SSI issue - Shallow spread foundation on sandy soil

[MekGreek]

Hey to all the Asdea community!
I am opening my first topic, I hope that my doubt is useful for everyone.
My model is a shallow spread circular foundation made of concrete on a sand soil stratum with SANISAND-MS costitutive model. The model is an Onshore wind turbine.
I am loading the foundation with a vertical load to reproduce weight then cyclic moment application which simulates the wind effect in static regime.
So the body motion is pratically the so called "rocking", the foundation's rocking over the soil with cyclic loading and unloading.
The contact between the two bodies is direct, I've not introduced any equalDOF condition or contactElement.
The outputs of the first cycling analysis it works but the soil does not behave well, infact does not show any plastic strain, hardening and hysteretic behaviour.

I suppose there is a problem maybe on the modelling of the interface bewtween the two bodies.
Could you give me your clues and experiences please?

[kesavapraba]

Hi, Good to hear from you. Did you watch the following webinar on SSI?
https://www.youtube.com/watch?v=OGII3a0gQqI

[MekGreek]

Thanks a lot for your answer.
No, I did not watch it, I am going for sure to do that. I'll let you know how to figure out the problem if I'll find the solution.
Could maybe the Contact element method proposed by Sivapalan Gajan and Bruce L. Kutter be a solution?
Warm regards

[MekGreek]

Hello kesavapraba!
Really interesting webinar but sadly it ends right when the shallow foundation is added.
Do you know if eventually there is online the 2nd part of this webinar where the foundation is added?
Thanks a lot!

[STKO Team]

Can you share your file?

[MekGreek]

Good morning STKO team.

Thank you
Before to go in further investigation one moment:
as I've described in my model at the moment there aren't contact elements (as the zerolenghtASDimplex) so the soil and foundation element are directly in contact.
I did not apply any particular condition or interface elements cause experimentally there was not detachment or sliding.
Shall I add anyway contact elements bewtween soil and foundation as the zerolenghtASDimplex?

Actually, I've developed my model directly in Tcl envinroment scripting.
Is it nice for you if I share directly the .tcl script with all the model and the analysis written?
I think it's already clear to understand my problem.
Otherwise if you are not agree I ask you just a moment of patience because I have to update my stko model.

Warm regards!

[kesavapraba]

Hi, No problem skipping contact modeling if your analysis only focuses on the current loading and shows no movement between soil and foundation. However, for accuracy and to explore the model's behavior under different loads (larger than experimental load/dynamic), simulating contact is crucial. Because, it is not be sure at this loading whether the interface will be intact under all such loading cases.

When modeling contact (using zeroLengthASDImplex), please incorporate realistic interface properties based on relevant research or experimental data.

For easier visualization and utilizing the advanced features, creating the model in STKO is preferred. However, the Tcl script is also accepted for troubleshooting purposes.

[MekGreek]

Good morning Forum and kesavapraba!

I am so glad of your reply, behind this posts there are struggles.

Excatly, my analysis focuses on the tilting under overturning moment and vertical load of a shallow foundations.

So, now I've got a crucial answer: the output of the analysis of the model in which there is no interface but direct contact has given results, actually a bit of horizontal sliding there is, in the order of 1*10^-4m. As expected that is not the relevant phenomena (my study is interested in the tilting rotatation of the foundation) but anyway THERE IS.

Since the sliding is not 0.0m; Does the simulation of the contact, so modelling an interface, make an improvement of the performances of the SSI behaviour in general, so also for different aspects as the tilting rotation?

For example my Supervisor is conviced that having an interface is pointless because he says "there is no sliding", but by FEM numerically is not deeply true.

So many thanks and warm regards!

[kesavapraba]

Hi, The answer depends on the context of the problem; in your case, you can test it out if it is doubtful. I can see that the relative displacement is small (0.1 mm); however, please ensure that it does not significantly influence other structural responses or the failure mode. You can make two minimal examples with/without contact to understand the problem well and be confident.