AbsorbingBoundary3DAuto

[Satoru]

I am performing a non-linear SSI analysis considering soil nonlinearity, and I have the following questions about AbsorbingBoundary3DAuto.

1 : Can AbdoringBoundary3DAuto calculate non-linear free ground response? Checking STKO, the default method is to specify elastic parameters (G, ν, ρ), so it seems that AbdoringBoundary3DAuto can't consider nonlinearity of the free field. But if I set a non-linear material tag, is it possible to calcurate non-linear free ground response? It says UNDER BETA TESTING, when will it be available?

2 : When performing 1D ground response analysis, the sides of AbsorbingBoundary are not needed. So, Is it possible to apply AbsorbingBoundary3DAuto only to the bottom for the purpose of performing a nonlinear ground response analysis with input as 2E? If there is any other manual way, please let me know if there are any webinars etc.

Best Regards,

[STKO Team]

1 : Can AbdoringBoundary3DAuto calculate non-linear free ground response? Checking STKO, the default method is to specify elastic parameters (G, ν, ρ), so it seems that AbdoringBoundary3DAuto can't consider nonlinearity of the free field. But if I set a non-linear material tag, is it possible to calcurate non-linear free ground response? It says UNDER BETA TESTING, when will it be available?

It is already available (but you need STKO v 4.0.0 and OpenSees v 3.7.0). It's marked "under beta testing" because we still need to make some automation and we still need to find a unified way to update the dashpot coefficient based on the current shear modulus.

Drawbacks in the current implementation:

• Works only for the 3D version, not for the 2D one.
• The FF columns now need the same self-weight (if any) given to the inner soil domain. Therefore you cannot use the ASDAbsorbingBoundary3DAuto, but you have to use the manual version (ASDAbsorbingBoundary3D), in this way, you have the extrusions of the absorbing layers on which you can apply the selfweight. On the contrary, the ASDAbsorbingBoundary3DAuto extrudes the absorbing layer "on the fly" when STKO runs the analysis. We need automation to make it work with the Auto version
• Now the procedure to update the dashpot coefficients takes the current G modulus from the tangent matrix of the nonlinear material because this is the only output available for every material model in OpenSees. We still need to understand if this is sufficient or if getting a sort of "secant" shear modulus is better.

This is a simple model that shows you how to do it:

nl_abs.zip

(251.17 KiB) Downloaded 122 times

And this is the presentation we gave to the last CompDSSI workshop:

SSI-OS-Petracca-Day01-2024.zip

(17.36 MiB) Downloaded 146 times

2 : When performing 1D ground response analysis, the sides of AbsorbingBoundary are not needed. So, Is it possible to apply AbsorbingBoundary3DAuto only to the bottom for the purpose of performing a nonlinear ground response analysis with input as 2E? If there is any other manual way, please let me know if there are any webinars etc.

You can do it, but also in this case you cannot use the Auto version.
Try this file:

nl_only_bottom.zip

(143.36 KiB) Downloaded 119 times

[Satoru]

Thank you for teaching me!

[STKO Team]

You're welcome.
Let us know if you have any doubt