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R: Addendum to wind load calculations



HI Bob and Murray

I have seen the film  showing the Tacoma Narrows Bridge crash many years ago
but i have experimentet on my skin the infamous vibration effect described
by  VK2KGM
Early on 1977 to 1980 i  was pioneering  70 cm EME using a 16 x 21 elements
yagi in wich unfortunately the
aluminum structural was resonating around 2 Hz
Even a a very light  wind  was able to get the most extended part of the
booms vibrating at a rate of approximately two runs per second while the
entire structural emitted a particular sound similar to that of a
double bass
The result was the rapid wear af the boom aluminum  in all  16 antennas and
every day i founded a pice of boom on the floor of my terrace.
No vibration was induced in the array above or belove a certain speed and
direction of the wind

73 de i8CVS Domenico


----- Original Message -----
From: MCGWIER ROBERT <rwmcgwier@home.com>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, May 15, 2001 1:49 PM
Subject: Re: [amsat-bb] Addendum to wind load calculations


>
> ----- Original Message -----
> From: "Murray Peterson VK2KGM" <vk2kgm@ihug.com.au>
> To: "AMSAT-BB" <amsat-bb@AMSAT.Org>
> Sent: Monday, May 14, 2001 10:08 PM
> Subject: [amsat-bb] Addendum to wind load calculations
>
>
> > Hi Everyone,
> >                         if you have been reading my email about
> windloading
> > on structures, I thought I better add that wind is a dynamic load, note
> just
> > a static load and so wind induced vibration should also be avoided.
> >
> >     The most hazardous mechanical resonant frequency to avoid is 0.3 Hz
> > (dynamic wind loads have most of there energy at this frequency - ie a
> gust
> > every 3 seconds) but if in doubt, is is better to have all mechanical
> > resonant frequencies above 10 Hz as there is usually almost no
significant
> > component of wind loading above that frequency.
> >
>
> I wonder how many people here have seen then now infamous film
> of the wind induced vibration, with frequency about 1/3 hz, on the
> Tacoma Narrows Bridge.  If not,  everyone should see it once to
> see the power of this dynamic loading.
>
> Bob N4HY
>
> > Regards,
> > Murray Peterson
> > VK2KGM
> > (Yes - I am a Structural Engineer)
> >
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>

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