ASD vs. LRFD, Who Decides? 5

[vmirat]

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.

 

[jrw501]

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.

 

[ash060]

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.

 

[271828]

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.

 

[271828]

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.

 

[JAE]

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.

 

[kslee1000]

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.

 

[vmirat]

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.

 

[271828]

"...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?

 

[vincentpa]

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.

 

[271828]

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.

 

[vincentpa]

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

 

[271828]

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.

 

[vincentpa]

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

 

[JAE]

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.

 

[BAretired]

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

 

[nutte]

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.

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.

 

[271828]

"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.

 

[vincentpa]

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

 

[271828]

That's a good one! LOL!

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

 

[kslee1000]

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.