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).

Table 1. Seismic Design Category Based on Short Period Response Acceleration Parameter (Table 11.6-1)
Value of S_DS	Risk Category I, II and III	Risk Category IV
S _DS < 0.167	A	A
0.167 ≤ S _DS < 0.33	B	C
0.33 ≤ S _DS < 0.50	C	D
0.50 ≤ S _DS	D	D

Table 2. Seismic Design Category Based on 1-s Period Response Acceleration Parameter ( Table 11.6-2)
Value of S _D1	Risk Category I, II and III	Risk Category IV
S _D1 < 0.067	A	A
0.067 ≤ S _D1 < 0.133	B	C
0.133 ≤ S _D1 < 0.20	C	D
0.20 ≤ S _D1	D	D