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SV: roto-hammers, masonry & city of LA

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Can we getb some Drawing....

Félix..

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> Från: BCainse <BCainse(--nospam--at)aol.com>
> Till: seaoc(--nospam--at)seaoc.org
> Ämne: Re: roto-hammers, masonry & city of LA
> Datum: den 20 januari 1998 07:47
> 
> In a message dated 98-01-18 16:48:33 EST, Tom VanDorpe, P.E. wrote:
> 
> << f I am not mistaken, Anaheim Stadium had some very serious problems
with
> this
>  song in the early '70s due to concert fans bouncing to the music.  The
>  solution at that time was to attach cables to  the cantilevered portion
of
> the
>  club level  in order to pull the cantilevered end down a bit and hold it
in
>  tension.   >>
> 
> 
> [Bill Cain]  In the late '70's, when I was working for the Office of the
State
> Architect, I was called on to evaluate the balcony at the San Jose Center
for
> the Performing Arts for vibrations occurring during dance performances. 
The
> problem was encountered when a Greek dance troup was performing and the
> audience started moving in time with the music producing uncomfortable
> vibrations.
> 
> The balcony is a bridge type structure with two large plate girders
spanning
> about 125 feet. The balcony capacity is about 750 people. Its period of
> vibration was somewhere in the 1/2 second range.  I remember standing in
the
> middle of the balcony and jumping at approximately the structure period.
> After about 6 to 8 jumps, the resonance was sufficient to make me queasy
and I
> don't get motion sickness easily.
> 
> We did some testing to verify the period and damping.  The damping as I
> recall, was something less than 1/2% when we pulled a tension at the
center
> and released it rapidly.  Our analysis showed that it was unlikely that
> dangerous levels of vibration could be produced by an active audience but
the
> vibrations became very uncomfortable quickly.  
> 
> The City of San Jose did further investigations on ways to solve the
problem.
> I don't know what, if anything, they came up with.  I know they quickly
> rejected the idea of adding columns under the plate girders at midspan  
:<).
> 
> Bill Cain, SE
> Albany, CA
> 
>