With 4 guys at 90 degrees apart there are only 4 degrees out of 360 degrees
when one guy is holding the whole system up. With a 3 guy system at 120 degrees
apart, there are 90 degrees out of 360 degrees when one guy has all the tension
to support the whole system. This is the engineering reason for closer in
spacing with a four guy system. The three guy system has each guy individually
capable of providing for supporting the entire system 25% of the time the wind
is blowing whereas the four guy system has each individual guy providing for
support of the entire system less than 1% of the possible wind directions. All
other than these 4 degrees out of 360 degrees there are two guys doing the wind
load support work. This was quite an extensive tread about 4-5 years back and I
guess some non-believers then still think its OK to use Rohn's guying standard
for the fold over series of towers, which needed four guys to clear the
backbone strut, on a conventional system using three guys. NOT! -=Rog-K9RB=-
----- Original Message -----
To: <TOWERTALK@contesting.com>; <K9RB@arrl.net>
Sent: Monday, September 02, 2002 5:26 PM
Subject: Re: [Towertalk] Tower Buidling 201
> Do you consider 15% to be a SIGNIFICANT increase in strength?
> I don't.
> Worst case for a 3 way guy arrangement is at 30 degrees
> to any one of the guys. Force in the guy is equal to the
> in line force divided by COS 30 degrees (= 0.866) = 1.155
> or 15.5% more tenstion that an inline force which is the worst
> case for 4 way guying.
> The old 80% guying guideline applied to the FULL rated height
> of the towers (200 ft for R25). At 70 ft or less, the tower can take
> more of the load from close in guys since it does NOT have to
> support the weight, guy tension, and resolved wind load
> of a tower extended to the full rated height.
> Tom N4KG
> On Mon, 2 Sep 2002 08:53:46 -0400 "Roger Borowski" <K9RB@bellsouth.net>
> > ----- Original Message -----
> > From: <email@example.com>
> > To: <TOWERTALK@contesting.com>
> > Sent: Monday, September 02, 2002 3:01 AM
> > Subject: Re: [Towertalk] Tower Buidling 201
> > >
> > > Note that for tower heights under 70 ft, Rohn shows a 35 ft (50%)
> > > guying radius for their (discontinued) fold over tower
> > intallations.
> > >
> > > Tom N4KG
> > >
> > That is because the fold over series must be guyed with FOUR guys,
> > 90 degrees
> > apart, which is a significantly stronger method of guying vs. three
> > guys at 120
> > degrees apart. There was a tread about this about 4-5 years ago.
> > 73, -=Rog-K9RB=-
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