On Feb 22, 2010, at 8:00 PM, WA7DXZ@aol.com wrote:
> I want to erect a Rohn 25G tower, 30 ft above ground. A small 3 el
> tribander on it. I have to satisfy my county engineers as to the safety of
> the
> tower installation. It will also be bracketed to the house in two
> directions.
> Problem is, I cannot really go 3 ft by 3 ft, by 4 ft deep for a
> hole/concrete. The tower is too close to my house. Rohn makes a
> concrete/baseplate,
> that sits in concrete, the legs of the tower slip over that. Would that be
> of any use to me, rather than bury 3 ft of tower in concrete?
>
> What is the minimum size hole I can dig, considering it is only 30 ft tall,
> and has a tribander (CushCraft A3) on top.
> Right now, the tower sits on 3-- 3/4 inch pipes buried 3 ft deep,,, tower
> slips over those, they are simply pounded into the hard AZ ground. Then
> bracketed to the house in two directions. It is solid as a rock, but... not
> sure that would satisfy the "engineers". One thing they want to make sure
> of, is that it wont fall off your property, mine wont, by a long shot.
>
> I need some "expert advice". They ask for Mfgr specs, I cant find any
> for a 30 ft tower, bracketed.
Sorry to respond to an old message.
I'm not sure why you need to use a 3 foot square base. For a bracketed tower of
Rohn 25G, you can use a 2 ft by 2 ft by 4 ft base, which is also the standard
for guyed tower. Because of the bracket, the overturning moment isn't applied
at the base.
You should use substantial brackets. The HB25G from Rohn are the minimum you
should use. And you shouldn't just attach them to the rim joist with lag bolts.
You need to use large carriage bolts and you may need to re-enforce the wall to
carry the forces from the bracket to the wall.
The Rohn catalog has a lot of engineering data on bracketed installations.
I put up my bracketed tower almost 9 years ago. The tower is 44 feet of Rohn
25G, with almost 6 feet of mast out the top. It has an Cushcraft A3S/A743 on
top. I have two brackets at 26 and 17 feet.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
Web: http://boringhamradiopart.blogspot.com
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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