It depends on how complicated you wish to get here. The tie rod model is the only thing different here.
You could either:
1 - Instead of modeling the tie rod, just do not specify an effective bellows diameter (to ignore the pressure thrust which will be carried by the tie rods) and check the elbow displacements - they should not move towards or away from one another
2 - model the tie rods as a single element down the centerline from one elbow node to a CNode'd restraint to the other elbow node
3 - a really complicated model with all tie rods modeled around the pipe
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Dave Diehl