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2000 IBC v 1999 UBC code question

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The 1/3 stress increase is totally unrelated to the load duration factor for
wood. The 1/3 stress increase is a load combination adjustment factor that
accounts for the reduced probability that two or more loads, other than dead
loads, acting concurrently will each attain its maximum at the same time. such
adjustments are applicable to all materials, but it unfortunately got
incorporated on the resistance side of the equation rather than the loads side.
it has been moved from the resistance side of the equation in ASCE 7 (and IBC)
to the load side of the equation in the form of a 0.75 adjustment (inverse of
1.33). so, you are still permitted the adjustment, but it's now taken on the
loads in accordance with IBC 1605.3.1.1.

The ASCE 7 Commentary section C2.4.3 and NDS Commentary section has more
detailed discussion of this for those interested.


Buddy Showalter, P.E.

From: "George Richards P.E." <george(--nospam--at)>
To: "'seaint(--nospam--at)'" <seaint(--nospam--at)>
Subject: 2000 IBC v 1999 UBC code question

Fellow Engineers:

I am reviewing the impact the IBC will have on how we design out West.

Using 1997 UBC Alternate Basic Load Combination 1612.3.2 we are allowed a
1/3 stress increase for wind or seismic only loading regardless of if the
material is wood, steel, or concrete.

Using 2000 Alternate Basic Load Combination 1605.3.2 we are NO LONGER
allowed a 1/3 stress increase for wind or seismic only unless specifically
given in the material section.  This means wood only.

First question:  Did I read this correctly?

Second question, {mostly for those of you in Texas where I know that every
home is Engineered :)} where the IBC has been adopted are you still using
Simpson numbers or since they have also included a 1/3 increase on steel are
you down grading them?

Thanks in advance.

George Richards, P. E.

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