To: "INTERNET:seaint(--nospam--at)seaint.org" <seaint(--nospam--at)seaint.org>
Subject: Re: ASD vs. LRFD
From: Mark Gilligan <MarkKGilligan(--nospam--at)compuserve.com>
Date: Sat, 12 Jun 1999 22:10:14 -0400
I find myself in an interesting position on the use of ASD vs LRFD.
During school I was exposed to both concrete WSD and USD with an emphasis
on USD. At my first job I pushed enough and got permission to design using
USD. In that era there were many engineers who did not want to change, one
of whom was the senior partner of the firm who saw USD as scam. Even so
the transition to USD was a lot faster then. One way that they made the
transition faster was that ACI came out with design aids that were
formulated the same was as familiar WSD design aids.
The advantages in the amount of steel and concrete saved by USD was clear.
In addition when you were modifying an existing building you could
typically gain some extra capacity by use of USD.
Currently I find myself in a position of prefering ASD. It may be
partially familiarity but I believe that the extra complexity is not
justified in most situations. I have no problem with LRFD when justified.
I have attended some AISC seminars on LRFD but I did not find them very
useful and it wasn't clear that the savings were across the board.
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.
The problem is that the use of LRFD has become a religious issue with those
in academia and the steel industry on one side and most other engineers on
the other. I realize that what I will say next is overstated but much of
the retoric implies that THEY are trying to force us to use LRFD because it
is the only CORRECT method. This is not productive.
I suggest that what should be done is:
- AISC continue to develop in parallel ASD and LRFD.
- Schools should teach both ASD and LRFD.
- Engineers use the method that is most benificial for the particular
- The steel industry should focus on showing us why it is advantagous to
Much of engineering is about making pragmatic decisions in order to get
something built within the constraints of making a profit and keeping a
AISC which is controlled by the steel industry, has not helped their
position by threatening to stop publishing the ASD code.
>From the point of view of the steel industry the question is does the
continued use of ASD result in a failure to sell steel becuse concrete
structures are more competative? I would suggest that this is not the case
and where this is so, they should focus on showing the engineer how to
improve his profit by designing with steel.
Mark Gilligan SE
" Paul Crocker" wrote:
>The "young" guys use LRFD because that is what is taught in the schools.
Schools do not teach ASD. I have heard of many newly minted engineers
told to throw away their LRFD books when they start work, because their
supervising engineer doesn't want to deal with it or check over calcs done
that way. That's certainly understandable, because after 10 or 20 years of
using any system, it gets really easy, so why slow yourself down? Without
ASD being formally taught, or supported in updated steel manuals, I have a
hard time seeing how it will exist in another 20 years. A few UBC issues
down the road, will they really want to reference a decades old (by then)
ASD manual when there will be fresh new LRFD manuals around? Eventually,
the engineers who have been getting out of school lately will ascend to the
corner office, and they won't care whether ASD or LRFD are used, since they
will have learned one in school and one in the work place. When the new
guys under them, fresh from schools of the future, want to work is LRFD, no
one will stop them, and ASD will be dead, even if the UBC/IBC hasn't killed
it some time before then. That is why the future is LRFD.