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Re: '97 UBC Design - Are you too old to change your ways???

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Bill,
I agree 1000+ACU-.  You have hit this nail squarely on the head

Randy Vogelgesang S.E.

-----Original Message-----
From: Bill Allen +ADw-Bill+AEA-AllenDesigns.com+AD4-
To: seaint+AEA-seaint.org +ADw-seaint+AEA-seaint.org+AD4-
Date: Wednesday, September 22, 1999 4:58 PM
Subject: RE: '97 UBC Design - Are you too old to change your ways???


+AD4-If I had the opportunity to retire (or change professions for that matter),
+AD4-I would have done it long before the 1997 UBC hit the streets.
+AD4-
+AD4-Other than that, I vote for something in between. It is obvious to me
(based
+AD4-on how I have read the code and what I know of the background of some of
the
+AD4-code authors) that the seismic provisions of the 1997 UBC were not written
+AD4-with wood framed, residential construction in mind. Best case, this class
of
+AD4-structure may have been merely accommodated. IMO, between July 1, 1998 and
+AD4-at least until the 2001 IBC hits the streets, there will be
+AD4-misinterpretations abound as well as a significant amount of, dare I say,
+AD4-over-engineering.
+AD4-
+AD4-It has not been demonstrated to me that the typical custom home located in
+AD4-even the highest seismic risk area has been subjected to a significant
+AD4-amount of damage as compared to, say, unreinforced masonry, wall ties of
+AD4-tilt-wall buildings, soft story designs and open front designs.
+AD4-
+AD4-Where I am going with this is that I believe there might be a need for an
+AD4-intermediate code. Something more prescriptive than Conventional Framing
+AD4-Provisions and less restrictive than the 1997 UBC. Maybe a One- and
+AD4-Two-Family Dwelling Code. What a concept+ACE-
+AD4-
+AD4-To me, the seismic design of these kinds of structures are relatively
+AD4-straight forward. First of all, select a base shear coefficient expressed
as
+AD4-a percentage of gravity. Visualize that I am reaching up in the air as if
to
+AD4-grab a knat. Some number between 0.15 and 0.20 g (in zone 4). O.K., now do
a
+AD4-vertical redistribution of forces in some rational manner. Either inverted
+AD4-triangular distribution or rectangular. Doesn't really matter that much.
+AD4-O.K., now do a horizontal distribution of forces in some rational manner.
It
+AD4-doesn't really matter if it's flexible, rigid, or rigid-flexible. Just
+AD4-something rational. Now, stand back and look at the structure. Make sure
you
+AD4-have a load path from the roof to the foundation. Now, when the design goes
+AD4-into construction, make sure the design engineer (not a proxy) makes enough
+AD4-jobsite visits to ensure that the design has been accomplished. Outside of
+AD4-some special conditions (like addressing rotation, etc.), this is the bulk
+AD4-of what we need as far as a seismic code for residential construction, in
my
+AD4-opinion. If you like this, you should see my solution for federal income
tax
+AD4-:o).
+AD4-
+AD4-It may be true that the +ACI-young pups+ACI- might be more +ACI-software friendly+ACI-, but
+AD4-I doubt this is the case in the big picture. Some of us +ACI-old dogs+ACI- have
+AD4-figured out how to turn on a computer. In addition, we have seen a lot of
+AD4-structures built and I believe we have a better +ACI-feel+ACI- on what makes sense
+AD4-rather than just possessing the ability to crunch numbers at blinding
speed.
+AD4-
+AD4-Regardless of the limitations of the +ACI-old dogs+ACI- and +ACI-young pups+ACI- it doesn't
+AD4-make much sense to double the amount of engineering hours it takes to do a
+AD4-lateral analysis of a house if there is no real benefit in doing so other
+AD4-than being able to say that you have enveloped every conceivable possible
+AD4-way a seismic load can pass through this shear wall. This is nuclear power
+AD4-plant design mentality and is not rational in residential construction. If
+AD4-the perception now is that rigid diaphragm analysis is the more appropriate
+AD4-way of analyzing wood framed structures, this method should be adequate.
Not
+AD4-both. However, it would be hard to justify to me how a procedure practiced
+AD4-in a wide geographic region over multiple decades can be so much at fault.
+AD4-Look at Kobe. Look at Turkey. Look at Greece. Look at Taiwan. Look at
Mexico
+AD4-City. Look at Iran. O.K., now look at Northridge and Loma Prieta. What is
+AD4-the difference? Certainly not flexible vs. rigid.
+AD4-
+AD4-O.K., I'm done.
+AD4-
+AD4-Bill Allen, S.E.
+AD4-ALLEN DESIGNS
+AD4-Laguna Niguel, CA
+AD4-