Question about mesh and modeling in STKO

[Jamildouier]

Hello STKO Team,

I created this model as a test for a larger model. The idea is to model an upper raft and a lower raft connected by supports and insulators, and to account for the effects of an earthquake. Several buildings, modeled as stick models, will stand on the upper raft.

This model is initially just a working sample. However, I'm unsure whether the mesh needs to be built exactly as in this model, or if there's a more efficient method for analysis. The final model will be significantly larger and more complex than this sample.

Thank you in advance for your help.

[STKO Team]

The 2 shells in your model are actually useless and you can remove them:

• The bottom one is completely fixed. Even if in the second stage you remove the fix in Ux, you impose a displacement (with GM), so all the nodes in the bottom shell move as a rigid body
• The top shell is completely linked with a rigid link, so also in this case, a rigid body

[Jamildouier]

Hello,

Thank you very much for your feedback.

Yes, that is correct in this case, because I assumed that there is only one representative building on the upper raft and one representative column underneath it on the lower raft. Therefore, I initially considered a simplified model.

However, the task description indicated that both the upper raft and the lower raft need to be modeled.

When I extend the model and make it slightly larger (see the attached new example), it no longer works.

Could you please take a quick look and let me know where the problem might be?

Thank you very much.

Best regards,

[Jamildouier]

Sorry, I accidentally forgot to upload the model. Please find it attached.

[Jamildouier]

Hello,

this is a kindly reminder.

thanks

[STKO Team]

This is not the way to use rigid links.

If you want to use rigidLinks, you have to carefully create cuts on the shell with the same shape of the pile cross-section. Then you will have to rigidLink every node of the pile to the corresponding cut-surface on the shell. In this way you exectly make rigid only the portion of the shell that is connected with the cross section of the pile.

Another, approximate way (without cutting the shell and using incompatible meshes) is to use the Embedded constraints (see the attached model).
If you want to know more about the embedded constraints, we have dedicated webinars you can watch

[Jamildouier]

Hello STKO Team,

Thank you for your feedback.

Unfortunately, I didn't quite understand the first option, especially how it can be implemented. Both the upper and lower rafts must be retained.

The second option with the embedded constraints didn't work for me.

Therefore, I ultimately set up the model as shown in the attachment, and the analysis runs. However, the eigenmodes exhibit unusual behavior: It appears as if the structures are tilting and as if there is no connection between the lower beams and the upper plate. I created the connections between the beams and the lower raft using merges and modeled the connections between the upper raft and the beams using rigid links.

The modes should actually represent displacements and rotations, not this kind of tilting behavior.

Could you please take a look at the attached final model and help me identify and correct the error?

Thank you in advance for your support.

[Jamildouier]

Hello stko Team,

this is a kindly reminder.

Thank you for your support in advance

[STKO Team]

This is how it works with embedded constraints:
1) One element-to-node interaction, where the master is the EMBEDDING domain, in your case the slab, and the slaves are all the vertices that should be EMDBEDDED into the slab
2) Assign to it a Embedded conditions with a properly calibrated penalty value (there is a description in the Editor)

Then, if you want to make the slab rigid, just make it's material stiffer, that's it!
Let us know if it works for you

[Jamildouier]

Dear STKO Team,

it worked—thank you very much for your help.

However, I have another question. I am working with the same model, with the only difference being that the plates must not come into contact with each other. I would still like to connect these plates without them touching (i.e., without a node-to-node connection).

In the eigenvalue analysis, the plates currently deform independently. I would like them to move and deform together instead.

Could you please advise how this can be achieved?

Thank you in advance.