# RE: wood diaphragm revolt.

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: wood diaphragm revolt.
• From: "Kenneth Tarlow" <k.tarlow(--nospam--at)worldnet.att.net>
• Date: Fri, 16 Feb 2001 15:49:12 -0800
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Dear Mr. Merrick,

I thank you for your response.

As I see it engineers build models of buildings, on paper, in a computer or
maybe in their minds.  They push and pull on the model and reinforce the
areas where possible weakness exists. The criteria for the pushing and
pulling on the model is from the code.  In this we both agree. However, what
if the model is flawed.
Wood buildings do not rock back and fourth during earthquakes. They vibrate
up and down back and fourth, and some, like the Meadows apartment building
twist.  Now, what do these motions have to do with rigid diaphragms?
Answer; in our ability to rationalize a mode of behavior we fabricated the
concept of a rigid diaphragm.  We invent some bizarre criteria that if the
stiffness ratio of the diaphragm/shearwall is greater than 2 than the
building will behave one way and if it less than 2 it will behave another.
Great, except what if the ratio is 1.98.  Now what?  Oh by the way when
figuring on the stiffness of the shearwall do we include the drywall or
stucco cladding that cover the plywood?  Some walls have both.  How about
all the walls that are present, none shearwalls, especially in residential
construction that are not considered shear walls don't they dampen the
diaphragms, don't they inhibit the diaphragm from deflecting.  Oh, and by
the way, how much dead load did you figure 10 psf or 12 psf, what is it
really?  Did you calc the carpet, the carpet pad, hwo about the plumbing and
electrical lines.

I am sorry, it appears I am taking my frustration out on you. What I would
like to do is show that the rigid diaphragm analysis is superfluous for wood
buildings.  I believe that is true.  With a group of building a I can show
this to be true.
Anyone who is frustrated with the direction our profession is going.  That
somehow, a few engineers who are more in love with their computers than
their lives here is a way to maybe put some breaks down.  A good rational
study that will the plancheckers the authority to act reasonably.