Assume you have a bend - 10-20-30.

Assume that you have a trunnion on that bend - 29-1010.

We insert expansion joints into 10-20 and 20-30, such that EJ1 is 10-15. Thus 10-20 is length of bend plus length of EJ1. 20-30 is immaterial.

We now break the trunnion so we have 29-1005-1010. 1005-1010 is EJ2 and its associated length.

Now we put in a CNODE restraint at 10 and 1010. Let's make them anchors for now, and let's say they connect to 9 and 1011, respectively.

And now we add our tie rod. That's a rigid element from 9 to 1011, which is also the length of 10-1010.

Now, we may have to change those two anchors to CNODE x/y/z/rx/ry/rz, minus one or more of these. If it allows compression but not tension (sometimes common) then one end might be a +x and the other a -x. If they allow rotation, then you might exclude rx/ry/rz. Etc. Consult your expansion joint detail accordingly (or plan to spec out the joint accordingly).

If desired/needed, you might consider replacing your one rigid element that represents x tie-rods with 3 rigid elements per tie-rod in your design.

Finally, don't forget to reduce bend flexibility by calling it two flanged (1 for the expansion joint, 2 for the trunnion). Also don't forget to calculate SIFs and input those, as well.