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Re: LONG FLOOR JOIST SPAN

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Dave-

That's a better description.  The most problematic situation I've seen
was about 20 ft spanned with open web floor trusses that were only 12"
deep.  Town home with tkitchen over the garage, a real nightmare.

what is the plan area of the room?

Bob

On Apr 5, 2005 1:02 PM, DA <dnae2(--nospam--at)sbcglobal.net> wrote:
> Bob,
> 
> thanks
> 
> I just wonder  what is the limit of span for floor normal
> residence house
> It is in S. CA  14 Inch deep TJI (1.5x3.5 top and bottom flange , 3/8 to 1/2
> inch web) @ 16 inch on center
> for 18 to 20 feet long span there is no problem
> if it spans more I double or go to deeper
> but 28 ft to 30 ft  I see that problem even if the calculation shows 3/8
> inch deflection
> because I'm not sure how it will behave
> so, just wonder what is the limit of span  and when I should stop
> Thanks in advance
> 
> Dave A., P.E.
> 
> ----- Original Message -----
> From: "Robert Kazanjy" <rkazanjy(--nospam--at)gmail.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Tuesday, April 05, 2005 11:35 AM
> Subject: Re: LONG FLOOR JOIST SPAN
> 
> > Dave-
> >
> > Ralph's comments are right on target, I cannot emphasize too strongly
> > that this could generate problem that dwarfs your design fee.
> >
> > Talk to the customer (end user ideally).
> >
> > This really could be a problem downstream depending on the room usage
> > & their perception of the floor performance.
> >
> > I highly suggest reading
> > Canadian Building Digest
> > CBD-173.  Floor Vibration
> >
> > http://irc.nrc-cnrc.gc.ca/cbd/cbd173e.html
> >
> > I've done a fair amount of dynamic floor vibration testing & once
> > people get sensitized to it, it can be a real problem making them
> > happy.
> >
> > I suggest forgetting about span/360 or span/whatever
> >
> > deflection less than 1/32" under a 220 lb load is a good check.  Also
> > joists at 12 o/c are much better than 16" o/c.  Blocking is generally
> > not effective in achieving load sharing for vibration loading.
> >
> > I'm not exactly clear on your floor system layout
> >
> > You've also got to consider the dynamic response of the steel beams in
> > conjunction with the timber; the floor system as a whole.  If the
> > customer is involved, has informed consent & is aware of  possible
> > consequences of the "cheaper" solutions you're much better off.
> >
> > To prevent vibration you need stiffness or mass; your choice.
> >
> > cheers
> > Bob
> >
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