To: "SEAOC Newsletter" <seaint(--nospam--at)seaint.org>
Subject: Re: Who's using ASD or LRFD?
From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
Date: Sat, 29 Jan 00 13:46:50 -0600
>They are not pushing LRFD. AISC has given
>us choices. It is for us to progress (LRFD) or stay behind (ASD).
Truth to tell the AISC seems to have given us the choice to do play with
their rules or piss off. Like Sgt. Dagineau in Beau Geste--'March or die!'
The interesting thing is that LRFD is enough like ASD (except for
provisions for plastic hinging in beams) so that it's almost like a
distinction without a difference. The AISC publication 'Essentials of
LRFD' (a good read) gives the impression that they've simply jacked up
design loads, jacked up the allowable ASD stresses in the same
proportion. To wit:
The LRFD column load tables are the old ASD column loads increased by a
factor of 1/0.7.
The compression element stability requirements (Table B-1) are the same.
The design philosophy for tension members is the same for LRFD and ASD.'
(Quote from 'Essentials of LRFD')
The Cb factor is different, but it looks to be applied in the same way.
Connections are still expected to remain elastic, so there's not much
I'm left with the very strong impression that this isn't so much new
methodology as the old methodology tarted up with a new vocabulary. Seems
like we engineers do that a lot.
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)