Bob Kellow, W5LT wrote:
> If you want to guy a self supporting tower it needs to be done very
> carefully (read: professional analysis).
> But then, isn't the title an oxy-moron? If it is self supporting, why does
> it need to be guyed? If it is designed according to industry standards for
> the applicable wind zone and antenna loads, it should not fall down (at
> least it is no more likely than any other type of tower).
> But to the subject at hand: most others have touched on the real issues: the
> tower is being applied in a manner for which it was not designed, at least
> in most cases; and the stresses applied are distributed differently than the
> designer assumed.
> The original proposal mentioned a single set of guys at the top,
> "pre-tensioned at normal values" what ever that is. With only one set of
> guys, the tower becomes one long, unsupported slender column and is subject
> to over-all buckling, not the local buckling that was considered by the
> designer. This was mentioned in one message.
> On the subject of "guy tension", consider that the tension must be such that
> all the wind loads are transferred to tension in the guys and compression on
> the tower. These must be quite high, because you do not want the tower to
> move under load. If it does, the leeward guy will go slack, with
> unpredictable results when the wind gust stops. Also, the top sections of a
> typical slender SS tower are not designed for very high compressive loads
> (like the lower sections are) and would be more prone to fail under the
> loads required by a single set of guys. Unknown resonances are also likely
> to be created which would have unknown effects. Please note that slender SS
> towers are allowed to move under load, they shed load that way and
> efficiently transfer loads to the base.
Guy wire is normally pre-tensioned at 10% of minimum
breaking strength.
Some of what you wrote is conjecture, just like my
theory is.
Just think of this as an academic exercise then.
If it turned out that reasonable guying never
compromises a tower, and usually strengthens it -
wouldn't that be useful information?
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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