We need to install a 15′ 3″ at the top and 6″ at the bottom flag pole. How big do we need to make the footer? We plan on setting 8″ anchor bolts.
Thanks
Tim
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Replies
Depends on soil conditions.
The first place you should look is to the flag pole manufacturer. They should be able to get you some guidelines, if only design guidelines.
The horizontal surface area is not as much of a concern, because the flag pole doesn't weigh a significant amount, relative to how much lateral force is pushing and pulling on your giant cantilever. Logic would suggest that the foundation need to be relatively deep, when compared to a typical house spread footing, to resist the lateral push. Exactly how deep would depend primarily on the lateral load.
You should also look into the load on the anchor bolts, and the depth to which they must be set to resist the uplift. It sounds like a PIA, but properly designed by an engineer (or a MFR with an engineer on staff) sounds like the way to go, unless you want to take the chance of replacing it.
You must consider the max wind load in your area as well as the size of the flag and the exposure, in addition to the soil conditions previously mentioned. The location and height of the property might also be important.
This is a routine engineering calculation. If you are good at that sort of thing, you might just want to Google it. Otherwise, call up a couple of engineering firms in your area and ask what they would charge to do the calcs for you. It should be a nominal charge, especially if they are a patriotic company, which most engineering companies are, almost by definition.
Give them your flagpole specs and your geographic location. It should only cost a few bucks. You will basically be paying for their time and their liability, both of which are good ways to spend money.
If you Google "flagpole foundation calculations", you will find more than enough information to keep you busy.
the sign company next to me installs alot of large flag poles... and this is what they do... (now these are 30'-50ft poles) 24"-30" sonotube with a 12"-16" sonotube in the center.... the outer ring is placed concrete... the inner hole for the pole... is where the pole is placed in fine white sand... thats it... the pole is captured in the sand only... anywhere from 36" to 60" deep depending on the pole size...
p
Yep, we did a 60 foot pole at the church, 60 feet up, 6 feet under ground. Sand. I would guess it has a damper effect on the wind vs. the pole.Greg
i think thats the main reason... the second might be... i'm not sure you want to set anything alum in concrete...
p