United States Department of Transportation
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TRIS Online Accession Number:00667595
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Edition:Interim Report July 1990 through May 1994
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Abstract:This report documents methods of fatigue analysis for overhead sign and signal structures. The main purpose of this report is to combine pertinent wind loading and vibration theory, fatigue damage theory, and experimental data into a useable fatigue analysis method for overhead sign and signal structures. Vibrations and forces induced by vortex shedding were studied analytically and measured experimentally. Analytical models were extracted from the literature. Drag coefficients, generally assume to be constants or simple functions of Reynolds number, actually depend on the amplitude of vortex shedding vibration. The amplification of drag coefficients can have a significant effect on resulting forces. Fatigue and the concept of fatigue damage quantification were discussed. Fatigue was described as a failure mode which results from cyclic application of stresses which may be much lower than the yield stress. Fatigue damage was quantified using the Palmgren-Miner linear damage equation. Available stress cycles for each applied stress range are calculated by expressing published S-N fatigue data for welds or anchor bolts as N-S equations, where number of available cycles (N) is the dependent variable, instead of stress range. The use and limitations of fracture mechanics methods were discussed. Stress concentrations were discussed as a vital parameter in fatigue analysis.
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