You might be able to get the floor loading by taking the total differential axial load and divide it by the total tributary area of all columns/shear walls of that floor. Dead load is thickness of the slab, everything else is SDL + LL. You'd need a bit more info about how the floor is being used to see how the SDL + LL is divided. I really don't recommend this approach as the floor loading can vary (rec rooms, hallways, hotel rooms, etc). But it sounds like you have to go off very little information, and it's a far better approach than using column moments.