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Re: ICBO Seminar for 1997 UBC Earthquake Regulations

• To: seaoc(--nospam--at)seaoc.org
• Subject: Re: ICBO Seminar for 1997 UBC Earthquake Regulations
• From: Stan J <hawneng(--nospam--at)wac.com>
• Date: Sat, 02 May 1998 13:31:01 -0700

```Dennis S. Wish wrote:
> ...
> Bill, I've stopped arguing this one since I am only interested in
> understanding how the code requirement accepting the lower R value for the
> construction with a wood diaphragm?
>
> Dennis

Here is one method of visualizing the problem,
that could shed light on the other point of view.
I know others who agree with you.  For wood
diaphragms trib area rules.

Here, however is another way of looking at
things.  In the "Big One" our half and half
building is going to be in the inelastic range.
Despite our common assumption of flexible
diaphragm, if the "bad" end performs particularly
poorly, extra force may be distibuted to the
"good" end because that is the only end that is
providing strong resistance.

Suppose that you are designing a twin engine jet
aircraft.  For the right engine you are using a
manufacturer that has a long history of making
tough, reliable engines.  For the left engine,
however, your boss makes you use a different
manufacturer (owned by the boss' golfing buddy)
that makes engines that tend to be highly
unreliable.  Trying to make up for the possibility
that the left engine should lose half of its power
unexpectedly, you double the power rating on that
left engine.  If, however, that left engine fails
completely, perhaps it would a good thing to have
some extra juice in the right engine too.

Of course, it seems overkill to use Rw=3 for the
shear wall end of things.  Perhaps a compromise is
in order in those cases where the difference in Rw
value between the two systems is so large.

Stan Johnson, PE, For an extreme example imagine
using, instead of a cantileved column system, a
glass block moment frame!   :o))))))))

```