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Re: Garage Floor Design

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Both Henry +ACY- Ernie are right, the code was revised a few years back to the
20 sq in area.

I also do a lot of residences with raised garage floors up here in the
mountains.  For years the standard in this area was to use 2x12's at 12+ACI-oc
spanning 12' (+-/-) with 3/4+ACI- ply +ACY- 3.5+ACI- of concrete (not just my office but
most of the
raised garages built up here).  The code change to the 20 sq in and the
lowering of the timber stresses a few years back made the 2x12's not calc.
These 2x12 floors have performed well and I did not see the reason to change
from the 2.5 ft sq to the 20 sq in .  I also use to use an area of 2.5' x
2.5' (three joists), but that was in the days when the you were allowed to
use a little judgement.  :)
After the code changed, I had to fight like hell to get plancheck to accept
using just two joists +AEA- 12+ACI-oc to support the point load.  They must be
trying to fix a problem that doesn't exist.  I have been thinking of trying
to use the Caltrans S/4 criteria along with
the APA report +ACM- 139 that I mentioned in a previous post so I can get back
to using reasonable size lumber.

By the way I have seen 25 year old garages with 2x10's +AEA- 16+ACI-oc spaning 12',
5/8+ACI- ply with no concrete , and the Surburban parked inside+ACE-

Randy Vogelgesang S.E.
S. Lake Tahoe

-----Original Message-----
Date: Friday, November 20, 1998 8:25 PM
Subject: Re: Garage Floor Design

+AD4-Maybe there is something that I've been missing but getting away with. I've
+AD4-designed several hillside homes with elevated garage floor systems here in
+AD4-Angeles. The construction has been very similar to the one you've
+AD4-If I'm not mistaken, Section 1607.3.3 +ACI-Concentrated Loads+ACI- in the UBC,
+AD4AIg-...placed upon any space 2 1/2 feet square,+ACI-. This does not state 2 1/2
+AD4-square feet. I've always interpreted this to mean 2 1/2 feet x 2 1/2 feet
+AD4-which would distribute the 2000 pound point load over three joists and not
+AD4-two. This reduces the load to 667 pounds per joist. At this point, a
+AD4-live load of 667 pounds/2.5 feet (266 pounds/foot) would be applied to that
+AD4-area of the joist. Using this methodology, the joists might calc-out.
+AD4-I would be interested in other engineers' takes on the subject. I've never
+AD4-a problem getting a plan checker to buy into this, and I've never had a
+AD4-performance problem with any of the floors I've designed using this.
+AD4-Greg Riley PE