4"x4"x1/4" steel tubing lehigh valley PA

I'm erecting a shade sail over a patio and planning to use 4"x4"x1/4" steel tubing on the four posts that will carry the fabric. The fabric will be
tensioned so that it barely flaps in anything but a very strong wind. I'm told there will be between 2000 & 3000 # pull at the connection points. The tube steel will be embedded in concrete 3' or more below grade depending on the height out of the ground. Two of the tubes will be 9' above grade and opposite from one another. Another will be at 10' above grade and the opposite one, the highest, at 11' above grade. Can anyone tell me if A500 B grade 4"x4"x1/4" tubing will do the job?
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On Tue, 17 Jun 2014 18:18:02 +0000, Jim wrote:

11', 3000# = 33,000 ft-lb at the base of the tallest post.
Go look up what that tubing can withstand, and let us know.
I think you need to worry more about your anchors pulling out of the ground with that much bending moment being exerted on a post with only a three foot deep base.
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Tim Wescott
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On Tue, 17 Jun 2014 18:18:02 +0000, Jim

If I'm interpreting your description properly (that's a big if), the tubing is nowhere close to strong enough, even if the footings are adequate.
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Ned Simmons

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On Tue, 17 Jun 2014 16:22:19 -0400, Ned Simmons wrote:

Come to think of it, the tension on the tube walls at the base of the 11' section is something over 100,000 psi. Even if it didn't buckle on the compression side, it'd bend right over.
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Tim Wescott
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Where did you locate the neutral plane? -jsw
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On Wed, 18 Jun 2014 14:05:52 -0400, Jim Wilkins wrote:

I figured that for a quick calculation that was going to say "it'll break anyway", I'd rearrange the walls of the pipe so that they're 8" long, 4" apart. 1/4" thick walls gave me (1/4")(8") = 2 sq in.
That's going to result in an overestimate of the strength of the pipe -- but if the stronger pretend thing breaks, then surely the real, weaker, thing will break.
I put the neutral plane half way between the walls, so the force from the moment is
(33,000 ft-lb) / ((2")/(12 in/ft)) = 198,000 lb
Dividing this by the area gave me 99,000 psi, which is close enough to 100,000 given all the wild approximations.
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Tim Wescott
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On 6/17/2014 1:18 PM, Jim wrote:

I use 4" sch 40 galvanized pipe in 3' diameter hole 5' deep. They have standing and doing well for over 5 years.
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Weight is easy. You also need to calculate the wind loading effects. The overturning moments can be quite large, and the footings have to be big enough not to be uprooted.
Joe Gwinn
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