All this discussion about the 55G base got me to finally open and look at
the new catalog they sent me a month or two ago.
1. Assuming there are no typos in the specs listed.
2. The book states: "Tower and foundation installations should be
performed by qualified and experienced personnel using construction
drawings. This document is to serve as a guide for sizing and buying 55G
tower."
3. There are some assumptions made detailed in the "Design Notes"
section about "level ground" versus unusual terrain, "Antenna and mounts are
assumed symmetrically placed at the tower top.", etc.
4. Depending on wind speed, exposure and load (at the top) the base
size scales up. For 100 foot towers and up the lowest requirements, 90 mph,
recommend the CB1 - 2 ft- 6in square x 4 foot deep foundation up to 140 ft.,
at higher requirements (110 mph wind, etc.) that bases' application stops at
110 feet. The highest requirement listed, 130 mph starts at using the CB2 -
3 ft square x 4 foot base dimensions and gets larger (as do the lower
requirements at taller tower builds).
5. I have several older commercial Rohn catalogs going back to the
1980s but did not look up anything for comparison but as one might expect
they appear to be getting more conservative (ref. what K1TTT said stated as
"fact" - 180 ft in his documentation) as time goes by. More feedback from
real life installations/failures driving insurance input plus better failure
analysis software?
6. Also, it goes without saying that terrain, soil type, local frost
line considerations and all other departures from "level ground" (presumably
vague to elicit inquiries) at the very least requires further research at
their Website rohnnet.com as they recommend and/or contact with the factory
for more detailed drawings plus consultation with local knowledgeable
soils/structural engineers before settling on any design.
7. I did not see any notes (in this limited products buying catalog)
that said anything about allowing wire mesh as a part of or a substitute for
the rebar it does specify.
8. A little extra steel and concrete is cheap compared to the hassles
of dealing with a tower that comes down because of it.
FWIW
Kimo Chun, KH7U
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