L and C Shape Columns in STAAD.pro

Columns are of Steel or concrete?

Columns are of Concrete.

I've not yet used STAAD with concrete as I have SAP.

Nonetheless, what you'd like to do falls into shape customisation. And with concrete, this would be an interesting area since most codes deal with L/T-beam, rectangular/circular section.

STAAD should be having a section-addition provision or simply a section wizard.
Remember though that with whatever shape you'd like to add, you'd also like to be familiar with its geometric properties such as the area/volume(easy to get), inertial-moments, sectional modulus, location of center of gravity, torsional constants, e.t.c. The program(STAAD in this case) would definitely request for them. If lucky enough, its 'section wizard', if it exists, should be able to automatically get these values as some of these values already exist in various steel sections.

But I still see a problem for STAAD to do the reinforcement bit for custom shapes, especially for the C-columns.

Nathan.

you can refer a book of "Reinforced Concrete Design" by S.N. Sinha for L,T,C,Plus shaped columns design.