Please don't get upset! I don't intend to actually do this!
All you antenna experts out there. If I have a tower say 60 feet tall
and
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

What are the forces that the wind exerts on a tower and are these
forces evenly
distributed?

Thanks for your help.

wrote in message
ups.com...
Please don't get upset! I don't intend to actually do this!
All you antenna experts out there. If I have a tower say 60 feet tall
and
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

What are the forces that the wind exerts on a tower and are these
forces evenly
distributed?

Thanks for your help.


AS you said , not recoomeded for only one set at that heigth but the top set
of guy wires always go near the top of the tower.

I would put them at the center
as I see buckling as the worst danger.
I have also done this with a 60 foot boom antenna
with no problem. I was forced into this position in the first
place because I have a fold over tower and eventualy stopped
using the top guy wires thru lazyness.
Art




"Ralph Mowery" wrote in message
ink.net...

wrote in message
ups.com...
Please don't get upset! I don't intend to actually do this!
All you antenna experts out there. If I have a tower say 60 feet tall
and
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

What are the forces that the wind exerts on a tower and are these
forces evenly
distributed?

Thanks for your help.


AS you said , not recoomeded for only one set at that heigth but the top
set
of guy wires always go near the top of the tower.

Did you ever take any ME courses Art?

Simplest back of the envelope approximation is 2/3 is best, ignoring
toewr resonance and lower wind as you get closer to ground level, so,
lower points would put more torque on the tower. With an antenna
mounted, it would move the optimal single guy point upward.

It's possible I may have this cimpletely wrong, if so, correct away folks.

tom
K0TAR

wrote:
I would put them at the center
as I see buckling as the worst danger.
I have also done this with a 60 foot boom antenna
with no problem. I was forced into this position in the first
place because I have a fold over tower and eventualy stopped
using the top guy wires thru lazyness.
Art




"Ralph Mowery" wrote in message
ink.net...

wrote in message
roups.com...

Please don't get upset! I don't intend to actually do this!
All you antenna experts out there. If I have a tower say 60 feet tall
and
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

What are the forces that the wind exerts on a tower and are these
forces evenly
distributed?

Thanks for your help.


AS you said , not recoomeded for only one set at that heigth but the top
set
of guy wires always go near the top of the tower.

wrote in message
ups.com...
Please don't get upset! I don't intend to actually do this!
All you antenna experts out there. If I have a tower say 60 feet tall
and
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

What are the forces that the wind exerts on a tower and are these
forces evenly
distributed?


If the tower is 4 feet across at the base, you may not have a problem,
otherwise - If you do that, be sure the tower is more than 60 feet from your
house - so it will miss the house when it falls.
Most of the water towers you see are a hundred feet or higher, but have no
guy wires, because the base is pretty wide.
guying at the top only may cause it to bow in the middle during a windstorm
to such a degree as to collapse.
I would guess the tower manufacturers would have wind and static loading
data available.
You have wind loading and the static loading due to gravity - which begs to
become dynamic.

try practicing with half-inch pvc water pipe - see where the guy wires do
the most good.

wrote:
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

According to Rohn specs, a single set of guy wires limits
your tower to 40 feet maximum height - sorry about that.
--
73, Cecil http://www.qsl.net/w5dxp

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That wasn't the question.

"Cecil Moore" wrote in message
...
wrote:
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

According to Rohn specs, a single set of guy wires limits
your tower to 40 feet maximum height - sorry about that.
--
73, Cecil http://www.qsl.net/w5dxp

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CW wrote:
That wasn't the question.

No, but that was the answer AFAIAC.

"Cecil Moore" wrote:
According to Rohn specs, a single set of guy wires limits
your tower to 40 feet maximum height - sorry about that.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil, !5DXP wrote:
"According to Rohn, a single set of guy wires limits the tower to 40 -
feet maximum height - sorry about that."

Well, it depends on the Model No. and how you will load the tower. It is
best to follow thw manufacturer`s recommendations to the letter.

There is a length that you can stack which will endure without guys in
most cases. Towers usually come in 20-ft. sections. Often one or two
sections is all it is safe to use without guys. Windloading the tower is
expected to withstand, often determines space between guy points.

Wind exerts force on the tower and its appurtences, often expressed in a
sum of pounds per square foot on the area facing the wind.. Resistance
(drag) produces a differential pressure on items in the wind. Force is
proportional to the projected area in the wind, and varies with the
shape and roughness of the item in the wind. Windload on a tower is not
uniform. The wind usually blows harder at higher altitudes. Wind tries
to turn the tower over but until something yields, it is in equilibrium
and the summation of of forces about the base of the tower is zero. The
summation of torques is zero.

Guywires exert force in yje only way they can. They have tension in the
direction of the wire. This may be resolved into vertical and horizontal
components. This prevents movement and increases base loading when the
wind blows.

Pressure on items in the wind (pounds per square feet) is a function of
the square of the wind velocity (miles per jour).

One formula considered useful is named "Ensewiler" which is said to
give:
22.5 psf = 85 MPH
45 psf = 134MPH
60 psf = 155MPH
75 psf = 173MPH

Best regards, Richard Harrison, KB5WZI

On 9 Apr 2005 14:22:06 -0700, wrote:

Please don't get upset! I don't intend to actually do this!
All you antenna experts out there. If I have a tower say 60 feet tall
and
I can only put one set of guy wires up, should they go near the top of
the structure or near the middle?

What are the forces that the wind exerts on a tower and are these
forces evenly
distributed?

This is really a complicated subject and off the cuff remarks and
supposition are worthless.

The forces *can* be analyzed as uniformly distributed but usually, the
wind pressure is stronger near the top, particularly if there is an
antenna up there, which is the normal reason for a tower.

You might be inclined to say aha, then the top is the place for the
guys. But, guys turn horizontal force into vertical force that tries
to drive the tower into the ground. With the top and bottom
restrained, then the middle might be inclinded to deflect horizontally
under wind load. With it so moved, then the down force from the
weight of the tower and the additional force from the guys can cause
the tower to buckle.

Another concern is mechanical resonance. Top guying is going to make
the top resemble a string on a musical instrument with the wind trying
to pluck it. It has been my (sad) experience with a Cushcraft AV-80
tubular vertical that guying half way up, is equally bad. I had a
resonance set up and the tubing bent to yield and broke in two right
*under* the guys.

When I installed it I didn't have the data sheet but knew that it
needed guys. So I guessed at 50% up. Since then I've acquired the
data sheet and the recommendation is to guy about 2/3 up from the
bottom.

The bottom line is to listen to the manufacturer.