Evaluation of Common Method for Eyebar Tension Measurement

摘要

The flame shortening procedure often used to adjust tensions in the eyebar members of steel railroad trusses relies upon observed vibrations of the eyebars to predict dead load stresses in these members. The method is based on a model that assumes pinned-end conditions, but for vibrations about the minor axis of an eyebar, the potential exists for a significant degree of rotational end restraint. This paper develops the analytical model for fixed-end conditions and demonstrates that when such conditions exist, the use of the conventional pinned-end model can result in significant error, particularly for eyebars of relatively low slenderness. Field test results are discussed that show eyebar behavior to be consistent with fixed-end conditions when pin joints are tight. Charts are presented that enable the accurate determination of dead load stresses for fixed-end eyebars; these tools may have additional utility for bridge inspection and rating.