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Re: ASD vs. LRFD

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> From: "Bohm, Gabriel" <GBohm(--nospam--at)TechnipUSA.com>

> About a year ago I was in a structural engineering seminar in the Los
> Angeles area. At one point, the gentleman running the show asked: "How many
> of you are familiar with ASD?"  Everyone was, of course. His next question
> (And how many of you are regular LRFD users?) generated no response at all.
> 
> The future is undoubtedly LRFD. AISC hardly even mentions ASD, but for now
> it seems that, in terms of LRFD implementation, the structural engineering
> community is quite a few steps behind. Is this assertion correct? I think it
> would be of interest to all of us to find out how widespread the use of LRFD
> really is. 

The G8 (top 8 global economies) is metric and limit states except the
U.S. The U.S. steel design profession is isolating itself if they are
not coming to grips with the international cooperation of the standards
development agencies and associations like AISC. As AISC becomes more
international in scope, their publications will follow and, eventually,
the only relevent design evolution will not include ASD.

> From: "Fountain Conner" <fconner(--nospam--at)pcola.gulf.net>

> AISC likes LRFD; I don't.  No one has yet convinced me of an advantage.

> I will use LRFD when either:  1.  The codes demand it; 2.  The client
> demands it; or 3.  I recognize some advantage in time saving (my time) or
> substantial savings of material (the owner's money).

This indicates a lack of understanding of the philosophical differences
between the two design approaches. This is very common and reflects the
lack of education penetration into the operating profession. It is not
an issue of advantage to the designer.

To complicate matters, there is a movement towards the next step in risk
based design philosophy - worldwide uniform risk-based design factors
that account for local variations in material/load and occupancy
expectations. Excuse me if this is slightly misrepresented since its new
to me, too.

> From: "Dan Vines" <dan(--nospam--at)willettengineering.com>

> There have been rumors (some substantiated, some not) that there will not be
> a 10th edition of the ASD manual.   AISC is committed to LRFD, those who
> feel that it's too complicated and unecessary be damned.

> Personally, I took LRFD as an undergrad, but was taught (largely by myself)
> to use ASD "on the job."  I would be hard pressed right now to design even a
> simple beam per LRFD.  In my (admittedly limited) experience, LRFD is only
> worth the trouble in large structures that are highly repetitive.

Can you imagine the pressure exerted by an unconvinced profession to
bring out that next edition ....

> From: "Ritter, Mike" <mritter(--nospam--at)lgt.lg.com>
> 
> The engineers around here (Tennessee) don't use LRFD either (unless
> forced to do so).  My company does work all over the world and I've used
> it twice.  I've been to numerous AISC sponsored seminars where the
> presenter laughed and made jokes (along with the audience) about LRFD.
> I've been to other AISC sponsored seminars where the presenter was very
> serious about LRFD and kept making comments about never updating the 9th
> Edition Steel Manual.  These "serious" guys appear to be the young ones
> and I wonder if they've ever been responsible for designing a building.

This shows how the stereotypes are stacking up. At the AISC NASCC in
Toronto last month, there were a lot of white-haired presenters touting
the benefits of LRFD, despite the wise-cracks. You would recognize most
of the names.

You make two significant statements: 1) your company works all over the
world and 2) you have used LRFD twice. So you can possibly shed some
light on practices around the world. For which locations have you
provided those 2 LRFD designs and when? Secondly, is there any
differences in expectation between the so-called 1st, 2nd and 3rd world
economies in their acceptance of limit states vs. ASD design?

International work in developing countries is frequently spec'd to a US
model code when the owner is a US based multinational and comfortable
with their home base practices. Frequently, this is better than might be
locally mandated, anyway. This is a form of design risk management and
costs more than than they would be legally required to spend for the
capital project.

> From: Paul Crocker <PaulC(--nospam--at)ckcps.com>

> 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 being

> 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.

It will also be pushed by a more sophisticated consumer, whether that be
public or private. The private sector is becoming increasingly more
concerned about quality of engineering issues - been to any multi-level
shopping malls (read trampoline) lately?

> From: "Bill Polhemus" <polhemus(--nospam--at)insync.net>

> Once you get over a small learning curve, LRFD is actually easier to use,
> particularly if you are accustomed to strength design of concrete. All the
> bogus "stress checks" of ASD are just so much hot air anyway.

There is no basis for comparison of stress ratios between two paragraphs
let alone two chapters in ASD, except as specifically prescribed for
interactions. Last time I checked, the relationship between independent
orthogonal stresses was not linear.

> From: RoyLevy(--nospam--at)aol.com

> Many years ago my mentor, the late Professor Robert B.B. Moorman mentioned
> "Mathematical refinement based upon a foundation of unsupported guesses"
> Was he anticpating LRFD?

Or commenting on existing practices ... LRFD is not mathematically more
complex than ASD but it does not hide the warts the way that ASD does.

> From: "Brian K. Smith" <smitheng(--nospam--at)dos.net>

> What does ASD stand for Ancient Steel Design?????

ROTFL!!!

> Brian K. Smith, P.E. (I don't do ASD)

Damn, I'll do just about anything that somebody wants, if they pay me.
ASD, WSD, LSD, LRFD, BS, GBJ, AIJ, AS, EC, SN&P, ...

-- 
Paul Ransom, P. Eng.
Civil/Structural/Project
Burlington, Ontario, Canada
<ad026(--nospam--at)hwcn.org> <http://www.hwcn.org/~ad026/civil.html>