AISC 9th edition vs. 13th edition
AISC 9th edition vs. 13th edition
(OP)
My company uses 9th edition, Allowable "Stress" Design and not 13th edition Allowable "Strength" Design. Our work in the petro-chemical, offshore, and general industry usually means that time is more important than saving 10% steel weight. We must order steel often before sizes can be finalized and schedules are always critical. Stress design is crutial to our work. I would like AISC, or another organization, to produce an updated Stress design.
AISC is still pretending that everyone uses and loves Strength design. Using their own publications and magazines such as "Modern Steel Construction, I believe that they have monopolized the conversation. When a question regarding 9th edition is posed, AISC ignores that and says to use 13th ed.
I'd like to know where the typical engineer stands on this matter. What book does your company use? Did you move to 13th edition because you felt you have to because of codes?
And PLEASE, don't try to argue that 13th is just as fast. That argument is settled.
Comments?
AISC is still pretending that everyone uses and loves Strength design. Using their own publications and magazines such as "Modern Steel Construction, I believe that they have monopolized the conversation. When a question regarding 9th edition is posed, AISC ignores that and says to use 13th ed.
I'd like to know where the typical engineer stands on this matter. What book does your company use? Did you move to 13th edition because you felt you have to because of codes?
And PLEASE, don't try to argue that 13th is just as fast. That argument is settled.
Comments?






RE: AISC 9th edition vs. 13th edition
That being said, it is based on the latest research. Why should we not be designing with the latest information?
RE: AISC 9th edition vs. 13th edition
The 13th edition is definitely NOT as fast as the 9th edition. However, I would say that (other than the new analysis requirements) it is probably the easiest to use strength based code that AISC has released.
No longer do we have to rely on lamda_c or lamda_o or some greek letters that I've never been able to read or pronounce. We're back to use b/tf, h/tw, KL/r, et cetera.... That alone is a real breath of fresh air for me.
RE: AISC 9th edition vs. 13th edition
Thanks for your input. My understanding for strength design is that, besides being the latest, it usually results in lighter structures thereby making it more competitive with concrete. Savings could be up to 10% per beam and less than that on an overall project.
However, a quick stress design benefits my clients more. Additional steel weight is outweighed by getting oil wells online earlier. At 100,000 barrels per day for an offshore platform at $50 per barrel (conservatively), our clients would be happy to save one week.
I think there is room for a dual system, Stress design and Strength design.
Incidently, 9th ed is legal if clients agree.
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
The allowable stress is still in the 13th Ed. formulas, it just takes some algebra to take the strength and relate it to stress on the section modulus or area.
It probably seems odd to rewrite these equations into stress, but I have a difficult time getting a "feel" for strength design.
Joel Berg
RE: AISC 9th edition vs. 13th edition
I agree 100% with being forced to use 13th. I do not like the idea, at all, of taking all of my years of experience in stress, and now trying to redevelope a feel for structures based upon moments and strengths. I believe that it reduces the public's safety in that the "feel" factor is removed.
Good engineers are made as much by art as science. I hear engineers backing the 13th addition from time to time, and almost every time, is by someone from AISC, or in academia, or who doesnt own the engineering business.
I understand both approaches (LRFD and ASD). I can use both. Having done so, ASD is by far my preferred method.
And think about existing structures. Structures with low allowable stresses and shapes that havent been made in years. You absolutely have to have a feel for the stresses to work with these structures.
I think there's a place for both methods and both should be supported.
RE: AISC 9th edition vs. 13th edition
In college I was taught strength design, When I went to work I was taught allowable stress design. When I went to grad school I had to learn strength design again. Back to work and back to ASD. Then 3 years later AISC came out with the combined spec... now I have to learn a version of strength design again.
At this point it doesn't really bother me. I find the 2005 spec does a better job of explaining issues that were left out of the 1989 spec.
Most of the older people I work with basically don't want to learn the new spec and rely on me to make the necessary adjustments to their calcs.
RE: AISC 9th edition vs. 13th edition
I have about 29 years in the business as a structural engineer.
I learned in school based on ASD.
I learned LRFD on my own in the early 1990's.
I've used ASD and LRFD both.
I don't see a significant difference in the resulting sizes unless live load is higher or lower than "typical".
LRFD, or strength design concepts in ASD, are not that difficult to learn and use.
I have a feel for structural behavior whether it is with stress or strength - it really doesn't matter to me.
And finally - I've seen over the years many...many structural engineers resistant to change. Once I worked with an older engineer who was using ACI concrete methods from the late 1950's in 1985. Never bothered to learn strength design in concrete. I swore I'd never let myself get that archaic.
So many of us loose an edge in learning as engineers. We get used to, and comfortable with, certain ways of designing and calculating and after a few years in the business find ourselves sometimes overwhelmed and perhaps even scared of all the new knowledge and technology that comes flying at us from new codes and standards. I can certainly empathise with this. But my view is that we engineers must always keep learning and growing in our field or we become dinosaurs.
RE: AISC 9th edition vs. 13th edition
I like what you have to say. I fully agree about learning more and keeping up with the latest developments. I wish that engineers would not be forced to get PDH's because they should want to advance themselves, but that's another matter.
I acknowledge that LRFD (and Allowable Strength Design) is more realistic and accurate, though I find myself somewhat gratified that you find little difference in design. Maybe I'm wrong, but I think that the difference from stress to strength design in steel is not as dramatic as concrete design may have been.
I guess my gripe is that strength design offers little difference in steel cost, but makes our engineering costs less competitive so we have to use 9th edition just like all of our competitors in offshore work. The 9th edition is very effective but has been abandoned.
RE: AISC 9th edition vs. 13th edition
I for one for brought up with WSD (but now use Limit State design). I have a feel for sections and spans but still cannot quite wrap my brain around Limit state design. If you design the section by a plastic method then surely analysisshould be be a Plastic design and not elsatic procedure.
Under AS 4100 we do not have a choice but Limit state design.
RE: AISC 9th edition vs. 13th edition
If you want to abide by the modern codes AND rattle off designs at a healthy clip, how about using some computer software?
RAMS Beam costs a pittance and will see you through the vast majority of your steel beam designs. The output even calculates stresses for you so that you can FEEEEEL the answer!
You don't have to look too hard to see that modern codes often assume that designers will be using computer aided solution methods. Heck, after a few more code cycles, my money says lateral analysis will only be permitted using non-linear dynamic simulation.
Computers. By all means: doubt 'em, check 'em, hate 'em. Just don't forget to use them.
RE: AISC 9th edition vs. 13th edition
I was taught both WSD and USD for concrete as the industry was just making that transition while I was in school, and had no problem using USD in practice.
I learned LRFD during my graduate work (2000+) and understand its concepts. At that time I was not thrilled that the load factors were different than those for concrete. We were carrying factored and unfactored loads through the system for steel design/serviceability and concrete design and saw little benefit in carrying a different set of factored loads for the LRFD design.
Once the load factors were made similar I thought it would be time to finally make the transition, but never quite got there.
I've purchased all of the AISC Manual revisions, read most of them, and really studied the 13th during slow times at work - but still haven't made the switch.
I do agree with Kootenaykid that the use of computer programs in imperative, and I try to model even the most rudimentary structures, even individual columns with more complex load combinations. I still choose the ASD design option out of habit.
When designing individual beams, I do it the old way.
GJC
RE: AISC 9th edition vs. 13th edition
I've designed buildings for 9 years--first 3 years using ASD89 and last 6 using LRFD. During those last 6 years, most projects were complicated and on heinous fast-track schedules. I really don't see the big deal in going from one spec to the other.
This reminds me of how I felt when they took my 99 SBC away and made me use the IBC2000. Not being a seismic expert, I was put-off by having to now deal with MORE terms that I didn't understand: Sds, etc. versus Av, etc. The guys who knew their seismic design didn't care either way. ASD89 vs ASD2005 is the exact same thing. You'll never read something from a steel expert bemoaning ASD89 vs ASD2005. It's always from folks who don't have a particular interest in studying steel, so they've fallen behind.
RE: AISC 9th edition vs. 13th edition
Can you come up with a specific example of this? I've seen it several times, but there was no sinister motivation as you suggest. The motivation was simply that there was not an ASD89 way to approach the problem without the designer inventing his own mutilation of equations that were not intended for the purpose. The 2005 Spec. includes tremendously more situations than does the 89 Spec.
For one example of many, many possible ones, consider a crane beam with cap channel. One could use Sect. F4 of the 2005 Spec. with very little modification. What do you do with the 89 Spec.? I know the answer: use the typical equations in Ch. F. The problem is that these equations were derived for the case of doubly-symmetric I-shapes. You'd have to beat the square peg to fit the round hole to use the 89 Spec. and who knows whether the approach would be accurate.
To make matters worse, the vast majority of 89 Spec. users wouldn't even know that they were using an equation for something other htan what it was derived for. This is because there are so many approximations and constants embedded in ASD 89 equations (in efforts to make them simpler) nobody can look at them and understand the origin. That's why modern specs have such larger equations: they leave the variables and equations as close to the model as possible so the physical interpretation isn't buried and lost. The size of the equation is irrelevant anyway because any sensible engineer will either buy programs or write his own. It's not some diabolical plot from AISC and academics to screw over the other guy, LOL.
RE: AISC 9th edition vs. 13th edition
It is true that computer programs can handle frame problems and beam problems as such.
There were so many little niggling things which could easily be checked or designed by using WSD (which I still use today) e.g. connections, stiffeners, plate thickness etc which in my opinion is crazy to check for Limit states. So much easier and better to check/design using working stress design.
RE: AISC 9th edition vs. 13th edition
I have said this many time in this forum, and I will say it again. In my opinion, computer software should be used for ANALYSIS, not DESIGN. I am more comfortable allowing the computer to tell me what moments, axial forces, and deflections are, while I choose the final member sizes and design the connections.
Our ultimate goal as structural engineers is to design structures which are safe and serviceable. The public should not care if we use allowable stress design or allowable strength design.
I still use ASD, but use LRFD when it is advantageous (for example, adding load to an existing member which has a lot of dead load).
DaveAtkins
RE: AISC 9th edition vs. 13th edition
I do not understand this and would appreciate it if you'd help me to understand.
If I check a double angle connection with ASD89 and ASD2005, the number of design checks is either the same or very similar. Most or all of the equations are about the same--bolt shear, angle shear rupture, angle shear yielding, block shear, welds if it's welded--even that funky eccentric weld to the support side is unchanged--been the same since the 20's unless I have the date off a little.
If I check a stiffener for compressive loads, I have the same design checks to perform--compressive strength, local buckling, welds, etc., regardless of whether I'm using ASD89 or ASD2005.
No offense intended, but I'm getting the feeling that you're not doing all of the design checks because they're not spelled out as clearly in ASD89.
RE: AISC 9th edition vs. 13th edition
Dave, I totally understand the part after "while I choose"--I think the blind usage of sizes that are spat out of a program is about the most dangerous common practice today. I have a great example of this that I typed here about a year ago probably. It was a composite bldg designed using the most popular automated system. The engineer had the shored button turned on and ran the design. There were 34' long W12x14 beams and 30'+ girders which were W18x35 or 40. The first bay to receive concrete started to collapse until they jammed a forklift under it to hold it up. If ANYBODY with >2 years of experience had looked at the actual sizes on a full-size strl sheet, this would've been caught.
That being said, you're not saying to not let the program do design *calc* are you? I wouldn't personally go that far. Say you have a large, 5-6 story structure with a couple dozen moment frames of lots of different bay sizes. I don't think you're going to try to get forces for every load combo, find the worst, and go through Ch. E, F, and H calcs for every member. My view is that one should very harshly scrutinize what the program's doing in this area and then use it to do the calcs. Then a HUMAN eye and a highlighter mark goes on every last size to make sure it makes sense. Just my opinion.
RE: AISC 9th edition vs. 13th edition
Dik
RE: AISC 9th edition vs. 13th edition
The main point being a response to someone who said that they have a good "feel" for the efficiency of the beam based on the stress, but not based on the moment capacity.
Obviously, if you are using a computer program then the program is going to report BOTH the bendings stresses in the beam and the capacity of the beam.
As others have pointed out, those arguments only really hold true for member design. Not connections. But, I for one, have thought that the seismic connection design has always been more rational and straight forward for LRFD or strength based loads. The ASD seismic detailing provisions were always IMHO more complex or convoluted.
Josh
RE: AISC 9th edition vs. 13th edition
That may not be the fact with someone relatively new to structural design.
But when time is so critical to schedule and with all of the intricacies mandated by the Codes, in terms of load conditions, it makes the most sense to take advantage of the design functions. We provide typical connection details and only draw special details where they are really warranted.
It is imperative that a "Sanity Check" is done before any design drawings are issued, but whether the design is done by hand or in the computer should be irrelevant.
GJC
RE: AISC 9th edition vs. 13th edition
271828 - I think this may be a case of LRFD not being as intuitive as ASD89. Perhaps some checks that can be dismissed by observation (or a quick calc)in ASD cannot be as such in LRFD -OR- it could be a lack of experience in LRFD. I'm inclined to believe it's a combination of both.
RE: AISC 9th edition vs. 13th edition
Folks very naturally dislike digging into the new Manual in large part because it's organized differently. LOL, here's a good one along those lines. A couple of weeks ago, I needed to go back to the 7th Ed. ASD Manual and try to find the bearing check and "poison bolt" stuff. (I was told that the concept was used back then.) After several minutes of searching, I gave up and couldn't wait to put it back on the shelf--very frustrating. Nothing wrong with the Manual--I just don't know where things are and didn't want to know badly enough to keep at it.
RE: AISC 9th edition vs. 13th edition
I've got to challenge this statement. Do you really think you are saving a significant amount of time by using the 9th edition?
I can only speak based on my experience, but majority of the time the computer is doing the code check which takes no virtually no time, and the stuff that I do by hand in 13th edition takes very little time. AISC has done an excellent job incorporating tables and design aids for beam, columns, connections, composite action, studs, etc. I just don't see logistically why it should take you any longer if you are using the ASD method of the 13th edition. It is just a game of units!
RE: AISC 9th edition vs. 13th edition
Thats certainly interesting. The Client I am currently working for (one of the big ones) does not allow the use of WSD/ASD for new steel designs. It is all LRFD, but not to AISC but API.
RE: AISC 9th edition vs. 13th edition
I imagine that this is rarely true. If the state requires you to use the 13th, the client has no say-so.
I can't speak for the offshore folks, but is it really true that there is no jurisdiction for codes out there? My offshore experience is from the early '90s and the 9th was still accepted widely...
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RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
I was just trying to say that some are interested more in other subjects: concrete, loads, wood, marketing their business, getting off at 5 and going home to their family (good goal IMO), whatever. They *don't* have an interest in learning how to design steel using the latest knowledge. That's not an insult, but a fact. Folks with a particular interest in steel, in my experience, never complain about the 13th Ed.
I have no interest in learning the latest way to design wood. LOL, if someone tries to make me, I might be on here whining about it too!!
That being said, you're typing about which was "first" not which is "best." I'll not try to say the 13th Ed. is more accurate--I could, but that's the harder one to argue because people point out the lack of precision in real design. The 13th Ed. IS a lot better, IMO, because it covers tremendously more cases than did the 9th Ed.
RE: AISC 9th edition vs. 13th edition
Thanks, but I wasn't referring to your or any particular post. so, no apologies are necessary. I do think that people who have resisted LRFD have been unfairly criticised as, uh, stuck in a rut. I think that engineers are inherently curious people who will give new ideas a fair shake. In this case, I think the community gave LRFD a look and said, no thanks. When the drivers saw the response, they figured out a way to force the change.
The LRFD debate has been going on in this forum for some time. I believe we have a problem, but the problem is not the strength method, it's all the load cases that are mandated by ASCE7. It used to be that the engineer made a judgement as to the governing load case, and performed hand calculations. With so many required load cases, hand calculations take too long. As we switch to computerized calcs, I believe we lose our feel for how things work. In the end, I see a net loss.
RE: AISC 9th edition vs. 13th edition
LOL, then again, the folks who sleep with an ASCE 7 under their pillow would say that you and I are both stuck in a rut!
This argument will probably be taken to a new level in the next couple of decades with probabilistic design. For example, in floor vibrations--one of my specialties--almost every new paper seems to be heading that direction. Saying it's OK or NG won't be adequate soon--one will have to say there's a 0.2% (or whatever) chance of problems.
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
I have a tangential and possibly stupid question. What is "poison bolt"?
I tried looking it up and all I got was a pile of role-playing game stuff. I gave up after about the 10th game-related term I excluded from the search. Who knew I'd ever use "-wyvern -dragon" at work?
Hg
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RE: AISC 9th edition vs. 13th edition
Newer methodology lets you take the controlling limit state of each bolt and sum them (for instance the bolt nearest the edge might be controlled by tearout and the interior controlled by bearing).
So "poison" bolt means that one devious bolt near the edge would screw the whole connection capacity.
RE: AISC 9th edition vs. 13th edition
Hg
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RE: AISC 9th edition vs. 13th edition
It's the law. Like Prohibition (Metrication, Hitler?), we'll never know how many went along willingly. Some people just obey the law. I'm pretty isolated, so I have no idea.
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
Also, I am getting the feeling that those of us who prefer stress design are getting unfairly characterized as slow to learn. LRFD is better, about 5% better at most. I just want a stress design updated for 2009, a stress design that will produce mostly the same sizes.
Ussuri - Unless I miss my mark, our offshore clients (two of the biggies) still use API stress design (not LRFD), but I'll double check this.
RE: AISC 9th edition vs. 13th edition
That's the 13th edition black book.
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
I'd say you're breaking the law if the building permit authority that controls the jurisdiction of your project has adopted the 2006 IBC as it's building code (unless they have a specific provision to allow the 1989 AISC code). IBC 2006 section 2205.1 requires steel design to be in accordance with AISC 360 (no mention of the API spec is made).
If your jurisdiction has adopted the 2003 IBC, you're likely OK, because the 1989 specification is still one of the referenced standards.
We should all be designing with the building code adopted by the controlling jurisdiction, otherwise, we're technically breaking the law. I'm not saying that the older codes are unsafe, or wrong, just what the law says.
RE: AISC 9th edition vs. 13th edition
There's always been some debate whether the building codes (which are geared towards residential and commercial buildings) are truly appropriate for heavy industrial construction. I would put mining work in the same category (heavy industrial) as petrochemical and power plants.
Because of this reason, I would not necessarily say that your client is breaking the law by allowing ASD 89.
However, that argument is getting weaker and weaker with each code cycle. Member of some of the large industrial engineering companies (Fluor, Bechtel, et cetera) have put alot of effort in the code writing process over the last 10 to 20 years to make these building codes more appropriate for industrial.
At the very least, I will say that some jurisdictions will argue that they are breakinng the law and would not allow the old code.... Certainly the City or County of LA would not!!
RE: AISC 9th edition vs. 13th edition
I hope you all don't interpret my earlier posts as suggesting laziness or lack of brains. Nothing like that was intended.
My view, though, is that we engineers tend to follow this: we learn a means-of-design and use it, feel comfortable with it, and begin to trust it over time.
Right?
Nothing wrong with that at all.
But on the other hand, as new codes, specifications, etc. come out, I think it is essential that engineers stay on top of these requirements and methods and not allow themselves to sit back and remain comfortable with older methods when current, legally adopted codes mandate the newer methods. Mostly where the design is under a legally mandated code that requires certain methods and this would probably most apply to buildings.
In construction engineering and industrial settings perhaps this isn't as big of an issue.
RE: AISC 9th edition vs. 13th edition
nutte,
The 13th edition is NOT stress design as you suggest. That is the fallacy that is being perpetuated. "Stress" and "strength" are two words that AISC is attempting to use interchangeably. Just because the English language provides us these 2 words that sound similar and both begin with the letter "S", that doesn't mean that ASD89 = ASD05.
In the end, people should want to use this code because it is better, not because they are forced to, which in most instances is the case.
RE: AISC 9th edition vs. 13th edition
DaveAtkins
RE: AISC 9th edition vs. 13th edition
If I'm using ASD89, I can work in terms of allowable moments instead of allowable bending stresses, right?
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
You make a valid point. People do tend to stick with familier methods, even if better ones come along. I think the main reason some resist LRFD is that we're under such time pressure to get the job out. There's not enough money in the budget anymore to bury time spent learning new methods. Our project managers keep a very close watch on time charged to each project. (That's why my posts here are usually very short) Who wants to spend weekends and vacations learning a whole new design method?
RE: AISC 9th edition vs. 13th edition
IBC 2000 did allow that.
DaveAtkins
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition
It is my understanding that AISC 360 is a new number created for the 2005 spec. It does not apply to any former spec. The ones before this are only referred to by their date. I assume that subsequent revisions will be issued with a year designation - the first one is AISC 360-05, the next would be AISC 360-10, etc.
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RE: AISC 9th edition vs. 13th edition
Nobody does, but shouldn't we expect to do some of this as highly-educated professionals? Not saying every night and every weekend, but some, right?
RE: AISC 9th edition vs. 13th edition
Hg
p.s. Yes, I know, as many PDH systems are implemented, teaching yourself new stuff wouldn't count. Separate topic.
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RE: AISC 9th edition vs. 13th edition
At work, I've used ASD almost exclusively. That is definitely the preference of the PE's that I work under because they have a better feel for it. ASD has become my preference as well. While it is true that for members controlled by strength, you can usually use slightly smaller members running an LRFD analysis, I find that you end up giving that savings right back when the beams are designed for serviceability anyway.
RE: AISC 9th edition vs. 13th edition
Anyway, I however find that I greatly prefer the 13th edition over the 9th edition probably because 90% of my work is done using a computer model so it's easy to get a stress ratio from that. I think about the only two things I liked about the 9th edition is the better quality paper used in the book and the fact that their tables go down to the small W sections (seriously why does the 13th ed. stop at W8 sections!?)
EIT with BS in Civil/Structural engineering.
RE: AISC 9th edition vs. 13th edition
RE: AISC 9th edition vs. 13th edition