In TBDY 2018 Table 3.2, Earthquake Design Class is determined according to the short period design spectral acceleration coefficient SDS and Building Risk Category for DD-2 earthquake level.
Since the short period design spectral acceleration coefficient is SDS=0.565 and BKS=3 at the DD-2 earthquake level for the building, DTS=2 is determined.
When the analysis settings wizard is used, the DTS selection is automatically given according to the SDS and BKS determined in the previous steps.
Sections that cannot be selected in the Analysis Settings Wizard as per TBDY 2018 are automatically closed by the program, as shown by the shaded region in the image above.