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Analysis of the Shear Behavior of Rail Pad Assemblies as a Component of the Concrete Sleeper Fastening System

To meet the increasingly rigorous performance demands due to growing heavy-haul freight operations and increased high-speed inter-city passenger rail development worldwide, advancements in sleeper fastening system designs are imperative. Improvements to the rail pad assemblies that protect the bearing area, or rail seat, of concrete sleepers will enhance the safety and efficiency of track infrastructure for railways all over the world. Rail pad assemblies provide a protection layer between the sleeper and rail base by reducing the dynamic loads imposed on the sleeper rail seat and distributing the loads to acceptable stress levels. Additionally, the assembly, typically composed of a rail pad and abrasion frame, interacts with the other fastening system components in order to restrain the rail and maintain desirable track geometry. Understanding the shear behavior of pad assemblies is critical to improve the performance of track components and avoid potential failure modes such as rail seat deterioration (RSD), that are caused by large lateral forces in curves. Normal and shear forces exerted on the components of the fastening system can result in displacements and lateral deformations of rail pad assemblies with respect to the rail seat. The high stresses and relative movement are expected to contribute to multiple failure mechanisms of the fastening system and result in an increased need for costly maintenance activities. Thus, the study of the mechanics of the rail pad is of paramount importance for the improvement of railroad superstructure components. In this study, the shear behavior of rail pad assemblies will be investigated from a mechanistic perspective that combines laboratory and field experiments to explain how the surfaces interact, show how the materials deform, and quantify the amount of relative displacement between the fastening system components. The expected results will allow the industry to develop a mechanistic design approach that enhances the performance, efficiency, and durability of current fastening systems. Furthermore, this work will lead fastening system design to a new level of sophistication by including considerations for shear design, ultimately resulting in recommendations that will reduce the need for preventive measures and maintenance related to track component deterioration.