Guy tension ??

Ian White, G3SEK
Thu, 15 Aug 1996 07:50:53 +0100

Stan Griffiths wrote:
>I would not call it "slack" either, but it DOES have some sag in it.  Any
>sag at all allows the tower to move slightly when pushed by the wind.  More
>slack, more movement.  I have heard that guyed towers can "resonate" if they
>are allowed much movement in the wind and this can bring it down if allowed
>to oscillate with much violence.  Although I don't see this in the Rohn
>book, there are those who advocate guying a tower at UNEVEN levels to
>prevent the entire structure from resonating in the wind.

The tower will always have resonances - several of them - and so too
will the guys. One effect of guy tension is to move these resonances
around in frequency, and also to alter their degrees of damping and
mutual coupling. It's very much like several interconnected tuned

The wind will try to excite all available resonances, and a strong wind
will pump in as much energy as the resonances allow. If a major tower
resonance coincides with a guy resonance, you're in real trouble.
The effect of normal good guying practise is to keep these resonances
well separated and as well damped as possible; but they always exist.

That's the limit of my 'hand-waving' knowledge, but it does give a feel
for the subject. Yes, it would be interesting to hear from a real
structural engineer!

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)
IFW Technical Services     Clear technical English - world-wide.