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# [SEAOC] Re: [SEAOC] FEA of residential wood structures

• To: seaoc(--nospam--at)power.net
• Subject: [SEAOC] Re: [SEAOC] FEA of residential wood structures
• From: "Martin Johnson" <mwj(--nospam--at)EQE.COM>
• Date: Thu, 15 Aug 1996 09:20:57 PST
• Priority: normal

```> using ETABS to model typical residential wood structures
>
Regarding ETABS: it can be done, but you have to know the program and
be careful.   As a general "default" ETABS assumes that roof and
floor diaphragms are rigid, however, wood diaphragms tend to be
either flexible or semi-rigid.  A general FE program like SAP might
be better, or at least more obvious.

I have modeled semirigid metal deck diaphragms by making separate 2-D
simple-span models of the diaphragms using arbitrary material
properties, and making a separate hand calc of what the deflection
SHOULD be, based on the diaphragm flexibility factor determined from
manufacturer data, or as calculated in the Tri-Forces Manual.  I then
"calibrated" what the material properties would need to be to produce
equivalent deflection.  I then used these properties in my general
model, however, I did two separate analysis, using 50 percent greater
and less properties, and then used the maxima from these analysis for
my design.  I suppose that the wood diaphragm deflection formulas
(nail slip, etc.) could be used to do the same thing.  For plywood
shearwalls, deformation of uplift anchors would also need to be
considered in the deflection analysis.

This approach would really only be applicable for simple wall and
diaphragm geometries.  If a lot of openings and odd shapes were
added, relatively coarse simplifications would need to be used to
estimate panel deformation.  i would then suggest increasing the
"range" used in the bounding analysis to greater than 50 percent.

Also,
>
>.  If anyone knows Mr. Crosby or how to reach him,
>
try the following:

Patrick Crosby,
The Crosby Group