UniformExcitation Pattern soil column

[kamyarsa]

Hello all,
I am modeling a soil column in Openseespy. When I apply the acceleration time history as uniform excitation, is it applied to all the base nodes?

besides that, when the acceleration is applied by using this pattern, the acceleration time history is zero at the base nodes and increases gradually to the top of the model(where the acceleration is higher than the input file). Shouldn't the acceleration time history at the base nodes be equal to the input time history ?

I would appreciate it if anyone could help me with this.

[mhscott]

The uniform excitation only applies equivalent earthquake forces, M*i*\ddot{u}_g. The support nodes do not move.

[kamyarsa]

Thank you very much for your response.
The uniform excitation input file is an acceleration time history. Are there any sources to know how the equivalent forces are calculated?

Furthermore, the other way to apply dynamic load is using velocity time history and dashpots. In using the uniform excitation pattern, should we also use dashpots for the base nodes, or should they be fixed? ( when the base nodes are free, the model moves like a rigid block)