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RE: Residential Garage (Help!)

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> From: Forrest Braun [mailto:fbraun(--nospam--at)bbfm.com]>
> Sent: Wednesday, March 27, 2002 7:59 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: Residential Garage (Help!)
> ...
> The second part is that the floor in question is a wood system with a
> relatively thin concrete topping where punching through the topping and
> sheathing will be important.  The point load would need to be considered
> to act on a joist with little or no load shearing to adjacent joists.


I agree, partially.  If you put the point load at the end of a joist and are
looking at shear, then no, there is no load sharing (no deflection).
Actually, shear could be a problem, along with bearing.  You might need to
reinforce the joists?

However, if the load is in mid-span, then there *will* be deflection.  Since
you have a relatively rigid (as compared to the wood) concrete deck, one of
two things *have* to happen - either the slab cracks and allows the loaded
joist to deflect un-aided, or some of the load is transferred to adjacent
joists.  To aid in load-sharing you can specify solid blocking or cross
bridging at mid-span.

For the specific problem that started this thread, however, I don't think
this is needed.  With a relatively short span (7 feet), doubled 2x12's will
work.  So use double 2x12's with the joist spacing determined by how far the
plywood/concrete deck can span.   The extra 2x12's are cheap compared to the
added labor of blocking or bridging, or the added design time to prove
load-sharing.

-----
Jason W. Kilgore, P.E.
Leigh & O'Kane, L.L.C.
(816) 444-3144
jkilgore(--nospam--at)leok.com



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