I am analysising a huge slab in Staad pro. But I find no mater I put the self weight or not, it present me the same result, that means the self weight for slab does not work. If some body has the experence to deal with it, please reply. Thanks a lot.

Please check if you defined the slab material density correctly.Maybe it equal to zero

maybe you forgot to define thickness parameter for slab.check it again pls.