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[TowerTalk] RE: Fiberglass guy rods

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Subject: [TowerTalk] RE: Fiberglass guy rods
From: (Mark, N1LO)
Date: Mon, 22 Mar 1999 11:15:00 PST
Ty wrote:
<<Then we can go back to comparing similar tensile strength materials 
and realize "Hey, 3/8" diameter fiberglass rod IS a lot lighter than 
5/16" EHS guy cable...even without the extra insulators, grips, etc"
Please do us all a favor...
Get your nose out of the textbook and into the real world.
Compare actual products in realistic terms and applications.
Until then, please stop misleading everyone on this reflector.
73, Ty K3MM>>

I'll try to be as objective as possible here. If you are proposing 
substituting 3/8" dia fiberglass rod (about 13,250 lb breaking strength) 
for an application where 5/16" EHS steel (about 11,200 lb breaking 
strength) is specified, on the basis of equivalent breaking strength, 
then you will definitely reduce the safety factors of your tower 

When you deviate from what the manufacturer, such as Rohn, recommends, 
be it a guying plan or materials, you are getting into a gray area.

On the contrary, I would be letting the list down if I didn't point out 
that substituting guy cables solely on the basis of breaking strength is 
not a complete solution when the two materials have such a widely 
varying modulus of elasticity as do steel and fiberglass. You will have 
to oversize the material that has the lower modulus (fiberglass being 
more elastic) or accept higher bending forces on your tower legs in the 
wind. How much higher depends on your configuration and the windloading.

I'm not saying that your tower will fail. The ultimate strength of each 
installation is highly variable. If you want to be sure about it, have a 
P.E. check it out. That is the best recommendation I can make.


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