if I have solid slab system (one way or two way R.C Slab supported on R.C beams)
how can I model this system in Revit 2014 so that it would understand that the load is transferred from a slab to the beams ?
in order to finally get results from revit extensions showing that the beams have moments from the self weight in addition to that from their share of the load of the Slab
Revit and the Revit Extensions do not calculate loads based on weights of slabs and the tributary areas for beams.
You would need to export your analytical model to an analysis package with this capability.
Alternately, you could do the calculation and apply a representative line load to the element in Revit.
Joe