Large Sign Pole Design 2

[CBSE]

I have been asked to design a 65ft tall pole for a sign. See attached dimensions. They want a break at 25ft, and then another pole break at the sign which is supposed to have a HSS Tube behind the sign for attachment. Does anyone have any ideas on how to attach these together besides a plate splice with bolts? Is there a way to do some sort of sleeve at the first break from the ground so it looks a little bit cleaner?

I imagine there will be some sort of frequencies that need to be considered with this as well.

Thanks

 

[KootK]

Keep an eye on fatigue issues.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

Thank you! By the way, what book is that taken out of?

 

[KootK]

What book? Totally made it up myself. Send $15 CAD.

I bought it a decade ago after my first sign and it's been shelfware ever since. Six homes and two countries later, somebody finally asked the right question. I pretty much trampled my wife on the way to the basement to fetch the detail.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

Awesome! Thank you for the reference. I'm going to buy this book, and it will probably sit on my shelf for the next 10 years as well BUT, you can never have too many references!

 

[KootK]

Ask your wife about that. The book is actually pretty mediocre beyond that one detail. Caveat emptor.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

Does it at least have a design example for that one PDF? I can recreate it, but sometimes it's nice to see something to reference it against.

 

[CBSE]

My wife will probably roll her eyes at me and then tell me to go clean the dust off the rest of my books/manuals.

 

[KootK]

Does it at least have a design example for that one PDF?

Nope.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

An interesting feature of the detail is that it uses fillet weld pairs in bending to resist gravity loads. We usually try to avoid using welds that way. Small loads I suppose.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[CBSE]

Yeah, I was noticing that and trying to figure out if something was missing like a knife plate thru the pipe section welded to the top ring.

 

[CBSE]

Or even gusset plates

 

[KootK]

There's an alternate mechanism other than the cantilevering plate. A little weirder to evaluate though.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SAIL3]

the plug weld on the bottom ring may be tricky and expensive.....one could eliminate the plug welds (but still have a snug fit)and have the top ring take all the axial loads either by increasing it's thickeness or adding gusset plates....

 

[SAIL3]

on further thought...in resisting the applied moment the lateral load in the bottom ring will have to be resisted by the wall of the pipe.....the plug welds distribute this lateral load more evenly...without the plug welds the bottom ring would just bear on the wall of the pipe so I might add an external ring to the pipe at that location rather than trying to analyze the wall of the pipe for that loading.....

 

[CBSE]

KootK: you just made me dizzy and almost hypnotized.

Sail3: my first inclination before KootK sent the detail was to let the pipe slide down into the larger pipe 3-4ft, but then realized it probably would be unstable. The welds certainly will be expensive, but so far, I haven't seen anything different or another method. The forces are to great to do a standard plate splice with gussets, so the sleeev solution seems to be it.

 

[KootK]

Yeah, it always seems as though there's just gotta be an easier way.

How many separate pieces do you expect this thing will be in when it ships?

Also, do you know the minimum access hole size that will be required for wiring etc?

When they step ski lift and utility poles, there's sometimes a truly tapered bit at the transition. I could see that being expensive for a shop not set up for that though.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[BAretired]

Don't forget to check vortex shedding.


BA

 

[CBSE]

KootK: I'm anticipating (3) sticks.

(1) Large pole for the base...probably a 32 Std pipe
(1) Smaller pipe for the piece between bottom pole and bottom of sign
(1) HSS from the mid pipe for sign attachment that I will do a typical plate splice with on top of the pipe. I think the HSS will provide for more reliable connection of the sign.

Not sure on access hole sizes.

 

[damorim]

Is there a reason that a dodecagonal tapered shaft hasn't been considered? Large A/F at bottom tapering down to a minimal A/F at top. Depending on the thickness required, you would need to check with a typical pole fabricator (like Valmont) to see the minimum A/F required to bend the steel sheet. You can likely just get away with slip joints. Would be more expensive to fab then using standard pipe I guess but would look a lot better than having the sudden reductions in sizes. As KootK said, make sure you double check all your details for fatigue whatever design you end up using...