Review of Critical Factors Influencing Longitudinal Track Resistance

Abstract

Longitudinal track resistance is one of the most critical parameters required to accurately analyze longitudinal load propagation and refine rail neutral temperature (i.e., stress-free temperature) maintenance practices. However, longitudinal track resistance has not been consistently defined and has been quantified using multiple methods that should not be conflated. This paper documents common definitions of longitudinal track resistance and the two methods regularly used for its quantification: track panel pull test (TPPT) and single rail break (SRB). Further, this paper documents the differences in mechanics between these methods, summarizes and discusses the critical factors influencing the longitudinal track resistance values found in the literature, and adds novel TPPT longitudinal track resistance values for timber sleeper track to address the current scarcity of data found in the literature. In summary, TPPT values provide insight into the mechanics of load propagation and pre-buckle analysis while the SRB values aid in the maintenance and restoration of rail neutral temperature after a rail break or destress. Additionally, the TPPT longitudinal track resistance values reported in the literature were independent of panel length, were influenced most by the presence of a vertical load, and were reduced by 25% when the ballast was disturbed. Finally, novel TPPT results indicated the longitudinal resistance of timber sleeper track was 19% lower than concrete sleeper track and that unfastened sleepers still transferred longitudinal load when the cribs were full and ballast was compacted.

Effect of Critical Factors Influencing Longitudinal Track Resistance Leveraging Laboratory Track Panel Pull Test Experimentation

“…This value is very similar to the median reported concrete sleeper TPPT resistance value of 7.5 kN/m (42.8 lb/in.) reported by Potvin et al (8) and is 20% greater than the timber sleeper panels (i.e., 6.3 kN/ m [36.2 lb/in.]). This 6.3 kN/m (36.2 lb/in.)…”

“…Force is applied to the panel until a maximum or relatively steady-state resistance value is reached to quantify the maximum panel resistance. In their review, Potvin et al ( 8 ) found that longitudinal resistance was independent of panel length when comparing the results from these typical panel lengths to the 108 sleeper panel executed by Mohammadzadeh et al ( 16 ). While field tests have the advantage of quantifying the revenue service track conditions, laboratory tests can provide researchers with the flexibility to investigate more track configurations.…”

“…Many of these researchers are using longitudinal track resistance and stiffness values found in the literature. Based on a review of the literature by Potvin et al ( 8 ), 14 of 16 (88%) studies that leveraged track panel pull tests (TPPTs) to quantify the longitudinal resistance and/or stiffness studied concrete sleeper tracks ( 9 – 19 ). However, because 90% of North American track is constructed using timber sleepers ( 20 ), there is a need for additional longitudinal track resistance and stiffness data for timber sleeper tracks to support these analytical models.…”

“…TPPTs and single rail breaks (SRBs) are the two most common methods used to quantify the longitudinal track resistance and stiffness ( 8 ). Potvin et al ( 8 ) recommends leveraging TPPT results, the values will be used to perform a load propagation analysis.…”

“…TPPTs and single rail breaks (SRBs) are the two most common methods used to quantify the longitudinal track resistance and stiffness ( 8 ). Potvin et al ( 8 ) recommends leveraging TPPT results, the values will be used to perform a load propagation analysis. Further, as longitudinal track resistance is a measure of longitudinal force per unit distance provided by the ballast, sleepers, fasteners, and rail ( 10 ), these are the parameters that should be considered when performing additional research.…”