SSI springs-dashpots ground motion input

[MPazidis]

Hello,

I am trying to model the soil-structure interaction of a bridge with a shallow foundation, using springs and dashpots at its base. I model the springs using the Uniaxialmaterial Elastic and the dashpots using the UniaxialMaterial Viscous. My question is can I use the UniformExcitation pattern and use an acceleration time-history as an input, or do I have to use the Plain Pattern a velocity time-history, similar to the procedure of soil response analysis that uses the Viscous material to model boundary conditions (Lysmer-Kuhlemeyer (1969) dashpot). Also, if the case is the latter, what load factor should I use in the Plain Pattern for the velocity time-history?
Thank you in advance.

[fmk]

i suggest you look at the examples

http://opensees.berkeley.edu/wiki/index ... s_of_Slope

[MPazidis]

I am sorry if I wasn't clear. I don't want to model the soil, i want to assign 6 springs and 6 dashpots at the base of the pier to take in account Inertial Interaction. I have calculated the springs' stiffness and dashpot coefficients for each dof, using available equations. I then create the Elastic and Viscous materials and place them in parallel using zeroLength elements.
So my question is given the presence of the Viscous Material, do I have to use Plain Pattern Path Series with a velocity time-history as an input, and if so which load factor should I use?
Thank you

[fmk]

you apply time varying nodal forces .. you can do it whatever way you wish, the Path Series makes the most sense for what you want to do .. the factor depends on whether or not the values in the path have been scaled or not.