Pole Fatigue Calc for Key West: AASHTO Spec & Vc of 45mph

  • Thread starter Thread starter Fat Ryan
  • Start date Start date
  • Tags Tags
    Fatigue Pole
Click For Summary
SUMMARY

The discussion centers on performing a fatigue calculation for a 50-foot, 16-sided tapered steel pole intended for speaker installation in Key West, utilizing the AASHTO standard specifications. The specified wind velocity (Vc) is 45 mph, with an importance factor of 1.0 and a detail category E' resulting in a Critical Allowable Fatigue Load (CAFL) of 2.6 ksi. The user reports discrepancies in required loads, suggesting potential errors in wind pressure calculations and drag coefficients. Key considerations include the critical section at the pole's base and the distinction between static and dynamic loads in fatigue analysis.

PREREQUISITES
  • AASHTO specifications for structural supports
  • Understanding of fatigue calculations in structural engineering
  • Knowledge of wind load calculations and drag coefficients
  • Familiarity with structural analysis software or spreadsheets
NEXT STEPS
  • Review AASHTO specifications for fatigue calculations in detail
  • Learn about wind load analysis and its impact on structural integrity
  • Investigate drag coefficient values for various shapes and their implications
  • Explore best practices for verifying units and calculations in structural spreadsheets
USEFUL FOR

Civil engineers, structural analysts, and anyone involved in the design and analysis of structural supports for outdoor installations, particularly in high-wind environments.

Fat Ryan
Messages
48
Reaction score
0
I was asked by the CE to do a fatigue calc for a speaker pole going up in key west. I am using AASHTO standard spec for structural supports for highway signs, luminaires, and traffic signals. he said to assume a Vc of 45mph, an importance factor of 1.0 (from category I-lights in the cantilevered section) to be conservative. he also said to use the detail category E' for the CAFL, which results in a CAFL of 2.6ksi. all the specs from the pole and speaker set are from another spreadsheet we have here. its a 50' 16-sided tapered steel pole. to give you an idea, the diameter ranges from 21.2 to 14.2 inches with an X-section area ranging from 16.5 to 11 in^2. the speakers mount atop the pole and weigh in at 440lbs.

ive attached my spreadsheet with the calc. I've never done a fatigure calc and this AASHTO spec is god awful at explaining what to do. I am getting a required loads that are like 50,000 times higher than the CALF lol. I am guessing the "conservative" 45mph wind speed would play a large role considering its squared in the pressure equation. and the drag coefficient i have for the speaker seems awfully high. but i also don't really even know what I am doing in the first place. I am assuming the critical section is at the poles base (by the fillet weld to the base plate). It seems that'd likely be where fatigue cracks would form in my mind.

so am i doing something wrong here? perhaps I am missing some key theory...
 

Attachments

Engineering news on Phys.org
One thing you are doing wrong, self weight is a static load and cannot induce fatigue damage.

It is not possible to verify the equations in your spreadsheet, but you might be working with the wrong units.
 
Last edited: