[TowerTalk] wind load revisited

[K7LXC@aol.com]

In a message dated 99-07-12 18:11:53 EDT, brunet@us.ibm.com writes:

> I looked through my notes from a discussion on this reflector a while back 
> and
>  want to rediscuss it just to be sure our plans are OK.  Let's assume 70' 
of 
> 45G
>  at 70mph.  The flat spec is 9.5 sq ft.  Since our tower will not have the 
> side
>  arms mentioned in the notes we can add 8 sq ft for a total of 17.5 sq feet 
 
> We
>  are only going to have 3 or 4 runs of RG213 and the specs include 2 
> transmission
>  lines per face, so I will add the wind load for the 1/2" and 7/8" 
> transmission
>  lines on one face or (1/2 + 7/8) / 12 * 70 * .67 = 5.4 for a total 
allowable
>  flat spec of 22.9.
>  
>  I was told on this reflector that the specs for ham antennas are numbers 
> that
>  can be directly related to the flat spec numbers.  A C-31XR has a rating 
of 
> 10.7
>  and a XM240 has a rating of 5.5.  A 2" x 20' mast will have a flat spec of 
2 
> /12 * 20 * .67 = 2.2 so the total is 18.4 which is within spec by 4.5 sq 
feet.
> 
>  Are there any errors in any of my assumptions, especially the 5.4 added in 
> for the unused coax lines?

       Not really. Your juggling is successful and since you're below the 
tower rating, you're in fat city. By using the 'flats' spec, you've actually 
decreased the tower rating since the antennas and mast are 'round members'. 

Cheers,   Steve   K7LXC
Tower Tech
Champion Radio Products

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm