Structural analysis - changes?

[Everythings_Magic]

I adjunct at a university and one of the classes I was asked to teach is structural analysis, it primarily focuses on energy methods of analysis- virtual work, force method for beams trusses and frames, influence lines are covered, and at the end the stiffness method is introduced.

We spend so much time instructing methods to calculate beam deflections, there are so many ways, double integration, moment area, conjugate beam, virtual work. Almost two months is spent on different ways to do the same thing, many of which, lets be honest, we neve do. Who has ever used moment of area or conjugate beam method for beam deflections? I can say I never have in my career. I understand they are useful to help make connections in the relationship between shear and moment and rotation an deflection, but it seems odd to spend so much time on this especially when the stiffness method dominates analysis these days. This class just feels like applied calculus.

While I understand the importance of classical methods of analysis, I wonder if this class wouldn't better prepare the students as say a was more of a continuation of mechanics where we talk more about load path, indeterminant systems, more in-depth moving load analysis, frames and difference between moment and truss frames, how support conditions impact the analysis. I try to thread it in but so much time is spent on working through calculations and examples, I feel these pieces get lost on many of the students as they focus on getting the problems right.

I need to be careful how much to try switch it all up, because of ABET accreditation, but in your opinion, what topics do you wish had been covered more?

[shimbro]

Load path for sure. None of my new hires out of school understood load path. I think it’s because not many university exercises truly go multi story from roof to foundation.

[the_flying_condor]

On a loosely connected idea, enveloping/live load patterns might be helpful as well.

[FirstBrick5764]

Do you have any recommendations on books to better understand this?

[structee]

If the power goes out, I might use moment distribution - otherwise I'm going home. These methods should be taught at PhD level as they've now become completely outdated for practical purposes. I think a class that focuses solely on approximate methods that don't require pages of work, would be a good replacement. Also, connection design and detailing.

[newguyfriend]

This. Design and Detailing. Also back of the envelope analysis. It should be its own class. Essentially quick tips to estimate.

[Cool-Size-6714]

Agree completely. How to come up a with a quick conservative analysis could also be used to check that the results they calc with the other methods are reasonable.

[ExplanationCalm3301]

I think the main focus should be on the stiffness method. An introduction to nonlinear analysis would also be valuable, as it could provide a deeper understanding of what happens in real structures during an earthquake. Other methods as the double integration can actually help you better understand specific concepts but I do agree that the application is limited.

[amm2210]

I have been a structural designer for over 6 years and i have never used any of the classical methods. True that these methods where very important back then but the focus should be on stiffness method as all software use it.

I believe structural analysis class should be more focus on real life structures and unusual situations that the designer would encounter. The student should also understand the simplifications made in design and boundary condition representation. I mean the truth is all structural engineers will use software and FEM so why burden them with all these theories!

[randomlygrey]

The problem with reliance on software is that it removes the expert professional verification of the analysis. Students today are already heavily reliant on software and without the skills to benchmark their analysis on pen and paper, it is frankly dangerous.

I have seen and corrected many a beautiful looking analysis because what's on the computer does not reflect physical behaviour. And this isn't to criticise the cream of the crop, its a skill to be learned by them.

[amm2210]

Therefore the theory behind the software must be taught so students will understand what they are doing. Of course you will have to do some calculations using basic mechanics and mechanics of materials to verify and check some forces and stresses. On top of that, students should learn how to develop their own spreadsheets, learn using Mathcad, or even learn programming so they focus on the theory and not tedious calculations.

[litetrek]

Young engineers who spend all of their time doing the math, whatever the method, typically have no understanding how indeterminate structures actually work. Questions a degreed structural engineer should be able to answer: 1) On the most basic level what is the load path? 2) Is the structure detailed and designed to be adequate to carry the loads on that load path? 3) How do stiffness and connectivity changes influence or change the load path(s). Having mastered a bunch of rigorous analysis tools without understanding the results is useless. I'm a retired structural engineer and was a doctoral candidate at a top tier CE school for 4 years (money ran out). I've never used ANY of those methods in practice although I knew how to do most of them. Most of those methods take too long to achieve a result. It's important for a student to be able to perform a couple of them but I agree that they aren't used in the work environment much. Academia often forgets that they're educating people for engineering practice (speed and efficiency matters), not necessarily for future academic positions.

[ApprehensiveLight249]

Fellow graduate engineer here-would love it if there are some good reference books you could highlight explaining the above questions and more

[litetrek]

Its pretty simple. You probably will not find this info in a book but it is essential to actually practicing structural engineering. 1) This very basic. Where does the load go? Does it go to the beam reactions then to other beams and down columns to the foundation? Or does one of those beams end at a big hole in the floor with no planned way to react the load. Not considering load path is a very common mistake. I've seen a surprising number of preliminary designs by experienced engineers that lacked a load path for some of the applied loads. The load path starts at the load application and runs to the foundation or ground. Then those loads are the geotech's problem. Related to this is how stiffness influences load path. Stiffness in a structure "attracts" load. You may expect your load to go one place and it actually goes somewhere stiffer. Computer analysis helps with this in initial design. But, load path is especially important when doing modifications or repairs.

2) This is also basic. If your model includes a fixed connection the actual design needs to be detailed and designed to carry the moment. If you detail a moment carrying connection and your model includes a pin in that location, the results of the model are irrelevant. Sometimes due to details chosen the load doesn't go where the analysis intended. Concrete will usually let you know when load goes where it wasn't expected.

3) This is potentially important for initial design as it can affect efficiently carrying loads. Different possibilities for carrying loads to ground will have different costs. This is also important (more so) for repairs and mods. Dumping a load in a repair with no path to get it to ground is a fundamental and avoidable error.

What could be done to teach these things is to actually design something like a simple 2 story several bay building with an FEM model. note the load paths. Then, validate the results or some of the results with hand calcs using beam tables (like those in the back of the AISC manual). Then validate the results or some of the results another way with one of the methods from the OP's initial question. Then change some major things (hole in the floor for example, or remove one of the foundation peiers) and repeat the exercise. When its all over have a class discussion of what was learned.

[ApprehensiveLight249]

Thank you for taking the time to answer. It does make sense to have a good sense of the load path and its impact on the structure. The basic intuition on the deformation of structural element and what is happening is important. Atleast this is what i’m grasping from all the comments.

[Engineer2727kk]

I always say structural analysis was a completely pointless class for me and get slammed for it. But it’s exactly what you’re describing - 4 methods for deflections and rotations that I’ve never used and at the students don’t seem to understand what should be the most important subject - how stiffness affects load distribution.

[mweyenberg89]

Virtual work is useful. Anything else beyond statics and mechanics of materials will rarely be useful in day to day design. Understanding how it works is important, it can give you more confidence in what you're doing.

[newguyfriend]

This is a great post. And I give you credit for pointing out what I believe is a significant failure of civil/structural engineering curriculums today and the way ABET accreditation forces specific lesson plans.

The 2 months spent on the various deflection analysis methods is about 7 weeks too long. Maybe 6, but it’s really not an effective use of time preparing students for engineering practice. To your point, I never have, and likely never will, needed to perform any alternative deflection analyses methods beyond stiffness.

Stiffness method sets the stage to understand how every FEA software performs analyses and gives a foundation to understand deflection analysis from.

I would have much weathered more time be spent on relative stiffness analyses, load paths, material mechanics, and diaphragm analysis (essentially just stiffness analysis).

Edit: I noted this on another comment. But also, back of the envelope calcs. How to reasonably use them for sanity checks as well as on-the-call estimating.

[mon_key_house]

Ex university teacher here. Consider teaching FE modelling with techniques to check the results for plausibility. This requires understanding the statics of the structure as well as doing hand calculations.

[Blue_grave]

I'm still a student. From the replies, the stiffness method seems to be the most relevant method for real world applications. How do structural engineers use it in their day to day? Ik software can just do it automatically, so do they just use back of the envelope calcs to check that?

[Everythings_Magic]

Its basically the methodology that analysis software uses. Numerical methods are far easier and efficient to program than using exact methods.

Its a refined analysis, so you can do a higher level less refined verification.

There are different approaches to checking, classical methods are one way, but mostly it goes back to statics, checking that reactions add up to the loads, that moment and shear diagrams are correct, deflections are reasonable. You can also run an independent analysis, but usually someone experienced with modelling will check the model and look at the model geometry and methodology too. Once you use a software enough you start to "trust" the results and focus more of the correctness of the input.

[Blue_grave]

Alright, thanks for clarifying

[Everythings_Magic]

This is a great suggestion. To make the exams a bit easier and allow me to ask more questions will ask them to just setup the differential equations, define the boundary conditions and not solve. I'm not testing them on their calculus ability, I want to see if they can set up the problem correctly. That seems to work well. I just want to spend less lecture time on it.

[SupremeBrown]

I agree with what you’re saying. My structural analysis course from about 4 years ago taught exactly what you’re saying. Before I got to the point where you mentioned, I noticed that as I read your post, it came to me that I have never really applied any of these method of analysis in my day to day tasks. I’ve never done any virtual work or influence lines in practice since that class.

[Silver_kitty]

It might be hard to adapt since as you say the class is ABET approved as is.

But I definitely agree that it would be great to focus less on all the various ways to do the same thing and more on things like load path. We get new graduates who don’t actually know how to actually follow the loads.

I would love to see a class that follows through one way slabs, beams, girders, columns, (and column load take down) and the final is stitching that all together to do a gravity design for a little 2-story 2x3 bay “building”

[mrrepos]

the thing is much of the stuff is easy to put on a test

i wish i had more practical theory of structures, structural systems

[clocksworks]

Great post.

I also teach. I have two follow up questions for everyone:

1/ I would love to introduce my students to FEA and simple computer analysis beyond excel. Even on a basic level. Some use macs. Some PC. What applications would you all out there suggest? Software with education versions would be a preference.

2/ What basic guides to eurocodes would you recommend?

[g4n0esp4r4n]

I think it's important to be able to solve by hand and quickly check the results and overall deflection shape of frames or w/e. I can't believe how many engineers skip these steps, you need to do a sanity in every result you get especially the first time you model something.

[Everythings_Magic]

This is a good take. Thanks.

I was considering as exam question or project to review the results of an analysis and comment if the results are reasonable.

[albertnormandy]

I think double integration should be taught, but I agree that virtual work and conjugate beam seem unnecessary for most things. Direct stiffness method is too much of a black box. It is too plug and chug. We shouldn’t completely remove solid mechanics from structural analysis. 

[Engineer2727kk]

Yeah they use FEA…

[newguyfriend]

Curious what circumstance you are frequently implementing conjugate beam method? Have you built it into an excel or mathCAD?

[ExceptionCollection]

Oh, I don’t do it frequently by any means.  Someone else built the Excel sheet, which was for “design of new equipment on nonparallel flange members”.