[TowerTalk] 4 point guying...how?

[Kurt Andress]

hasben@ix.netcom.com wrote:

> On 04/02/99 17:30:20 you wrote:
> >
> >
> >On 4/1/99 10:41 AM, Gary McDuffie, Sr. at mcduffie@scottsbluff.net wrote:
> >
> >>THIS IS NOT SOMETHING I'VE SEEN RECOMMENDED BY A TOWER MANUFACTURER, ITS
> >>JUST AN IDEA THAT CAME TO MIND WHEN READING THE QUESTION.
> >>
> >>                      \        /         X = Tower
> >>                       \      /          : = Equalizer or splitter
> >>                        \    /          -- = Short guy to Equalizer
> >>                         X--:
> >>                        /    \
> >>                       /      \
> >>                      /        \
> >>
> >>Again, angle on the right pair of guys wouldn't be critical, as long as
> >>they were equal and not too shallow (the ascii diagram looks too shallow
> >>to me).
> >>
> >>Take aim guys.  Fire away.  Is this doable?
> >
>
> Hi Gary,
>        Trying to get the "Short guy Equalizer" balanced would be absolutely impossible.
> The best method is as Steve said....... Put two guys on one point of the guy bracket
> (use three shackles) then put the other two guys as normal onto the other two points.
> I would never wrap the guy around the tower leg, use a proper Rohn guy bracket, they are
> cheap enough.
>
> 73 de Richard K0XG
>

I agree with this viewpoint.

Here's why.
The configuration above is just fine if the wind is anywhere between the left pair of guys
or directly centered between the right pair. Any other wind attack angle will result in
increased tower deflection and torsion loads.

For a soft link like cable:
Worst case would be with the wind between the upper pair or lower pair. In this scenario the
working pair of guys  want to share the load based on the attack angle. The guys on the left
side of the diagram start working immediately, the ones on the right can't until the short
link swings around to align itself with the appropriate right side guy anchor.
This causes unnecessary tower twist and horizontal deflection.

For a hard link like an offset bracket:
The right side guy will start working sooner than above but will still result in tower twist
and horizontal deflection, when the system reaches equilibrium.


The thing to remember is that we always want the guys acting along lines that all come
together at the center of the tower (from a top view).

The best solution for putting 4 guys on a 3 sided tower is to fabricate a rigid bracket that
allows the connection of the two righthand guys (in diagram above) to be located in the same
places, relative to the tower center, as the two on the left side. This way all guys act
along lines that again coincide at the tower center.

The next best solution is to connect the righthand pair to the righthand leg as suggested.
This will result in additional torque and deflection, but is better than moving them further
away from the tower center.


The guy bracket is preferred because it provides additional bracing at the location of the
guy loads on the tower section. This distributes the guy loads around the tower section and
reduces the stress concentrations at the bracing/leg welds.


Happy Easter to all!

--
73, Kurt

K7NV "That's K7 "Nevada" (ex - NI6W)

YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/



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