[Top] [All Lists]

[TowerTalk] An Engineering Question

To: <>
Subject: [TowerTalk] An Engineering Question
From: (Gene Smith)
Date: Fri, 30 May 1997 10:58:19 -0400

If someone already presented this information I'm sorry for repeating
it, I just got in on the thread.

Paul Schrader was correct in saying "There is nothing magic about how
far out the guy anchors are".  The further out the guy anchors are the
more of an angle you have in the horizontal plane and therefore the 
less strain on the wire and anchor.  If you move the anchors in you
 simply need stronger wire, or possibly the same wire with less of a 
safety factor, and a stronger anchor.  How much stronger?  You can 
calculate your antenna wind areas and determine the pressure on the 
antenna at its height.  Then it's a basic lever to determine the 
pressure at where the guy wire connects to the tower.  If you could hook 
a horizontal (0 degree) guy wire at that point it would need to support 
the calculated pressure plus some for a safety factor.  But because the 
guy wire proceeds at an angle the pressure that the wire will have to 
handle will be your calculated pressure divided by the cosine of the

This is all possible but there is an easier way.  You say you are using
1/4" EHS rated at 6600 lbs.  I can't remember from your email how far
out your guys are now but let's just say we have a tower 125' tall and
the guys are currently 100' from the tower which is 80% of the height.
The ASSUMPTION being made now is that the 1/4" EHS at 6600 lbs is
at the already existing guy anchor location of 100' from the tower.  Now
let's say I need to move the guy anchor so that it is only 50' from the
tower instead of 100'.  Well I know that 6600 lbs at 100' is acceptable,
remember this was the assumption.  Therefore if you make a right
out of the tower, guy wire and earth you will find the angle of the wire
from the horizontal plane to be the ARCTAN of 125/100 which is 51.34
The pressure on the tower is therefore 6600 lbs * COS 51.34 which is
4123 lbs.

Now working with this 4123 lbs let's make another right triangle of the
tower, earth and this time the wire at 50'.  We find the angle to be
ARCTAN of 125/50 which is 68.20 degrees.  The amount of pressure the
wire must now handle is 4123 / COS 68.20 which is 11,102 lbs.
Get a wire to handle 11,102 lbs and you can move the anchor from 100'
to 50' and keep the same safety factor you had at 100'.  As far as
how much additional concrete to use in the anchor at 50' I don't know.
Maybe there's a concrete guy listening who can help out with that.
As far as clamps, connectors, insulators, etc. they must all now
support 11,102 lbs as well.

Dave if you don't know basic Trigonometry which is what I used here to
determine the pressures it's really not that hard.  Grab some highschool
or college kid and he can show you.  It would be a little difficult for
me to explain it through email.

Hope this helps Dave.


FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>