Well, I asked! Seriously, I see now what you mean. I never thought of guys
as adding to the vertical load, but of course they must if they're anything
less than 90 degrees to the tower. Thanks. Jerry K3BZ
----- Original Message -----
From: "Chuck Lewis" <clewis@knology.net>
To: "Jerry K3BZ" <k3bz@arrl.net>
Sent: Wednesday, April 16, 2003 7:24 PM
Subject: Re: [TowerTalk] Guyed self-supporters (was "Concrete suggestions")
> Jerry, K3BZOK writes:
>
> >Chuck...I have to ask: what would be "counter-intuitive" about adding
> > guys to a self-supporting tower? What "unintended consequences" would
> > result from that? Wouldn't it just be a little insurance?
>
> Jerry,
>
> Self-supporting towers are designed to withstand bending loads (from
wind),
> but their capacity to withstand vertical loads is based on just the weight
> of the tower itself and the antennas it supports (plus the usual safety
> factors). When guys are added, the lateral wind forces are converted to
> vertical loading on the tower (the tower doesn't deflect as it was
designed
> to do, and the lateral loads are all picked up by the guys). Depending on
> the angle of the guys, these forces can be huge, often exceeding the
> vertical strength of the tower. On the other hand, towers intended for
> guying are designed for high vertical and very low lateral/bending loads.
>
> This has been discussed on Towertalk several times by structural
engineers;
> I'm just an EE, so I am only parroting what I've seen them say, but it
makes
> a lot of sense. I remember that one of the older self-supporting towers
was
> reported as allowing supplemental guys, but I sure wouldn't do it unless
the
> tower manufacturer built that into his design requirements! This is
> particularly important (so they say) in the case of crank-ups, where the
> vertical strength is provided only by the cable. But even crank-ups with
> latches should not be expected to hold up to guying, unless the capability
> is designed-in.
>
> Sure, there are plenty of guyed self-supporters that are still
> standing....but perhaps with less margin. Your "just a little insurance"
is
> the intuitive assumption that is 'counter' :>).
>
> Chuck, N4NM
>
>
>
>
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