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Re: We're Not Getting Older, We're Getting DUMBER

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Christopher,

You misunderstood my reference to "better".  I am 100% in agreement with
you and Charlie that for all intents and purposes the building doesn't
know or care which method you use to design it.  You could design it by
Grandma's secret recipe/method (assuming that Grandma's method is a
reasonable good method that reasonably approximates real life behaviour)
and the building would not know or care.

The caveat is that this assumes that both methods (ASD and LRFD) are
nominally equal and have both been kept up to date with the same
"advances" (i.e. revisions/changes) in knowledge.  That has NOT been the
case with ASD steel design in buildings.  The AISC spec has not been
updated since 1989 for all intents and purposes...until now.  So, the
point is that the currently in place ASD (1989 spec) is rather dated
relative to the LRFD specs...and the new 2005 spec, which does finally
update ASD.

And my point is that I am sure that there will be plenty of engineers that
will continue to want to use the 1989 ASD spec rather then update to the
2005 spec.  And that has very little to do with the ASD/LRFD debate cause
the 2005 spec has both.  It will more to do with the 1989 ASD spec will be
more comfortable and likely less complicated than the ASD from the 2005
spec and people like to use what is easy and comfortable, even if there is
better/newer information out there.

As to LRFD, where I have found it to be "better" in for seismic design.
Seismic design in its very nature is done a limit state/strength level
(i.e. nominal/ultimate), so LRFD/Strength design is easier for me to "see"
when doing seismic design.

Beyond that I think that Eric gave a couple of good reasons why LRFD is
"better" than ASD.  But in reality, I could care less which a person
chooses to use as long are both are nominally equal in terms of
"technilogical advances"...and that is NOT the case in concrete design and
has not been the case until NOW in steel design.

Regards,

Scott
Adrian, MI


On Wed, 25 Jan 2006, Christopher Wright wrote:

> On Jan 25, 2006, at 11:17 AM, Scott Maxwell wrote:
>
> > Point is that I agree that there are quite a few engineers that are
> > more than happy to bury their head in the sand and conintue to use
> > what they are used to using even though there is new and typically
> > better knowledge (or codes) out there.
> I swore I'd stay out of this, but I can't help myself. This thread is
> only half a discussion--a lot of people saying 'newer and better' but
> no one saying what's improved. Could someone please tell me what's the
> improvement with limit design? Are fewer buildings collapsing than
> before? Is the owner's cost noticeably smaller? Are structural design
> fees going up? Or down? What's been gained by changing our jargon to
> include 'limit state?' So far we know that academia loves it and so
> does Canada.  New graduates seem to like it but they're taught nothing
> else, which isn't much of a reason. Anyone know why they teach it
> instead of ASD? Can anyone cite any examples of hazards avoided? Are
> buildings built under ASD design rules being scrapped because they're
> dangerous or unsatisfactory? Any correlation  between seismic
> resistance and the code rules? It is suddenly easier to determine
> loading or characterize plastic collapse?
>
> As an old fart who's gone from slide rule design of pressure vessels in
> the 60's to FEA I've seen some real Code changes and the improvements
> they led to. The most profound was a realistic consideration of
> fracture toughness in design and the second set out an analysis-based
> design approach which allowed lower design margins in return for
> greater attention to secondary stress and fatigue. Both of these
> embodied significant performance and safety enhancement that everyone
> could point to. And like LRFD, they still haven't been universally
> embraced or understood, even as Code provisions are being regularly
> upgraded. So I think I understand the process and the reasoning as well
> as anyone. Let's have it--why is LRFD an improvement? Will there be
> fewer bodies or do people like it because some academic told them to
> like it?
>
> I've said a hundred times on this list that I don't do buildings, so
> maybe I've misunderstood something. In the years we've discussed the
> topic I haven't gotten much of an explanation of why LRFD is
> better--maybe this time it's different. It's been repeated a hundred
> times on this list: steel doesn't care what the design rules are--it
> always behaves like steel. Charlie Carter pointed that out a couple of
> days ago, and he's right, but there's still this undercurrent in this
> whole thread of shifting paradigms and 'better' designs, along with
> snickering about old farts who who stick with what works, just because
> it's what has worked, tee-hee.
>
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw(--nospam--at)skypoint.com   | this distance" (last words of Gen.
> .......................................| John Sedgwick, Spotsylvania
> 1864)
> http://www.skypoint.com/~chrisw/
>
>
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