Dear Richard/Dave sir,

I have used the single bellow tied expansion joint procedure given in CAESAR II app. guide. I have following clarifications in the modelling method,

1. Tie rods are modeled as rigid element with axial restraint and rotational restraint. Thought that this restraints will simulate the effect of tie rod infinite stiffness(in axial & bending direction). If it is so, why do we need to give infinite value in axial stiffness and leaving bending stiffness blank to allow CAESAR II to calculate the stiffness(hope it will not be an infinite value)?

2. Even after using the axial and rotational restraints (to bring tie rod effect), i am getting displacement in axial and rotational direction between start and end of the bellow. Please explain the basics of those displacement?

3. In the first run, i have got load in axial restraint twice the pressure thrust load. Then, i have reduced the infinite stiffness value to 10e6 from 10e12 and found the loads in axial restraints are matching with thrust load. Is that correct procedure to tune the stiffness value, please advise.

Regards,
Satheesan D

The simple model with the tie-rod in the center of the expansion joint is an approximation of the behavior. In a real joint the tie-rods are outside, so we setup the CNODE restraints to simulate the behavior of the real rods.

I'm a little surprised you're seeing axial displacements - you are talking about relative axial displacement between the joint ends - yes?

The joint should see lateral deflection between the two ends. Overall the joint can move as a whole. This means the ends of the joint can appear to translate and rotate in the global model space.

If you still have problems determining if the joint is behaving properly, please open a Support Request on Smart Support and send in the job so our Tech Support group can look at it.