Guy tension ??

[Stan Griffiths]

>No Stan, I WAS in fact referring to guys on the same level being equal.  I
>agree that one would think that all tensions would be "automatically" equal
>out, but doesn't seem to work that way in real life..for me anyway.  (In
>another life, I've spent hours and hours adjusting guy tensions on a 150'
>trailer mounted crankup I used to be involved with.  It had 5 sets of 3 guys
>and what a job!)  Anyway, I would utilize a transit to check plumbness of the
>tower while adjusting the guys and still do likewise on the towers at the QTH.

I know this:  If you have 30 or 40 feet of unguyed tower standing there,
either above a set of guys or just protruding out of the ground, you can
move the top several inches off plumb in any direction with very little
pull.  You could pull it off plumb several inches with one guy and then
apply tension on the others until the tensions in all guys were equal.  It
would not necessarily be plumb when all tensions were equal.  It is hard to
imagine why the guy tensions would not be equal when the tower is plumb.
There are only two things I can think of that might cause that:  1) the
tower is set in the concrete at a slant and it takes considerable guy
tension on one side just to make it plumb again, or 2) the distance from the
tower out to the various guy points is not the same for each guy point.
Steeper guys would have to be tensioned more than shallow ones to have an
equal horizontal component of tension.  I think that when the tower is plumb
and set properly at its base, the horizontal components of guy tension have
to be very close to equal, otherwise the tower would flex toward the
stronger horizontal force and would not be plumb.

>I also at one time figured the inverse of your statement....i.e. if all guys
>on a level are equal tension, that implies the tower must be plumb to that
>point...not true either.

I agree with that.  You can have equal tensions and not have a plumb tower.

>Bottom line in my experience is that one is looking
>at two variables when adjusting.... 1) Tower relationship to plumb, and 2)
>individual guy tension.  If I'm wrong on this, I'd like someone to point out
>what I'm doing wrong and save me alot of WORK!!

What I can't imagine is a plumb tower, guy points equal distance from the
tower base and accurately spaced at 120 degree intervals, base properly set
in concrete, and unequal guy tensions . . . but I have to admit, I have not
measured this . . .

>And one more comment about the 10% rule ..... a 3/16" guy with 300lbs of
>tension is not "slack", so why is 600lbs better?

I would not call it "slack" either, but it DOES have some sag in it.  Any
sag at all allows the tower to move slightly when pushed by the wind.  More
slack, more movement.  I have heard that guyed towers can "resonate" if they
are allowed much movement in the wind and this can bring it down if allowed
to oscillate with much violence.  Although I don't see this in the Rohn
book, there are those who advocate guying a tower at UNEVEN levels to
prevent the entire structure from resonating in the wind.

>   Of course, may have
>something to do with the fact that when the wind is such that your "windward"
>guy has increased from 300 to 600lbs from the wind load on tower, the
>"leeward" guys may have decreased from 300 to 200lbs (or some such)? 
>Potential loss of "control" there?  It's the only answer I can think of....but
>that again begs the question "why 10% vs 5% or 15%?".  Where's the mechanical
>engineer in our midst?

Again, I guess 10% percent is just somewhere close to the middle of the
acceptable range.  Yes, Mr. Mechanical or Structural Engineer, where are you?

Stan  w7ni@teleport.com