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ASD vs. LRFD, Who Decides?
5

ASD vs. LRFD, Who Decides?

ASD vs. LRFD, Who Decides?

(OP)
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.

RE: ASD vs. LRFD, Who Decides?

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.

RE: ASD vs. LRFD, Who Decides?

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.....

RE: ASD vs. LRFD, Who Decides?

AASHTO is also pushing LRFD and I heard ACPA is moving towards LRFD for concrete pipe design also.

RE: ASD vs. LRFD, Who Decides?

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.

RE: ASD vs. LRFD, Who Decides?

(OP)
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)?

RE: ASD vs. LRFD, Who Decides?

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?

RE: ASD vs. LRFD, Who Decides?

(OP)
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.

RE: ASD vs. LRFD, Who Decides?

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.  

RE: ASD vs. LRFD, Who Decides?

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.

RE: ASD vs. LRFD, Who Decides?

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.

RE: ASD vs. LRFD, Who Decides?

2
I feel your pain because I remember how much gnashing of teeth I did back when I had to lose my SBC and start using the IBC2000.  I cussed at it for probably 2 years and my errors in applying it actually did cause problems on at least one job.

As for ASD89 vs LRFD, I really don't see the point, though.  It is HIGHLY debatable that the 89 Manual is better organized and easier to use than any of the LRFD or the unified Manual.  Earlier manuals were even worse.

For example, depending on web slenderness, one could end up all over the place in the 89 Spec. trying to compute the allowable shear and moment.  In the 2005 Spec., these areas are extremely well organized in Ch. F and G.  Same for columns.  Depending on slenderness, one can end up digging through appendices for Q factors and such.  Ch. E is very well organized and has everything one could need for a compression member.

There's also the fact that the newer specifications have provisions for so many more cases than did the 89 Spec.  For example, if you have an I-shape with unequal flanges, you end up beating a Ch. F equation to fit the situation even though it wasn't derived for that case.  The 2005 Spec. has Section F4 which is directly applicable and leaves little to wonder about.

To me, the biggest enhancement going from ASD89 to LRFD is the way equations are presented.  The old ASD equations embed so many different constants into one constant that it is impossible to know what's really going on in the equation.  The ASD89 Ch. F Fb's are great examples of this.  Check out the Salmon & Johnson derivation for those constants--there are pages of derivations IIRC!  The designer has no prayer of looking at those equations and having a clue where they came from.  In the LRFD specifications, this is far less of a problem because the variables are still broken out in most cases.  THe downside is that equations are longer, but ever designer has a computer nowadays anyway.

As for whether academia or industry drives this stuff, I'd say it's both, but admit that academia plays a big role.  (Full disclosure: I'm a professor who teaches the steel classes at a university, but I designed buildings for about 10 years.)  

Like it or not, universities force professors to crank out research, and a lot of it, or they're fired in the form of not getting tenure.  They also don't get paid for 3 months out of the year if they don't bring in enough to fund summer pay.  I'm actually more of a teacher than researcher, so if I had it my way I would just teach and then do research only when there was an actual problem that could be of immediate practical use to industry.  Unfortunately, I would not get tenure if I did this.

If any of you guys don't like the way professors have to crank out papers and more research, then I'd suggest voicing your opinions to the universities.  The university would point out that their tax dollar budgets are shrinking and that money doesn't grown on trees, though.

RE: ASD vs. LRFD, Who Decides?

(OP)
hokie66,

I think we both had our share of cadet (or Keydet) antics!

Being a '66 grad, I'm assuming you've had a considerable amount of engineering experience.  What was your educational experience like, with respect to steel design?  Was it mostly theoretical or did they cover code-related issues such as safety factors (I'm not sure what the steel code was in '66)?  How would you compare your educational experience with what their teaching today?  Specifically, is it necessary to teach a code system?

RE: ASD vs. LRFD, Who Decides?

(OP)
271828,
Thanks for your candor.  I appreciate hearing from the academic side on this.  I would imagine that there are many professors on code committees, so I can see how this can become a circular argument.  What latitude do you have in what/how you teach steel design?  Would you be run out on a rail if you taught ASD or even no code system at all?

RE: ASD vs. LRFD, Who Decides?

Yes, I'd say there are a fair number of professors on the Spec. Committee.

Lower level classes have very specific topics that must be taught.  My Steel I class is senior level, so I have a lot more leeway.  I'm sure the industry advisors would complain if their students came out of school knowing ASD89 instead of LRFD/ASD2005, but I could choose to teach ASD2005.  However, I probably wouldn't because I suspect that the ASD part of the Spec. will evaporate over the next 2-3 manuals so there's no sense getting used to omega instead of phi.  I wouldn't be doing anybody any favors by teaching them something that's likely to become vapor.  

As for teaching "codelessly"(? LOL), I'm sure that the industry advisors would complain about that because their new guys would be even less useful (LOL again) than they are now.  The other constraint is the FE exam.  Our guys have to be able to answer the steel questions.

In the advanced course, I have complete freedom to do whatever seems most beneficial to the students, simply because this course isn't a prereq for any other class.  I try to focus on behavior because those topics are timeless.  For example, say I teach a prescriptive part of hte Spec., those provisions might change, making that part of the class worthless.  (Other profs teach enough worthless stuff!)  If I teach with an emphasis on behavior, then less of that will happen to my guys throughout their careers.  In a way, this class is closer to being "codeless" than the first class.  I try to teach both as best that I can, though.

This reminds me of anther common industry question: why don't we teach them how to read drawings, develop sections, etc.?  I used to ask these questions.  The reason is that there is so much variability from office to office that a class like that would likely be considered worthless to many engineers.  Also, the way things are done changes all the time.  Take BIM for example.  Teaching guys to put drawings together might be worthless in 10 years.

Hey, hello from another Hokie!  I have 2 pals from VMI.  I really respect the toughness of anybody who survived their engineering program along with the rest of the VMI experience.  I never would've made it.  VT was hard enough without the military activities.

RE: ASD vs. LRFD, Who Decides?

vmirat and 271828,

Nice to have a conversation with fellow Virginians, at least from a uni standpoint.  To answer vmirat, my steel design courses at VaTech were woeful in hindsight.  I had a steep learning curve on the job.  I hope and trust that they do a much better job today.  It's just the luck of the draw as to which professor you get.  On the other hand, my other structural courses were good, and I had Prof Richard Barker for concrete, and he was tops.  It is inevitable that Codes will be included in coursework, but I think that there is too much emphasis on the current code, as it will always change.

By the way, when I was there, the Corps at Tech was bigger than the VMI Corps, and compulsory for 2 years, so this country boy had a big shock the first few weeks, both with the Corps and with the coursework.

Vmirat, what type work do you do?  The stereotype of a VMI engineer used to be that they either worked for the Army or the Virginia Department of Highways.

RE: ASD vs. LRFD, Who Decides?

In 1986, the VT steel design curriculum changed a lot when Dr. Murray came there.  Last time I checked, there were 3 main steel design courses, a course in cold-formed steel, and an entire course in connection design.  He just retired, so who knows what'll happen with those courses as time goes on.

I also had Dr. Barker years ago.  I thought he did a good job.  I bet you had Don Garst too, right?

RE: ASD vs. LRFD, Who Decides?

Don was more of a contemporary.  Bob Heterick taught some of the general structural courses, then he went to head up the computing center, I think.  I understand he recently passed on.  Yes, Dr Murray certainly helped the VT reputation.

RE: ASD vs. LRFD, Who Decides?

Unlike reinforced concrete design, which is largely developed under experiment and controlled testing, the elastic/plastic theories/behaviors of metals were well estabilished and verified for years. I am not familiar with LRFD, but judged from USD for RC, I couldn't resist to post the question: would those factors causing us to lose sight on foundamentals, especially when we need to link the real world phenomenons with the theories behind. If it is the case, we will be much more practical, efficient, with a lesser brain. However, if the change (ASD-LRFD) is similar to the change from slide-rule to hand-held calculator, then what is the difference.   

RE: ASD vs. LRFD, Who Decides?

kslee1000, I don't understand where you're going with your post.

"would those factors causing us to lose sight on foundamentals, especially when we need to link the real world phenomenons with the theories behind."

You're not trying to say that the newer steel specifications make it easier to lose sight of the fundamentals, are you?  If so, then I disagree--see the 5th paragraph of my first post.  I think the older specifications did a good job at hiding the physical phenomena behind the equations.

RE: ASD vs. LRFD, Who Decides?

271828:

I don't "disagree", nor I "agree". You have read my post correctly. If I am still in practice today, there will be no doubt that I will stay with the trend, but be glad to have the knowledge of something that is fading (similar to the time from WSD to USD for RC).

While we are lucky to have walked from A to B, for the fellows start directly from B, would they be missing something that is originated from A? I won't make comment on something I don't have full knowledge on, but to openly discuss with reservation of doubts. Remember plastic design method?     

  

RE: ASD vs. LRFD, Who Decides?

(OP)
hokie66,

I'm a civil/structural engineer with DoD.  I served six years active duty and took a job with the government.  It's been a very interesting career, going places most people would never go.

I agree that the issue of codes in the classroom are inevitible, but I would argue that they belong in a class by themselves, and discussed in a broader sense versus biasing to one method or the other.  As many posters to this site have stated, the use of ASD for steel is still very much alive and forcing LRFD-only on future engineers does a dis-service to them.  It's kind of like the metric system.  My structures class at VMI was taught purely in metric.  In my opinion, it's not up to academia to determine how the industry works, their just suppose to prepare us for it.

RE: ASD vs. LRFD, Who Decides?

My steel design class was taught in ASD.  The next year they switched over to LRFD, and I was a teaching assistant, so I had to learn it too--on my own, since I wasn't a student in the class.  

IT WASN'T THAT BIG A DEAL.

Hg

Eng-Tips policies:  FAQ731-376: Eng-Tips.com Forum Policies

RE: ASD vs. LRFD, Who Decides?

...but I'd argue that the current steel design curriculum does a better job than if it was modified as you suggest.

I believe that ASD will evaporate completely in the next few years.  Our job, right now, is to prepare engineers for the long haul, not the next 2 or 7 years.

There is a very good reason why there are not two steel classes, one focusing on behavior and one on codes: nobody would take two undergrad classes.  If we took that approach, then everybody would take the code-oriented class because the student would be thinkig short-term.  Now we have a bunch of technicians who don't know squat about steel behavior.

Sorry, but in my opinion, the two steel design classes I'm familiar with (they're all about the same at the major universities, I *think*) are about as optimized as they can get in the sense of teaching the max amount of behavior along with enough Spec. provisions so that the students are as useful as a new guy can be.

I've actually found this entire subject to be pretty funny over the last couple of years.  This stuff goes both ways.  Professors who've never designed (a crime in my opinion) might fall into the trap of thinking they know how designers operate.  Similarly, when I retired from design to be a teacher, I thought I knew it all about how teachers should be doing everything.  I see that every time a thread like this comes up around here.  The thing that goes both ways is: "it's a lot harder than it looks" LOL.

RE: ASD vs. LRFD, Who Decides?

27128:  Perhaps you have it backward?  You teach students one way, and they have to learn a second way at some point in their career.  If they learn ASD now, they'll be prepared for the offices that use ASD.  Ten years from now, if ASD is gone and LRFD is the norm, they're in a much better position to pick up a new method.  The alternative is teach them something they won't use now (LRFD), forcing them to learn another method (ASD) right out of college, when they have little experience.

Of course, if they go to an office that uses LRFD, they're out of luck.

I would prefer to see the universities teach both methods.  Light gage steel design is the only class I had where they taught us both.  Now with the 13th edition, we do have parallel equations and methodologies, so this should be an attainable goal.

It will be interesting to see if you're right about ASD dying in ten years.  The biggest disadvantage in my mind, which has been mentioned in this thread and others, is having to run both cases anyway for serviceability.  Sure, you can provide a more reliable factor of safety (abstract as that is), and you might save a few pounds on a beam here and there.  In practice, who's desigining that close?  Would not the vast majority of designs come out the same regardless of the method used?

RE: ASD vs. LRFD, Who Decides?

Minor correction to above post: you said "next few years," not "10 years."

RE: ASD vs. LRFD, Who Decides?

The universities should also teach the 'three legged stool' where you spend a ton of design time on joint geometry, web crippling and code check, but liability and lack of client interest keeps you in the office after your plans go out for rubber-stamp code approval, then off into the field, and later you read in the young inspector's notes that your slip critical joints were 'hand tight' so 'no problem'; the steel delivered to the site 'appears to be Chinese origin', and the welder wasn't certified for those full-pens, but don't worry, he scarfed the inclusions out and did a heavy cover pass on the second try to make up for the heat stress warpage. % )
That's why ASD makes more sense, than saving on steel weight.

RE: ASD vs. LRFD, Who Decides?

2
ACCURATE SAFETY FACTOR?????!!!!???!?!?!

In what universe?

Unless we have very specific design information from a manufacturer for a specific loading, we can never have an accurate safety factor because we cannot accurately determine loading!  Even dead load is estimated for most design purposes, usually well over-estimated. Live load... forget about it!  Accuracy is a misleading word to use. Accuracy depends on quality information on which to base a design.  Since we cannot accurately determine the loads, we cannot accurately determine a safety factor.  Therefore the arguement that LRFD produces a more accurate safety factor is moot.  In fact it is laughable; something that could only be debated in the world of academia.  Also, if you are designing to a gnats behind, you are doing a disservice to everyone. There is fat built into every design... I hope.

271828,
If you are correct in that the ASD spec will disappear I will make a prediction.  If the ASD code disappears, no engineers will use LRFD. The engineering community will use the 89 green book or the 13th Edition ASD. The engineers will complain to AISC until AISC reinstates ASD... again.

If AISC removes ASD in the future, it will only go to prove my theory that intelligence and foolishness are often mutually exclusive.  (BTW 271828 that was not directed at you.)

RE: ASD vs. LRFD, Who Decides?

Bliman,
Right on! Not only have most professors never designed, they've never been to a jobsite. Even with inspectors there, the structure will not be built as designed. Put fat into it! Going onto a jobsite will put the fear of God in you.

RE: ASD vs. LRFD, Who Decides?

ASD in Steel design is dead all ready.  In you look in the AISC 360 2005 spec or 13th edition black book, and find the definiton of ASD; it will not say Allowable Stress Design. It will say Allowable Strength Design.

There is not one mention of Fb or Fv in that book. There is no 0.66Fy.

The code has switched to only LRFD; there is not two sets of equations, just two different sets of safety factors.

Just go to page 2-7 in the Black Book and they will tell you that there is no allowable stress design just limit state checks both use the same principles.

So you can use either. I mean the spec itself rarely refers to ASD or LRFD except in the beginning of the chapters where they list the safety or phi-factors.

For example look in chapter E of the spec. They only mention safety factors in one section E1, and no where else. Equations are the same for LRFD and ASD.

  

RE: ASD vs. LRFD, Who Decides?

ash060, there is no difference between old ASD and new ASD, even if AISC says, "but the S is different."  They are the same, merely updated to reflect what we know today.

They don't say Fb = 0.66 Fy.  They say Mn = Fy Z, and omega = 1.67.  Z is about 1.1 S, and 1/1.67 = 0.6, so Z / omega is the same as the old "0.66 S".  An algebraic rearranging of equations does not constitute a new design method.

RE: ASD vs. LRFD, Who Decides?

No mechanics has not changed but the old method calculated with stress the new method uses forces.

I can't take an applied moment to a beam and divide it by "Z" and get the stress at the extreme fiber. I have to divide by "S" to get the stress which I compare to Fb. In the plastic case I know the stress right away, it is Fy.

The process is different. Allowable stress compares stresses, and allowable strength compares forces.

Z is not new. We have know about inelastic behavior before we started writing steel specs.

Testing and mechanics helps make specs and testing is all most always done up to ultimate. I mean they don't load the beam a little bit and stop, they load it until it breaks.  

RE: ASD vs. LRFD, Who Decides?

vincentpa, the term "accurate safety factor" isn't a very proper phrase to use.  

It sort of misses the point of LRFD.  LRFD doesn't claim to have "accurate" safety factors....just more rational ones.

What LRFD does do is look at the different loads (dead, live, etc.) and attempts to weigh their variability in real life....basically what you then state emphatically when you say "...dead load is estimated for most design purposes, usually well over-estimated. Live load... forget about it"

You basically are making the case FOR LRFD by stating the fact that some loads are more understood than others.  ASD doesn't even address this.

There have been measurements of materials over the years where we do have a pretty good understanding of what a structure's dead load is as well as its variability.  

As for live loads, there have been studies over the years that have attempted to pin down various live load values in actuality (in place on a floor) and also attempts at measuring LL variability (do a search for Bruce Ellingwood as he has done a lot of research in reliability over the years).

I think you have a good point in that live loads are pretty loosey-goosey in real terms.  But I don't agree with you when you state all that and then imply that ASD is better....or just as good...or we are foolish to use LRFD.

LRFD provides a similar level of safety but also takes into account live load uncertainty.

I grew up on ASD in school and used it for the first 12 years or so of my work experience.  I learned LRFD on my own in 1993.  So I think I'm one of those engineers you suggest won't use LRFD if ASD goes away.  I do use LRFD and actually prefer it now.

I would second the opinion given above by HgTX - "IT WASN'T THAT BIG A DEAL."  and it isn't that big of a deal to learn it.




 

RE: ASD vs. LRFD, Who Decides?

(OP)
JAE,
Going back to the intent of my original post, what do you think about academia teaching one method exclusively?  Should the college professor be the one making the decision for the industry?

RE: ASD vs. LRFD, Who Decides?

If I was the student....or if I was hiring a student out of school, the "good" student would know both.  We do get called upon at times to review other's work, past calculations, and past designs.  We should, as good engineers, be able to decipher either method.

Since AISC has combined the two in one specification, it seems to me that they could easily incorporate both methods.

Do they have the right to choose one over the other?  I would think they do if they have the internal control over the curricula.  However, it would seem to me that they'd be under pressure to produce good engineers coming out of university and most would (or should) decide that both methods are necessary.

Now as time goes on, and if one method becomes more prevailent, then perhaps they will eventually abandon one over the other.

 

RE: ASD vs. LRFD, Who Decides?

Are some of you suggesting that ASD89 be taught in 2009?  If so, then which half of the following topics should be deleted to make room for it?  Columns, braced beam flexure, shear strength, base plates, bearing plates, unbraced beams, deflections, beam-columns, bolted tension connections, welded tension connections, tension members, and composite beams.

For the record, I learned LRFD in school, then was forced to use ASD89 for 3 years, then switched back to LRFD for 6 years before I became a professor.  Honestly, for someone who will study, it's not a big deal either way.

vmirat, I can tell you with 95%+ assurance what would happen if I mixed ASD2005 with our current curriculum.  The upper half of the class would trivially go back and forth between the two methods.  The bottom half of the class would struggle figuring out when to factor the loads, otherwise would find the issue to be trivial.  The end result would almost certainly be that the inclusion of ASD added nothing to the course and muddied the water a little for the weaker students.  This muddying would take away their attention from more important aspects like behavior.

As for the question of whether profs should decide the curriculum, that's an easy one: No, not alone anyway.  We have industry advisory boards who give their input, and it is very often used to make internal decisions about the curriculum.  

Also, I can't speak for other profs, but I spend a LOT of effort to try my best to help the students develop what I *think* will serve them best in industry.  I don't know anybody who uses the engineering classroom to try and ram something down industry's throat.

Why is it that some design guys want profs to respect their experience while not offering the same in return?  Imagine what would happen if a prof who'd never been in an engineering office tried to supervise the design of a building--total disaster!  Likewise, I can tell you all that after 9 years designing, I thought I knew what profs should be doing but then found that I was completely unprepared for the task of designing and teaching a class.  How 'bout not automatically assuming we haven't thought about why we're doing what we're doing?!

RE: ASD vs. LRFD, Who Decides?

"However, it would seem to me that they'd be under pressure to produce good engineers coming out of university and most would (or should) decide that both methods are necessary."

I agree totally.  Looking back to my old school, Virginia Tech, all 5 steel courses were taught with LRFD exclusively.  I'd hazard a guess that nobody in his right mind would claim that VT's steel design curriculum is lacking.

If we're talking about quality, why not get to the *real* issue behind quality: sorry teachers who get tenure and stay there forever.  If universities focused on hiring and keeping the best teachers instead of focusing 90% of hte hiring decision on research, then the teaching quality would go way up.  If some of you guys just have an activist itch that needs scratching or are spoiling for a fight, then I humbly suggest you go find some non-trivial issues like this to work on.

RE: ASD vs. LRFD, Who Decides?

"If you are correct in that the ASD spec will disappear I will make a prediction.  If the ASD code disappears, no engineers will use LRFD. The engineering community will use the 89 green book or the 13th Edition ASD. The engineers will complain to AISC until AISC reinstates ASD... again."

Vincent, what tree did you scramble out from behind?

(JOKING!  I remember your affinity for hyperbole from a thread like this from a year or two ago.  I like it.)  

The IBC no longer references the green book, so engineers will not be using it forever.  

The 13th Ed. ASD is almost exactly like LRFD.  If someone insists on using Mn/Omega instead of phi*Mn, then it'll be for the short term.  After about 4 min. of using Mn/Omega, the guy will realize that he might as well use LRFD.  Then a spec. or two later when ASD goes away (my prediction, not AISC's, to my knowledge), nobody will care.

RE: ASD vs. LRFD, Who Decides?

nutte: "Perhaps you have it backward?  You teach students one way, and they have to learn a second way at some point in their career.  ...
Of course, if they go to an office that uses LRFD, they're out of luck."

LOL, I have no clue if that makes sense.  What's the current percentage of offices that use ASD89, ASD2005, and LRFD2005?  Again, are you saying ASD89 or ASD2005?

"It will be interesting to see if you're right about ASD dying in ten years.  The biggest disadvantage in my mind, which has been mentioned in this thread and others, is having to run both cases anyway for serviceability."  

Sure, but I think this is trivial also.  I designed bldgs for 9 years and used LRFD for 6 of those.  I barely noticed the difference between ASD and LRFD in this regard.

"Would not the vast majority of designs come out the same regardless of the method used? "

I believe that is true.  The main differences are in areas like metal bldgs.  ASD is a lot more economical for those due to the high L/D ratio, so the MBMA guys use ASD2005 for a good reason.

RE: ASD vs. LRFD, Who Decides?

Well, it's been fun, but it's getting late and I need to save some energy to screw over some industry guys tomorrow as I plan the Fall Semester's Steel class.  

LOLOL, joking of course!!  It's fun being the lone representative of academia in here.  You guys are a tough crowd.

RE: ASD vs. LRFD, Who Decides?

Having just taken my first steel course two years ago, I tend to agree with 271828 about the integration of both ASD05 and LRFD in the classroom.  My professor (who was absolutely horrid in that he's one of those who teach without ever having done) required us to learn and do problems with both methods.  It was pretty worthless in my opinion as it was something that certainly could've been picked up very quickly on our own time, but required twice the time to explain many topics (because now he was doing examples for both methods now) leaving out a lot of other information the class would've done better to cover.

If anything, a brief mention of common ASD89 formulas that we may encounter (or at least that ASD89 and ASD05 are formulated differently) would've been far more useful for times I run into Fb=0.66 Fy and the like from old designs.   

RE: ASD vs. LRFD, Who Decides?

A star for 271828, keep up the good work in the classroom. And try to spend some time on connections, their design is a lost art.

RE: ASD vs. LRFD, Who Decides?

Thanks ash060.  In the first course, we spend about 3 weeks on connections and in the second, about 3 weeks also.  Connections are my favorite topic and I wish there was more time for them.  

I tell the students that connection design is about the only calculation task in steel design that can't be done by using the right program.  (Slight exaggeration)  The designer of a difficult connection really has to know what he's doing.   

RE: ASD vs. LRFD, Who Decides?

Fellas, this thread has got me thinking.  I really do believe there are problems with structural engineering programs.  If any of you are on industry advisory boards, I'd highly recommend beating on somebody about the following issues:

1. Sorry teachers who get tenure and stay there forever.  There are people who don't even try to do a good job.

2. The use of research potential as 90%+ of the decision on what profs are hired.

3. The use of research papers and grants awarded as the vast, over-riding factors in deciding who gets tenure.

4. The lack of room for structures electives.  For example, at our school, all CEs must take both fluid mech and hydrology.  Hydrology?!  If the curriculum was a bit more flexible, the structures guys could take another useful class.  A lot of "never designed" profs don't understand that structural engineers are just distant cousins to the rest of CE.  We're closer cousins to MEs than environmental engineers, for example.

I wish there was a groundswell of pressure from industry in these areas.  I think there's where hte potential for better educated new grads could come from.

RE: ASD vs. LRFD, Who Decides?

271828,
Are you fingers tired yet?  Wow - posting production is way up here - and it's a good thing!

1.  Sorry teachers...a good example of why public schools are in such bad shape (my wife is a public school teacher and gets frustrated with so many people there with no work ethic).

2.  Research as hiring bait...Universities are hard up for cash.

3.  Research as tenure bait...see item 2 above.

4.  Lack of structural electives...derived from lack of good teachers due to items 2 and 3 above.

 

RE: ASD vs. LRFD, Who Decides?

There are two different groups of teaching proffesionals, I respect both for their unique duties/functions. I went through a colledge required more common core studies than mentioned above, it was heavy load at times since we were in quarter system. However, looked back, I glad I have through that traing that led me have a broader view/understanding on things we don't normally deal in a daily basis. I had both practitioner (PEs & SEs) and non-practitioner (researchers) professors, I appreciate both for the learning experience they provided. After a year or so in priding my academic standing and rejecting others, I started to learn a new language at work, humbly. However, without the teaching from both of the good, old teaching professionals, I won't be able to be here today.

To me, the most important role of higher education is to produce/equip a person with basic concept and know how to think. We shouldn't tilt one way or the other.

RE: ASD vs. LRFD, Who Decides?

(OP)
This thread has gotten a bit off track.  The intent was not to endorse one method or the other.  Neither was it the intent to slam teachers.

The question was whether the academic world should be the ones deciding code issues.  The LRFD method has been taught in schools for quite some time.  There are three entities involved here.  There is the academic world, the engineering/construction industry, and the code entity, in this case AISC.  I would assume that AISC would drive this train, seeking advice from the academic side and from the industry side to make a decision on code methodology.  I had originally made the opined statement that the industry should make the decision, not academia.  I based that opinion on the fact that the person using the system will most likely have more insite into its effectiveness than someone not CURRENTLY in the field.  Even if a teacher has design experience, once they leave the field of practice, they lose that day-to-day touch with the industry.

My position is that academia may not be the most qualified to make the decision as to which system to use and they shouldn't be pushing one system over the other, as evidenced by Salmon/Johnson/Malhas' book.

On the other hand, I fault AISC for draging its feet on this issue.  If LRFD is indeed the best method, then they should make the break and stop carrying ASD.  I sent them an email and asked them this question.

RE: ASD vs. LRFD, Who Decides?

"...than someone not CURRENTLY in the field.  Even if a teacher has design experience, once they leave the field of practice, they lose that day-to-day touch with the industry."

Upon what facts or direct observations do you base this?  I speculate that it's purely an opinion.  You made the claim--can it be backed up?

RE: ASD vs. LRFD, Who Decides?

JAE,
I didn't call you a fool. I called the act of removing ASD from the Steel Design Manual foolish. Please read my post more carefully.

271828,
Please change your name to something catchy!!! I can't remember all of the numbers. I have crawled out from under tree or out of the gutter depending on your point of view. I changed jobs recently to a place with quite a few senior engineers. I was working in a place where I was the senior engineer with all of my 12 years of experience... That is one the biggest reasons why I left!

For all of those arguing about ASD89 being taught and those of you arguing about the difference between Allowable Strength Design and Allowable Stress Design, you are missing the point.  First, The true arguement is between Factored Loads and Services Loads. When using Service Loads, I only use one set of loads and load combinations. When using Factored Loads, I use 2 sets of loads and load combinations. In a world of tight budgets, I prefer the one that takes less time!  Second, real world construction dictates that fat should be built into every design; not a huge amount of fat but extra capacity. The structure will NEVER be built as designed even with inspectors on-site. If you ever want to be horrified, go on-site and check bolts, look at welds, look at reinforcement, etc, etc, etc... If ASD (Allowable Stress or Strength) gives me a little extra fat,... GOOD!  The owner will never have to thank me for it when his structure never fails.

I actually like the 13th edition. It has its problems but overall AISC did a good job. It is an improvement.  The safety factors are a pain in the a__ though. I use it now instead of the 89.  AISC still punts on many subjects but many more subjects are addressed in the 13th than in 89.  I like the extra fat and the ease of calculation offered by ASD (allowable stress or strength). I will continue to use it until I retire even in AISC retires ASD. After all, I can see we need a new code from all of the buildings falling down around me.

RE: ASD vs. LRFD, Who Decides?

vmirat, I typed the text below in a previous post and you didn't have a response.  Do you buy this or not?  I think it is the true reason why LRFD is taught in school, not become someone's trying to ram LRFD down industry's throat.

"vmirat, I can tell you with 95%+ assurance what would happen if I mixed ASD2005 with our current curriculum.  The upper half of the class would trivially go back and forth between the two methods.  The bottom half of the class would struggle figuring out when to factor the loads, otherwise would find the issue to be trivial.  The end result would almost certainly be that the inclusion of ASD added nothing to the course and muddied the water a little for the weaker students.  This muddying would take away their attention from more important aspects like behavior."

LOL, since we're into idle speculation at this point, I'll speculate that you don't have a response to this and that the next best thing is to try to come up with a reason why I'm not qualified to have an opinion--seeing as how I'm not a "currently practicing" engineer.

RE: ASD vs. LRFD, Who Decides?

271828,
I agree with you that both LRFD and ASD shouldn't be taught. It would take too much time and other topics would not be covered. It would only serve to confuse the students. It would be like teaching Spanish and Italian in the same class and then ask the students to have a conversation. You also say you want to spend time on steel behavior. I agree with this also. I disagree with you in that is a legitimate reason to teach LRFD. You can teach steel behavior in ASD.

A really good professor at WVU tried to get the rest of the faculty to focus on teaching not just research. It actually mattered to him that the students should learn something. He was met with heavy resistence. It never took off. He did teach a conceptual design of structures course using Daniel Schodek's book "Structures". It was one of the best classes I ever had. Thankfully I had this professor for 4 separate courses. I also had another professor for steel design that refused to teach LRFD until the deparment made him. He emphasized practicality as well as design and behavior. I had him for 3 courses. That is a rare experience. I was lucky. Most are not. Teach ASD. After all it is your choice, right?  You will feel better about yourself ;)

RE: ASD vs. LRFD, Who Decides?

Vincent, are you referring to ASD89 or ASD2005 in your first paragraph?

I don't claim that LRFD = teaching behavior.  I view teaching behavior and spec. stuff as two related topics.  Behavior is king and I have to choose which 2005 Spec. method to use.  So far anyway, it's seemed obvious to me that LRFD was the way to go.  I still think if a student has been taught LRFD2005 and then needs to use ASD2005 on the job, that it's a trivial transition.  Going the other way is borderline trivial also, though--I'll admit that.  In that way, it's somewhat arbitrary that LRFD2005 is chosen over ASD2005.

RE: ASD vs. LRFD, Who Decides?

271828,
read my post, two posts up; the post before the last post. does that even make sense?

RE: ASD vs. LRFD, Who Decides?

vincentpa, when did I suggest you called me a fool?  You didn't and I didn't think you did.  So no offence and no problem.


As to teaching only ASD, big mistake.  Either LRFD only or both.  I prefer both.  It...just...isn't...that...difficult.

Both use the same dang equations.  Both require resistance to be greater than specified strength.  The safety factor is just distributed differently and one takes into account variability of loads while the other doesn't.

I have younger engineers working with me and they have NO problem understanding either method.

In the world of engineering that we inhabit, we should understand both methods as they historically have been, and are being, used in real projects.  A good engineer should know both methods.  

 

RE: ASD vs. LRFD, Who Decides?

ASD vs. LRFD, Who Decides?

In Canada, the NBC (National Building Code of Canada) or one of the Provincial building codes (which are near replicas of the NBC) decides which method to use.

We call it Working Stress Design (WSD) vs Limit States Design (LSD).  LSD started about thirty years ago.  For about two decades (I'm not sure about the exact dates), both methods were permitted.  WSD was gradually phased out and now, LSD is the only method recognized by our code.

I am not aware of a test case, but I believe that, in the Province of Alberta today, an engineer using WSD in the design of a structure would be chastised by the Practice Review Board and ordered to adopt the recognized method, namely LSD.

BA

RE: ASD vs. LRFD, Who Decides?

Quote (271828):

What's the current percentage of offices that use ASD89, ASD2005, and LRFD2005?
That is a good question, one that hopefully is looked into by the advisory boards that assist code writers and academia.  When I look around town, ASD is alive and well.  Of course, I'm looking at a small sample size, so I don't mean to say it's the same across the country.

Quote (271828):

Again, are you saying ASD89 or ASD2005?
I maintain that they are the same.  Before ASD2005, the engineer wanting to use ASD had no choice but to use the green book.  Thankfully, AISC corrected this misstep with the 13th edition.

I do understand your concern about confusing the bottom half students by teaching both methods.  I don't know how to avoid that, but I do think it important to teach both ways.

There have been many other good points made, but I'll refrain from mentioning them to stay on-topic.  271828, thank you for the professor's perspective.

RE: ASD vs. LRFD, Who Decides?

"When I look around town, ASD is alive and well.  Of course, I'm looking at a small sample size, so I don't mean to say it's the same across the country."

I also have no idea the %.  At the last two firms I worked for, LRFD was adopted almost from the time it came out in 86.  The other major firms in town also used LRFD.  I'm also not claiming that this proves anything.  

A few years ago (maybe 8?), I read that 15% of people had switched to LRFD.  I have to think that % is much higher now, if for no other reason that guys who graduated in 95 are now in prominent roles and aren't (as often) told by the older guys what Spec. to use.  Now there really is no significant differene between ASD2005 and LRFD2005, so I have to think this will increase the % much more rapidly.

Aside: Here's a thought for folks who get worked up over having D+L and 1.2D+1.6L combos to carry through.  What do you do when you do ACI concrete design?!  I betcha having two sets of LC floating around causes about zero extra difficulty, thought, or problem, right?  ANYWAY, back on track, LOL...

"I maintain that they are the same."

Except that ASD2005 provides equations for many more cases, right?  I view them as fundamentally similar, but the layout, organization, etc. are so different that they'd look totally different to a new guy.

I'm spinning my little mouse in the wheel that I call a brain trying to decide if I want to include a few ASD2005 problems.  I'm starting to think that I could do this with only a few of the students having trouble.  (They'll have trouble anyway...)  No way I'd consider ASD89 for several reasons.  First off, they wouldn't have the book and would freak at the idea of buying 2 Manuals plus a textbook--that'd what, $400 for one class?!  Secondly, dealing with two books with different organizational schemes would overwhelm them.  

These guys come into class not even knowing what a W-shape is or the very most basic properties of steel--sometimes it's hard in discussions like this one among professionals to keep in mind just how green those guys are.  No joke: half the class barely knows how to draw a moment diagram for easy cases.  Nobody knows M=w*L^2/8 for example.

RE: ASD vs. LRFD, Who Decides?

Green book for green engineers.
Black book for the souls of most professors.

RE: ASD vs. LRFD, Who Decides?

That's a good one!  LOL!  

Most are unsaved, I'd guess, so "black" is probably accurate...

RE: ASD vs. LRFD, Who Decides?

How about let's meet in the middle.

First to point out, it looks like LRFD is the worldwide trend, and covers the major industrial - steel, concrete, sheet metal...There is no sense to resist it.

However, in the interim, since a lot of designs and design professionals are using old ASD (not the newest), it make sense to maintain the knowledge. Therefore, I suggest the school should offer 2 steel design classes - one prepares the undergraduate for prevalent market demand, the other concentrates on the code left out from one above, and the evolution of design philosophy now and then. The second class can be an senior level elective.
  

RE: ASD vs. LRFD, Who Decides?

I would never suggest teaching ASD89.  But 5 years ago, it was the best ASD around, so engineers were using it, like it or not.

When I say the two ASDs are the same, I mean the same concept, just different evolutions.  The green book is a youngster, while the black book is the older, wiser adult.  I whole-heartedly agree with your points about the organization and breadth of topics covered.

As for checking D+L for concrete, serviceability controls less often, so it is less of a hassle.  After all, there are tables in ACI for beam depths so deflections need not be considered.

RE: ASD vs. LRFD, Who Decides?

kslee1000,

In a perfect world, I would agree with you.  I've love to teach two undergrad steel classes, but there is simply no room for two.

Even if there was another one offered, as you suggest, people would take something else instead. After the basic steel class, they'd move on to take prestressed concrete, wood, masonry, matrix analysis, or some other course instead.  Then they'd move toward taking a second class in a given material: Steel II, Concrete II, Nonlinear Matrix Analysis, etc.  

I hate it, but there's just not enough room due mostly to the requirement of so many non-strl courses.

RE: ASD vs. LRFD, Who Decides?

271828:

Make the 2nd one as summer class, since it really does not have much of materials to cover (sure you can beef up if you wish). As I have pointed out before, for my undergraduate program, we needed 2 (mandatory) class each from ME, EE, and one from IE, on top of 1 Env, 1 Geotech, 1 hydrolog/hydrulics. Yes, I had to spent a lot of time to perform self-study to catch up on work, maily in structural, but I am still given creadits to my all around studies.

I can understand your frustration from your standing, I had heard similar complains from two of my younger professors. I haven't been seeing them for a long while, but knowing both are doing fine. It must have take them a long while to adopt into the reality, and need - strategic/selective teaching. I don't mean to ignore something in teaching, but rather than teach your student line by line, maybe it is better off to teach them how to think and find answers themself. Above just my personal opinion based on my own experience.

RE: ASD vs. LRFD, Who Decides?

Like most other older engineers in the foram Ive always found it difficult to wrap my brain around LRFD.  But Ive tried hard.  I still do those ASD calcs aside to check things that I jus't cant do with LRFD.  

But legally in Australia with AS 4100 which is referred to In Australia Building Code we have no choose but to use AS 4100 that is LRFD.

I got some consulting design from an old engineer mate of mine lately and to my surprise it was all in ASD.  A certificate of Compliance was issued by his firm so it got through.

Can someone explain to me what sort of mess this is ?

RE: ASD vs. LRFD, Who Decides?

My point was that we in Australia have no choose but to use LRFD.  But older engineers still use it and get away with it with The Certificate of Compliance even though it's illegal.  

So I would be interested in hearing what others have to say about this point.

RE: ASD vs. LRFD, Who Decides?

Designing to the current code is a professional obligation of every structural engineer.  Failure to comply could result in sanctions by his professional association if they become aware of it.

To falsely declare that he has designed a structure in accordance with the current code is unprofessional conduct and unskilled practice or possibly both.  Engineers have lost their right to practice for such conduct.

If problems arise on a project for any reason and it is learned by the authorities that the structural engineer did not follow the current code, the consequences could be quite severe.  It would be prudent to retain a good lawyer before going any further.
 

BA

RE: ASD vs. LRFD, Who Decides?

Not sure about Australia but in the US the ASD and LRFD are both allowed by the codes so there's no issue there.

 

RE: ASD vs. LRFD, Who Decides?

As far as I'm aware (The Australian code) AS4100 is only a LRFD code.

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