Flag Pole Footing - 180' 1

[LHiggins]

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?

 

[MikeHalloran]

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

 

[oldrunner]

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.

 

[ztengguy]

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

 

[paddingtongreen]

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

 

[oldrunner]

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).

 

[LHiggins]

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.

 

[oldrunner]

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.

 

[LHiggins]

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

 

[LHiggins]

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

 

[oldrunner]

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

 

[JStephen]

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.

 

[oldrunner]

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_Tallest_US_flagpole_dedicated.aspx

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.

 

[LHiggins]

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.

 

[oldrunner]

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.

 

[LHiggins]

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.

 

[oldrunner]

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.

 

[boo1]

ASCE had an article on ACUITY's 400 ft tall flagpole in Sheboygan, Wisconsin

http://www.asce.org/cemagazine/Article.aspx?id=23622330812

 

[JStephen]

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!

 

[boo1]

Acuity flagpole wobbling in 15mph wind

https://www.youtube.com/watch?v=0mBJtqg9LfA