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RE: SEAOC Blue Book C805.3 Lateral Force Distribution[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: SEAOC Blue Book C805.3 Lateral Force Distribution
- From: "Bill Allen" <Bill(--nospam--at)AllenDesigns.com>
- Date: Tue, 17 Aug 1999 21:35:01 -0700
Not that I am supporting this (enveloping FDA and RDA) methodology, but it brought back memories to the "Good Old Days" when I used to know how to design a moment frame. Back then, there was only one kind of moment frame. Yeah, it was pretty ordinary. You could actually calculate and design the moment connection. Yeah, really. You shoulda been there. Anyway, this was also before FEM programs on every desktop, so I used to design the frame based on a point of inflection somewhere between 0.4 and 0.6 times the height of the frame. I would design the moment connection between the beam and column based on the point of inflection at 0.4 times the height of the frame and I would design the base and grade beam based on a point of inflection at 0.6 times the height of the frame. That was back when I was more conservative. What the heck. I didn't have to answer the phone with the contractor on the line. Of course, this is quite a bit different than enveloping FDA and RDA. I believe it's possible that the majority of foks proposing to do both FDA and RDA are folks who a.) don't do wood frame design for a living and/or b.) think they will avoid a lawsuit if they do every conceivable analysis. Don't get me wrong, if we have data and the technology to do a better design, I'm all for it. I also won't deny the science behind the rationale to perform RDA on a significant number of wood framed structures, particularly custom homes. But, there has to be some common sense (engineering judgement?) included. First of all, LOTS of custom homes have been designed using FDA that have performed wonderfully during significant seismic events. Why make life complicated for no apparent benefit? Sure, there are some problem building configurations that need to be specifically addressed, but we can do that, can't we? Getting past the "if it's not broke, don't fix it" arguement, another problem is the paradigm. Yeah, we are really "high tech" and precise when we calculate the deflection of an unblocked diaphragm, aren't we? How about blocked just at the 1/4 ends? As Chuck Utzman (and others) have pointed out, we don't really have a good handle on the four components of a shear wall deflection calculation, do we? And then there's the reality of ignoring all that non-structural stuff that ties a house together. >From a pure science point of view, I can understand enveloping FDA and RDA. The problem is what we do is not pure science. It's called the Business of Engineering. Apparently, some folks think we make a lot of money designing wood framed structures. I guess some might say I have the "old dog" syndrome and don't like change. Maybe so, but I still haven't gotten over the 1991 NDS where the allowable stress for a 2x6 is different than a 2x8. Gimme a break. How many engineering hours has THAT cost and how much benefit have we received as a result? I am intentionally attemping not to blame any individual or organization for the mess we are now in. That wouldn't do anyone any good. I would just piss some people off, e-mail would just get more caustic and I would end up unsubscribing again. To what gain? My goal today is to try to figure out the best way to use what we have, cover my ass the best I can and try to make a buck in between. Is that an unrealistic goal? Bill Allen, S.E. ALLEN DESIGNS Laguna Niguel, CA > -----Original Message----- > From: SDGSE(--nospam--at)aol.com [mailto:SDGSE(--nospam--at)aol.com] > Sent: Tuesday, August 17, 1999 8:57 PM > To: seaint(--nospam--at)seaint.org > Subject: Re: SEAOC Blue Book C805.3 Lateral Force Distribution > <snip> >Since we are at it, let's envelope our steel beam > designs for > fixed and simple span conditions regardless, so we cover any > possibility, and > forget the economics. <snip> > > Regards, > > Oshin Tosounian, S.E.
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