Roger:
I think you have it half right. The only time 1 guy will see all the
lateral load is if the lateral load is in line with the guy direction.
This holds true for a 3 guy, 4-guy, or 20-guy system. It is a matter of
simple vector statics and the fact that guys are not rigid elements nor
can they take compression loading. Guys are tension only elements and as
soon as the line of force is not in line with the guy it is partially
shared by another based on the vector statics and the angle of force on
the guy system. Here I am talking in plan view or from above looking
down on the system.
As far as the distance from the base is concerned the closer the guy
points are to the base of the tower the higher the actual tension will
be. This can cause problems with the compressive strength of the tower
section and the pull out strength of the guy anchor point. As to whether
you use 4 or 3 or even 6 guys is a matter of land area available, anchor
capacity and amount of torsion reduction desired in the completed tower
system. Using 4 guys closer than 80% or 3 guys closer than 80% is not
wrong you just have to calculate the forces in the guys, in the anchors
and the tower to make sure everything is within allowable force ranges.
N4KG is correct in saying that the maximum guy force will occur when the
line of applied force is at 30 degrees to the guy direction in a 3 guy
system and equates to 1.15 the amount that would be seen if it were in
line with the guy direction. It is all a matter of vector mechanics and
the concept of equilibrium of forces.
On a couple of other notes: Galvanizing will not last indefinitely in a
salt air environment, neither will aluminum. Stainless steel especially
304 will even rust in a marine environment. If you put ferrous metal no
matter how protected in this environment maintenance of the coating will
be required, period.
The TIA/EIA 222 F standard is just that, a standard for the design of
the towers not a regulation of the protective coating. I know of no
building code in the US that prescribes protective coating requirements
as part of any regulation or permit. The coating specifications are by
the manufacturers or designers to give product or design life
specifications for an item but are not regulations. The ASTM galvanizing
specification was developed to give a standard of practice if one wants
to utilize this particular standard. Nothing more nothing less.
I hope this clears up this thread somewhat
All the best
73
Hank Lonberg, S.E.,P.E. / KR7X
Lonberg Design Group
-----Original Message-----
From: towertalk-admin@contesting.com
[mailto:towertalk-admin@contesting.com] On Behalf Of Roger Borowski
Sent: Monday, September 02, 2002 4:58 PM
To: n4kg@juno.com; z-TowerTalk
Subject: Re: [Towertalk] Tower Buidling 201
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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