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RE: ICBO Seminar for 1997 UBC Earthquake Regulations

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Thor, I think you pointed out (if we are on the same track) the same proof
of diaphragm deflection that was visible in relatively stiff (500 plf)
diaphragm in URM buildings. After both Whittier Narrow and Northridge
Earthquakes, the diaphragm deflection was evident in the amount of
out-or-plane damage that occurred at the floor level. Although this is the
reason for tension connections of the exterior wall to the diaphragm, the
damage was almost classic since it occurred close to the diaphragm's point
of greatest moment or between crosswalls.
My point is that a wood diaphragm can not be stiff enough to distribute
loads by rigidity. The only exception I can make here is where shearwalls in
the same line have different stiffness. I believe SEAOC is working on a
relative stiffness methodology for distribution of shear from top story down
in the same line of shear.
If you don't agree with me, please explain.
Dennis Wish PE

-----Original Message-----
From: T [mailto:vicpeng(--nospam--at)]
Sent: Tuesday, April 21, 1998 9:25 AM
To: seaoc(--nospam--at)
Subject: Re: ICBO Seminar for 1997 UBC Earthquake Regulations

This an example of how we neglect the boundary effects of diaphragms.  At a
recent seminar it was demonstrated that depending on all aspects such as
wall material, shape, diaphragm alignment etc the loads to the walls can
change dramatically.  I no longer think that it is a matter of "good
judgement".  There is software that will include boundary conditions.  "Good
judgement" will check if the computer data is sensible or not.

Thor Tandy
Victoria BC

Subject: Re: ICBO Seminar for 1997 UBC Earthquake Regulations

>Regarding the use of Rw=3 on one wall line only where the cantilever column
>occurs, I'll be carefull about this. We have to use our judgement.
>Just my opinion.
>Ernie Natividad