For a finite length expansion joint, the bending and lateral stiffnesses are releated. So in CAESAR II you can only specify one of them, not both. I'm a little surprised the vendor would give you "rigid" for bending, but then 118.13 kg/mm for lateral. I suggest you use the lateral value and let CAESAR II compute the bending (which will not be rigid).
For the "rigid" stiffnesses, enter 1E12.
You can not call the expansion joint a "rigid element", this is why you are getting the message about "inconsistent element definitions". In CAESAR II, a rigid element is (typically) a valve or a flange.
To include the 2000kg weight, put a rigid end piece on each side of the bellows, and set each weight to 1000kg.
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Regards,
Richard Ay - Consultant