considering several in-track conditions. The results showed that the load transferred to spikes during insertion and train passing could cause spike stresses higher than the fatigue limit and therefore lead to the permanent bending of spikes. Moreover, the bending moment was primarily carried by one of the four spikes from the same plate. This paper provides an overview of the development of instrumented spikes as well as the results of the in-track testing using these spikes. The findings from this study will guide future revenue service testing, for which a high-grade, high-curvature location will be considered to further investigate the broken spike issue.