huangyhg

asd vs. lrfd, who decides?
i just bought the fifth edition of salmon/johnson/malhas "steel structures - design and behavior." this text book is focused on the lrfd method. in the preface, they state, "this modern philosophy of design [lrfd], discussed only briefly in one section of the second edition, is moving toward being the predominant approach to design."
there have been many posts to this forum about asd vs. lrfd. several people have commented in this forum that they were taught lrfd in school but that their engineering firm uses asd. it seems apparent that academia has made the decision that lrfd is the best method and therefore the only method to be used. the question is whether academia should be driving this train or the industry? there is a form of social engineering (pardon the pun) going on here if academia is making the decision for us as opposed to the code committees.
some have commented that, as far as the 13th edition of the steel manual goes, the results are pretty much the same regardless of which method you use. if so, then why the push for one method over the other in the academic world? since both methods are related to code compliance, perhaps academia shouldn't teach either one and leave the code issues to on-the-job training or offer a separate course that covers all the code aspects.
my own personal desire is for one method for all materials: steel, concrete, wood, masonry, etc. i don't really care which one it is, as long as it's consistent. but, in my opinion, the decision as to what system is used should be made by the industry, not the teachers.
aisc, an industry group, began the push for lrfd years ago. it is believed that structures designed with lrfd would be lighter than those designed with asd, and as such steel would have an advantage over other materials. the practitioners (engineers) have not all followed aisc's lead. i'm glad that aisc recognized this and put out a unified specification, the one found in the 13th edition manual. now you can use either way without having to rely on 20-year old technology.
i think using solely one method for all materials isn't likely. there are benefits to each method, and some materials are better suited for one than the other.
your local building code will dictate which you use.
there are so many of us "old" engineers - i am 56 - that never learned lrfd - that we just stick with asd - easier to use and understand.
i have "young" engineers that have trouble with lrfd - and they just got out of school!! parts of it just don't make sense.....
aashto is also pushing lrfd and i heard acpa is moving towards lrfd for concrete pipe design also.
vmirat,
your post sounded very familiar to me. i wrote a similar letter about 20 years ago to the institution of engineers australia about the then proposed as4100, steel structure code. no answer was received. academics have won.
hokie66,
so this is a world-wide phenomenon? i wonder if this translates to other fields, like the legal profession.
by the way, i don't suppose you're a vpi grad (hokie reference)?
yes, it is worldwide. i think the us is resisting a bit, like with the metric system. i am a hokie, class of 1966. there are a few of us hanging around on this site. you?
vmi class of 80 (hence the vmirat moniker).
my steel design course was just a brief overview of the process of using steel. although we were required to buy the aisc steel manual (blue edition), we had no clue what we were doing with it. our instructor told us what to use out of it. of course, that was all asd, so it wasn't an issue at the time. but my point is, our instructor really didn't focus on the code aspects of steel design. we could have done without it. heck, i didn't even know how to read a blueprint until i starting working, let alone understand the intracacies of codes.
of course young engineers have trouble with lrfd.... they have trouble with everything! that and they don't have engineers with years of experience in lrfd to explain to them why they are having trouble.
for what it's worth, i have always used both. i learned lrfd in school. worked under other engineers using mostly asd, but some lrfd. then when i became a lead, i ran my projects mostly in lrfd.
also, i'm not sure the push for lrfd was really related to cost as the two methods are relatively comparable in total project cost... at least for the industrial work that i did. instead, the basic argument that i heard was related to a more uniform factor of safety based on probabilty theory of load and failure and such. since you usually have a better idea of what your expected dead load is, then you can use a lower factor of safety for dead load.... et cetera. if brittle failure is dangerous then put a larger factor of safety on that type of failure.
that's the reason why i switched.... though i have to admit that it is really annoying to have to carry one set of load combinations for deflection and another one for design. that is the best argument i've heard for why asd is better.
vmirat,
i must be getting slow in my old age not to pick the meaning of your handle. after all, i am only a hokie. i was around in the days when the vpi-vmi game was the thanksgiving day classic. we got in a lot of trouble one year by kidnapping a couple of keydet rats before the game.
to date i have yet to have anyone explain to me clearly what the advantage is of using limit states design (or lrfd) over asd.
i would suggest that the same can be said for metric versus imperial units.

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