A sustained increase in heavy axle loads and cumulative freight tonnages, coupled with increased development of highspeed passenger rail, is placing an increasing demand on railway infrastructures. Some of the most-critical areas of the infrastructure in need of further research are track components used in high-speed passenger, heavy haul and shared infrastructure applications. In North America, many design guidelines for these systems use historical wheel loads and design factors that may not necessarily be representative of the loading currently experienced on rail networks. Without a clear understanding of the nature of these loads and how design processes reflect them, it is impossible to adequately evaluate the superstructure in order to make design improvements. Therefore, researchers at the University of Illinois at Urbana-Champaign are conducting research to lay the groundwork for an improved and thorough understanding of the loading environment imparted into the track structure using wheel loads captured by wheel impact load detectors. This paper identifies several design factors that have been developed internationally, and evaluates their effectiveness based on wheel loads using several existing and new evaluative metrics. New design factors are also developed to represent the wheel-loading environment in a different manner. An evaluative approach to historical and innovative design methodologies will provide improvements to designs, based on actual loading experienced on today's rail networks.
With use of concrete sleepers increasing for rail-transit applications in the United States, it is becoming more critical to quantify their revenue service flexural demands to improve sleeper design and maintenance practices. Rail-transit concrete sleeper bending moment field data were collected and processed to address topic areas relating to (1) overall field bending moment magnitude relative to design moments; (2) moment variation from sleeper to sleeper resulting from support conditions; and (3) seasonal variations in moments. Data from field locations on light and heavy rail-transit properties show levels of reserve flexural capacity (factors of safety) that reach as high as 6, significant sleeper-to-sleeper variability attributable to support conditions that can be as high as 100%, and seasonal variation in bending moments that is measurable but far lower than daily variability caused by temperature by a factor of 2. These data provide a valuable baseline for the future generation of mechanistic design standards for track infrastructure components.
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