Hello,

I have been trying to insert a rubber expansion joint, but the data requested by Caesar II is not supplied by all of the vendors at my disposal. They all give you movements and in some cases degrees. But I need the torsion and bending stiffness, or the way to calculate it with the information supplied by the vendor.
Which data do I need and how do I calculate it?
Or better yet, do you have a catalogue with this data for a 36" rubber XJ?

Many Thanks

S. Rizzo

Hi Rizzo

Rubber bellow stiffness and over all length is much less than metallic bellow .
Caesar default bellow data is from some metallic bellow vendor. So for rubber bellow you have to manually edit all those properly.
Rubber bellow vendor generally supply axial stiffness, lateral stiffness, overall length, permissible angular movement.
In our practice we feed in Caesar axial stiffness , lateral stiffness & overall length data supplied by vendor & torsional data ( Caesar default data –conservative ).

Regards

Habib

For rubber and any other type of bellows that is not standard U shape metal bellows it is best to enter all stiffness values. CAESAR II will calculate the missing stiffness value using formulas valid only for metal bellows. Leaving value out can result in very stange results. I had a case where pipe moved about 180 degrees.

Hi Everyone,

For rubber expansion joints, note that compression stiffness and elongation stiffness are not the same. So you should use the proper axial stiffness acording to compression or expansion loads. If you search the web, you'll find many rubber bellow suppliers' catalogues. Find a similar material to your exp. jt. and use it. Also note that stiffness values tolerance are +/- 20% in some manufacturers catalogues.

Regards,
Farhad Salehi