If you don't have room for a new larger pad, then taking out the old one
would probably be a waste of time/money. It has become somewhat a
construction standard to epoxy foundation bolts into a cement pad. Use of
the existing pad would be the first constraint with the caveat that the pad
was built correctly (seems questionable if using rebar for foundation
bolts). Rohn self-supporting foundation pads show that 2.5 cu yards (4 ft x
4 ft x 4 ft) of re-barred cement would work for their self-supporting tower
of no higher than 40 feet. Rohn's foundation bolts (12 bolts for their
self-supporting triangle shaped towers) are 30 inches long for
self-supporting towers up to 160 feet tall; the pad depth is constant at 4
feet. Rohn bases this on wind loads (30 psf) and soil conditions (4000
psf).
I use the Rohn commercial products catalog as my go-to design reference.
Good luck. Ken K5RG
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