Alternatives to 1D Beam and Truss elements

General Questions
1

Hello everyone, I’m new to PrePoMax and to this forum, sorry in advance if I am not posting in the right place. I’m currently working on a custom scaffold composed primarly by beam elements, and would love to use open source software for its structural design. However, PrePoMax currently does not have this implemented, even though Calculix does. I read in this thread that this is one of the next things the design team is going to implementate, and i’m really excited to it.

However, I would like to know if you guys have some idea on how can I model and use 1D beam elements using open source software ? I thought on using FreeCAD an its native Calculix processor, but I would like to know if there is any other softwares (or maybe PrePoMax with some input file modification).

Thanks! Greeting from Brazil.

1 Like
2

FreeCAD supports CalculiX’s beam elements but be very careful when using them (regardless of the preprocessor). Beams in CalculiX are prone to errors. In most cases, it’s enough to just refine the mesh significantly or change the type of beam element but there might be also errors that can’t be solved this way. At least with general sections (user beam element).

3

Hello FEAnalyst, are you the owner from the Youtube channel with the same name? It’s a pleasure to talk with you.

Why do you say so? Their formulation has errors? When you say general sections, do you mean user defined section or pre-implemented sections (rectangular, circular, pipe…)?

I will be careful whenever using them. Thanks for the advice!

4

Yes, I prepare YouTube tutorials for PrePoMax.

What I mean is a type of beam section that has no predefined shape but is defined using section properties. Here’s the bug that still hasn’t been fixed:

Apart from that, there are some problems with accuracy, especially when plasticity is involved. But in such cases it’s enough to just refine the mesh significantly or use a different type of beam element:

1 Like
5

many beam implementation out there, such as classical (linear, Euler/Bernoulli, Timoshenko), fiber (nonlinear-material/geometry, slender sections, global stability), composed (nonlinear-material/geometry/boundary, deep sections, local/global stability).

anyone need to digest the capabilities and limitation of each software being used. if i may say CalculiX beam element has many advantages, challenging another beam implementation.

accuracy and validity much depend on how the user creates a model and cases. since most of my problem are nonlinear, so i like to says it’s about reliability rather one of them.

hope i can discuss further with Matej after the first and basic implementation of beam element in PrePoMax. exploring beam element capabilities in CalculiX, submit a model and document verification, or any necessary.

1 Like
6

Hi @lucas_bueno, my workflow for beam modeling is made the cad modeling in Solidedge as 3D sketch (the only kind of lines that will be exported in a step file, sometimes I make a classical 2D sketch for getting all the constrains tools, but after I have to convert to 3D sketch lines), or use FreeCAD (here the 2D sketch is exported), and create again a step file with all the lines. After that I import in Salome to create the mesh, and maybe some groups for material/section/bc definition (that will be critical if you plan to work with only open source tools).

After that I use Mecway FEA (ooopsss sorry, but beams are not supported yet in Prepomax) to create the model in a visual way, but you could do it by hand using any text editor and running CCX from command line, as in the old times :slight_smile:

In Salome you must export the mesh as UNV, and then use some conversor as UNICAL to translate to .inp format.

I suggest you install the Bconverged CCX suite, that came with Scite, a text editor with CCX cards markup, but also will let you pre/post with CGX and run CCX directly without using the command line.

Two important thing to note: If you made the CAD in FreeCAD, is very common that the intersection of two lines is not perfect, so two nodes will be generated in the mesh and they will be two separated members, unless you stich the nodes manually in Salome (dear @Matej a tool to stich nodes at certain distance is very needed for beam meshes imported from Salome, is a very common problem) . And the second, if you install Bconverged CCX, don’t forget to replace the old CCX/CGX executables with the new one from the CCX site, or from the Prepomax installation.

My final advice is that first you use Mecway for creating the models until Prepomax have it enabled, even if is a comercial program, will let you work for models bellow 1000 nodes (that for beam modeling can be enough), but also will let you check the beam orientation, something that CGX as far as I know can´t do.

Best regards from a neighbor from Argentina!

1 Like
7

i prefer Salome CAD/CAE to modeling, make group of element by section or distributed load and group of nodes by support or point load. meshing 1D using number of division then export to UNV, there’s available converter.

in case of 2D analysis models with less number of sections type, distributed load, point load, support. you may use QCAD to create DXF files, i make some converter placed on GitHub. no meshing is required since it generates FBD files with setting. the converter also work for 3D models, but i did not found any good opensource software to create the model easily.

1 Like
8

Understood, @FEAnalyst. In my case, I’m only interested in the elastic behaviour of the structure. I will use the elements carefully, especially when choosing the type (as I have perceived, the one with normal integration has the worst results). I’m planning on conducting simple tests to validate (or not) using analytical formulas from Roarks’s book before analyzing my desired structure.

Probably I will consider using solid elements as last resource. Thanks for the help!

9

I wasn’t aware of the formulation errors, I will be cautious with this in my projects from now on. Hopefully PrePoMax will get support for beams and trusses soon.

10

Hello @SergioP1975 , thanks for the advices. Since my model is naturally 3D, the preprocessing is very important and would help me a lot. I have no experience with Mecway FEA or Salome, I will try them out. When I first tried Calculix on Windows, I tried to install Bconverged executables but they did not work, not sure why. What worked for me was to install Ubuntu on a virtual machine and this video helped me to install the 2.16 version and run some example *.frd files.

Probably my section will be circular (pipe or solid), so beam orientation probably won’t be a issue, but for future analysis I will be aware of this. Definitely I will check Mecway, sounds like a good software to start with. Thanks for the help!

11

Hello Lucas

If you use the Linux distribution I have given the link below, you will not encounter library incompatibility problems. All engineering applications come pre-installed.

1 Like
12

You could start from scratch in Mecway, just defining the corner nodes of the structure by hand (coordinates), and then creating beam elements between them. After that you could refine this beams to have more elements and choose the appropiate section and material for them. In Mecway you can work with two solvers, internal and CCX, so you have a point of comparation to start. Seeing the real section while you preprocess is also nice and could help you to prevent some mistakes.

What kind of problems do you have with Bconverged? I just installed yesterday on my laptop and was straightford as always, just unzip, install and choose a temporal folder for the example problems. After that you just need to replace the CCX/CGX executables.

1 Like
13

Such a interesting tool, @ali , thank you for sharing.

It would help me a lot, Sergio. Also, having a friendly user interface is always useful. Again, thank you for sharing this software.

I did as mentioned in README, to replace the CCX ang CGX executables for 2.19 ones but when I opened some *.frd results, couldn’t see the stress or displacements. The “Data Sets” from the menu of CGX were missing from list and I could not access them. I followed the tutorial from this link. Not sure what I did wrong.