[TowerTalk] Question on R-TA-45 Torque Bracket
Bob Shohet, KQ2M
kq2m at kq2m.com
Fri Jun 14 13:54:20 EDT 2019
The use of star guys reduces the wind induced torque on the tower by reducing the amount of twisting in the winds. This reduces the twisting and stress experienced by the legs of the tower. There are differences between whether the wind is coming from the direction of the guy vs opposite it or between the guy wires so it would not be accurate to assume that that a wind of “x” mph exerts a twisting force of “y” when the twisting force can vary significantly because the wind is coming from 45 degrees and the guy wires are at 45 degrees 165 degrees and 285 degrees vs. if they were at 100 degrees. 220 degrees and 340 degrees. Although we don’t normally think about this, the wind direction relative to where the guys are can, in an extremely dangerous storm, make the difference between failure or not.
My 130’ of Rohn 45 tower is star guyed at the 80’ and 120’ levels and I can tell you that from watching it in two tornados and two hurricanes, the guy wires, at the same tension as before the star guys were installed, definitely move less now than they did before. I do know (as explained to me by a P.E. who is a ham) that by using star guys, the tower can handle a larger wind load in a given speed wind than if it just had one set of guys and that is because the amount of tower movement in the wind is reduced and that in turn results in less torque on the tower legs, hence less mechanical stress and reduced chance of structural failure.
The wind loading on the tower is actually increased because the weight of the star guys creates additional compressive forces on the tower, especially with ice, but this is more than made up for by the decrease in torque on the tower and particularly the tower base, which can be reduced further by using a pier bin and a swivel base rather than the common practice of burying the first tower section in concrete.
Star guys have another practical aspect to them. Since there are TWO guys per tower leg, it is possible to raise a heavy antenna to the top vertically by loosening and unhooking one of the two guys, pulling up the antenna to the second guy, reattaching and tensioning the first guy, then loosening and detaching the second guy, pulling the antenna through, and then reattaching and tensioning the second guy. N2NT and I have done this with excellent results. This is especially useful if there is not enough room or if the angle is too steep to use a tram line. It also allows the tower worker to climb the tower and guide the antenna up instead of it dangling on a tram line and possibly getting caught on something.
Star guys are cheap and effective insurance to help protect a tower and tower installation and much better than using torque brackets alone.
A P.E. can do calculations for a tower installation with and without star guys so that you can get an accurate picture of just how much it may help you. Well worth the money to do if you want peace of mind.
From: k7lxc--- via TowerTalk
Sent: Friday, June 14, 2019 1:24 PM
To: towertalk at contesting.com ; k9mk at flash.net
Subject: Re: [TowerTalk] Question on R-TA-45 Torque Bracket
> I had one of these on the top guy set of my 110' R45 tower. And I had torque arms on the lower two guy sets.
> My question is aside from twisting, does this change any of the wind loading numbers?
> My suspicion is the double guy sets per face can only help but I have never seen it quantified.
Since the capacity of a tower is determined by the leg strength, I'd say that the use of a star guy bracket doesn't really do anything to change it. I'm not an engineer so I don't have any calcs to provide.
Cheers,Steve K7LXCTOWER TECH
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