To model slabs with variable thickness and loading in SAFE, it is best to create a base slab which spans the entire floor, then draw slabs of variable thickness over the base slab to adjust local geometry and loading. Contained-area slabs drawn over the base slab will take precedent. This applies to every area object except drop-panels. To apply variable loading, assign NONE properties to contained-area slabs, then select Assign > Load Data to specify load magnitude and direction. When assigning loads to NONE areas in both programs, loads will be added to the exiting base slab.
Notes: 1- Shell rigid diaphragm must be explicitly assigned to null areas in ETABS for their loads/additional mass to be included in modal analysis (seismic mass).
2- For semi-rigid diaphragms, the contained areas are recommended to be assigned with the same structural properties of the base slab in lieu of null areas. The latter may cause local modes when their load/additional mass are part of the lateral mass source.