[TowerTalk] 45G Wind Load

[K7LXC at aol.com]

In a message dated 9/14/2009 10:04:05 A.M. Pacific Daylight Time,  
towertalk-request at 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