The AN Wireless Tower foundation as I view is a specialized pad since all
three legs are attached to a contiguous piece of concrete. I calculate that
it would be at least 10 cu yards of concrete for a foundation F at the
desired wind load. The type K foundation is probably 18 cu yards from the
slightly inadequate dimensions given in the original post. I see that AN
Wireless provides a DIY estimator that may have resulted in what was posted.
I would view that as a very viable estimation, whether it is accepted by the
City or not is an unanswered question. The depth of the AN Wireless pad is
held constant which makes for a large pad. The same holds for Rohn's self
supporting tower (SSV) pad foundations. Rohn increases the both the depth
and width of the their pier & pad designs (for each leg) as the tower height
increases but only starting at a tower height of 140 feet since anything
less than this results in a pad foundation. So depending on the soil
analysis and wind load, it would look to me as if one could decrease the pad
width as the depth increased or as KK9A stated, use an alternate foundation
design. But this knocks out the AN Wireless pre-provided stamped drawings
as I would guess is being implied in the original message. As a PE, I would
never stamp a design without a soil analysis anyway. For the magnitude of
both the AN and Rohn pad foundations, I would view the tower foundation as a
reinforcement to the house foundation as long as nothing was under the house
foundation. It sure was the case for my tower's pad foundation since it was
the only area of the house that didn't require a slab foundation repair
after 30 years in the Texas gumbo. Ken K5RG
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