[TowerTalk] Re: Tensioning Rohn 45G guys

[Bud Hippisley, K2KIR]

K1IR asks a great question -- a question that highlights an interesting subtlety in the relationship between Rohn specs for towers and their data for guy wires:  Rohn's tensioning rules for guy wires do *not* directly reference tower leg strength! 

Instead, the delicate relationship between proper guy wire tension and allowable downward force on the legs of Rohn 25, 45, 55, et al. is documented (dare I say "hidden"?) only in Rohn's choice of guy wires shown in their drawings of tower height versus guy wire spacings.  Of course, downward force in tower legs also comes from antenna, mast, tower, cable, and rotor dead weight, plus the overturning moment from a generally horizontal wind load on all those materials.  Thus, the drawings showing guy wire diameters, tensions, and attachment heights for various heights of Rohn tower sections are valid only when the antenna loads are less than or equal to those specified by Rohn on those same drawings -- and they're also valid only for the size, weight, strength, and positioning of guy wires shown.  No wonder K7LXC and others strongly urge using the services of a PE whenever you plan to stray from the Rohn catalog drawings! 

In short, "bigger" is not always "better" when it comes to choosing guy wire diameter or breaking strength.

Bud

At 07:07 AM 2003-07-09, Jim Idelson wrote:
>The 85 foot 45G tower is up. We used 1/4" guys at three levels. Rohn calls for 
>660# tension on upper 1/4" guys, and 400# tension on 3/16" lower guys - 10% of 
>breaking strength. I know many of you have used 1/4" guys for all levels. 
>What's the best choice of tension for the lower guys, noting that there may be 
>additional compression forces on the tower?