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I: Addendum to wind load calculations




----- Original Message -----
From: i8cvs <domenico.i8cvs@tin.it>
To: MCGWIER ROBERT <rwmcgwier@home.com>; <amsat-bb@AMSAT.Org>
Cc: <vk2kgm@ihug.com.au>
Sent: Tuesday, May 15, 2001 3:33 PM
Subject: R: [amsat-bb] 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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