Modeling of material damping in soil structure system

[tamhidia]

Hi

I've wrote a code for building a soil-structure system.I want to set 5% damping for structure and 5% material damping for soil. I modeled structure's damping by a damper in my structure and I've modeled radiation damping of soil, by using two dampers with special coefficients that read in the articles in sway and rocking degrees of freedom.But, As you know, soil has both material and radiation damping. I don't know how can I set 5% material damping to the soil. I'll appreciate it if you help me.

Regards
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Aidin Tamhidi
M.Sc. Student - Structural Engineering
Department of Civil Engineering
Sharif University of Technology

[skamalzare]

Aidin,

Soil material damping can either be presented by constitutive model through soil stress-strain response or by artificial Rayleigh damping. Rayleigh damping affects your whole system. Since you have 5% damping on both soil and structure, it can solve your problem. You can define 5% Rayleigh damping with your interested frequency corners in the analysis settings.

Bests,
SK

[tamhidia]

Thanks a lot SK
You mean after defining the radiation damping by putting two dampers in sway and rocking DOFs, Then I should define 5% rayleigh damping for the total system ( Structure plus soil ) ?

[skamalzare]

Yes, please note that, radiation damping is totally different from material damping. Radiation damping, is a damping you assign to boundaries to absorb waves reaching them. It dose not let any waves go back to the system. We use radiation damping to model infinite boundary conditions (i.e. boundaries without any wave reflections).

Material damping comes from inside the material. It has many sources like hysteresis stress-strain response, friction, heat generation and etc.

If you need infinite boundaries and have problem with wave reflection from boundaries, you need to use radiation damping (e.g. lysmer and Kulhaway damping).

If you need to define material damping (e.g. your constitutive model cannot provide you with proper damping) you can compensate your damping with Rayleigh damping.

In your case, I am assuming you need both of them. Therefore, you need to define both.

SK

[tamhidia]

Thanks a lot