Need a book? Engineering books recommendations...
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'" <seaint(--nospam--at)seaint.org>
- Subject: Re: Effects of the New Code on Wood structures - good or bad?????
- From: "Swingle, Mark" <Mark.Swingle(--nospam--at)dgs.ca.gov>
- Date: Fri, 23 Jul 1999 10:36:47 -0700
- Cc: "'mswingle(--nospam--at)earthlink.net'" <mswingle(--nospam--at)earthlink.net>
Lynn Howard wrote: < Prior to our starting on the project, I met with the DSA < and told them I was considering designing the diaphragms < as rigid, because that is what the Code clearly said. < They basically were not going to require the rigid diaphragm < analysis, and in fact WOULD NOT ACCEPT that type of < analysis alone. < I find it very interesting that DSA would not accept < the Code required analysis. < These people are aware of the Code requirements, < and do not accept it. It is not because the are ignorant < of the Code. Mark Swingle responds: Lynn, that is not what the code clearly says. What I am saying is that the code requires an accurate analysis of the ACTUAL stiffness of the diaphragm, but since we don't know how to do that, we can be conservative and cover all possible forces. Doing ONLY the INFINITELY STIFF diaphragm analysis is not sufficient (and by the way is not sufficient for many buildings other than wood). My point was that since there is no rational way to model the diaphragm accurately, then by doing both a flexible analysis and a rigid analysis, you always cover the worst cases for all walls, and so as I said, NO CONSIDERATION OF DIAPHRAGM STIFFNESS IS REQUIRED. Let me explain what I mean. In a "flexible diaphragm" analysis, all diaphragms are considered simple spans from wall to wall. The forces to the walls come from a simple span reaction, which does not depend on the stiffness of the diaphragm (reactions are independent of EI in simple spans). In a "rigid diaphragm" analysis, the diaphragm is considered infinitely stiff, and the forces to the wall depend ONLY upon the stiffness of each WALL, and their relative spacing. The resulting forces to the walls are independent of the diaphragm in this case also. Taking the highest load for each wall from the two cases will cover all possible forces from any possible diaphragm system. Some walls will have a higher force under the flexible diaphragm analysis, and some walls will have a higher force under the rigid diaphragm analysis, and that is most likely why the plan checker does not want the flexible analysis thrown away. My previous posts pointed out that there still remain serious problems with determining the stiffness of plywood shear walls, so we are still left without a rational way to comply with what I am proposing. I will not repeat that stuff in this post. Mark Swingle, SE Oakland, CA These are my views and not necessarily those of my employer. "Swingle, Mark" wrote: > What is happening is that the professional community is only now catching up > to what has been in the code for over 30 years. The design examples you > cite are just the first step in that catch-up process, but it is not a > result of any new code provision. As I understand it, these new examples > simply perform both a rigid diaphragm and flexible diaphragm analysis, and > simply use the worst case for each, so no consideration of diaphragm > stiffness is required. For the flexible case this is simple, and is the way > it has been done typically in the past.
- Prev by Subject: Re: Effects of the New Code on Wood structures - good or bad?????
- Next by Subject: Re: Effects of the New Code on Wood structures - good or bad?????
- Previous by thread: Re: Effects of the New Code on Wood structures - good or bad?????
- Next by thread: Re: Effects of the New Code on Wood structures - good or bad?????