Dashpot element (viscous damping device) in Opensees?

[Goulet]

Hello Group!

I am trying to do something really simple but I just don't know how. Here's the goal:
I want to model the frictional resistance at the soil/foundation interface and I would like to be able to include viscous damping.

I have used the procedures defined by Gazetas 1991 (ATC-40 recommendations) and I have a frictional stiffness (k [lbs/ft]) and a viscous damping coefficient (C [lbs*sec/ft]). All I want to do is to apply that to a uniaxialMaterial elastic if possible.

Silvia suggested the use of Rayleigh damping through the region command, but this seems a bit complicated for what I want to achieve. My damping coefficient is NOT frequency dependent. I just need a simple elastic material with stiffness and viscous damping.

QUESTIONS:
1) Does anyone know what the "damping tangent" term ($eta) refers to in the uniaxialMaterial elastic options?
2) Is there just a dashpot device in Opensees that I can add to my model?
3) Is there another simple solution available in Opensees?

Thank you in advance.

[fmk]

suggest you use the Viscous material with a spring at the soil/structure interface ..
both truss and zeroLength elements pass strain & strainRate to their associated
uniaxialMaterials .. the Viscous material just uses the strainrate to compute the stress
.. look in the manual for more info on this material.