The effects of fastening strength on the variation in stress-free temperature in continuous welded rail

Continuous welded rail (CWR) is a fundamental component of any modern track structure and has several advantages over former types of rail joining processes. The reduction in maintenance and related costs has become the most attractive property of CWR although careful monitoring and maintenance of CWR is essential to ensure safe train operations. Management of the stress-free temperature (SFT) of any section of CWR in order to prevent rail breaks and lateral buckling that could lead to derailments is a vital duty of the track maintenance team. Variations in the SFT are influenced by a number of external factors. This paper describes experimental field and laboratory tests carried out to investigate to what extent the fastening strength influences the variation in SFT in CWR track on Fist fastenings and two types of pads. The research established a nonlinear relationship between clamping force and rail movement through the fasteners as well as a strongly linear relationship between clamping force and the variation in SFT. It is also demonstrated that although the friction coefficient of the pad has an influence on rail movement through the fastener, the primary factor influencing SFT variations is the clip force. This paper concludes by quantifying the relationship between clamping force and the expected variation in SFT with clear guidelines on the management of the SFT in CWR.