Structural Performance of High Density Polyethylene Crossties and Use in Accelerated Bridge Construction

Hardwood timber has been the predominant material of choice for crossties since the establishment of the railroad industry in the US. Recently, several concerns, including higher speeds, heavier loads, durability and negative environmental effects associated with deforestation and wood-treating chemicals, have invoked the railroad industry’s interest in alternative materials for crossties. Currently, several manufacturers offer alternative and sustainable solutions using different recycled plastic composite materials. Thousands of plastic crossties are currently in service in a wide variety of railroad applications. Several researchers have been studying and testing these new materials, specifically High Density Polyethylene, however, their behavior when subjected to rail loading is not fully understood yet. Uncertainties in mechanical properties, failure modes, fracture, spike holding and loosening, tie-plate cutting and durability render their performance and safety questionable. More research is required to properly characterize, describe and model the behavior of these materials as well as assess the feasibility of implementing these materials in railway applications in terms of performance, safety, practicality, and economy. Therefore, the research effort presented in this thesis aimed to investigate the performance of plastic composite crossties through experimental testing and analytical modeling then evaluate the feasibility of implementing them in Accelerated Bridge Construction. A comprehensive testing program addressing several AREMA recommended test methods for engineered composite crosstie was conducted. The mechanical properties and behavior of the crossties and the fastening system assembly were evaluated for the individual components as well as the entire system. Analytical material models, capable of simulating the behavior of plastic crosstie and its interaction with the fastening system were constructed and calibrated using the experimental data. These models were then implemented in two full-scale modeling applications using Accelerated Bridge Construction techniques for railroad elevated structure applications. The plastic composite crossties demonstrated adequate performance throughout the experimental testing program. Additionally, the finite element modeling of the full-scale bridge applications served as a proof of concept for future implementation of plastic crossties in railroad bridges. This research also highlights the potential structural, social, and economic benefits of implementing High Density Polyethylene crossties in railroad applications.