Yes, I have a copy of the Rohn catalog and have been studying it. Yes, I
have been looking at the forces. Thanks to all who have already responded
so far. Reading this reflector has got me digging into the numbers a
little (OK, a lot <grin>), rather than just copying what all the others
are doing around here (no engineering). Some of the installations make my
skin crawl after learning better from this reflector. But they stay up.
I live in Gloucester County, VA. Thank you Steve, for looking up the wind
rating. We have been wondering when we will get a direct hurricane hit.
Usually, the outer banks of North Carolina take a lot of the OOOOMPH out
of the storms before they get up our way. We thought Fran was going to get
us. We got tornadoes and torrential rains in lieu of wind. Which is
worse???
I have a friend with 100 ft of Rohn 25 with guys spaced at only 35 feet.
Yikes!, now that certainly seems to cut it close. However, it has been up
for many years, through many storms. We both live in highly wooded areas,
providing shielding from maximum winds.
As Steve hs pointed out, it is possible to have less than 80% anchor
spacing. I have come to the conclusion that the Rohn spec is very
conservative, as you might expect for liability's sake.
Well, yes, I am a mechanical engineer and I do possess the skills to
analyze the forces, and so far, the numbers look ok. But it would be nice
to review the project with someone before I start, as I <humbly> could be
missing something. Rohn specs are *very* conservative, and building to
them is a very safe bet.
In the archives, someone once posted the max compressive load for Rohn
25 tower as 8430 lb per leg, 25,290 total, about what you'd expect for
steel. That's the best data I have so far.
The guy preload goes up from 10% to 15% to compensate for the loss in
horizontal preload, due to the geometry.
The compressive (vertical) loads do go up, but not that much for 45%
spacing. I don't own enough land for more spacing. I came up with 6518 lb
total compressive load, with the upwind leg being loaded the most at
around 3500 lb.
I haven't built anything yet, and still open to suggestion, persuasion,
education, and bonk-bonks on the head! <big grin>
--...MARK_N1LO...--
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