The design concept of RFEM 6 has been fundamentally changed, so the design cases are no longer available in the add-ons. When defining members and surfaces, you can specify whether to perform design and assign the design properties to the objects. Therefore, it is not possible to perform alternative analyses in the same model.
If you want to design some members according to different specifications, define a new design configuration for a limit state, and assign this configuration accordingly.
If you design both members and member sets, you can use the object properties to control whether to consider each member individually or to analyze the member set as a superordinate object.
Furthermore, RFEM 6 and RSTAB 9 provide you with the option to design objects with common properties using representatives.