This report is the first of three volumes which describe a comparative study of concrete tie track in the U.S. revenue service and at the Facility for Accelerated Service Testing (FAST). The work was undertaken to develop an understanding of the degree to which FAST represents the “real world” of revenue service. The loading environment, structural characteristics and long-term performance of concrete tie track at FAST were compared with corresponding data from four concrete tie track segments in revenue service.
The major conclusions of the study include:
a. Impact loads of high magnitude relative to nominal wheel loads occur because of small percentages of freight and passenger traffic in revenue service. These impact loads are caused be wheel tread irregularities and produce bending cracks at the rail seats of concrete ties. Without detection and removal of the worst wheel tread conditions or attenuation of the impact loads, the service lives of the concrete ties may be significantly shortened.
b. While FAST has the highest mean loads of any site examined, crack-producing impact loads do not occur at FAST because of the extremely good (untypical) FAST consist wheel maintenance program.
c. Track surfacing maintenance (raising and tamping) loosens the ballast structure, reduces the uniformity of support and contributes to large variations in relative track settlement. Uniformity of initial track support conditions is a key to good track performance.