conceptual mass to structural slab with analytical model ?

[Anonymous]

greeting .
i am trying to assign a structural floor to this conceptual mass by "floor by face" but when i point at the mass it is not seem to be selected (not glowing) . However, when i use roof by face the mass is selected and i can assign an architectural slab which i don't  want it.
so , my question now is there any way that i can make an analytical model for this mass in order to export it to robot knowing that it is desired to design it as  concrete shell .

[Rafal.Gaweda]

See:

http://forums.autodesk.com/t5/robot-structural-analysis/special-surface-shell-created-in-revit/m-p/5...