FIELD INVESTIGATION OF A TRUSS SPAN ON THE GREAT NORTHERN RAILWAY

A.R.E.A. Committee 30 - Impact and Bridge Stresses, has an assignment for the study of stresses and impact in steel bridges. In connection with this assignment, the committee requested the Technical Center to conduct a study of the Priest River Bridge on the Great Northern Railway near Priest River, Idaho. This work was conducted in September, 1966 and this report contains a description of the work and analysis of data obtained on the 200 ft. open deck, Warren type, through truss span. The purpose of the investigation was to determine the impact effects and maximum stresses in various truss members by use of a test train operating over a wide range of speeds. It is known the effect of the spring-borne weight of the locomotives oscillating about a longitudinal axis is to increase the pressure on one rail with a corresponding decrease in pressure on the other rail, although it would be unlikely that all cars were rolling in the same direction simultaneously. The variation in pressure on the rails produces a change in the direct mean stresses of the truss members. The roll effect at the centerline of rails observed during runs of the test train is shown of Figure 3. This value was obtained by computing the vertical forces, applied at the rails, that would produce the same moment as the forces recorded in the trusses. The roll forces in the truss members were obtained by expressing the difference between the mean stress for the member in one truss and the average of simultaneous mean stresses for corresponding members in both trusses, corrected for eccentricity of the load, as a percent of the average static mean stress. The effect of roll on the end post and upper chord indicates an increase with an increase of speed. It can be noted that the lower chord values are scattered and the maximum equivalent roll of 21 percent occurred at an intermediate speed. With the exception of two values, all roll effects were within the A.R.E.A. Specification limits. The highest equivalent maximum roll effect was 21.2 percent at a speed of 32 mph which occurred in bottom chord member L2L3. The following stresses or effects were reported on:1. Static Stresses, 2. Roll Effect, 3. Total Impact, 4 Maximum Stress.

Media Info

  • Features: Figures; References; Tables;
  • Pagination: 9 p.
  • Serial:
    • Volume: 29
    • Issue Number: 2

Subject/Index Terms

Filing Info

  • Accession Number: 00096571
  • Record Type: Publication
  • Source Agency: Association of American Railroads
  • Files: TRIS
  • Created Date: Jul 24 1975 12:00AM