It occurred to me that my 45' tall tilt-up vertical made
from 2" O.D. thin wall tubing may be germane to this
discussion:
http://www.dellroy.com/W4EF's-Ham-Radio-Page/Stew-Perry_El-Mirage/El-Mirage.htm
The preceding picture shows it fully erect with two
sets of guys. The top set is a combination top hat/
guy wires and the bottom set are 5/16" dacron. This
thing is so flimsy that it is quite frightening to look at
before the guys are set (very high pucker factor).
Without guys it looks as if any small gust of wind will
fold it right over. This is what it looks like going up:
http://www.dellroy.com/W4EF's-Ham-Radio-Page/Salton-Sea-05/video.htm
(the fat lumbering bipod in the video is yours truly after
a few too many sleep deprived days in the field).
Here is a still (top photo) after the guys are set:
http://www.dellroy.com/W4EF's-Ham-Radio-Page/Salton-Sea-05/Salton-Sea.htm
Notice that deflection in the top section. This is a
combination of high winds and the fact that the
tensions on the four top hat wires weren't set evenly
(I was too tired to go back and make it look pretty).
With the wind and the eneven guy tension on the
top section you can see the top tubing section tending
towards a buckling mode. The middle and lower set
of guys prevent the structure from buckling, however.
If I had to rank the survivability of the various
configurations of this mast in order of lowest to
highest based on my gut intuition after having
watched it get blown around in the wind a little, I
would guess the following:
1). Free standing (no guys wires at all)
a. lowest survivability
b. probable failure mode - tubing "fold over" near base
2). Single set of light guy wire at top (e.g. just the top hat wires)
a. low to moderate survivability
b. probable failure mode - buckling of tubing near the middle of
the structure
3). Three sets of dacron guys at moderate tension
a. highest survivability
b. probable failure mode - ropes break or guy stakes
come out of ground
I still think the top only guys would improve the
survivability over the no guy case, but the structure
is so flimsy I think that it would stand a good
chance of buckling at a moderate load without
the lower guys to keep the middle of the structure
from deflecting appreciably with the wind. With the
lower two sets of guys added in, this thing looks
and feels really solid. When the wind hits it hard
you can see the load distribute between each of
the three levels of windward guys. The whole
structure moves a little as the guy ropes stretch,
but overall it stays pretty straight.
73 de Mike, W4EF..........................................
----- Original Message -----
From: "Steve Maki" <steve@oakcom.com>
>
> What it boils down to is that with just a top guy on
> a relatively tall structure, the leg forces are not
> as balanced as I expected - that's for sure. BUT, it
> still seems to be a large improvement over the unguyed
> state for typical self supporters.
>
> I'd still be interested in any other data points you
> can think up related to middle tower components that
> turn out to be more stressed in the guyed state. I can't
> imagine what they could be - but I guess imagination
> shouldn't be a part of this!
>
> Steve K8LX
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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