Author: David L. Cackovic, Kerry D. Hopkins, David Tyrell

Date of Publication:  May 1994

Sponsoring Agency:  U.S. DOT - Federal Railroad Administration, Office of Research and Development

Performing Organization:  Association of American Railroads, Transportation Test Center, Pueblo, Colorado

Report No: FRA/ORD/94-11

Abstract:

An investigation of the effects of variations in side bearing clearance on the vehicle dynamics of loaded freight cars with relatively high centers of gravity was conducted.

Data from the Vibration Test Unit (VTU) showed that increasing side bearing clearance significantly affected railcar roll responses. Jump response was exhibited. When testing on-track, the limitation in test zone length made it impossible to replicate the jump response shown during the VTU tests. Results from the tests are as follows:
 

• Compared to nominal gap clearance data, an increased gap produced significantly larger roll angles, at lower peak resonant frequency, over a wider range of frequencies.
• Increased gap produced slightly less wheel unloading on the VTU. Due to safety considerations, it was not possible to test on-track at wheel-unloading conditions to determine which configuration was more severe.
• Increased side bearing clearance allows more roll without involving suspension components.
• On-track testing produced car body roll angles, displacement responses, and wheel loads which were similar in characteristic shape of amplitude level versus speed to the VTU test data, but not in amplitude and frequency. This is probably due to variances in the simulated VTU waveform
• It was found that slight changes in the input to the wheel/rail interface may cause major variations in dynamic response. This was most prevalent with the 3/4-inch roller side bearing gap clearance.

No. of Pages:  68