FATIGUE ANALYSIS OF OVERHEAD SIGN AND SIGNAL STRUCTURES. INTERIM REPORT

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 usable 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 assumed 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. Methods for estimating K sub t for fillet welds and anchor bolt threads were extracted from the literature. Experimental data were collected for a representative traffic signal structure. These data included stress range and frequency response for ambient wind loadings, dead load stresses, strain as a function of vertical tip deflection, vibration frequency due to ambient winds, and strain response due to controlled-speed wind loads. The instrumented details were tube to base plate circumferential fillet welds and anchor bolts. Wind speed data were collected at a traffic signal site in Springfield, Illinois, for seventeen months. Factor of safety equations for use with welded details were discussed. Sample fatigue life calculations using both strain gage-derived and analytically estimated stress range-frequency histograms were performed as examples to the reader. Calculations using static conditions were also performed. The results differed significantly from the other solutions.

  • Record URL:
  • Corporate Authors:

    Illinois Department of Transportation

    Bureau of Materials and Physical Research
    126 East Ash Street
    Springfield, IL  United States  62704-4766

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • South, J M
  • Publication Date: 1994-5

Language

  • English

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: 118 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00667595
  • Record Type: Publication
  • Report/Paper Numbers: FHWA/IL/PR-115, PRR-115
  • Contract Numbers: IHR-319
  • Files: NTL, TRIS, USDOT, STATEDOT
  • Created Date: Oct 5 1994 12:00AM