Absorbing boundaries modelling (SSI)

[shahinhus]

Dear STKO Team,

I'm working on a soil-structure interaction model. There appear to be two approaches to modelling absorbing boundaries:

1. Adding free-field (FF) boundaries:

FF_SC.png (113.67 KiB) Viewed 2466 times

2. Assigning absorbing boundary material:

FF_AB.png (31.23 KiB) Viewed 2466 times

In order to validate the second option, I'm trying to model soil using the first option. But I have some issues:

• In the first option, why do we need shear columns at both sides and all corners? In other software programmes (e.g., FLAC), only adding a single shear column and linking all sides of the soil to it suffices.

• Is it also necessary to use an elastic-isotropic FF material with a higher stiffness and density? If so, how do we determine those parameters?

Thank you.

Kind Regards,
Shahin

[STKO Team]

In the first option, why do we need shear columns at both sides and all corners? In other software programmes (e.g., FLAC), only adding a single shear column and linking all sides of the soil to it suffices.
Is it also necessary to use an elastic-isotropic FF material with a higher stiffness and density? If so, how do we determine those parameters?

The old way of doing it in OpenSees (the first approach you mentioned) was an approximate way of doing what FLAC does. It was missing one component (the transfer of stress from FF columns to the soil)

Use the second approach. We implemented it to overcome the issue of the first one

[shahinhus]

Dear STKO Team,

Thank you very much for your response. Then I'll only use the second approach.

Kind Regards,
Shahin

[STKO Team]

You're welcome