Technical Reports

Investigation of the Effects of Tie Pad Stiffness on the Impact Loading of Concrete Ties in the Northeast Corridor

  • 01
  • Nov
  • 1983
AUTHOR: Federal Railroad Administration; F.E. Dean; H.D. Harrison; R.H. Prause; J. M. Tuten
SUBJECT: Tracks & Structures
KEYWORDS: Concrete ties, Fasteners, Track stiffness
ABSTRACT: This investigation was conducated in response to the discovery in June 1980, that rail seat bending cracks had developed in many concrete ties which had been in service on the Amtrak Northeast Corridor track for periods of a few months. The study was initiated by the Federal Railroad Administration to investigate the cause of the cracks and to identify a solution which would arrest further crack development while minimizing the retrofitting of components. The study was conducted in three phases: a. Exisitng load and tie strain data were examined over a large frequency band width (0-1200 Hz) to deteremine whether impact loads could be identified at levels above that known to cause tie-cracking. Such high- frequency impacts were found on a small percentage of high-speed passenger trail wheels. These impacts were caused by wheel thread irregularities. b. Laboratory impact tests verified that major reductions in tie pad stiffness could significantly reduce the tie bending moments resulting from impact loads. c. Field measurements of impact loads and tie bending moments were conducted in a test zone where more flexible tie pads were subsittuted. The tests verified that flexible tie pads which are adaptable to teh current fastener system could reduce the occurance of bending strains which can crack ties. However, it was shown that the elimination of tie cracking will require both a more flexible pad and a progrma to eliminate the wheel conditions causing the highest impact loads of Northeast Corridor passenger trains.