How to model a Trapezium like shape in CAESAR II.

Is it possible in CAESAR II.

Do you mean a "trapeze spring hanger" support?

If so, yes you can do this. The simplest way is to put two dummy rigid elements, transverse to your pipe, and put the hangers at the ends of the rigids.

My question is trapezium shape duct.

Nope of course not... Piping is a round circular tube the Piping codes do not have any listed components in them for a trapezium shaped pipe!

Not only is what John said true, but CAESAR II is set up to only calculate stresses on circuar cross-sections. You could use the "Structural Modeler to define a "user cross-section", and define your model there. This will give you only displacements, restraints, and element forces.