[TowerTalk] Poly rod, Fiber glass rod, Fiber Protrusion rod tension?

Grant Saviers grants2 at pacbell.net
Tue May 15 14:54:22 EDT 2018

I think the idea in different tensions vs height is to generate the same 
horizontal restraining force since that changes with the cosine of the 
guy angle with the ground.  i.e a horizontal guy (zero deg) provides 
100% of its tension horizontally to the tower, and a vertical guy (90 
deg to ground) zero force.

To stay < 10% of break strength, larger guy diameters are used for upper 
guys and need to be stronger since it takes more ultimate strength to 
restrain the tower from sway.  The amount of strain (stretch) with high 
wind forces increases the sway so larger guys stretch less per pound of 
tension.  (see the K7NV finite element analysis) btw EHS from what I've 
read, even though very high yield strength, does start to stretch 
permanently at about 60% of break strength.  So that is the "normal" 
limit of allowable tension. While stretch is only a few percent of 
length when stressed that high, that can change the initial tension.  
After a max wind "event" it is probably smart to check tensions.

So with that in mind, I think the correct tension is what is specified 
for each guy level by the tower manufacturer, independent of the 
strength of the guy.  My considerably oversized guys (1/2" Phillystran, 
25k# break) were specified by the PE at near normal Rohn pretension 
levels.  Another limiting factor is the compression yield strength of 
the tower sections.  The bottom section has the weight of all the metal 
above plus the vertical component of the sum of all guy forces from 
every guy level.

So if your polyrod break specs are the same or better than 5/16 EHS all 
is well, follow what Rohn specifies for pretension.  One small 
difference might be the pretension stretch vs EHS, which is very low.  
Anyway, by tensioning to the Rohn spec that initial stretch is removed.

Since you have a dynamometer, leave the Loos gauge in the toolbox.

Grant KZ1W

On 5/15/2018 9:20 AM, john at kk9a.com wrote:
> What is the breaking strength of the rod?  5/16 EHS is 11200 pounds and
> typically you tension it at 10% of breaking strength. I am not sure what
> diameter Polyrod is. If it is large, measuring its tension with a Loos
> gauge may be a challenge.
> John KK9A
> Ed K5OF wrote:
> Question: For those that have used what is commonly referred to
> depending on discussion “poly rod”, “fiber glass rod”, “Fiber protrusion
> rod”, etc. in lieu of ehs or phillystran what is the recommended tension
> of said rod for 5/16” rod?
> I have done quite amount of research both on line and contacting
> manufacturers and have found nothing that I can use for a reference or
> make any sense due to the engineering specs the manufacturers provide me.
> I am not an engineer and cannot figure out what the recommendation would be.
> I have my current tower project spec’d on ROHN 55G 130 mph at 130 feet
> 100 % guying (130 feet) and it calls for the lower guys if using EHS
> spec ¼” at 665 lbs tension per guy and 5/16” at 1120 lbs tension per guy
> for the upper guys. (3 sets of guys, the two lower ¼”, the final upper
> at 5/16”)
> If I am correct if I was using phillystran the tension would be the same
> based on the same equivalency of that material used to the EHS guy specs.
> Since I am using this 5/16” “rod" on all three guy levels I want to make
> sure I do not under or over tension.
> Rod provided was second hand (no issues, brand new) and was a great
> deal! I am all set to go up with tower but want to get this right before
> proceeding further. I have Loos gauges and Dynaometer at my disposal
> along with everything to get this project up as described above. Hope to
> get going when I get back from Dayton. From what I have determined so
> far it is best to tension everything up of course beginning with bottom
> set of guys to roughly 250 lbs + or -, get plumb and go from there with
> turnbuckle adjustment and get somewhere in the ball park of a safe and
> secure tension on final product as we go up to the final set of guys
> (#3) at 130 feet. 250 lbs is far off from 665 and 1120 but because of
> the material possibly those tension specs are not in the ball park of
> EHS or Phillystran? What say the group with any knowledge of using this
> type of guy material? When I get back from Dayton I am working on
> getting the tower up with a successful and safe out come? Thanks in
> advance , if you see me at the Crowne or the venue stop and say hi! 73!
> Ed K5OF
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