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Re: ASD vs. LRFD

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>I wonder if part of the reason that ASD has retained its popularity is that
>an elastic analysis is more appropriate for a steel structure than for a
>concrete structure under service loads.
Also aluminum or anything else such as fatigue where service loading 
governs. Lots of structures around with a high percentage of live and 
cyclic loading and others that'll likely never see an ultimate load. I 
doubt many owners would be much taken with the argument that LFRD may 
protect them against some very unlikely event which may occur at some 
unspecified future date, but we really don't much care whether 
connections get squirrelly after a few years of gust loading or thermal 
cycling. (Giving credit where it's due, I think the testing programs I've 
heard about on this list are laudable, but only a first step. There's a 
big difference between the strength of new construction and the same 
detail after 10 years of service and environmental exposure.)

And all the statistical arm-waving with 50 year recurrences and 
confidence levels leaves me equally unimpressed--sounds like a claim to 
know things we don't complete with excuses if things don't work out. 
(Yeah, I know, it's the best we've got. We do the same thing with nuke 
plants, and so did the people who did the Challenger.) "Mathematical 
refinement based upon a foundation of unsupported guesses" (great 
summary, Roy) pretty much wraps it up. 

Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw