The 80% rule is just a recommendation, at least that seems to be the
standard in the U.S. A common problem is lack of space and many towers are
installed with less than the 80% spacing. I had a tower in Aruba with
around 50% spacing on two of the anchors and it held up fine. I am not a
PE, but I believe that smaller spacing puts more stress on the tower, guy
wires and anchors and they need to be properly engineered for this
configuration. I would expect that going to more than 80% spacing would put
less stress on the tower and components. I seem to recall one rotating
tower component manufacture recommending 100% guy radius, for less force on
their rings. Using a larger guy radius also allows for more clearance for
antennas to turn. Unless you have a specific reason for changing the
manufacture's recommendation, I would follow it. Since you are installing a
substantial tower (46" face, 180' high) you will need some very large and
expensive guy wires. Using more guy wire than needed may be just a waste of
money.
GL,
John KK9A
To: towertalk@contesting.com
Subject: [TowerTalk] Maximum Guy Radius
From: Dorn Hetzel <kb4eq@hetzel.org>
Date: Wed, 21 Sep 2011 09:33:28 -0400
If I have a tower of a specific fixed height that I will be erecting,
and I have plenty of room to do so, I would estimate that I should
gain *some* additional strength against wind-load by moving the
guy radius from 80% of height to 100% of height, since this will
move the guy angle closer to horizontal and reduce the down
force on the tower and increase the horizontal back-force for
a given guy tension and a given stretch in a guy due to motion
of the tower.
Can anyone comment from either a practical experience or
engineering point of view whether this estimate is sound?
73,
Dorn Hetzel
KB4EQ
kb4eq@hetzel.org
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