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Re: Why LRFD vs ASD (was: We're Not Getting Older, We're Getting DUMBER)

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On Jan 26, 2006, at 11:02 AM, Paul Ransom wrote:

more consistent "factor of safety" in ALL design checks (e.g. ASD is
not consistent for beam vs. connection
That's only half an answer. What have been the effects? Fewer bodies? Lower costs? Safer construction.

And I guess my experience with connections has been that connection analysis is far less accurate than even analysis of plastic hinge formation or instability. Arguably the consequences of connection failure seem to be more of a safety threat.

Judging from the way the topic has been kicked around on this list, and from the moment connection failures during Northridge) I claim connections need more of a factor of safety.

But that's only a for-instance to answer your for-instance. The real question is whether limit analysis has solved a safety issue or an economic problem.

However, the "law" is interpreted to permit a designer to meet ASD 9th minimum, in some cases, to the detriment of public safety.
Now we're down to it. Does the 9th edition truly represent a safety issue? If so are all buildings designed to the 9th edition present a significant hazard?

I'm with you on the development issue: Codes should be improved as significant issues come up. But I daresay that ASD Code development only slowed because LRFD was going to be the Next Big Thing. It isn't of course. Limit analysis was written into all the old steel codes and into the nuclear codes back in the 70's. it's been around for dogs years. And damn useful for special cases like impact. Makes me wonder why the change came all of a sudden.
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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