Build zero-length element between beam end and the solid element

[Yu-WeiHwang]

Hello,

Sorry to bother all!
I have a question is about building the zero-length element between beam end and the solid element in three dimensional domain.
My problem will be look like this:
-----------
| ---------|
| ---------|
| ---------|
| ---------|
*---------*
| foundation |
-------------
Note : the symbol, *, represents the location of the zero length element.
The attached is the STKO model I used to build the model!

Thanks a lot!! I will appreciate any help!

[STKO Team]

Dear Yu Wei,

Can you be more specific on the problem you have?

I had a look at your model and I noticed the following error:
You used a finite element 20_8_Node_BirckUP, which has 20 nodes, while in the mesh controls you used a Quadratic hexahedron with 27 nodes. You should use "Quadratic (serendipity)" that has only 20 nodes (i.e. no mid-face and mid-volume nodes, only corner and mid-edge nodes)

The only thing that I noticed about the zero-length elements, is that you used the same type to connect the columns to the beam, and the columns to the foundation. However the zero-length is 3D-U, so only 3 translational dofs. In this way you are releasing all rotations. Is this what you want to do?

[Yu-WeiHwang]

Hello STKO team,

Thanks for your quick reply.
Yes, I used the serendipity element but I don't know why in the mesh control the color will be the same no matter I used Quadratic or Quadratic serendipity element.

To make the connection between column and foundation, I think the only connection I can use is 3 translational dofs, but I am not sure how can I do that. When I directly build the node-node interaction between column end and foundation, and apply the zero-length material and element to that interaction, the program will tell me that I am building a 2D zero length element. The only way I can do is to build a general link (master: beam end, slave: foundation) and a node-node link (master: foundation, slave: beam end) at the same point and same time, then apply the zero length element and material to the general link then I can build a 3D zero-length element for column to foundation. However, when I tried to run the model, it will always showed nan error. Is there any better way or did I do something wrong?

I appreciate your help!

[STKO Team]

Dear Yu-Wei,
Looking at your file, it looks like you made it with a very old version (pre-Beta) of STKO. Can you try to do the same with the latest version?
There should be no problem linking a 3-DOF zero length between a solid and a beam.

Now keep in mind that in this way you are crating a pin at the column-foundation interface. If instead you want to make a continuity also in rotation:

• create an interaction with:
  • master = beam node
  • slaves = faces of the foundations that coincide (more or less) with the cross section of the beam
• assign a condition to this interaction of type BeamSolidCoupling

[Yu-WeiHwang]

Dear STKO team,

Sure, but can you help me check the attached file first? It is my reference model. I use the same method to build the model. However, in the old version of STKO, it will let me generate the script but in this version it always showed
"different dofs on same node"
I am not sure where is the problem...It looks like there are some conflicts when I use fix and equalDOF at same time....but why it will have this problem?

Many thanks for all your help!

[STKO Team]

Dear Yu-Wei

I found the issue. It is related to the fact that the 20_8_Node birckUP element has the extra Pressure dof only at the corner nodes, while only Displacement at the mid-edge nodes.

Then when you assign a EDOF or FIX command with U-P it complains about the fact that some nodes (the mid-edge ones) do not have the pressure dof that you want to constraint.

We created this error to let people know when they are constraining a DOF that do not exist in the model.
Now we can solve it by removing this error.
However what is going to happen is that, whenever you try to constrain a DOF that do not exist on a node, you will not see any error...

Today I will send you (by e-mail ) a modified version of the some python scripts in the external_sover directory. Then I will include it in the new release.

[STKO Team]

Dear Yu-Wei,
Sorry for the delay, I'm sending you the modified "external_solvers" folder with the necessary changes to fix your issue. When you donwload it, replace the existing one (C:\Program Files\STKO\external_solvers) with the new one. Let us know if it solves your problem.

Then these new version of the "external_solvers" folder will be present in the new version of STKO in the following days.