In a message dated 9/14/2009 10:04:05 A.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:
> According to my Rohn manual, if I understand the drawings correct, the
maximum wind load for a 70' 45G tower is 15.2 sq.ft. Can someone please
confirm for me that this is correct?
Yes, at 70 MPH. You should add in the 8.0 sq.ft. for a symmetrical
mount at the top of the tower that's deducted per General Note #4 which will
give you a realistic capacity of 23 sq.ft. @ 70 MPH.
> The reason I'm concerned (this will be
my first tower) is I see pictures of contest stations with five or six
pretty big yagi's on Rohn 45G towers which I think must really be exceeding
the wind load spec.? I am planning on (following the Rohn recommendations
for tower installation) installing two OptiBeam yagi's, the 40m 2-el and
the
tribander 16-el, which have a combined wind load of 19.4 sq.ft.
Amateurs are well known for overloading Rohn towers and Rohn towers are
well known for tolerating these conditions.
> I live in the south part of Georgia where the A58.1-1982 ANS shows my
area
between the 80 and 90 MPH wind speed zones.
Go to _http://www.championradio.com/windspeed.php_
(http://www.championradio.com/windspeed.php) for a better idea of your
windspeed conditions.
Contacting your local building department is also recommended.
> Understanding (somewhat) the 'safety factor' included in engineering
tower
design, am I putting my tower/yagi system at great risk with a wind load
that is 4.2 sq.ft. over recommended specs.?
Follow the above steps and you'll more realistically see where
you are.
Cheers,
Steve K7LXC
TOWER TECH
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