• Registered: 2022-09-28
  • Posts: 3

Topic: Loading of a 4-Point-Bending-Beam

Hello,

I am trying to model a four Point Bending Beam made from FRC. I am using Gid Science in combination with ATENA Studio and "Cementious 2 user" as material model. The Model is a 3D Beam.
My first attempt was similar to the 2D Tutorial for FRC. I applied the same displacement on each loading plate. As the main Crack didn't developed symetricaly I got positive Forces in one of the boundary plates (Which wouldn't happen in reality).

I`ve read in the forum about a similar Problem and a developer suggested two methods to face those difficulties:
- loading via a force at each point and solving this with arc-length-solver (I tried this but the analysis always got really bad convergence after second crack started to develop)
- modelling the moveable beam of the testing machine as in reality -> That's where my question refers to.

Now I tried to model the beam of the Testing machine, which is able to rotate and therefore a uneven displacement of the loading plates is possible and therefore no pulling at the boundary plate can happen.

I tried to model the hinge by the conection of the beam of the testing machine with the loading plates via "fixed contact for line".

When I am trying to run the analysis now a warning message in Gid appears:

',4MPa' Expected identifier at position 1
Warning: Some selection of condition Fixed_Contact_for_ MASTER has zero size. ContactName =Prüfmaschine links
Warning: Some selection of condition Fixed_Contact_for_ MASTER has zero size. ContactName =Prüfmaschine rechts
Warning: Some selection of condition Fixed_Contact_for_ SLAVE has zero size. ContactName =Prüfmaschine links
Warning: Some selection of condition Fixed_Contact_for_ SLAVE has zero size. ContactName =Prüfmaschine rechts
Info: Input file was written and is executed in AtenaStudio

Moreover ATENA Studio won't start at all, stating:
"Can not Start analysis - Input file was not specified or doesn't exist"

I would highly apreciate your help. Thanks in advance.

Nils Rittel

Quote Post 1

  • From: Finland
  • Registered: 2019-03-28
  • Posts: 138

Re: Loading of a 4-Point-Bending-Beam

Nils,

It would be easier to understand your problem if you share some images of your experiment setup and calculation model. Links to OneDrive/GoogleDrive would be fine.

Arc length method is not the best way when simulating experiments (unless experiment is force controlled). I would refine boundary conditions and use NR instead.

What does moveable beam mean? I suppose that if the loading beam stiffness affects experiment results then the experiment is not conducted properly.

If pulling/tension needs to be avoided, interfaces shall be used instead of fixed contacts. Generally fixed contacts should work fine and if any errors occur that means that there is a problem in the model rather than in the program. Check fixed contacts definitions, there are multiple videos/guides on how to do that.

Keep in mind that "fixed contact for line" is intended for 2D models only.

BR, Pavel.

Quote Post 2

  • Registered: 2022-09-28
  • Posts: 3

Re: Loading of a 4-Point-Bending-Beam

Hello Pavel,

thanks a lot for your quick answer.

Here are some pictures and also a scan of the actual Code whrer the experiment setup originates from.

https://bauthmde-my.sharepoint.com/:f:/ … w?e=ryQ3hQ

The force controlled experiment was a actual suggestion of the developer, as you wont have pulling force by modelling it like that. Even though the experiment should be deflection controlled. As it didn't work anyway and I would like to stick as close to the real eperiment as possible in order to be able to compare it Iwanted to model the real testing machine including the beam on top.

I think you understood me wrong, the beam ist very stiff as it's a part of the testing machine and therefore has little effect on the results.

I'll try to check the fixed contacts later this weekend. I'll do research on interfaces as well, I read about it but didn't understood how they worked or are applied and therefore tried it with fixed contacts.


Thanks again!

Kind Regards
Nils

Quote Post 3

  • From: Finland
  • Registered: 2019-03-28
  • Posts: 138

Re: Loading of a 4-Point-Bending-Beam

I got it, the problem is that the real beam doesn't crack symmetrically, therefore different displacements occur under the loading points.

My first idea would be to model only one side of the beam assuming it behaves symmetrically. However, this is not your case. It probably happened due to random nature of concrete material, small inaccuracies in the experiment setup and other non controlled issues. Usually in this kind of experiments a small crack inducer is made so that first crack occurs in the midspan.

Of course you can make a pre-defined crack in the concrete beam as per the experiment results (not certain if such simulation can be considered as "pure", you'd better discuss it with your supervisor). Even though the beam cracks unsymmetrically in ATENA, I don't see any problem with the loading frame. You have to define only Z- contacts and restrict X-displacement.

I would highly recommend to start with 2D model because the result should be identical for that kind of problem but calculation time is much less. You can later create 3D model when you get adequate results from 2D model.

There is a sample FRC beam model in ATENA example folder. Just modify the model for your geometry, that's it.

Quote Post 4