Dear Sir

Iam a user of CAESAR II ,we can analyze pipes but can we analyze rectangular ducts in Caesar.

Also if a pipe is supported on a column then all the three moments Mx My And Mz will come or one moment which is about vertical axis should be zero iam confused can u please help.

CAESAR II assumes cross sections are circular, i.e. pipes. You're only alternative here is to model the cross section as a "user defined shape" in the structural modeler, and build the model there. Note that this analysis will only yield displacements and reactions, no stresses.

That depends how the pipe is attached to the column.