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Flag Pole Footing - 180'

Flag Pole Footing - 180'

Flag Pole Footing - 180'

(OP)
I'm designing a 180' flag pole with a 40’x80’ flag. I used NAAMM's FP1001-07 but updated loads using ASCE 7-10. My question has to do with the footing and embedding the pole. The pole base is a 42" diameter steel pipe sitting in a 52" corrugated sleeve. The manufacturer/installer insists that the sleeve be filled with sand and that no grout is necessary. The footing itself is 6’ diameter and 19’ deep concrete. I’ve agreed to the sand but am insisting on 6” of non-shrink grout at the top so that the pipe has something to bear on and transfer the force to the footing at the top. Is there either a specification or standard somewhere that would shed some light on the grout/sand installation?

RE: Flag Pole Footing - 180'

Flagpoles and related issues have been discussed here before:

http://www.eng-tips.com/viewthread.cfm?qid=32235

Separately, and claiming zero expertise, I wonder if the sand is intended to act as a semi-flexible anchorage that will yield a bit in uncommon storms, and not act as a stress raiser as the pole vibrates in any kind of wind.

If the pole someday suffers a brittle fracture at the top of your grout, will the pole manufacturer accept any responsibility?



Mike Halloran
Pembroke Pines, FL, USA

RE: Flag Pole Footing - 180'

You would want to seal the sand so that it doesn't settle when it get wet. Know of a 338 foot pole that this happened to and it had an 8' tilt later on.

There is one of the NAAMM manuals that describes the generic ground set pole with guidelines - including grounding and a seal at the top of the hole. Hope you have some decent ground.

I didn't know that ASCE 7-10 had a formula for the flag forces. Is your pole a tapered pole or a step-tapered pole?

Hope your installer isn't from Texas.

RE: Flag Pole Footing - 180'

Its too bad the manufactures of these devices wouldn't engineer the footings. Same with metal buildings.

RE: Flag Pole Footing - 180'

I'm not sure about your 6" of grout, if it works, it may provide a high pressure spot on the pole; I feel that at 5" wide, it is not sufficiently contained.

What is the installer's track record?

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

RE: Flag Pole Footing - 180'

Actually some of the pole manufacturer's and metal building manufacturer's will engineer the foundations. You will have to provide them with the geotechnical report as well as some civil engineering information and will also have to pay for it. Over the years we have done many metal building foundations as well as many, many pole foundations - some over 400 feet high.

But we have seen instances of surprises when a ground-set pole shows up and the ground turns out to be rock. (or under water) (or just plain crap).

RE: Flag Pole Footing - 180'

(OP)
Thanks everyone. Yes there are some threads covering poles but most of them are for insignificant size poles and the ones that are for larger poles do not cover the foundation details. The pole is stepped with the base being 42" diameter x 1/5" thick steel and steps about every 40'. The manufacturer was supposed to submit calculations but his version of calculations was to submit the NAAMM's FP1001-07 pages (no actual calculations). In Washington it's considered a significant structure and requires an SE stamp. I don't think the manufacturer is used to jurisdictions with building codes. Soils are really good. I was hoping someone might know of a specification somewhere that discusses the foundations. Oh, and ASCE 7-10 doesn't have the flag load per say, it's just that the NAAMM copies an older version of ASCE 7's wind design to get a wind load for the pole.

RE: Flag Pole Footing - 180'

I would be very careful with this project. .20" thick base section steel is pretty thin. I know of another project that was slightly better (but still had to be taken down) that sounds like this. You are correct that your state may require calculations - but there are those who don't - especially back East. If you would like to discuss this with me, I'm at nmasengr@gmail.com.

RE: Flag Pole Footing - 180'

(OP)
sorry, type-0 42" diameter x 1/2" thick.

RE: Flag Pole Footing - 180'

(OP)
oldrunner...You brought up Texas, is there a reason I should be worried?

RE: Flag Pole Footing - 180'

The pole that I am familiar with was "designed" and fabricated in Texas as well as the foundation.

RE: Flag Pole Footing - 180'

Cool, but informative video:
https://www.youtube.com/watch?v=uNtsny9-48M
Flagpole swaying:
https://www.youtube.com/watch?v=N9k7ajsCTJ4
Story on the pole, scroll down to the "Flag" link, I assume this is the one referenced in the "Texas" comment above, note that it has been replaced/reworked 3 or 4 times now:
http://en.wikipedia.org/wiki/Acuity_Insurance
I recall an inquiry coming in a several years back on the replacement of the 338' pole, as a fabrication-only job, all design was by others.

In regards to the original question, it seems to me that one obvious approach would be to inquire about previous flagpole installations of similar or larger size that used this same kind of construction.

I assume that the NAAMM standard is intended for generic flagpoles, and when you get into the "biggest flagpole in the world" type stuff, previous favorable experience on smaller poles might not be adequate.

RE: Flag Pole Footing - 180'

The videos shows Acuity Insurance Company pole #4. For a while they had misfortune's in constructing a long lasting flag pole. Pole #1 was 150 feet and was ok. Pole #2 added an extension to about 220 feet and failed eventually. Pole #3 was a 338 feet pole designed and fabricated in Texas by a firm no longer in business. It developed a lean and was probably difficult to maintain. Pole #4 is the one in the video, also 338 feet but was up just for a couple of days before it was dismantled. It was designed and fabricated by local company's. Pole #5 is a 400 foot tapered pole. Technical data is here: http://www.arup.com/News/2014_07_July/10_July_Tall...

There are much higher flagpoles now in the world with more coming. The preliminary design of the Acuity flagpole was based on the AASHTO Standard Specification for Structural Supports for Highway Signs, Luminaries, and Traffic Signals, 6th edition for a F2 wind, -40 degree F temperature, 5" of ice and infinite fatigue criteria. The information in the NAAMM standard basically comes from the AASHTO code except for the flag loading. The NAAMM standard also provides a methodology for doing preliminary designs.

RE: Flag Pole Footing - 180'

(OP)
Well if it is the same manufacturer I can understand why it didn't work. I upsized all of the pole by 6" in diameter after he had turned in his supposed engineered pole. In general I'm not worried about the pole itself and after the comments I'm feeling better about the footing connection. My guess on the 338' high pole was that they didn't engineer the hole in the bottom to put a door into it big enough for a man. That would have severely weakened it. Not sure what the building codes and building departments are like in Wisconsin, my guess is no one told them about the door.

RE: Flag Pole Footing - 180'

From your comments, I suggest that you obtain a structural engineering firm to review your work, say someone like Arup. They were the designers of the Dublin Spire.

RE: Flag Pole Footing - 180'

(OP)
I am a PE in a structural design firm. My post was more to see what was generally being done around the country. The Aquity Insurance Pole was most informative. Thank you very much.

RE: Flag Pole Footing - 180'

Has anyone in your company design any kind of tall pole? The people that designed Pole #4 were also very good engineers - but it was their first pole.

RE: Flag Pole Footing - 180'

It's a known issue with stacks and similar items that you can get vortex shedding/cross wind vibration. The problem is, if there had never been a stack built that had that problem, it wouldn't occur to anyone to check for it, either. I get the impression with the "big sway" video that this was probably a wind/pole interaction/vibration issue that just wasn't considered in the design.

I meant to say that my first video was UNinformative, sorry about that, cool to see but doesn't tell you anything. Except that half the cost of that thing was probably moving the crane in!

RE: Flag Pole Footing - 180'

Is it possible for a continously tapered pole/stack to develop resonant wind vibration??. The critical wind velocity that causes this is directly based on the diameter of the pole.

RE: Flag Pole Footing - 180'

I would assume so. Keep in mind that the wind velocity also varies as you go up, so it's not a perfect correspondence anyway.

RE: Flag Pole Footing - 180'

JS..I think you may be correct, at least, on these super-tall poles where the taper is very slight. I can visualize, say a 50ft length of these poles where the combination of the small increase in diameter and the normal varying of the wind that it could set up a vortex shedding situation. I still find it difficult to accept that the driving force developed from this segment of the pole would be large enough to drive this vibration, unless these tall poles are more flexible than I anticipate. The final Acuity pole design was tapered and also has a damping system perhaps to cover that possibility.

RE: Flag Pole Footing - 180'

(OP)
I found this paper on vortex shedding and pole structures. It's taken me a hole day just get to the model shapes and their forces. I'm still doing research to figure those out. (Have been having fun converting to metric to match the equations) and trying to match the equations to the output in the examples. The good thing about my pole is the first 100' will be in pretty turbulent air as there is a high overpass that runs by it. Turbulent air means no vortex forms.

http://www.wceng-fea.com/vortex_shedding.pdf

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