Simulation of the Thermal Effects on Engineered Polymer Composite Ties

Engineered polymer composite (EPC) ties offer a potential alternative to solid sawn timber ties. These materials are especially attractive for use in regions where wood is susceptible to degradation by moisture and decay organisms. However, recent research at the Transportation Technology Center’s (TTC) Facility for Accelerated Service Testing (FAST) in Pueblo, CO, found that track supported by EPC ties experienced more gage widening variation due to temperature changes than track supported by wood ties. Specifically, the track gage was about 0.2-in. wider in the afternoon than that in the morning on the EPC tie tracks. It is believed that the direct sunlight in the afternoon makes the top surface of the tie expand more than the other parts of the tie, thereby causing the EPC ties to bend and widen track gage. Another observation related to the EPC thermal bending effect is changes to the ballast support condition. When temperatures are cooler, EPC ties tend to experience a center-bound ballast support condition, therefore generating more bending stress on the ties. This paper presents results from computer simulations of the thermal behavior of EPC ties. Future study will focus on field testing to further understand the thermal effects in support of recommendations on the use of EPC ties.