To: "SEAOC Newsletter" <seaint(--nospam--at)seaint.org>
Subject: Re: ASD vs. LRFD
From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
Date: Sun, 13 Jun 99 13:30:36 -0500
>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)