I did a lot of calculations before I erected my 85' aluminum tower. I was not
able to get the "required" 120 deg between the guy wires and I instead opted
for using 4 guy wires instead. That gave me a lot more flexibility were to put
the anchors. During my calculations I decided to see what was the optimum
distance between the tower and the anchors were. I believe my calculations
showed that the anchors should be placed about 130% from the tower. If the
attachment is 23 meter up, the anchors should be ~30 meter from the tower. That
will give you the least flexing of the tower.
I, myself, strongly recommend the 4 guy wire solution. If you go to my Facebook
page you can see all the photos of my tower. The album is called "Tower, tower.
I have used 4 wires on all (3) installations and I am happy with the results. I
haven't lost any tower yet, knock on wood. The single set of guy wires are
fasten at 75' up the tower. That is the point that gives minimum bending force
on the tower in my case.
BTW The maximum load on the three guy wires installation is when the wind is
blowing ~15 degrees from the symmetry line, and blowing towards the slacking
wire. You would think the maximum load is when the wind is blowing directly on
the symmetry line, but that is not the case.
Good luck with your towers and 73 de N2JFS
Hans
-----Original Message-----
From: Jari Jussila <Jari.Jussila@oh2bu.pp.fi>
To: towertalk@contesting.com
Sent: Tue, Jul 27, 2021 3:47 am
Subject: [TowerTalk] How critical is the 120 degree ...
Hi ...
I'm sure these topics have been discussed earlier, but could not find
any thread ..... Sri ...
We are at our club erecting two towers. A rotating steel tower being 31
m high and a aluminium telescope mast 18+18 m = 32 meters.
A) How critical is the rule that guy wires should be "exactly" 120
degrees apart?
A professional guide says, that the anchor point can be 50 mm from that
120 degree (119,9-120,1 degree) but some say, that a maximum of two
degrees is OK. That meaning 118-122 degree.
What's the tower community advise?
B) The steel tower height is 31 m - it's a rotating tower - but the
upper bearing is at 23 m ( leaving 8 meters for the antennas) and the
lower bearing at 11 meters.
Whats the advise of anchor point distance? Some say, that the 60 %
(distance for the tower) should be calculating from the total height
(31 x 0,6 = 18,6 meters).
Some say, it should be calculating from the upper bearing (23 m x 0,6 =
12.8 m)
Whats your opinion?
Jari, OH2BU
For OH3AC Club Station
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