Why is it that whenever I model a Hinged or Gimbal Expansion Joint using Caesar's Expansion Joint Modeler and check the joint movements using Caesars' Expansion Joint Rating application, I am getting values for Axial Displacement due to Lateral?

Should lateral movement of the expansion joints be restricted since hinges are present?

Thanks

Hi Zero_1
In case of caesar default modeller lateral , axial & longitudinal movement is already arrested at the hinge point of expansion bellow. One or two angular rotation is free based on it’s a hinged type of gimbal type expansion joint.
You don’t have to do any more manual setting whenever you are using caesar default.
If you check end point to end point relative movement of bellow you will find vary small amount of changes it’s due to hinge/gimbal rotation. If two or more hinge or gimbal expansion joint is used in same system there will be sufficient movement due to same reason.

I understand that hinge and/or gimbal expansion joints already restricts axial and longitudinal movement. What I am confused with Caesar is that, why is it calculating for Axial Movement due to Lateral when the joint has been modeled as hinged or gimbal using Caesars Expansion Joint Modeler to avoid any input errors. But Caesar still calculates axial movements due to Lateral whenever I do a Rating Check in Caesar's Analysis applications.

Could it be that the rigid representation of the hinges/gimbals are not rigid enough that it is allowing some lateral movement of the joint (just a guess)?

Has anyone experienced this with Caesar?

Hi Zero_1
I am not sure whether I understood your problem or not.
Is your question is (Say 60 is your hinge point),you are checking operating displacement at node no 60 & getting some reasonably good values ?
If that's the question Check connecting point of 60 (Say 61)also you will get same operating displacement. Only one or two angular rotation will be different based on it's a hinged or gimbal expansion joint. So relative displacement is same.
If problem is something else you can upload your caesar file here mentioning exact problem Or can send me mail habibur21@gmail.com
I shall try to identify the problem.

I appreciate the help "shr", but i do not know how to upload files in this forum.

You are correct about the hinge point relative displacement. The hinges seem to be maintaining its relative position. One way to find out what I have been mentioning is to model a simple piping layout and insert a Hinge Joint using Caesar Expansion Joint Modeler. Then try to get the Expansion Joint Total Axial movements using Caesar's Expansion Joint Rating in the analysis tab.

It seems that Caesar will always report an Axial Displacement due to Lateral inspite of modeling the joint as a Hinge (with the aid of the Expansion Joint Modeler).

Is Caesar interpreting the displacements correctly for a hinged/gimbal joints? (just a guess). But will have to do a manual calculation on this and compare with the Caesar results then.

The CAESAR II XJ Modeler produces a flexible element with length. While the hinge plates restrict the motion of the joint ends (to rotate about the pin), they do not necessarily eliminate lateral and axial movement of the flexible element. I would have to think that the lateral and axial motion is quite small in your model.

For many years, most XJs were modeled as points in a piping system. If modeled as a "zero length" XJ your results would not show this relative lateral and axial movement.

I had reviewed EJMA's description of the lateral movement and about the hinge joint.

It seems that Caesar is recognizing the lateral diferrence due to angular rotation between the "i" and "j" end of a hinged XJ as an lateral deflection by an ordinary XJ. And since Caesar's XJ Rating Analysis does not have the an option to identify if the joint is hinged or not, it reports a significant amount of axial displacement due to lateral of the bellow, normally more than the axial movement due to rotation.

My question is that, do we need to consider this lateral difference due to angular rotation (in other words, the axial displacement due to lateral in Caesar's XJ Rating report) when we evalualate a hinged/gimbal XJ? Or are we only to consider the angular rotation and/or the axial displacement due to rotation for this type of joints.

Would appreciate your opinion.

In a gimbal or hinge compensator the hinge pin(s)are positioned in the middle of the flexible elemet. Unit rotates around the pin. If you model the flexible element with length and you check the element connection point movements you will see 2 or 3 dimensional movement in x, y and z directions. Those point movements are relatively small but they are there.

I have not found any mistake in CAESAR II hinge or gimbal calculations if modelled correctly and system is used for metal compensators only.

I too have not seen any mistake with Caesar modeling hinged and gimbal joints. It's the interpretation of the XJ Rating Analysis software.

It does not recognize Hinged or Gimbal joints and assumes that the XJ is a standard type. That is probably why it is computing for the Lateral displacement, which is actually a lateral difference of both ends of the bellow due to angular rotation.

Hi Zero_1
I think you are checking global co ordinate between end point to end point of bellow at operating condition.In that case you will find the lateral difference due to angular rotation of hinge point from simple geometry as Mr Dave already mention.If you use 2 or more bellow in different direction you will see more significant difference.
Obviously it is valid for finite element bellow only. If model with zero length bellow it will not happen.
So your understanding mention above is correct in my point of view.

Yes, that's what i've been doing and i needed a finite element bellow (be it hinged or not) in order to use Caesar's XJ Rating Analysis feature. It is a neat tool to get the movements of a bellow and compare with the Vendor's allowables, but it requires a finite element to do so.

Should I then just ignore the Axial displacement due to Lateral in the report as a result of lateral differences due to angular rotation and just consider the Axial Displacement due to Rotation? Because the lateral is contributing majority of the Total Axial Movements of the bellow in the Caesar results.

I think it should be OK.
By the way what is bellow size & what is the value of lateral & axial movements.

I am actually working on 72" ductworks and using Caesar to evaluate loads and expansion joints.

Generally, I am observing an average ratio of 60:40 (60% axial disp. due to lateral from the angular rotation lateral differences) for hinge joints.

What's the rotation of your hinges? What's the span between the two hinges?

Bellows design codes consider only angular rotatation movements for single hinged and gimbal units. Bellows designer will get totally confused if you give lateral and axial movements. He will come up with some very special and expensive design or tells you to get lost or declines to offer.

If you have two bellows units connected with hinge or hinges you give the designer lateral movement of the unit and specify double or single hinge arrangement, lengths, pipe material etc. If you specify axial movement you will get slotted hinges, if you specify rotation in addition to lateral the designer will assume that ends rotate.

I recommend you use EJMA form as a bases what you need to give to the bellows design company.

I am not sure that I can figure out your configuration. If you like send a sketch directly via e mail and I will have a look.

Hi Jouko
Thanks for your comments.
I want to clarify one point with you.
"If you specify axial movement you will get slotted hinges"
I think in that case pressure thrust will again be a problem & have to do some special arrangement for that.

Sorry for late answer.

If you have slotted hinges you have to consider full pressure thrust in your stress analysis.

Thanks Jouko
For your Clarification.

Regards
Habib