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Re: effective length factor for sway moment frames? K for frames wit h partially restrained connections?
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- Subject: Re: effective length factor for sway moment frames? K for frames wit h partially restrained connections?
- From: "Scott A. Dunham, PE" <sadunham(--nospam--at)gte.net>
- Date: Fri, 30 Mar 2001 10:56:25 -0600
Being from the old school (I did my homework using a slide rule back in college), I guess I fail to appreciate that FEA (finite element analysis, I assume) as the "only" way to get the correct value. Bearing in mind that most of the loads that we apply to the structures we design, and that the true material properties we use are at best guesses, what's the big deal about getting the "exact" number to arrive at a less that exact solution to the problem at hand. Having spent the bulk of my career working in the production side rather that the design side of this business, I can tell you for a fact that there are a lot of Engineers that can't see the forest for the trees. Sorry for the sermon, but I think Mark has a valid point. We as Engineers need to spend a little more time getting it right rather than getting it perfect. Scott A. Dunham, PE Dunham Engineering Services Dothan, AL 334-678-6948 ----- Original Message ----- From: "Mark Gilligan" <MarkKGilligan(--nospam--at)compuserve.com> To: <seaint(--nospam--at)seaint.org> Sent: Friday, March 30, 2001 10:00 AM Subject: RE: effective length factor for sway moment frames? K for frames wit h partially restrained connections? The author of the following response implies that because we have computer access we should compute the K factor using the computer. I would like to suggest that such practices often take longer than quicker but less exact methods. On numerous ocassions I have seen engineers spend considerable time creating spread sheets to perform a calculation that could be done quicker by hand. Given limited design fees and a limited schedule how exact should our calculations be? Similarly how much effort should we spend to reduce construction costs when the fee is limited? Have computers in many instances actually increased our work load? >>>Theoretical results satisfy all the governing conditions. The theoretical K factor is theoretical exact. They are more reliable than the ones from alignment charts. Those alignment charts were introduced before computer. For the time being, almost every structural engineer has a computer for analysis. Why should we keep applying those inaccurate charts? When computers were not available for most structural engineers, engineers used some approximate methods, for example, two cycles, to analyze frame structures. No one uses two cycles since computer is everywhere. All the results are theoretically analyzed on computers. FEA of K factors is a must.<<< Mark Gilligan
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