Roger,
I politely suggest you do the CALCULATIONS to determine
EXACTLY how much benefit there is in 4 guys vs 3 guys.
At 5 degrees off line, the IN-LINE wire carries 99.6% of the
load. NOT much help from the side wires IMHO). (I assume
you do know how to resolve a force vector into orthogonal
equivalents as it is rotated).
Further, I suggest you do the calulations for a 70 ft tower
guyed 3 ways at 50% of the tower height. I'm sure you will
find that the loads placed on the tower are WELL within
the R25 ratings and the guy wire ratings assuming a
nominal antenna load under 12 sq ft.
There are many thousands of towers that have withstood the
rigors of weather for many decades, all using 3 WAY guying,
testifying to the soundness of this approach. If 4 way guying
was so much better, then why don't ANY of the BIG tower
designers use it? I expect that if all the guys in ONE direction
were removed from a guyed tower, the tower would still FALL
DOWN, whether it was guyed in 3 or 4 directions.
BTW, Percentages of wind direction is MEANINGLESS.
Any guying system MUST be capable of supporting the
tower 100% of the time. RUN the NUMBERS. It's the
RATINGS that count, not the number of directions the
tower is guyed.
Tom N4KG
On Mon, 2 Sep 2002 Roger Borowski" <K9RB@bellsouth.net> writes:
> 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 -----
> From: <n4kg@juno.com>
> 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>
> > writes:
> > >
> > > ----- Original Message -----
> > > From: <n4kg@juno.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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