Older post but I have not been around here for a long time either.
I have not used later versions of CAESAR II but I do not think that there are many changes in expansion joint modelling.
Pressure thrust is always present in expansion joints. Question is if there are unit restraints to hold it or not. Unrestrained expansion joint pressure thrust have to be "carried" by main anchors on both side of the bellows element. Such element can accommodate axial, lateral and rotation movement. Element should not see torsion moment. If such exists you have to specify it in your technical specification to order the unit.
Correct guiding of a line having expansion joint is absolute must. READ EJMA to get it right.
I recommend the simple modelling is not used. Use the complex modelling and model rods and other restrains. Rods can expand due to increased temperature and they can get longer due to loading. There are other elements also and not one of them is rigid. In critical applications work together with EXPERIENCED expansion joint designer to get usable values.
Unrestrained expansion joint connected to a vessel or pump or similar has a pressure thrust. But not full pressure thrust is on the nozzle. Nozzle load is bellows pressure thrust less pressure thrust calculated using pipe ID. Vessel/equipment anchor sees the full thrust plus bending moment. EJMA has very good sample and explanation on this issue.
Expansion joint has also spring rates. Large number of pipe designers specify very low maximum spring rates. Result is unstable system. Designer should also realize that expansion joint stresses go often past yield point and the element deforms. Spring force direction changes! Use always as stiff element as possible! It is safer and system is more stable.
Expansion joint modeler in CAESAR II used to be very good. I expect the same be the case with the new versions. There used to be one issue with 2 rod joint modelling. See my old postings from 2006 to 2008 for details.
As a general issue. I work constantly on expansion joints, piping and training. I see constant problems and mistakes. And they are increasing. Some of them have resulted in fatalities and system failures. Never use expansion joint if you do not know fully what is required!
_________________________
Regards,
Jouko
jouko@jat.co.za