1) A slip joint comes in single or double slip joint configuration. The pipe is allowed to telescope with pipe-in-pipe design. Double slip joints are anchored in the center.

2) As an expansion joint, or 2 expansion joints on either side of an anchor.

3) In reality, as it's pipe in pipe, you would expect a lateral stiffness equal to that of pipe when extended, and double that when collapsed. CAESAR doesn't understand that, though, so you should use a stiffness that makes sense. Zero axial stiffness for static analysis.