Can we model rectanglar duct with rectangular expansion joint in CII for analysis?

Thanks.

No, all cross sections are assumed to be circular, which means that Iyy = Izz and so forth.

Thank you Mr. Ay

Why not ?
Its possible with structure elements.
Calculate moments and forces, but no stress calculation.

Well yes there is the "user defined section" possibility in the Structural Modeler. However, the expansion joint presents a problem, and I'm sure there will be others. So while you could use the Structural Modeler to create an element or two (to be included in a piping model), I think this would be overly cumbersome to use for the entire model.

Aren't there software packages out there that specialize in "ducting"?