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Re: LONG FLOOR JOIST SPAN

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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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