Analytical Nonlinear Modeling of Rail and Fastener Longitudinal Response

Abstract

Comparatively little attention has been given to the quantification of fastener demands, especially in the longitudinal direction. Research quantifying fastener demands is justified by the more than 250 FRA reportable derailments on mainlines and sidings in the United States caused by “defective or missing spikes or rail fasteners” over the last 20 years. Failed fasteners are rarely caused by loads acting from a single direction (vertical, lateral, or longitudinal); they occur from a combination of these loads. A literature review identified that though multiple models have been developed for analyzing track, they were not designed to quantify fastener demands, especially those in the longitudinal direction, and some make assumptions that could be improved on based on more recent research into the mechanics of fastening system behavior. This paper advances the mechanistic–empirical (M-E) track analysis and design approach through the development, validation, and application of a 3D nonlinear parametric track model that quantifies longitudinal fastener demands. Key research findings include: bilinear approximations, in combination with considering the interaction between vertical loads and slip, were necessary to accurately quantify fastener forces; ballast and fastener stiffness had a direct logarithmic relationship on fastener load; and for well-supported sleepers, changes in component resistance to slip produced minimal changes in fastener demands because the vertical applied load increased the required load to produce slip. Going forward, this validated model could be used to quantify fastener and track demands for additional loading and operational scenarios to further optimize component design for improved track safety and reliability.

Review of Critical Factors Influencing Longitudinal Track Resistance

“…Between 1999 and 2018 there were 250 Federal Railroad Administration (FRA)-reportable derailments on mainlines and sidings in the United States caused by “defective or missing spikes or rail fasteners” ( 14 ). Dersch et al ( 14 ) found that most fastening system failures are a result of a combination of vertical, lateral, and longitudinal loads and that there is a current disconnect between the demands and component’s design strength. This disconnect has led to a variety of fastening system failure modes ( 14 ).…”

“…Lateral resistance is an absolutely critical parameter required to perform an accurate buckle analysis and has been studied by many authors previously, a few of whom that can be cited here are Mohammadzadeh et al ( 7 ), Kerr ( 8 ), Allen et al ( 9 ), Esmaeili et al ( 10 ), and Shenton ( 11 ). However, longitudinal resistance, which has been studied less, is also considered to be one of the most critical parameters required for longitudinal load propagation analysis ( 12 – 14 ) and RNT maintenance practices ( 15 – 17 ) in CWR track. Together, both the lateral and longitudinal track resistance provide stability to the track structure.…”

“…Further, longitudinal resistance has been quantified using multiple methods that should not be conflated with each other, though this has not been explored and discussed previously. And while it is understood that vertical loading and uplift from the wave action of the rail affects the longitudinal and lateral resistance and stiffness of track ( 14 ), accurate quantification of the range of longitudinal resistance values is required before considering the impact of train loading. Therefore, this paper documents common definitions of longitudinal track resistance, why it is a critical parameter, and how it has been quantified.…”

Evaluating glass fiber reinforced composite sleepers to mitigate elastic fastening system spike fatigue failure: A finite element study

“…2 Several research studies have been conducted to determine the root cause of these broken spikes in the elastic fastening systems with timber sleepers. [3][4][5][6] It was found that spike fatigue failures occur most commonly in timber sleeper tracks constructed with elastic fastening systems. These elastic fasteners change the load path and increase the longitudinal demand placed on the spike due to (1) lack of anchor; 1 (2) loss of friction at the plate-sleeper interface due to rail uplift; 6,7 and (3) higher stiffness.…”

“…[3][4][5][6] It was found that spike fatigue failures occur most commonly in timber sleeper tracks constructed with elastic fastening systems. These elastic fasteners change the load path and increase the longitudinal demand placed on the spike due to (1) lack of anchor; 1 (2) loss of friction at the plate-sleeper interface due to rail uplift; 6,7 and (3) higher stiffness. 6 Therefore, locations most likely to experience spike overloading fatigue failures include higher degree curves, special trackwork, steep grades and other locations subjected to high longitudinal and lateral loads, tractive effort, and braking forces as these are the most common locations elastic fasteners would be installed to prevent railrollover derailments.…”