Determining Remaining Fatigue Life of In-Situ Mast-Arm Traffic Signal Support

Wind induced vibration of Mast-Arm Traffic Signal structures is a significant problem. These vibrations and the corresponding wind induced structural stresses and strains can reduce the service life of the structure via fatigue. That is, numerous cycles of alternating moderate structural stress can accumulate damage and result in structural failure. This mechanism is the likely cause of many observed failures of traffic signal structures in the U.S. In the simplest model, wind induced vibration of mast arms is a function of the wind speed and the wind angle of attack. In relation to wind direction, vibrations are larger when the wind angle of attack (e.g., wind out of the north) is perpendicular to the span direction of the mast arm (e.g., mast arm orientated in the east-west direction). In relation to wind speed, vibrations are larger when the natural frequency of the mast arm/support column is the same as the frequency of vortex shedding from the mast arm. The vortex shedding frequency (in cycles/sec) is proportional to the wind speed and the so-called Strouhal number (typical value 0.2 for circular shapes), and inversely proportional to the mast arm diameter. When the vortex shedding 'forcing' frequency matches the structure's natural frequency, a resonance phenomenon 'lock-in' occurs resulting in large crosswind (vertical) vibration of the mast arm. For a system at resonance, the amplitude of structural response depends strongly on the structure's inherent damping (internal energy dissipation). The overall objective of the applied research project is to develop a general methodology to assess the remaining service life of mast arm traffic structures in New York State.

Language

  • English

Project

  • Status: Active
  • Funding: $199999.00
  • Contract Numbers:

    55505-01-04

  • Sponsor Organizations:

    New York State Department of Transportation

    50 Wolf Road
    Albany, NY  United States  12232
  • Project Managers:

    Mooney, Deborah

  • Performing Organizations:

    Rensselaer Polytechnic Institute

    Department of Civil Engineering
    Troy, NY  United States  12180-3590
  • Principal Investigators:

    Letchford, Chris

    O'Rourke, Michael

  • Start Date: 20110901
  • Expected Completion Date: 0
  • Actual Completion Date: 20140630
  • Source Data: RiP Project 29287

Subject/Index Terms

Filing Info

  • Accession Number: 01548336
  • Record Type: Research project
  • Source Agency: University Transportation Research Center
  • Contract Numbers: 55505-01-04
  • Files: UTC, RiP
  • Created Date: Dec 23 2014 1:01AM