Vertical Load Path Under Static and Dynamic Loads in Concrete Crosstie and Fastening Systems

An improved understanding of the vertical load path is necessary for improving the design methodology for concrete crossties and fastening systems. This study focuses on how the stiffness, geometry, and interface characteristics of system components affect the flow of forces in the vertical direction. An extensive field test program was undertaken to measure various forces, strains, displacements and rail seat pressures. A Track Loading Vehicle (TLV) was used to apply well-calibrated static loads. The TLV at slow speeds and moving freight and passenger consists at higher speeds were used to apply dynamic loads. Part of the analysis includes comparison of the static loads and the observed dynamic loads as a result of the trains passing over the test section at different speeds. This comparison helps define a dynamic loading factor that is needed for guiding design of the system. This study also focuses on understanding how the stiffness of the components in the system affects the flow of forces in the vertical direction. The study identifies that the stiffness of the support (ballast) underneath the crossties is crucial in determining the flow of forces. The advances made by this study provide insight into the loading demands on each component in the system, and will lead to improvements in design.