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Abaqus standard: Nonlinear buckling tutorial
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- čas přidán 14. 08. 2024
- Greetings dear engineers of youtube!
This is nonlinear buckling example of a channel section used as beam. This example is going to be helpful for everyone doing nonlinear buckling analysis, especially for asymmetrical or uniaxially symmetrical cross sections.
Basic data:
Cross section: UPE180
Material: Stell S355
Beam: simply supported, length 2,8 meters
Loading: 4 point bending
*License: provided by faculty
Your tutorial has just saved me, tnx a ton
Thank you for warm feedback :)
Thank you Ivan. You are the man!
Thank you for the feedback man
Very nice and detailed. Thank you for such a nice tutorial.
Pradipta Biswas , thank you for the nice feedback
What does that mean in keywords model 2: "Imperfection, file=job-1, step=1 1,28.0" - what is it "28.0" ?
It is the magnitude of the imperfection. Since I modeled in millimeters, it means the initial imperfection is 28 millimeters. File=job-1 and step=1 means we are taking imperfection shape from the Job-1 file after loading step 1. Regards!
Thankyou sir! You need make more videos and help university students 🙏🏻
Thank you for the reply. In the future I plan to make a video on aluminium column modelling. Regards!
can you do a tutorial for a solid steel I beam ASTMA572 with both linear and non linear analysis? Thanks for this tutorial. Great job sir
Thank you! Your tutortial saved my evening :)
Thank you for the kind feedback!
That’s valuable even in 2024
Great tutorial. I think you should use 18.7(1/150) as Imperfection because your buckling curves is C according eurocode
Great video Ivan!!! Thanks for it..
I'm really glad it was helpfull
Expecting more videos from u :)
Thanks a lot, very simple explanation straight to the point !
Can you help. With an imported part to do the same the maybe use an undeformable part instead of the shell
Thank you very much
Good job Ivan, waiting for other videos
Excellent Job! Thank you ^^
I appreciate it
Hello, thank you for your great video, it has been really helpful to me. I have a question tho, at minute 36:55 you mentioned that you calculated the ultimate load after the imperfection introduction using the Eurocode. Could you please tell me which equation you used to solve for this critical force?
I used the procedure given in EC1993-1-1 (general method). I can not give you that procedure because it's copywritten. I do have to say I chose buckling curve 'd' if I'm not mistaken. Regards!
Ivan Cudina thank you very much for your response you’re the best 👍🏻.
Would it be big difference if you have used true stress strain curve instead of bilinear?
It is difficult to say with fem analyses. However, since I conducted parametric analysis later on it would be too much time consuming to make model with true stress strain curve so I did not try. Also, my results were fairly good with bilinear stress strain curve.
Very informative video, thank you! But why did you use this BC, instead of just fixing beam in it ends?
To simulate the fork boundary conditions as close as possible.
@@ivancudina93
thanks for the quick reply, and yes it makes sense. I thought there was some trick)
info.simuleon.com/blog/buckling-post-buckling-imperfections-modelled-with-abaqus-fea
for anyone that is currently struggling for the Imperfection part, check the link above, it might be able to help you :)
thanks a lot very help full
@@SalahM07 You're welcome bro
Thank you for the video Ivan. Its really helpful. Just want to ask, what means by the first eigenvalue? Is it directly refers to minimum loading which causes a single curvature lateral torsional buckling to the channel section?
First eigenvalue is the minimum load (or if you wanna be accurate, the smallest number that multiplies load applied to the beam), that would be required to cause buckling of a beam if the behaviour of the beam was ideally elastic. Which means that strength-strain curve of the steel would have to be completely linear and there would not be initial bow of the beam nor any residual stresses. That is only possible in theory that is why eigenvalues have purely theoretical meaning.
Similarly, second eigenvalue is the minimum load required to cause the buckling of a beam in the shape of the second eigenmode. Since the first eigenvalue is always lower than the second, beam always buckles in the shape of the first eigenmode. Second eigenmode also have purely theoretical meaning.
Thanks a lot for the explanation!
I want analysis 440×240 mm steel plate under shear loading. (Load is apply 440 mm edge).How can ı obtain geometrical imperfection value for shear buckling analysis. I will be pleased if you answer....
I'm sorry, but I wouldn't like to answer that because I am not entirely sure about the answer. I have never studied buckling resistance of steel plates exposed to shear loading.
Great Tutorial!
Thank you for your very useful and detailed video tutorial. Currently, I am doing my thesis on studying the stability of steel I beams that combine initial deformation and residual stress. Can you help me how to incorporate residual stresses into the nonlinear buckling model? Thank you very much. Hope to contact you soon.
Load -> Predefined fields -> Stress
Good Luck
Thanks for this useful video!
I found that force control is used in your video. Will it be any different to use displacement instead? The reason that I am asking is that I found that the result obtained by force control and displacement control is different for LTB analysis in my study.
Many Thanks!
Delon
It is possible. Finite element modeling is a very complex procedure and engineers often encounter illogical results. That is why numerical modeling without experimental background has very little meaning. I personly never investigated such phenomena but I would be interested in your research if you would publish it.
If we have a job with 2 steps, the first step is static, general and the second one is static, Riks. so how can we apply the imperfection for only the second job?
wish your helping!
This was a great tutorial. I have a question though. If we have to do a buckling simulation of a plate with multiple kinds of loading like Shear and Compressive,
Doing the initial buckling analysis how do we find the eigenvalue for this case. How does the Eigenvalue apply to both the loads?
thanks for this video, it is helpful, but what about residual stresses, they are not modeled. thank you again
I already answered that one
Load -> Predefined fields -> Stress
Good Luck
Thank you! that was very helpful.
Thank you my man
Thank a lot for the vedio.I have a doubt How to find buckling stresses
After nonlinear analysis is complete you can easily do it. Abaqus has a tool that allows user to obtain stresses from arbitrary point. I recommend using "von Mises" rule for stress calculation. Regards!
@@ivancudina93 buckling stresses and von mises stresses are different I guess..
@@mariajames6737 If you are referring to elastic buckling stresses (which is a theoretical value) than Abaqus does not have a function to determine such value. But you can calculate it using common rules.
can anybody help me how to do a buckling analysis with the biaxial problem in a plate.
Hello Mr. I followed your videos from Iraq. Could you please help me by Masonry wall.
If you have a time. How I can contact with you. Thanks
Hello!
Unfortunately, the scope of my research does not cover masonry structures, so I can not assist you in that matter.
Regards!
Dear Ivan:
I have few problems that in the first step of Buckle in Linear perturbation, I use displacement control to fit my experiment conditions.
I set for 6 eigenvalues and I can get the results.
And then for the static, riks step, I change the displacement control above to load and apply the first eigenvalue.
I want to make a stress-strain curve so I set the history output for RF3 and U3.
I don't really understand how to get RF3 and U3 correctly.
If I follow your step to multiply LPF and the first eigenvalue, the RF3 seems to be reasonable because it fits to my experiment results.
But if I take the results from history output, the RF3 seems to be weird.
Can you please leave your email? So we can continue there.
Thanks a lot. I have a question.
In my study, I am performing an analysis of an LSF system wall, made up of cold-formed U-type profiles. My question is: how to do the initial buckling analysis to find the initial imperfections? Should I run buckling models with isolated profiles? Or should I run the blucking analysis of entire wall?
Carolina, I am sorry but I don't have enough expertise in that field to give you a reliable answer. Best of luck on your research. Regards!
Thanks for the very useful video. I am modeling a composite joist and have successfully carried out the eigenvalue buckling analysis, however, trying to do the non-linear analysis using the Riks method, I kept getting this error message " A zero displacement solution was found in the first iteration of the Rik's step. The Analysis cannot proceed. the most likely cause is that all displacement degrees of freedom are constrained to be zero" Please, how can I solve this problem.
I can't say exactly without additional info. Try playing with the boundary conditions and loading to see if it will help. If not, send me the model, and if I find some time, I'll try to find the error.
Hi I find this video is very useful, Is the maximum loading we get from this buckling analysis the same thing from what we called collapse loading? I'm a bit confuse on the definition of buckling and collapse analysis. thanks so much for making the good video.
instead of deleting the old step, you might try "Replace" instead of "Delete".
So the largest value of the load from Excel is my new critical buckling load considering imperfections?
Yes. For this particular specimen modelled it is the ultimate load.
@@ivancudina93 I tried to do this but my LPF gets bigger than 1.0 - how is this possible?
I have used pure elastic material for your information
@@lw7474 It is completely fine to have LPF>1,0. It means that the resistance of your member is greater than the load you applied in the model. Regards!
@@ivancudina93 but I applied the load in the size of the first eigenvalue. So it shouldn't become bigger than 1.0 I guess...
Thank you very much for the video! Is there is a way to remove the applied load (add an additional step) after the non-linear buckling analysis, allowing the section to return to its original position (unloading)?
There is a way to do everything in Abaqus. Please send me more info to ivancudina93@gmail.com
Thank you very much. I just emailed you!
Thank you for an amazing video. I have few doubts regarding the significance of the command *NODE FILE U, what does the "U" represents in that command? Also I'm doing non linear buckling on a pressure vessel should I use the same command for node file extraction? Please reply when you find the time. Thank you.
Check the Abaqus keywords manual. I'll put the link.
dsk.ippt.pan.pl/docs/abaqus/v6.13/books/key/default.htm
@@ivancudina93 Thank you very much.
Hihi, great video. I have a question abou tht eimperfections. In the intro you state that residual stresses also need to be included in this analysis. Unfortunately i didn't find this back in the actual tutorial. Can you explain to me how to add this to the model? Thanks in advance!!
Load -> Predefined fields -> Stress
When I edit keywords, DATA check keeps saying: "NO STEP DEFINITION WAS FOUND", even if I undu the changes.
In which analysis? Eigenvalue or Riks?
Thanks for the video! It is really helpful. A few questions here, I'm doing nonlinear buckling analysis for rebars, and I'm a bit confused about the imperfection. In the keywords "*imperfection... 1, 28.0", how do you determine it is 28?
Second thing, for the nonlinear model, is "*imperfections, file=job1, step=1 1, 28.0" the only thing to add in the keywords? Do I keep "*node file, U" as well?
Third thing, can you make a tutorial on plotting stress strain curve in Abaqus?
Thanks in advance!
Hello there!
At around 3:40 you can see a table taken from Eurocode 3 which states that the size of the imperfection for this kind of cross section and plastic nonlinear analysis should be Length/100 which equals to 28 mm.
Regarding the keywords in the tutorial, I suggest you do exactly as I showed because abaqus is very sensitive regarding errors when editing keywords. You can find much more info on keywords in Abaqus manual if you are interested.
Finally, I don't plan to make any tutorials in the near future but it is very simple to plot stress-strain curves. However, it is not difficult and I am sure you figure it out on your own. Unfortunately I do not have Abaqus on my computer currently so I can not write exact steps.
Regards!
Edit: Nonlinearities used in the tutorial do not apply for the rebars!!
@@ivancudina93 Thank you for your reply Ivan! I followed your suggestion in the keywords and my model is finally working! And just to let you know I have figured out the stress strain curve. Thanks so much again your video helped my dissertation a lot!
@@antheaellis17 Thank you for your kind feedback. I am very glad my tutorial helped you!
Your video is just excellent! i learn a lot from that!! But i have a question which is the final LPF vs arc length graph, what is the physical meaning of the peak value obtained from there? Is it the maximum buckling strength of the beam? If yes, how the beam is failed as I dont see any buckling in the figure, and why the LPF is decreasing. Thank you!
Yes, LPF multiplied by the applied force respresents the ultimate buckling resistance of the beam. If you are asking why the displacement does not occur more suddenly, that is because channel sections as uniaxially symmetrical cross sections (unlike biaxially symmetrical I or H sections) behave differently. Not all elements buckle suddenly under load. For example, plates tend to show postbuckling resistance. Which means that after they buckle, you can continue to apply force of even greater value before they completely fail.
Cheers
Thanks Ivan! So how do you know about completely fail from observing the curve or graph?
The failure usually happens after peak value in LPF curve. There are few exceptions, but not in our case
Is there any academic document about value of geometrical imperfection definition? THANKS...
I took mine from Eurocode 3, table 5.1. But bare in mind it is not real geometrical but the equvivalent geometrical imperfection which takes into account all the imperfections and is a bit conservative. Real initial bow is much smaller and it can be aproximately taken as L/1000
Hi, thank you for your good training, and a question: what command should be written in the keyword to riks analyze a 4-meter span with 4 mm imperfection?
Leave everything the same but instead of "1, 28.0" write "1, 4.0".
Hi, thanks very much, an other question that, is lateral constraint of upper flange necessary in buckling and riks analysis of a pfrp I beam with 4 points loads or no?
@@omidalirostamzade3966 You can play with boundary conditions to achieve best results. There is no universal rule
Thanks a lot.
Thanks for this video. But I will ask a question about eigenvalue selection. how do we decide how many eigenvalue to request and why you select the mode I?
Give me your mail. I will send you the answer there
mrt.gund@outlook.com
How to apply point load at any point along the span in Abaqus. I mean how to apply a point load at midspan on a simply supported beam?
Just partition the model in such a way that you can place shell element on wanted position. In case od midspan, partition the model in midspan and add the shell element there. Alternativly you can try with reference points.
@@ivancudina93 Sir, am not that much good in Abaqus. Can you please make a 5 min short video of a simply supported beam subjected to point load. Please, don't mind.
Great video but I cant understand Why did you use 28 multiplication when added imperfection?
Because I took the size of geometrical imperfection to be Length/100. Since the length of the beam is 2800 mm, that equals to 28 mm. That's why I have to multiply imperfection size with 28, otherwise it would remain 1 mm. The actual geometrical imperfection is much smaller, but this is simplified way of taking into account residual stresses.
Ivan Cudina thanks for your intereset...
Why we are multiplying the imperfection from the first eigenmode with 28 in the edit keyword section?
Because the size of imperfection in any eigenmode is always set equal to unity by Abaqus. I wanted to apply the size of imperfection equal to 28 mm (span/100) because it is the value suggested by the Eurocodes. However, I believe now it is too much on the conservative side.
Regards!
@@ivancudina93 Great! thanks!
Super Helpful Video Ivan, Thank you Very much...
can you also make a video on imperfection, and why did you put 28 for 1st mode...?
what is the theory behind it?
Again Thank you...
Realistically, the size of geometrical imperfection is equal to L/1000. So, we can include that kind of geometrical imperfection into our model, but then we need to include residual stresses as well. However it is possible to model equivalent geometrical imperfection (larger then the realistic one) which will also include residual stresses. That is a simplified version of modeling nonlinear behaviour of the beam which I used in the tutorial. According to European codes (Eurocode), the size of the equivalent geometrical imperfection should be L/100 for channel sections. In our case, that is 28 mm because the length of the beam is 2800 mm. So we needed to multiply geometrical imperfection by 28 to get 28 mm.
Ivan Cudina Thank you Ivan for replying....I got the point about imperfections...
What if we don't add imperfections in our model ??
Another Thing I have want to ask is , how did you decide inputs for Rik's method, that is estimated arc length, maximum increment size etc...
If you do not add imperfections in your model, then you would get much higher value of buckling resistance. But eventually, the beam would buckle even if there are no imperfections included. You can simply try that but assigning the value of imperfection equal to zero.
And now the second part of your question. I just took some recommended values for arc length and increment etc. They worked fine so I did not go very deeply into that matter. If you want to understand that topic better, you should do some research on arc length method. Cheers
Ivan Cudina Thank you Ivan...
HOW FIXED IT
Error in job Job-2: The following results file(s) could not be located: jop-1.fil
I think you messed up keywords. Click on "Discard all edits" and type them again. If you still get an error, just do the whole model from scratch.
OK I WILL TRY
but the same error is still
Because you have not write .fil file (in that example you must write in model-1 keywords: *Node file U
thank you fore this tutorial
what about residual stress?
Load -> Predefined fields -> Stress
Good Luck
Thank you
are you have a tutorial about using UMAT ?
No, I don't
Hi Ivan, I am running an analysis for I-beam, but in riks analysis, I am getting linear lpf. I would be pleased if you could help me with this.
That means that your model is showing linear behaviour. It can be number of reasons. It could be that you are not applying enough load for the nonliear behaviour to manifest itself. It is also possible that the size of the imperfection in your model is not large enough. Or you failed to include any imperfections in your model.
@@ivancudina93 I have included 10% imperfection in my model and I am applying load as obtained in the first eigenmode. In the whole analysis, the load is increasing it is not decreasing and in the end, the analysis is aborted due to the convergence of increment.
What does 10% imperfection mean? What kind of model are you working on?
why did you put the load as 1N??
Can I have your email to ask you some questions please!!!
I am doing my dissertation in FEA LTB so i have some questions regarding it
The size of the force does not have to be 1N. But usually, in eigenvalue analysis, the force of 1N is used. Let's presume you get eigenvalue of 150 for example. That means that critical force is 150N. If you use the force of 30N for example, then you will get eigenvalue of 5 (because 5x30=150) which is a bit confusing.
My email is ivancudina93@gmail.com
I'll answer you if I find the time.
I am getteing 1.38 eigen value and Mcr as 58kN why is that..tho i followed ur step one by one!!1
For the Nonlinear Analysis, Can I use a different load, for example the self-weight or Should I always use the eigenvalue from the linear Analysis?
For some reason, when I use this eigenvalue as the applied load, it doesn't converge, and gives me lots of error. But If I applied the self-weight It gives me a result but I don't know if this result is accurate. is it?
I don't know. That is strange. It should converge in both cases. As long as the load case is the same, the results should also be the same. The only thing that is changing in regards to load value is the LPF. If you assign for example 10 kN and get LPF = 0.8, then for the same load, but with the value of 1 kN, you should get LPF=8.0.
So probably you have completely different load cases.
But I can't say is it correct or not because you did not give me enough data. If you could send more data to my e-mail about your problem, maybe I could help.
I don't know. That is strange. It should converge in both cases. As long as the load case is the same, the results should also be the same. The only thing that is changing in regards to load value is the LPF. If you assign for example 10 kN and get LPF = 0.8, then for the same load, but with the value of 1 kN, you should get LPF=8.0.
So probably you have completely different load cases.
But I can't say is it correct or not because you did not give me enough data. If you could send more data to my e-mail about your problem, maybe I could help.
Yes of course, I would appreciate your help! Could you tell me please your email?
hi ivan i'm really inspired with your tutorial, actually im just start trying to do my undergraduate tesis about inelastic buckling of tapered plate with circular opening .. and i got some trouble with modeling, i have two option about doing it with abaqus or with ansys workbench, i just started learning ansys about 2 weeks and, but its kind a hard for me to the nonlinear buckling with ansys workbench (i dont know how to input the initial imperfection etc) so i looked the abaqus tutorial of yours. well, do you have some personal contact? email maybe
Hello Raja
I'm really happy that you find my tutorial helpful
It's really impressive that you use abaqus on undergraduate level
I need more info to solve your problem, so send it on my mail
This is my email: ivancudina93@gmail.com
In the meantime, check this tutorial for workbench. It will show you very well how to include initial imperfection
czcams.com/video/aBmnTel4msc/video.html
But honestly, I prefer Abaqus ;)
what can i do
Error in job Job-5: Too many attempts made for this increment
I don't remember making Job-5 in my tutorial. I think easiest solution for you is to go through tutorial again and follow each step more carefully.
Did you solve the problem? If yes can you share how?
Sir, I applied concentrated loads on reference points but am getting an error when am submitting the job. It says "the points on which point loads are applied are not active". Sir, how can I activate these reference points in the model?
I also had problems with reference points. Try to introduce shell element on midspan od the beam and apply load there like I showed in the tutorial.
@@ivancudina93 Sir, I resolved the problem of reference points. Finally it worked, Bam. Thanks.
Thanku very very Much Ivan, I learnt very much from this video.
Please upload many more Videos like Non-linear Buckling Analysis of Column,
If not possible give your any Contact so that i can get help from u. Please.....
I got the mail in previous Comments.
ivancudina93@gmail.com
Thanks Sir
Ivan Cudina i request you to upload a video for calculate shear center using abaqus,i really need that help.
i also mail about the same on the e-mail given by you. Thanku in advance....
I will send some info on your email
Why you not model the beam by shell element (not solid element as your model)?
I explained it in the tutorial
6:35
why r we multiplying the eigen mode with 28
Realistically, the size of geometrical imperfection is equal to L/1000. So, we can include that kind of geometrical imperfection into our model, but then we need to include residual stresses as well. However it is possible to model equivalent geometrical imperfection (larger then the realistic one) which will also include residual stresses. That is a simplified version of modeling nonlinear behaviour of the beam which I used in the tutorial. According to European codes (Eurocode), the size of the equivalent geometrical imperfection should be L/100 for channel sections. In our case, that is 28 mm because the length of the beam is 2800 mm. So we needed to multiply geometrical imperfection by 28 to get 28 mm.
How did you calculate the Critical moment theoretically
I will put below a link for the paper where you can see the formula and its factors explained. That formula is valid only for doubly symmetric cross sections but I believe it can be used for channel sections if they are loaded centrically, that is through the shear center.
eurocodes.jrc.ec.europa.eu/doc/WS2008/SN003a-EN-EU.pdf
Will you please make a video on web buckling of plate girder.
Unfortunatelly I don't have time now for making any more videos
Ivan Cudina please do I'm also stuck in modeling a plate girder for failure in bending only (elasto-plastic analysis). Should i go through this same process and I'm using a uniformly distributed load instead of point load. Should my udl be 1lb/in as you used a point load of 1N to get an eigenvalue
You can use 1lb/in if you want, but you don't have to. You can use any value in eigenvalue analysis. With plate girders I would recommend using shell elements. I don't know exactly what is the scope of your research but try reading this paper on modeling of web crippling (www.steel-stainless.org/media/1117/25_bock_real_arragay.pdf )
Ivan Cudina I'm using shell. Please is there a way to reach you that way i can explain better. Email perhaps. I'm in dire need of help
Akaolisa Okafor ivancudina93@gmail.com
Can you share with us this presentation , please ?
Unfortunately, I don't have it anymore.
@@ivancudina93 Ok, thanks so much, sir
Excuse me, I am a new learner in Abaqus. So my question could be quite crazy.
But, Can you tell me how to calculate the critical moment (Mcr) and design momen (Mn) in Abaqus. Because your video stop when you determine eigenvalue
Thank you very much.
Son Tung Vy
Eigenvalue is easy
You have analitical equation that you can use, or some free simple software like LTBeam.
For the design moment you use
GMNIA analisis (like I showed in tutorial).
There are no design rules to get the design moment for channel section yet.
Actually, there are some proposed design rules that I can send you
Thank you very much,
However, Can you tell me how to calculate the critical moment (Mcr) and momen resistance (Mn) of a bended beam in Abaqus. Because I want to determine for other type of section (in LTbeam does not have this type of section).
Son Tung Vy
The eigenvalue gives you the information about critical moment
Also, in LTBeam you have option Section by properties
It works for any tipe of cross section.
To get the design moment you need to include the nonlinearities in your model like I showed in the tutorial, 2nd model (nonlinear stress strain curve of the steel and imperfection)
If this doesn't help, send more info on my mail (in description)
Dear Ivan Cudina, I am currently building up a model to determine the LTB critical moment for glass beam and i faced the same problem of determine the critical moment. I had set the model as 3D solid the same as yours therefore cannot obtain Mcr direct from the model. I though the eignenvalue value will allow you the determine the critical load only. How can we determine the Mcr from Critical load? or if there anyway can obtain it from the model?
oh using moment equation such as L x Pcr = Mcr directly will give me the answer?
More videos daddy
Can anyone please tell me how to find imperfection sensitivity for a cylindrical pressure vessel. Thank you in advance.