UniformExcitation Pattern

[aminrahmaani]

Hi,

I have a question on "UniformExcitation Pattern". I found somewhere that:

" UniformExcitation Pattern -- this type of pattern imposes a user-defined acceleration record to all fixed nodes, in a specified direction."

This means that if I want to excite a model in x direction, using this command: "pattern UniformExcitation $patternTag $dir(which is "1" here) -accel ..." would result in the excitation of all fixed nodes in x direction. right?
Now assume the model whose base is fixed in all direction and the lateral boundaries are fixed in x direction. I want to excite(in x direction) this model at the base. So it seems that "UniformExcitation" command applies the input ground motion to both the nodes at base and the nodes at lateral boundaries? Right?
How can I apply the input motion only to the base?

Many thanks,
Amin

[vesna]

Uniform Excitation Pattern applies load equal to (mass matrix)x(ground motion acceleration) to all dofs that are free in the direction of excitation.
To do what you want check Multi-Support Excitation Pattern:
http://opensees.berkeley.edu/wiki/index ... on_Pattern