How can we calculate total load of superstructure?

If you check structural desing programs you will fine the following:

Load Patterns:

Dead Loads : Own Weight, Finishing, Walls and Fixed Mechanical Machines including its curbs.

Live Loads : any moving loads including furnitur (refer to ASCE Code Table 4-1)You can seperate the above loads to many sub-category when you modeling the structure, so it will be easy to control.

Example:- Dead Load (OW Load, SIDL Load, Wall Load ----etc)