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

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> 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
2317 Broadway, Suite 20
Redwood City, CA   94063
415-367-8100 

Martin Johnson
EQE International, Inc.
mwj(--nospam--at)eqe.com

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