opening in slab
 

opening in slab
i need to create an opening in existing roof slab (reinforced concrete).shall i treat both ends of opening as cantilever beam with width equal to opening width (in main span direction only)

if the opening is small, perhaps the opening can just be cut but if it is large, framing may need to be added around the perimeter.
the answer will depend upon the size of the opening, the span, one way or two way slab, etc. will there be some load (equipment, skylight, etc.) supported by the edge of the opening? what is the existing slab thickness and reinforcement?