Soil Structure Interface Modeling

[STKO Team]

Is this just unchecking the Implex box in the zerolengthcontactASDImplex settings

Yes, If you want to use the standard Backward-Euler (implicit) integration scheme, just UNCHECK the IMPLEX setting.

Regarding time step, I cannot see that I specified the time step anywhere. Should I just increase the numInr in analysis settings

Exactly. If you want to decrease the time-steps size, just increase the number of increments keeping the analysis total duration the same

[kolozvari]

Hello, as I am continuing to refine my SSI model I am running into more issues and I would appreciate if you can help.

I am currently trying to model subterranean levels more realistically as they were currently modeled as a rigid foundation block (see 1st figure). In order to connect all walls to the basement level slabs, I have decided to divide the geometry so the slab and the walls connect (see 2nd figure) - that way I don't have to use embedment penalty constraints as I did in the previous iteration. However, this seems to complicate modeling of soil foundation contact, which is what I am currently struggling with.

It would be great if you can answer my questions:
1) I have created contact interactions for each face of the foundation-soil interface (X+, X-, Y+, Y-, Z-), However, it's graphical representation is different than before. The interaction shows only on foundation, but not on the soil (see figure 3). Is this normal? Did I make a mistake when creating these interactions? I am assuming this is because the geometries are not perfectly aligned. Btw, I found it was very challenging to select slave and master geometries because the faces are at the same location and I have created selection sets to do it. Please advise if this is correct way to do it.
2) Related to the previous topic, does it matter which one is master vs slave geometry when creating interaction (foundation vs soil)? which one is preferred way to do it?
3) Regarding contact elements, I used to use "From local axes option". However, this requires defining local axes and assigning them, which is a bit cumbersome. Does local axes need to go from master to slave or they only have to be aligned with the surface? Would using "From link direction" be correct in this case and would that be sufficient to make it work?
4) Finally, I receive an error that "Different NDF on same node". I used to have this error when I tried to connect beam to a solid, but this is not the case here anymore. It is possible that this is now because I am connecting a wall (shell) to mat foundation (solid). How do I solve this issue?

I attached the model for your convenience. Thank you very much!

[STKO Team]

1) I have created contact interactions for each face of the foundation-soil interface (X+, X-, Y+, Y-, Z-), However, it's graphical representation is different than before. The interaction shows only on foundation, but not on the soil (see figure 3). Is this normal? Did I make a mistake when creating these interactions? I am assuming this is because the geometries are not perfectly aligned. Btw, I found it was very challenging to select slave and master geometries because the faces are at the same location and I have created selection sets to do it. Please advise if this is correct way to do it.

Sometimes, when there are a lot of faces, we simplify the representation of interactions in the Geometry View. To visualize them correctly switch to the Mesh view. Do your mesh and check the interactions, you should see all of them.

2) Related to the previous topic, does it matter which one is master vs slave geometry when creating interaction (foundation vs soil)? which one is preferred way to do it?

If you are using compatible meshes (foundation and soil have a node-to-node alignment), and therefore you are using a node-to-node link, there is no difference. You only have to pay attention to the contact normal direction: IT SHOULD GO FROM MASTER TO SLAVE

3) Regarding contact elements, I used to use "From local axes option". However, this requires defining local axes and assigning them, which is a bit cumbersome. Does local axes need to go from master to slave or they only have to be aligned with the surface? Would using "From link direction" be correct in this case and would that be sufficient to make it work?

"From link direction" only works when there is a gap between master and slave nodes of the link (like in the zerolength elements in OpenSees). Because in this case, we compute the normal contact vector as (slave-master)/norm(slave-master)

4) Finally, I receive an error that "Different NDF on same node". I used to have this error when I tried to connect beam to a solid, but this is not the case here anymore. It is possible that this is now because I am connecting a wall (shell) to mat foundation (solid). How do I solve this issue?

Yes, it's the same exact problem, shell have 6 DOFs while solids have 3 DOFs. So you have to make them detached, and connect them with EDOF in Ux,Uy,Uz

[kolozvari]

Thank you for quick reply. I have a few follow up questions.

If you are using compatible meshes (foundation and soil have a node-to-node alignment), and therefore you are using a node-to-node link, there is no difference. You only have to pay attention to the contact normal direction: IT SHOULD GO FROM MASTER TO SLAVE

I am not using compatible meshes, which you can see in Figure 3 from the previous post, where soil and structure have different geometries, and therefore different meshes. It might be possible, but pretty difficult to make the meshes compatible. Is this a problem? Is there any simple way to make meshes compatible?

In case meshes need to be compatible, it seems that I should divide geometries of the soil in the same way as I divided geometries of the basement structure. Is there any easy way to do that without having to re-do the entire soil domain? Is there a way to simply "split" the soil geometries?

Yes, it's the same exact problem, shell have 6 DOFs while solids have 3 DOFs. So you have to make them detached, and connect them with EDOF in Ux,Uy,Uz

OK, just to make sure I understand, I need to create a new interaction and assign the equadDOF constraint with only Ux, Uy, Uz. This is only 1 interaction, correct? Please confirm.

Thank you!

[kolozvari]

Hello, I am working on aligning mesh between the soil and the basement levels/foundation, but I am running in some issues. I draw faces through the soil domain and performed MERGE command as you suggested in one of the other posts, and the geometry looks fine (see figure 1 below). However, when I create mesh I encounter an error saying "MpcSolidMesher error: front and back faces have incorrect number of elements (!= nx*nz)" (see figure 2). I am not sure why is this happening and what to do to fix it.

Regarding creating equalDOFs to connect walls to slid elements of the foundation, I am not exactly sure what needs to be selected as a master and what as a slave (see figure 3 below). Do I select foundation solid as a master and wall face as a slave or do I select foundation solid as a master and wall edge as a slave, or any other option is appropriate. Please advise.

Thank you.





Please let me know. Thank you.

[kolozvari]

Hello, I would really appreciate if you can respond to my message above soon. I have been stuck on this for a few days now.

Thank you.

[STKO Team]

Sorry for the late reply.

Problem 1: contact with non-compatible meshes.
If the master and slave faces of the face-to-face contact are not compatible, you can follow what we did in the webinar about the ASDImplex Contact Element.

• Create a node-to-element interaction
• The face with the coarsest mesh is the master
• The face with the finer mesh is the slave
• In the zeroLengthContactASDimplex element property, choose "Orientation Type" = "Element"

In this case you don't need to assign a local axes because the contact normal is taken from the master element (which in your case is the boundary face of a solid)


Problem 2: contact with non-compatible meshes.
For EqualDOF there is not difference in what is the master and what is the slave. I mean, no physical difference.
Note: If you use the Transformation handler, there is a computational difference, due to the fact that a node cannot be master and slave at the same time in multiple constraints. But if you use the Penalty approach there is not such a problem

[kolozvari]

Thank you for your reply. However, you didnt answer my main question, which is related to issue with meshing. I would prefer to have compatible meshes as the model seems "cleaner" that way. After I draw faces through the soil domain and merge the soil domain, the mesh gets totally messed up. Some elements that used to be quad become triangular, while part of the mesh didnt create at all. I really dont understand what is going on. I re-did this several times and although I am doing exactly the same steps, the mesh looks different. Please see my previous post for screenshots. I am sure it is something related to mesh settings, but I cant figure it out. I attached the model and I would appreciate if you can take a look.

Thank you.

[kolozvari]

You also didnt answer my question about equalDOF. I would really appreciate more direction on this.

Do I select foundation solid as a master and wall face as a slave or do I select foundation solid as a master and wall edge as a slave, or any other option is appropriate. DO I use node-to-node or node-to-element interaction?

Thank you.

[kolozvari]

Hello, I have created another two models using slightly different approaches comparing to the one sent above, but unfortunately I have issues with both of them (see attached).

Model V3.0:
- foundation and soil dont have compatible meshes and I am using Implex contact elements with "From element" orientation type per your previous suggestion. I would appreciate if you can check if this is done correctly.
- in this case I am trying to connect core and foundation walls to foundation with equalsDOFs, however, I am not sure how to do it. I tried few different options and even when I creating something that makes sense, I cannot assign equalDOF condition to the interaction. It simply wont let me "pick it up" and assign it for some reason. I would appreciate if you can help with this issue.

Model V3.1: I created this model to overcome issue with equalDOFs described above and I created foundation as a one solid geometry and I wanted to embed the core and foundation walls into the foundation using ASD embed note element. In this case there are two issues:
- there is a meshing error when I try to create a mesh and for some reason I cannot select the faces of the foundation block
- similarly to equalDOF above, I cannot assign embedment condition to the previously defined interaction. It simply wont let me "pick it up" and assign it for some reason.

At this point I have 3 models that are all different, but should be doing the same thing: 1) model with compatible meshes between foundation and soil that has issue with mesh generation (sent earlier), 2) model with incompatible meshes between foundation and soil and issue with equalDOFs assignment (attached), and 3) model with incompatible meshes between foundation and soil and issues with meshing and embedment assignment (attached).

I would really appreciate if you can help me make work any of these three models.

Looking forward to hearing from you. Thank you.