Quantification of vertical, lateral, and longitudinal fastener demand in broken spike track: Inputs to mechanistic-empirical design

Transportation Research Record: Journal of the Transportation R

Silva

Edwards

et al. 2022

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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.

Section: Objective and Motivationmentioning

confidence: 99%

Analytical Nonlinear Modeling of Rail and Fastener Longitudinal Response

Transportation Research Record: Journal of the Transportation R

Silva

Edwards

et al. 2022

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“…For example, with modulus of 2000 MPa (290,000 psi), to reduce spike stress below the fatigue limit for a 95 th percentile longitudinal spike load of 7.6 kN (1700 lb. ), 5 a compressive strength of 15.34 MPa (2225 psi) is required. Comparatively, considering a 90 th percentile longitudinal spike load of 6.7 kN (1500 lb.…”

Section: Resultsmentioning

confidence: 99%

“…A recent field investigation 5 on a heavy axle load (HAL) freight and passenger corridor reported the 99 th , 95 th , and 90 th percentile longitudinal spike loads to be 8.9 kN (2000 lbf), 7.7 kN (1700 lbf), 6.7 kN (1500 lbf), respectively, assuming that a single spike was subjected to 70% of the applied rail seat load. 4,33 Therefore, the maximum load, 8.9 kN (2000 lbf) was applied to the spikes in this study.…”

Section: Model Developmentmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Khachaturian

Proceedings of the Institution of Mechanical Engineers, Part F:

Liu

et al. 2022

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North American railroads have experienced spike fastener fatigue failures due to spike overloading that have led to multiple derailments. Failures have primarily been found in timber sleeper track constructed with elastic fasteners. This is likely because the elastic fasteners change the load path, resulting in spikes becoming a primary component to transfer the longitudinal forces. Mitigation methods to prevent spike overloading have been limited and thus, this novel study seeks an alternative method leveraging engineered composite sleepers to reduce spike stress. This paper first documents and compares typical composite and timber sleeper properties as reported in the literature. Then, this paper describes the development and validation of a single spike-in-sleeper finite element model (FEM) used to investigate the interaction between the composite sleeper and spike. A glass fiber reinforced composite (GFRC) sleeper was selected due to its high elastic modulus and compressive strength reported in the literature. The validated model was used to quantify the effect of these critical material properties on spikes subjected to longitudinal loads. The GFRC’s stiffness and compressive strength values lead to a 30% reduction in the maximum spike stress when compared to spikes installed in timber sleepers. The reduced spike stress in the GFRC fell below the spike’s expected fatigue limit. Finally, this paper provides required compressive strength for given longitudinal loads to ensure the spike stress falls below the fatigue limit in different operating environments. This characterization of required composite sleeper strength properties can be used to advance track system mechanistic-empirical design.

“…14 The vertical, lateral, and longitudinal rail seat loads, as well as an estimate of the friction at the plate-sleeper interface, are required because the vertical rail seat load and fastener friction govern the failure threshold load. 14 As such, Dersch et al 15 quantified the vertical, lateral, and longitudinal fastener loads in the field at a location that had experienced spike fatigue failures. However, these data only represent one location with a given fastening system and lacks the quantification of load transferred to the spike.…”

Section: Introductionmentioning

confidence: 99%

Quantification of longitudinal fastener stiffness and the effect on fastening system loading demand

Khachaturian

Proceedings of the Institution of Mechanical Engineers, Part F:

Edwards

et al. 2022

Self Cite

Over the past 20 years, there have been at least 10 derailments due to spike fastener fatigue failures in North America. These fatigue failures have been considered a moderate to severe challenge that require manual walking inspections that are both time and labor intensive. These fatigue failures have been found to result from spike overloading due to lateral and longitudinal loads. To date, there has been limited quantification of the vertical, lateral, and longitudinal fastener forces in track. This paper quantifies the effect of fastener type on fastener load to account for various track types and locations. Laboratory experimentation was performed to quantify the stiffness of multiple fastening systems and this data was input into a previously validated analytical model to quantify the effect of stiffness on fastener loading. Additional laboratory experimentation was performed to quantify the relationships between both fastening system type and vertical loading and spike strain. While the laboratory data indicate a significant variance in stiffness between fastening systems, the model results indicate that the load transferred to the fastening system is less sensitive. However, spike strain data indicate the load path was affected by fastener type and vertical load. The characterization of longitudinal stiffness of multiple fastening systems and the relationship to spike load as presented can be used to advance track mechanistic-empirical design and improve rail neutral temperature prediction and track buckling models.