Flag Pole

[ztengguy]

I have been asked to design a flag pole, 250' tall for a flag pole for a flag 50 feet long. heres the kicker, he wants to use old W shapes to make the pole, and have them cut to be tapered to make this thing. I am at a loss how to design this. Anyone ever done this before?

 

[paddingtongreen]

That sounds expensive, I hadn't heard of it before now.

Valmont used to make tapered square and rectangular tubes.

Perhaps you could use a rectangular HSS as the core and weld tapered plates to the short sides to give the impression of a wide flange.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[JStephen]

I can't really visualize how this would work. If it's being assembled out of a bunch of smaller beams, then fabrication may eat up any material savings from using existing material. Also consider coating/galvanizing cost, ease of future maintenance, birdnests, etc. Is there an access tube or ladder? Is the area clear of any airports?

 

[BadgerPE]

I have never been asked to do a flag pole design, but we have the possibility of one coming up in the near future so I was just researching last week. Per the attached document Eqn. 5, assuming a polyester flag, 90 mph wind zone and 50'x50' flag, the force from the flag alone is nearing 50 kips. I am not sure if you are going to be able to get forces like that to work with W-sections, or any for that matter. Another issue is torsional resistance, of which will be virtually nothing when using a W section.

 

[ztengguy]

Yea, its all from old W beams from a bridge. Sorta wants to connect them, then cut it to the taper. He then wants to use a piece of old concrete pipe as the base filled with concrete (or he said water), so he can move it around if need be.

 

[smb4050]

Is this a serious post? If yes first, get a retainer before doing anything. Second, check zoning ordinances if a pole that tall can be built (I wouldn't want it near my house), and aviation restrictions. IMO, this does not sound like something a sane person does unless there are extenuating circumstances that haven't been shared that makes it reasonable (still wouldn't want it near my house). I'm guessing the flag won't be coming down every night.

 

[AELLC]

I think this an April Fool post.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

 

[Archie264]

This would be no trivial undertaking, to say the least. For an idea of some of the issues you might be up against you might want to review this project:

https://en.wikipedia.org/wiki/United_States_Air_Force_Memorial

http://www.arup.com/Projects/United_States_Air_Force_Memorial.aspx

 

[BadgerPE]

"I think this an April Fool post."

If this is true, well done!

 

[LittleInch]

I think the flag (and pole) will be coming down every night once you get a small breeze....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[JStephen]

That thought occurred to me as well.

 

[ztengguy]

AELLC you are correct!! got to have a bit of humor in our lives.

 

[BadgerPE]

Well played zten, well played.

 

[AELLC]

LOL

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

 

[IRstuff]

Ensenada has a larger flag, but shorter pole:

http://en.wikipedia.org/wiki/Banderas_monumentales

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[SAIL3]

Had me fooled which is not hard to do nowadays. Since I have an opinion on everthing, I was getting ready to unload on this. Attached is an interesting flagpole case. I was under the opinion that a tapered pole would not develop vortex shedding resonance, just cannot explain how it is occuring in this case , unless the taper is not pronounced enough.

 

[JStephen]

Well, it's right on par with some presumably-real questions that come up.

Some time back, we got in an inquiry for fabrication of a flagpole, it may have been one of those Wisconsin poles, see the Wikipedia article about that.

Once you get above the height of a powered manlift, you pretty much HAVE to have some type of ladder in or on something like this. At some point, the rope will break, the pulley will snarl or something, and somebody's got to go up that thing and straighten it out. So in the case of the Wisconsin flagpole, I think it said it was 6' diameter at the bottom.

And yes, you COULD build it out of tapered wide-flange beams. Why you'd want to is a different question, as it would be a booger to repaint it or anything, and welding costs would probably offset material savings. See the attached sketch for how I'm visualizing the cross section.

 

[AELLC]

We are getting more student posts than ever, and the last one I wasted time with, the guy kept debating with me to get the last word in.

Just wait until he gets a job and debates with his boss. He won't last long.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.

 

[steellion]

Great job, ztengguy. Great example of Poe's Law. We get asked to do some crazy things, so I wouldn't be surprised if a client wanted a flagpole like you described.

"Poe's law, named after its author Nathan Poe, is an Internet adage reflecting the idea that without a clear indication of the author's intent, it is difficult or impossible to tell the difference between an expression of sincere extremism and a parody of extremism" -Wikipedia

 

[AELLC]

steel,

Archis ask us to do crazier things all the time.

The definition of a structural engineer: overdesign by a factor of 1.999, instead of the usual 2.