Technical Reports

Wheel Unloading of Rail Vehicles Due to Track Twist

  • 01
  • Feb
  • 1986
AUTHOR: D. Tyrell, H. Weinstock, R. Greif
OFFICE: RPD
REPORT NUMBER: DOT/FRNORD-85/14
SUBJECT: Tracks & Structures
KEYWORDS: nadal's limit
ABSTRACT: An analysis is presented describing the effect that track twist has on the loads carried by the wheels of a rail car. Wheel unloading is determined as a function of the difference in cross level between the truck centers of the car. The different vehicle characteristics that affect a car's reaction to track twist are determined. It is found that light, torsionally stiff cars are the most susceptible to wheel unloading due to track twist. Using the results of a previous study where lateral wheel/rail force was determined as a function of curvature, the difference in cross level between truck centers that will cause Nadal's Limit for wheel climb to be exceeded is determined as a function of curvature. This difference in cross level between truck centers is normalized to 31 feet so that maximum track twist, as it is commonly defined, is determined as a function of curvature. It has been found that for less than 6 degrees of curvature and at low speeds, most rail cars can withstand up to 1.5 inches of track twist in 31 feet. The amount of track twist that a car can withstand decreases with increasing curvature, and at 15 degrees of curvature the amount of track twist that most railcars can withstand has dropped to 1.0 inches.

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