Answer:
In RFEM 6, you can only design reinforced concrete members and surfaces. To do this, use the Concrete Design add-on. This is used to carry out the design for the ultimate limit state, stability, and serviceability limit state.
Reinforced concrete solids cannot be designed directly in RFEM 6.
However, it is possible to create solids with the "Concrete" material and determine the stresses within the solid, for example. Optionally, you can also insert a result beam into the solid, with which the results of the solid are converted into member internal forces. You can then design this result beam in the Concrete Design add-on.