Design and laboratory evaluation of spring washers as railway baseplate hold-down method to mitigate spike failures

The rising popularity of elastic railroad fasteners for use in timber sleeper tracks, delineated through their wide adoption across the North American freight network, is facing resistance since the derailment data attributes at least 13 derailments in last two decades to spike failures in sleepers leveraging these elastic fasteners. Previous investigations of the spike failure mechanism illustrated that rail baseplate uplift induced by the rail's wave-action during a train pass reduces friction at the plate-sleeper interface. This loss in friction transfers additional load (e.g., lateral and longitudinal) to spikes and causes the stress levels to exceed the endurance limits. Although installation of spikes with spring washers was suggested to restrain the baseplate uplift, the industry recommended Fe6 washers demonstrate inadequate resiliency (i.e., working range) resulting in failure to maintain the required hold-down load over time. To characterize the appropriate spring washer for spike failure mitigation, this paper presents an overview of the design criteria driven by engineering design standards while accommodating the standard fastener components. Moreover, this study quantifies the load and resiliency demands from spring washers based on spike pullout experiments as well as existing correlations and pertinent studies in the literature. Consequently, the maximum and minimum recommended hold-down installation loads are 22.2 kN (5000 lbs) and 4.5 kN (1000 lbs.), respectively, to protect the sleeper from premature failure while simultaneously reducing spike stress by 70%. To identify a washer that has an adequate working range, static compression experiments were carried out on a set of nine commercial and non-commercial washers. Results indicate that at least two of the washers considered – the Fe19 and polyurethane washer – can achieve working ranges that are 69% and 93% wider, respectively, with a 68% reduced timber stress compared to the baseline Fe6 washer. Results of this work provide insights into the selection of proper spring washer and the magnitude of installation load to mitigate spike failures.