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• To: seaint(--nospam--at)seaint.org
• From: "Jake Watson" <jwatson(--nospam--at)utahisp.com>
• Date: Mon, 7 Apr 2003 08:09:34 -0600

I saw someone ask about how I calculated the loads in the IBC last night, but didn't have the opportunity to answer.  Well, here are the calcs:

Per IBC section 1607.9.2:

Double-tee: trib area = 9'x54'=486ft^2,
R=0.08%*(486-150) = 26.88%,
LL=(100%-26.88%)x50 PSF = 36.56 PSF

Center Inverted-Tee: trib area=27'x54'=1458ft^2
R=0.08%*(1458-150) = 104.64% > 40%, therefore R=40%
LL=(100%-40%)x50 PSF = 30 PSF

Column: trib area > trib area for IT which already has R > 100%, therefore R=60%
LL=(100%-60%)x50 PSF = 20 PSF

You will notice that the limit of section 1607.9.1.2 does not apply to section 1607.9.2.  Whether intentional or not, that is how it is written.  That may not be the intent, but that is part of the reason I asked the question in the first place.

Hope that clarifies things a little.

Jake Watson, P.E.
Salt Lake City, UT