Technical Reports

Stub Sills on Tank Cars

  • 01
  • Mar
  • 1989
AUTHOR: W. J. Walsh, R. C. Rice, D. R. Ahlbeck
SUBJECT: Facilities & Test Equipment
KEYWORDS: Stress Analysis, Fatigue, Life Predication, Head Brace
ABSTRACT: The results of this study indicate that the head brace repair procedure provides an effective means for redirecting stub sill loads into the tank body, thus reducing stresses at the critical sill-to-reinforcing pad weld sites. Our analysis indicates that the stub sill to tank interface stresses from longitudinal coupler loads are reduced significantly (by about 15 to 20 percent) and the stresses due to vertical coupler loads are reduced dramatically (by over 75 percent). The longitudinal coupler loads are most influential in terms of crack initiation, while the vertical coupler loads were found to influence crack growth to a greater extent. Therefore, it has been concluded that the stub sill designs, with the head brace properly installed, will exhibit significantly longer service lives before fatigue cracks form (if they form at all). Perhaps even more importantly, the introduction of the head brace should offer an important margin of safety in terms of.crack growth life. In other words, even if fatigue cracks do form at the stub sill to tank interface and the head brace is intact, crack growth rates should be reduced to such an extent that the likelihood of properly identifying and repairing these cracks before tank rupture should be increased significantly. If the head brace itself cracks, the damage should be relatively easy to identify and repair. In summary, the introduction of a properly sized and installed head brace should offer an effective means of reducing the likelihood of both fatigue crack initiation and tank rupture. However, the procedure does not eliminate the need for periodic inspection of the region for fatigue damage.