Hi

In a very simple model with an axial expansion joint (that is attached) EXP displacement of node 180 is -9.284mm.
But by modeling limit rods with 15mm gap in X direction, EXP displacement at node 180 is +0.264mm and limit rods have forces. But we know limit rods should not have forces till EXP displacement approch to -15mm.
What is the reason of this result?


(I know this installation for an axial expansion joint is not true, but this is just an example for clarifying.)

But it DOES move 15mm. Don't look at the EXP case; look at OPE & SUS, those are the structural analyses.
Your pressure is closing the gap in both states. Expansion shows the "additional" effect of thermal strain.