I think that you will not need any further reference except for the code you are working with. The change of the cross section does not affect the behaviour of the element you want to design.
Analysis and Design of arbitrary cross sections Reinforcement design to all major codes
Moment Curvature analysis
Is the member you are designing a major structural element or not?
One point is that concrete at the interior face of you cross section may spall off just like you exterior cover.
Are you taking about a beam or a column? If it's a column, do a Google search. A hollow column has a different strain distribution than square & rectangular columns.
