Measuring Rail Seat Pressure Distribution in Concrete Crossties: Experiments with Matrix-Based Tactile Surface Sensors

A sustained increase in gross rail loads and cumulative freight tonnages as well as growing interest in high-speed passenger rail development is placing an increasing demand on North American railway infrastructure. To meet this demand, improvements to the performance and durability of concrete crossties and fastening systems are necessary. One of the typical failure modes for concrete crossties in North America is rail seat deterioration, and researchers have hypothesized that localized crushing of the concrete in the rail seat is one of the potential mechanisms that contributes to this failure mode. To understand this mechanism better, the University of Illinois at Urbana-Champaign is using a matrix-based tactile surface sensor to measure and quantify the forces and pressure distribution acting at the contact interface between the concrete rail seat and the bottom of the rail pad. Preliminary data collected during laboratory experimentation have shown that a direct relationship existed between rail pad modulus and maximum rail seat pressure. In addition, under a constant vertical load, a direct relationship between the lateral-to-vertical force ratio and the maximum field side rail seat pressure was observed. Given that all preliminary results indicate that various combinations of pad modulus, track geometry, and lateral-to-vertical force ratio create localized areas of high pressure, crushing remains a potential mechanism leading to rail seat deterioration. Through the analysis of rail seat pressure data, valuable insight can be gained that can be applied to the development of designs for concrete crosstie and fastening system components that meet current and projected service demands.