[TowerTalk] Adding guys to self supporting towers

[Patrick Greenlee]

I like the slack guy idea but you must be aware that when the wind does blow 
and the guy(s) take tension that a compressive force is contributed by the 
guy to the tower.  As always the greater the angle where the guy meets the 
tower the less compressive force is generated by wind. As mentioned a lot 
lately a 45 degree angle on the guy puts a downward force on the tower of 
one unit of force for every 1.414 units of force on the guy. Note that for 
every pound of lateral force on the tower due to wind there will be a pound 
of force downward on the tower with 45 degree guys.  I'm not arguing for or 
against guying any tower designed to be free standing, just pointing out 
that even a "slack guy" system generated compression in a wind.

Patrick AF5CK

-----Original Message----- 
From: K7LXC at aol.com
Sent: Tuesday, August 13, 2013 9:01 AM
To: towertalk at contesting.com ; richard at karlquist.com
Subject: Re: [TowerTalk] Adding guys to self supporting towers

>  The topic of adding guys to self supporting towers has  been
discussed a number of times on this reflector, but I am
still not  clear on exactly why it supposedly won't work.
If I have figured crrectly,  the worse case compressive load
on a leg at the bottom of a trianguler  tower
is equal to the product of the horizontal windloading
at the top  times the factor h/[w*sqrt(3)] where h is
the height and w is the width of a  face.


>  It seems to me the guyed tower is much stronger and  could
handle a considerably larger wind load based on this
simple  analysis.

>  Comments?

    First, I'm not an engineer so these comments are  semi-educated ones.
Second, the capacity of a tower is limited by the leg  strength so you don't
want to add unnecessary downward compressive force on  the legs; e.g. guying
a free standing tower.

    BUT IMO if the guys have little or no tension on  them, then they don't
add appreciably to the compression on the legs but some of  the wind forces
are transferred from the legs to the guy wires which is the  purpose of the
guys. Guys in this case are more tethers than guys; that is, they  limit
the forces on the legs without adding much to the total leg load.  Since a
self supporting tower doesn't require guy wires, adding them in the  above
scenario is more like a belt-and-suspenders approach with some added tower
safety margin.

    A possible problem is that with a bunch of slack in  the guy wires they
will tend to wind-slam when the wind gusts. That's why you  want a minimum
of initial tension.

Cheers,
Steve       K7LXC
TOWER TECH -
Professional tower services for amateurs


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