Seismic Design Category (Section 11.6)
The Seismic Design Category is either provided as a user input or it is calculated based on chosen risk category.
For Risk Categories I, II, and III structures with spectral response acceleration at 1-s period, S1 ≥ 0.75, the Seismic Design Category is set to Category E.
For Risk Category IV structures with spectral response acceleration at 1-s period, S1 ≥ 0.75, the Seismic Design Category is set to Category F.
For all other structures, Seismic Design Categories are determined according to Table 11.6-1 and 11.6-2 and the worst-case category is chosen (worst category indicated with higher letter designation).