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Re: Effects of the New Code on Wood structures - good or bad?????[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: Effects of the New Code on Wood structures - good or bad?????
- From: NDZ28(--nospam--at)aol.com
- Date: Sat, 24 Jul 1999 21:44:17 EDT
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. >>
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