Field Measurements and Proposed Analysis of Concrete Crosstie Bending Moments


As the use of concrete crossties increases for heavy-haul freight railroad lines in North America, it is becoming more critical to quantify their flexural performance in revenue service traffic in an effort to improve upon design recommendations and maintenance practices, leading to longer service lives, lower life cycle costs, and fewer in-service failures. Currently, center cracking is regarded as one of the most common concrete crosstie failure mechanisms in North America. Improving the understanding of crosstie flexure can help reduce the occurrences of center cracked crossties by ensuring designs are adequate for the field conditions that are encountered. Past work conducted at the University of Illinois at Urbana-Champaign (UIUC) found that crosstie flexure is highly dependent on ballast support conditions and this support can vary greatly from crosstie to crosstie. To measure the bending moments experienced in North American heavy-haul freight service, surface strain gauges were installed on ten concrete crossties along a high-tonnage, heavy-haul North American freight railroad line. These gauges were used to record strains at five critical locations along each crosstie. These strains were converted to bending moments using a calibration factor found in laboratory testing. Data has been collected from nearly 40,000 axles from 70 train passes over 8 site visits spanning 10 months. Prior to instrumentation, micro-cracking was observed at the center of most crossties in this test section, but among hundreds of thousands of measured bending moments, only two center bending moments of one crosstie exceeded the current industry standard design limits. Ballast support conditions were found to be a major source of variation in crosstie flexure and were found to be highly variable in both the direction of traffic and length of the crosstie.