Dick Flanagan wrote:
>
> I have no doubt the poles can hold the stress. However, since just today I
> poured 15 yards of concrete into a very large hole in my backyard, I am
> very sensitive to the question of tower bases. :) How big would one have
> to be to support one of those poles?
>
Hi Dick! I have a self-supporting 120' pole made by Power Structures in
Belle Chase, LA (a subsidiary of Lapp Insulator Co.). The foundation
was
required to resist an overturning moment of 500,000 lb-ft. It turned
out
be a pier 5' diameter by 18' deep with four 11' j-bolts @ 2.5" diameter.
The pier driller got into a layer of shale at about 16' down and got so
enthusiastic that by the time he was through the layer, the hole was 20'
deep instead. Oh well; it took 2 cement trucks to fill it, around 14
cubic
yards if memory serves me well (somebody can use a calculator to check
me).
It took about an hour and a half to drill the hole, and the concrete
guys
(who were welding up the rebar cage on-site as the drill was going on)
were
ready to pour as soon as the pier driller could pack-up and move the
drilling rig out of the way. The drilling rig was about 60K lbs. and
couldn't get license plates; the had to buy a permit by the mile to
drive it over to my site and back home. The whole job was about $2.8K
in 1989.
This pier resists 500 kip-ft for a pole 120' with 30 ft2 load in a 30
psf
wind. An 80' pole with 10 ft2 wouldn't need nearly as much.
Oh, by the way, if I had opted for a conventional, back-hoe-dug, roughly
cubic foundation, the engineers told me it needed to be about 40 cubic
yards of concrete. See: the pier idea is much cooler for poles!!
Pleasant dreams,
Mike - W8MM - Cincinnati
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