In ETABS non-uniform loads can be assigned to shell elements via Assign>shell Loads>non uniform.
This option allows the user to assign non-uniform loads in any direction based on global coordinates.
As an example below, assume we want to assign a triangular load to a 24 ft. long and 12ft high wall and located in the X-Z plane.
The load will have magnitude of 1000lb/ft. at the base and zero at top of the wall.
The values for A, and B are zero since the load will not change in the X or Y directions. The equations to solve are:
Cz+D=1000 at z=0 ft
Cz+D=0 at z=12 ft
Solving the system above: D=1000 and C=-83.33
After running the analysis, we can check reactions using basic statics to make sure the load has been correctly applied.
Total load = 1000*24*12/2=144000lbs or 144kips
Reaction at top of the wall =144*4/12=48 kips or 24 kips at each support
Reaction at bottom of the wall=144*8/12= 96 kips or 48kips at each support
