Using OpenSees!

Dear all,

I am considering using OpenSees software in plane strain SSI analysis
under cyclic loading. I have understood, roughly, how the structure of
the input file and the Tcl scripting language work. Nevertheless, I
would like to know; I understand that to model a rigid body, in
OpenSees, you can tie the horizontal and vertical displacements of the
nodes of the rigid entity. Is there any other way? Or did I
misunderstood?

Furthermore, how is definition of an interface in between soil and
structure carried out? I know that zero-length element definition exist;
however, I need an example for implementation

I am working on linking Gmsh with Opensees for pre/post processing! I
would like to share the link when its done, but if anyone had already
made one, please share!   

Regards,

Hisham El Safti