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Re: Rigid plywood diaphragms

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In a message dated 11/21/98 3:17:44 AM Pacific Standard Time, Michael Cochran

<<  I don't know if this would keep you out of litigation, but I think it
would address the fact that you at least considered the possibly of a rigid
diaphragm, especially if it governs the design of some of the walls when
compared to a tributary analysis. >>

[Bill Cain]  I don't know either.  But, if we all keep talking about how
unsure we are about how to do the analysis, that in itself might be our best
defense in court against rigid code provisions.  The argument being that there
is no widely accepted method as demonstrated by the extensive discussions on
the listserver.  Let's keep talking!  We'll either solve the problems or
provide a good case that there is no right way.

Personally, I try not to "max out" any shear element and try to have
redundancy wherever possible (with some architects, especially the one's who
like swiss cheese, it is a challenge  :<)   ).  Remember that an earthquake
doesn't know what rules we expect it to follow!  It just comes and does its
thing.  I've seen more earthquake damage due to connection failures (As they
say, the devil is in the details  ;o)    ) than element failures.  Detailing
shear walls with 2x edge framing, close nail spacing, large hold downs and
lots of eccentricity between the line of action of the sill bolts and the
plywood under high unit shear conditions is risky IMHO and I look for other
strategies wherever possible.

Another topic coming in wood design, LRFD, might also require us to do
additional analyses.  But it may also allow us to better understand where
capacity is available and where it isn't.  

Looks like we all need to be working either on establishing a new fee
paradigm, or new and simple design rules that get back to the basics: applying
good engineering judgement.

Bill Cain, SE
Albany, CA