The Application manual guide says the following: "that the single tied bellow is designed to absorb movement by lateral deflection only. There is no axial deflection or relative bending rotations at the joint ends". That is perfectly ok.
But how can be modeled a bellow with limit rods that permit the axial deflection while restraining the full pressure loading?

A joint with nuts on only the outside of the flanges (allowing bellows compression) can be modeled using a <em>directional restraint</em> on the CNODE of the tie-bar.

For example, if your joint is along the positive "X" direction, the CNODE at the "TO" end of the tie-bar would normally be assigned an "X" restraint (to the flange node). This would simulate a nut on both sides of the flange, preventing axial movement of the bellows. If a "+X" was used instead, the tie bar could move in the "+X" direction relative to the flange node, thereby allowing compression.