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Re: Balcony Floor Vibration

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In response to Mr Steve Kramer's query,It is suggested to check using 
castellated sections from W36 beams or similar beams to have more mom.of 
inertia.Thereby reducing deflection.This 'll increase the frequency .
OR  usage of some knee bracing  at a point below the cantilever portion 
,if possible, to reduce deflection.


CM Sinha
Engineers India Ltd
New Delhi


----- Original Message -----
From: Eric Ober <eric(--nospam--at)cagley.com>
Date: Monday, May 28, 2001 6:08 pm
Subject: Re: Balcony Floor Vibration

> Sounds like a pretty  difficult situation with the backup span not 
> greatlyexceeding the cantilever, and designing for rhythmic 
> activity rather than just
> walking.  It doesn't surprise me that you've had some experience 
> with other
> floor designs which don't meet the criteria.  In talking with Dr. 
> Murray(co-author of the Guide), he is seeing more and more 
> problems with vibration
> now than ever before.  I know he does a lot of consulting and 
> repairs related
> to these type of situations.  Generally, I try to meet the 
> criteria for
> servicability and vibration, unless there is some reason to 
> justify a bit of
> relaxation of them.  Dealing with a vibration problem in place is 
> expensive,difficult and potentially limits the use of the space.  
> I might try emailing
> Dr. Murray and seeing if he can give you any help (he'll probably 
> put in a
> pitch for his software) at tmmurray(--nospam--at)floorvibe.com
> 
> Eric Ober
> Cagley & Associates
> Rockville, MD
> 
> Steve Kramer wrote:
> 
> > I have a balcony with a 28 foot cantilever. The backspan varies 
> from 30 to
> > 45 feet. I'm trying to design for floor vibrations per AISC 
> design guide
> > 11. The balcony is for a church, and my thinking is that my natural
> > frequency should be at least 6 based on chapter 5 and my peak 
> acceleration> should be less than 0.5% g based on chapter 4.
> >
> > The problem is that this requires enormous beams, something like 
> W36x230 at
> > 5 feet on center just to get in the ballpark, way more than 
> required for
> > strength.  The problem seems to be the large deflection I 
> calculate for the
> > cantilever, that results in a very low natural frequency.
> >
> > Has anyone run into anything similar? Maybe I could use the 
> deflection at
> > some point other than the end of the cantilever. Maybe 3/4 or 
> 2/3 the
> > cantilever length, although even this doesn't help as much as 
> you might
> > expect. Past experience I have had with this design guide is 
> that almost
> > any floor I check doesn't work.
> >
> > Any advice or comments would be appreciated.
> >
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