Field Investigation of A Strain Gauge-Based Tie Reaction Force Monitoring System

Abstract: Tie reaction force under a moving wheel is a major track response parameter providing valuable information about track support conditions. Some of the existing track support condition monitoring systems are either very expensive, invasive in nature (requiring extensive track time) or are not suitable for long-term monitoring applications for various environmental and load-related factors. Most of the time, the limitations associated with the sensors have had a significant impact on their accuracy and long-term performance. The application of strain gauges to measure vertical wheel loads using Differential Shear Strain (DSS) theory is prevalent in the railroad industry. Recent research has indicated that the same DSS theory and the same rail-mounted strain gauge-based measurement system adjacent to a crosstie can be used to measure the tie reaction forces. Past numerical modeling efforts have demonstrated the viability of DSS theory in measuring tie reaction forces as indicators of track support conditions. A field validation effort was recently undertaken through a collaboration between the Federal Railroad Administration (FRA), ENSCO Inc., and Oklahoma State University (OSU). The objective was to study the accuracy and adaptability of rail-mounted strain gauge-based systems to measure tie reaction forces under varying track conditions and train operating speeds. Field tests were carried out in a yard track in Letterkenny, Pennsylvania, as well as along a section of the Railroad Test Track (RTT) at the Transportation Technology Center in Pueblo, Colorado. The two sites comprised timber and concrete crossties, respectively. Selected crossties were strategically removed during the field-testing effort to simulate ‘hanging tie’ conditions. Track response was recorded under varying locomotive speeds. The results demonstrated that the rail-mounted strain gauge-based systems could effectively measure tie reaction forces under moving wheel loads for both track types. Highest accuracies were observed under relatively lower operating speeds. This system presents a low-cost, non-invasive approach to measuring tie reaction forces and detecting changes in track support conditions. Implementation of this technology can facilitate proactive maintenance practices, leading to safer operating conditions.