Steve Maki wrote:
> Roger (K8RI) wrote:
>> Static load would increase on all legs. I'd expect to see the down wind
>> leg loading increase to a point, depending on guy tension.
> I want to understand exactly what you're saying here.
> In a strong wind, would you expect there to be more total compression in
> the downwind leg with guys attached? I would expect just the opposite...
Not at all and I hope I can put this into proper words. What I'd expect
in in a static, no wind condition would be more compression just from
the vector sum of the guy tension IE sum of the total COS angle of the
guys with the tower multiplied by the tension.
What I'd expect in any specific wind would be less percentage of the
*total* compression on the down down wind leg "at the base" with one
caveat. With guys not tensioned strongly enough I would expect the
compression to behave much like an unguyed tower up to a point where the
guys would stop the bending of the tower. The guys are going to have
some effect even at very little tension. IOW the tension would increase
on the down wind leg *until* that point was reached and then the % of
the total compression would become less on the down wind leg.
In the case of guying at a single level below the antennas with proper
guy tension I would expect the % of the total compression to be reduced
on the down wind leg "at the base", *but* at the guy point I would
expect the bending moment to cause a considerable increase in
compression just below the guys. IOW the load above the guy point would
act as a lever. AS a relatively extreme example, If the antenna was 10'
above the guy point and and was producing a force of 20# it would
produce a bending moment at the guys of 10' X 20#, or 200 ft pounds
where normally that skinny section of the tower would see very little
compression force. More typically the guys would be much closer to the
antenna producing far less leverage and bending moment at the guys.
In the example, if the tower were strong enough (which this one in the
example isn't) a second set of guys would be some where about 10' below
the first set or about the same distance below and the load is above.
(It's not quite that simple, but it's close with straight tower sections
of the same strength)
> In low winds, yes the static compression from the guys will add moderate
> extra loading, but I would expect the curves to cross at some medium
> wind speed.
> This is for a rigid tapered tower (which doesn't exist), but
> I'm betting the results are similar in most reasonable real life scenarios.
I used the BX series as they are relatively inexpensive and would
present an extreme example due to their characteristics. IE, that top
that's like a wet noodle. <:-)) The HDBX is much stronger, but doesn't
go as high and the sections are much heavier.
> Steve K8LX
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