I want to make viscous boundary for the lateral surface,and element type is quadUP。If the element is quad, we just need to define a zerolength element for viscous damper. But when use quadUP, 2 nodes for zerolength have different DOFs.Do I need to define it like the interface between pile and soil?
if the quadUP has 3 dof at each node, then no the truss will still work (the first 2 dof are translational and the 3'rd rotational (for which the truss will contribute nothing to the tangent matrix) .. if there are more than 3 dof then yes.