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Re: Garage Floor Design

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I am not sure that using the UBC excludes using the Caltrans spec or that
the two sources contradict each other.  Apply the 2000+ACM- load on top of the
slab over 20 in sq. (4+ACI-x5+ACI-?).  Now, is the slab and plywood combination
sufficiently rigid enough to distribute the load over three joists?, four
joists?  Obviously this is a complicated relative rigidity problem.  The
Caltrans manual IS a good source for determing the +ACU- of wheel load supported
by members.  Caltrans accepts that 4x timber is sufficient to spread the
point load to the framing using S/4.  The question is S/? for plywood w/
concrete.  The slab is
usually 3.5+ACI- thick with 6x6x10ww mesh.  An analysis of this as a
structural slab is not appropriate (I would not want to assume that the mesh
is properly installed).  This is where I found the APA report +ACM-139 useful.
I suggest anyone interested in this to get a copy, the report details the
test procedures and their recommendations based upon the results.  The
report demonstrated that plywood when toped with 3+ACI- of concrete has very
good structural capacities when subjected to point loads.  Naturally, the
APA was only concerned with the capabilities of their plywood and not how
the load was distributed to the framing below.

All things considered I would feel completely comfortable using a S/3 factor
when using 3/4+ACI- ply w/ 3.5+ACI- of concrete.  The problem is how to convince
plancheck.  It is my opinion that common sense is not all that common.

Randy Vogelgesang S.E.

-----Original Message-----
Date: Saturday, November 21, 1998 4:05 PM
Subject: Re: Garage Floor Design

+AD4-Unfortunately we can not use Caltrans S/4. We have to stick to UBC using
+AD4-20+ACI-x20+ACI- area as you said you have used. Although the distribution
+AD4-is the same. I also have seen old houses with 1 1/2+ACI- concrete overs 2x
+AD4-over 2x10 joists. As Greg said in his reply he has never been questioned by
+AD4-plan checker and has never had problem with the garages that he had
+AD4-using 667+ACM- on a single 2x joist. Maybe the answer is that the 2000+ACM- wheel
+AD4-never been to those garages and if it has, there is still some safety
+AD4-to take care of it.
+AD4-Oshin Tosounian, S.E.