[TowerTalk] Less Than Optium Guys

[Grant Saviers]

A thought experiment is to consider what happens as the guys are 
separated by even more than 120 degrees.  As 180 degrees is approached 
the tension needed in each guy to resist wind splitting the angle goes 
to infinity.  I think we would all agree only two guys opposing won't 
resist the wind between them and the tower falls down.  Conversely, a 
pair of guys at the same angle each only need one half the tension.  So 
at some angle between them the tension in each exceeds all the wind on 
one guy.

So then how to do the calculation.  To simplify the compound angle force 
vector calculations, I considered the tension to oppose a 1000# force on 
the antenna, if the guys were at 90 degrees and horizontal with the 
antenna.  Then calculated the increased tension needed if the angle to 
the tower was 45 degrees.

So from the thought experiment, we know the tensions at 120 degrees are 
higher than at 90 degrees. Maybe somebody would calculate the exact 
angle when it exceeds the wind directly on one guy.

I mentioned total downforce as an important tower design limit which is 
a result of guy tension, preload, wind load, guy weight, and tower, 
rotator, and antenna weight.  The PE calcs for my R65 tower show this 
loading component is the limiting variable.  There are other ways for 
towers to fail than exceeding the guy strength.  K7NV's (SK) FEA 
analysis of guyed towers is very informative.
http://k7nv.com/notebook/topics/feastudy.html

When another TT post a while ago said that wind splitting is worse did I 
question my belief that the tension is highest when wind is directly on 
one and do the calcs, which showed that post was correct.

Grant KZ1W


On 12/11/2022 07:27, Wilson Lamb via TowerTalk wrote:
> I see the implied disagreement with my post but I don't see any reasoning to back it up.
> So tell me why the ultimate guy load doesn't occur when th ewind is aligned with one wire.
> In that case, ALL the other guys are slack, so one guy is doing all the work.
> I haven't done the geometry, but wind going in midway between two guys at 120 deg apart may be worse...I don't have time for it now.
> WL
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