Adding simple soil springs

[kolozvari]

Hello,

I would like to add soil springs around the basement walls and beneath the building (see screenshot below). Can you please walk me through the procedure on how to do this?

Thank you,

[STKO Team]

• Duplicate the faces of the basement walls. On these duplicates do not assign any element/physical property. In this way STKO will generate only nodes. Fix all dofs of these new faces.
• Create a node-to-node interaction between the walls and the duplicates.
• Assign a distributed zeroLength with appropriate materials in X-Y-Z translational DOFs

[kolozvari]

That's what I thought, but wanted to make sure. A few follow up questions:
1) Should the duplicated faces be at the same location (overlapping) with the basement walls, or shoul there be any distance in between? If there should be a distance, what should it be?
2) Which one would be a master vs/ slave geometry?
3) In the case of uniform excitation, wouldnt this apply acceleration at the constrained sides as well? Is this OK?
4) What would be the stiffness of the soil springs? Does STKO under "distributed option" assigns the stiffness based on the tributary area? What would be the units of the soil springs?

Please let me know. Thank you,

[STKO Team]

1) Should the duplicated faces be at the same location (overlapping) with the basement walls, or shoul there be any distance in between? If there should be a distance, what should it be?

You can do whatever you want. A zero-length does not consider the distance between the nodes. But if you keep a finite distance there will be (only at the beginning) annoying warnings from OpenSees reminding you that you put a non-zero distance while it will not be considered by the zero-length (it's a spring after all).
I typically keep a distance for easy modeling of interaction. Then I move them back to avoid warnings. If you have many (tens of thousands) springs those warnings can slow down the processing of the file at the beginning

2) Which one would be a master vs/ slave geometry?

Not important, as long as the local axes of interest point from the master to the slave (it is important for non-symmetric behaviors). If the behavior is symmetric it doesn't play a role.

3) In the case of uniform excitation, wouldnt this apply acceleration at the constrained sides as well? Is this OK?

Yes, but it is ok. The fixed nodes are fictitious, you are modeling the effect of the (non-rigid) soil within the springs

4) What would be the stiffness of the soil springs? Does STKO under "distributed option" assigns the stiffness based on the tributary area? What would be the units of the soil springs?

You define a stress-strain law in the uniaxial material that you put in the zero-length (so the E will be force/area).
Then, with the distributed option, STKO will take the tributary area (because now your master and slave nodes belong to surfaces) and use it as a stress/tangent multiplier in a parallel material used behind the scenes.
Here is an example:

test.zip

(22.28 KiB) Downloaded 4 times

distr.png (10.89 KiB) Viewed 304 times

[kolozvari]

all makes sense. Thank you.

[STKO Team]

You're welcome