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RE: 3-D modeling - ASCE 7-05 12.7.3 needs an exception for light-frame timber

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ASCE 7-05 12.7.3 should have an exception for light frame construction that
says the model for light frame construction can use approximate methods for
wood panel shear walls on cantilevers, non-parallel systems and soft stories.

12.5.4 says that you can do a 2-D analysis for flexible diaphragms except
where required by 12.7.3. 

The more you read ASCE 7-05 12.7.3 the more you realize it has not considered
light frame structures or that the steel/concrete building eggheads were the
only ones in attendance to vote.  Light frame shear walls are set on
cantilevered floor joists all the time.  This is an out-of-plane offset.  The
code already has special requirements for framing supporting at the
cantilevers.  You already get tagged with a redunancy factor for walls full
of windows or garage door openings. As for non-parallel systems in wood
buildings - add an exception to the code to say the architect should be water
boarded.

The code writers should consider that 99.99999% of structural engineers are
not going to do a finite element model for light frame wood panel shear wall
structure. I worked at a busy building department for 8 years and only saw a
couple of designs with Woodworks which I don't know meets 12.7.3.  There were
a couple of residential designers that used Maxquake which I don't know meets
12.7.3. A vast majority of light timber designers did it by hand.



-----Original Message-----
From: Matthew Shear [mailto:MShear(--nospam--at)RMByrd.com] 
Sent: Tuesday, January 15, 2008 1:31 PM
To: seaint(--nospam--at)seaint.org
Subject: 3-D modeling

Based on ASCE Section 12.7.3, a 3-D model is required if a structure has an
irregularity type 1, 4, or 5.  Would this be required for a light framed
shear wall structure?  Or even on a structure with a flexible diaphragm?

 
Thanks
 
Matthew
 
 

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