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Wind load for rotating flags

Wind load for rotating flags

Wind load for rotating flags

Hello I am designing a flagpole which has a moving element at the top that allows the flag to rotate 360 degree in the direction of the wind. In this condition, what code do I use as per ASCE ? My manufacturer indicated a reduction of load to 20percent of the total flag size as the flag is a moving element. Can anyone guide me on this code?

RE: Wind load for rotating flags

ASCE recommends the use of ANSI/NAAMM FP1001 for flag pole design (7-05 p300). I would check that document.

RE: Wind load for rotating flags

Thank you for your response. However NAAMM FP 1001 does not provide for rotating Flags(360 Degree rotation). The calculation states in Equation 9 notes that the flag is secured via an external halyard, to a cleat near the base. This is a fixed flag, external halyard situation. My situation is internal halyard, free rotation flag. Any ideas/suggestions? Can some one give me an extract or code reference to substantiate my claims with the design team to reduce the visible flag load to 20% of total area? Is there any code to justify? Thanks in advance friends.

RE: Wind load for rotating flags

Assume on the day when you finally get that design wind load, say 10 years from now the flag doesn't rotate anymore. Assume 3 years from now the owner wont fix his rotating flag mechanism because he can't afford it and he goes bankrupt.

RE: Wind load for rotating flags

I can't remember where I saw the equation, but you might check for flags and banners towed behind airplanes. The flag has a drag and someone wanted to know how much airplane you needed to tow a banner. It seems like it might be appropriate to your situation. IIRC, you take the flag or banner area and multiply it with a factor that I think may be around 15%.

Many years ago I had to check one of our street light poles for a couple of banners hung on them to advertise something or another. Two small posts cantilevered from the pole and the banner would attach between them. Now, street light poles are pretty flimsy and if the banners stayed attached, it would fail the pole. I came up with the idea of the lower attachment being a snap away clip which would release in about a 30 mph wind. The banner then acted like a flag hung vertically and I could use the free banner equation to calculate the drag on the upper post to see if the pole was overloaded.

I have been called "A storehouse of worthless information" many times.

RE: Wind load for rotating flags

thank you for your response. Is there a NEMA/ANSI ref code? Will look up anyways.

RE: Wind load for rotating flags

A quick Google search found this web page about flag pole design:


The equation for the flag load says something about it being based on tests done by towing flags behind airplanes which is what I remembered from 20 years ago. I think you have already referenced this document and I have not done much reading of it, but I guess I don't get the distinction between a free rotating flag and what you describe as a fixed flag. They both flap in the wind and have some drag applied to the pole.

If you want lots of equations, I found this paper:

I have been called "A storehouse of worthless information" many times.

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