If you are interested to check diaphragm rotation, you can simply look into rY roration of the nodes where the diaphragm is defined. In STAAD, you can define rigid diaphragms.
At present, torsional provision for EC8 code has not been implemented. You can have that option in IS:1893, IBC 2012 implementations in STAAD.Pro
At present, torsional provision for EC8 code has not been implemented. You can have that option in IS:1893, IBC 2012 implementations in STAAD.Pro