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RE: Rigid plywood diaphragms

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Thanks to everybody who answered to my post especially to Charles Greenlaw.

I appreciate opinions of all that responded to my post on the applicability
of the rigid plywood diaphragm design.

But what I am trying to figure out is how can I do the rigid analysis if I
decide to, without any increase in my fees or with the minimum effect on my
fees.

DO YOU THINK THAT IT IS APPROPRIATE TO ESTIMATE THE RELATIVE THE RIGIDITY OF
THE PLYWOOD SHEARWALL (OR CLOSE APPROXIMATION OF IT) BY USING THE PRODUCT OF
WALL'S RATED CAPACITY TIMES THE LENGTH?

If this is all I am required to do in order to avoid any future litigation,
I am willing to spend a couple of hours doing the comparative analysis of
flexible and rigid diaphragm distribution.  If this requires an estimate of
rigidity for all the sheetrocked partitions and other structural and non
structural elements, then forget it.  As Lynn Howard said, the plywood
diaphragms and properly detailed plywood shear wall performed well in the
past earthquakes.  So why fix what is not broken.

Regards,

Sasha Itsekson

-----Original Message-----
From: Lynn [mailto:lhoward(--nospam--at)silcom.com]
Sent: Wednesday, November 18, 1998 5:38 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Rigid plywood diaphragms


"Since most residential buildings typically have deep, short span
diaphragms, it is virtually certain that these diaphragms can not be
considered flexible under [1994 Uniform Building] code definition and
that
force distribution to the shear walls must be made on the basis of wall
rigidities.  Engineers should adjust their design practices to conform
to
these 1994 and 1997 UBC provisions in order to avoid lawsuits at the
later
date"



Hahahahahahahaha!!!!!  That is a good one!

Who is going to sue me and on what grounds.  Certainly it WON'T be
because the diaphragm did not perform properly in an earthquake.  If we
are sure about ANYTHING it is that our seismic design of plywood
diaphragms (vertical and horizontal) perform very well on residential
construction.  This will be even more true now that the height to width
ratios are more restrictive.
I have a REAL hard time with this one.  There are plenty of structural
issues that are of real concern that talented people could be spending
their time on.  Plywood diaphragms perform well for residential
buildings as currently designed, period.

Anybody can sue for any reason.  And some people do just that.  There is
no protection from those kinds of people.  What should happen is that
there should be an exemption in the Code for certain kinds of buildings
with a proven history of successful performance during strong ground
motion.

I have a question for the engineers that are going to design future
buildings to this new provision.  Are you going to contact all the
Owners of buildings you have previously designed and notify them that
the plywood diaphragm building they own may not provide adequate
life-safety protection in an earthquake??
I would guess that no one will do this, because we all know that it is
simply not true.

Sorry to vent like this, but some things just really get to me :)

Lynn