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Re: Effects of the New Code on Wood structures - good or bad?????

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In a message dated 7/24/99 12:17:39 AM Pacific Daylight Time, 
chuckuc(--nospam--at)dnai.com writes:

I would like to add a note of disagreement here. I think the 1994 Northridge 
earthquake was the best indicator of actually how well wood building behaved. 
Keep in mind that a lot of these building were built based on the  typical 
type 'V' sheet. 

I looked at well over 500 dwellings and found that the majority of the wood  
structures  did exceptionally well. What I did find was that most of the 
damage that occurred to these buildings was due to poor workmanship, 
inadequate detailing, and soils problems. And yes there were some older 
buildings that were damaged due to lax older codes. At the same time, I 
inspected several fairly new apartment buildings with collapsed concrete 
garages. And we all know that we're using 'state of the art ultimate strength 
technology.'  Rather than reinventing the wheel, better quality control, 
better training for framers and better quality plans is what's required. We 
did not need a new code to complicate matters.

 Before you all jump on me, I call this a new code only because as far as I 
know, no one ever enforced or required a wood structure (houses, small 
commercial or apartment buildings) to be evaluated for flexible and rigid 
diaphragms.  I also don't know of any engineer who made it standard practice 
to analyze a structure for the more critical of the two.  As I noted in a 
previous posting, the City of Los Angeles specifically stated in their 
building code that wood diaphragms shall be assumed to be flexible, until at 
just recently.

I am getting so tired of listening to some of you talking about the 97 UBC 
allowing us to do better job and charging a little more. When I see formulas 
for wood structures using three and four decimals I know that were doing 
something extreme.
Again this is just a general posting not addressed to anyone specific, and I 
want to thank all those who are working on, and devoted their time to making 
this code more bearable.
Andrew

<< 
 Dennis:
 I am in complete agreement with Mark on this subject.  You seem to have lost
 your perspective on this problem.  Wood frame structures are extremely
 complicated under dynamic loading.  Material properties such as strength and
 stiffness are dependent on the rate of loading. The structures have a great 
deal
 of internal damping and the loading history is nearly completely unknown.  
Any
 attempt to accurately model the behavior of such a system will either be
 extremely complex, highly inaccurate, or both.  It will always be easy to
 criticize any proposed analytical model. We shouldn't take the numbers we
 calculate quite so seriously, they probably are not accurate to one 
significant
 figure.
 The fact of the matter is that many the wood framed structures did not 
perform
 acceptably during the Northridge earthquake.  As a consequence, some very
 knowledgeable and experienced engineers have proposed changes in the Code in
 order to improve the performance of wood frame construction.  Design loads 
have
 been increased and we are now being asked to evaluate our structures a little
 more carefully.  That is going to include an evaluation of rigid and flexible
 diaphragm performance, like it or not.
 Clearly we need more information on the performance of shearwalls.  We need 
more
 test data from walls of differing aspect ratios.  We need more test data
 regarding tie down deflections.  We need more information regarding typical
 construction defects.  IMHO APA should have provided us with this test data a
 long time ago .  Simpson has also been negligent in not providing us with 
usable
 information regarding tie down performance.  Be that as it may, until such 
time
 as the CUREE project has generated more test data, we are being asked to do 
the
 best we can. >>