Is the AISC STEEL CONSTRUCTION MANUAL as complicated as it looks? 4

[curiousmechanical]

Hello,

I am a mechanical engineer. I have been designing industrial equipment for the past eight years. I am somewhat of a reference book junky and I recently purchased the AISC STEEL CONSTRUCTION MANUAL (14th Edition). This book seems very useful, but it also seems like it might be over my head. On occasion, I need to design service platforms for our equipment. I thought this book might help me do a better job.

So here’s my question:

Is this book something that a mechanical engineer should be able to use; with a reasonable learning curve? Or, is this book very specialized and only useful to hardcore structural engineers? Right now, I am completely clueless. I don’t know anything about LRFD, ASD, etc. Also, I am worried this book will require the reference of other AISC standards. I don’t have an AISC membership and I don’t plan to buy any more structural reference books. If this book isn’t as complicated as it looks, does anyone have any advice on how to get up to speed quickly (i.e. how to learn the basic concepts, so I can take advantage of the various tables and formulas)?

Thank you for your help everyone!

 

[Ron]

LRFD is good if you have to rationalize an underdesign by another engineer....ASD makes actual sense and is less prone to error. If it ain't broke, don't fix it. Back to the original question....yes, AISC is a pain in the ass and has gotten moreso over the years. Relevant, but a pain.

JAE...where are ya? You LUUUV AISC!

 

[JAE]

Huh? Oh. Sorry, I've been busy updating my AISC manual via their erratae. That's plural for lots of errata.

 

[SAIL3]

I also aggree with Ron...but, unfortunately, the horse is out of the barn...

 

[RobertHale]

Okay, sorry to hijack the thread (or hop on the on going hijacking) but I am going to take exception to the "ASD is so much easier" assertion. At this point in time there are almost no jurisdictions that incorporate the old 9th Edition ASD (two to be specific: Connecticut and USVI) All other US/IBC jurisdictions are either on the 13 Ed. or the 14 Ed, and while these do include ASD provisions it is simply a matter of multiplying by a number less than one verses dividing by a number greater than one. ASD uses the same limit states that LRFD does. Furthermore the "Load combinations defense" (the statement that the load combinations are so much simpler because all factors are one) that I have heard so many times is fallacious. The ASD load combinations are no longer that simple, and the suggested serviceablity combinations are different from both the LRFD and ASD. I will get off my soap box now.

 

[rittz]

I have on occasion, for the fun of it, compared results with the text book I used in university namely "Steel Construction Manual - 1957 AISC". I bet few have a copy of it in their library. LOL.

It has side tabs to mark the page of key topics.

 

[DCBII]

How did this discussion go from "I'm a mechanical engineer that is thinking about practicing structural engineering" to "ASD is better than LRFD". I swear every thread heads this direction eventually.

At the risk of drawing criticism; the 9th Edition died a long time ago. It was never meant to handle structures as slender as computer software now allows us to create. The stability provisions were primitive at best. ASD and LRFD are practically identical now. Applying load factors to steel is no more difficult than it ever was applying them to concrete. Move along people... Hyahhh!

 

[curiousmechanical]

Even though this thread has taken a tangent, I've enjoyed reading the discussion. In the end, I did get what I was looking for. I now understand that structural engineering is for structural engineers. Also, I got a couple book recommendations in case I still want to learn about the subject (just for the sake of educating myself). Thanks guys!

 

[SAIL3]

DCB..."It was never meant to handle structures as slender as computer software now ALLOWS us to create"....computer software is just another tool....the engineer should be making the final engineering decisions...

 

[Bagman2524]

The code writers are too removed from actual engineering practice. If I'm designing a stair, equipment platform, pipe rack or some other miscellaneous structure, I just want a quick and easy engineering analysis, not something as complex as the 14th edition is now.

 

[TDIengineer]

Someone mentioned still using ASD. Be prepared for that to go away completely! It is my understanding codes will only have strength design in the near future. Everything will be a strength loads instead of allowable.

I steered away from LRDF for a long time. I have completely made the switch over and I love it. No more converting lateral loads back and forth between strength and allowable levels!

my 0.02.

 

[namanges]

The 14th and 15th edition steel manuals include design methods for both ASD and LRFD. However, the 14th edition ASD method is not the same as the 9th edition ASD method. In fact the acronyms are for two different things. The 9th edition ASD refers to "Allowable Stress Design" while the 14th and 15th edition ASD refers to "Allowable Strength Design".

As RobertHale pointed out, the most notable differences between the two methods are 1) the way the loads are derived (according to ASCE 7) and 2) the way that the design/allowable strengths are determined. Calculation of the nominal strengths are similar for both methods. Chapter B, Sections B3.3 (LRFD method) and B3.4 (ASD method) give a brief overview of each method.

namanges

 

[Ron]

Bagman...AISC does not apply to stair design. They specifically exclude it from being considered "structural steel"!

 

[Archie264]

But I think the point he made still applies. My $.02 worth, at least.

 

[Archie264]

Whoops, Ron, I saw after I posted that I was responding to you. Had I realized that I wouldn't have posted. I like to let my betters have the floor when they're participating in the discussion. Not attempted flattery, just reality.

 

[StructuralEddie]

I also design a lot of platforms for industrial use at my firm. The key to platform design is watching your deflections. The 100psf live load generally makes deflection govern over strength. The problem becomes clear when you walk across platforms designed for strength only- it's like walking across a rope bridge! The other consideration is rotational restraint of the beams that handrails and light fixtures are attached to. Again, platforms typically use light, thin wide flanges or channels and are susceptible to easily rotating- something you can feel while grabbing a handrail. The solution is torsion bracing every so many feet. All non-structural minds at my firm share the same viewpoint that these structures are simple. I do believe most people can design reliably safe platforms without much experience, but they generally are horrible designs in terms of serviceability.

Also- I vote for LRFD. The clear separation between service and ultimate load states does make designs more intuitive. If you do any seismic design you will stay away from ASD at all costs.

 

[Ron]

Archie264...I agree with you...his point does still apply and I agree with it. I should have said that in my post.
Code writers are not only "removed from engineering practice" ...they are often not engineers or architects. Code writing is a cumulative, political process that often loses sight of the technical need and importance...all for the sake of appeasing those lobbying for a particularly point or relief.

It is not a pretty process and is severely flawed...but it is what we have.

ps, Archie...I don't know any more than anyone else. While I appreciate your compliment, I have to admit that I've only been around long enough to learn a few things, one of which is how little I know. I learn from this site every day and thank those who teach me.

 

[wannabeSE]

Ron and Archie,
I am curious why you believe that the people who write the code are not engineers. I googled about a dozen names listed on the specification committee at the beginning of AISC 360-10. Maybe half work (or are principles) for consulting firms. The others are professors along with a couple engineers working for federal agencies. I went to the steel conference in St. Louis earlier this year and heard presentations by several of the committee members. They seem to understand the needs of the practicing engineers as well as the needs of fabricators and erectors. Perhaps, there should be "when in doubt make it stout" guide to steel design for those that find the current manual to be too complex.

 

[dozer]

Curiousmechanical, good for you for asking the question. It shows you're thinking. With the right guidance you could get the hang of it. A lot of mechanicals aren't even considering that they might not be designing structural systems correctly. Occasionally I'm asked to check a skid design and a trend I've noticed is that folks are using these really cool looking FEA programs that actually mesh the whole skid into a bunch of plate elements. Then all they do is find the maximum stress and say that it's less than the yield strength divided by a factor of safety. No consideration for things like columns buckling (like if they have a platform on legs connected to the skid) or lateral torsional buckling or nothing! It's just plain scary.

 

[Ron]

wannabeSE....AISC 360 is not a code...it is a standard. Many standards are written by engineers, including AISC and ASCE 7; however,the building codes are often written by a cross-section of technical and non-technical people.

The standards are not too complex...just a pain in the ass for interpretation and interaction in some instances.

 

[DCBII]

I use the 14th edition manual exclusively. I have no difficulty keeping up with the pace of other engineers in the office who still use the 9th edition manual. I found that if you take the time to learn and understand it (and the learning curve is steep if you're coming from a spec. that was issued in 1989) it's not hard to apply. Different, absolutely; "removed from practice" no. If anything, it's in touch with the 24 years of computer technology and structural research that has developed since the 9th edition rolled out. It's a spec. for the computer age.

Sail3: I agree, the computer is not a replacement for good judgement, but in the end a computer does give the engineer the ability to design more slender structures. If I run a P-Delta/delta analysis (which is next to impossible by hand) and take my K factors as unity I'm going to find I can design more slender structures than I could using the old K alignment charts and Cm factors. The computer will also pick up stiffness from secondary elements that in the past were neglected.

Bagman2524: Certainly the 14th edition doesn't eliminate simple hand calculation methods either. Although a second order analysis is now required, good judgement can be used to identify whether it will make a difference or not. I certainly don't do a complex analysis on every stair stringer that comes across my desk just because I'm using the new edition.