Erik Kostson
Ansys Employee

Just take away the steel beams you mention and use a Displacement boundary condition (not a remote displ.) on the slab (UX,UY,UZ). That is fine and that is typically OK, as seen in an example of punching shear (slide 9 in the link below, where the steel beams are just modeled as a displacement BC there) - use also this workflow below to model RC structure.

Closing this post as it has been answered - if you have any other question open up a new one.