CEMP-E
TI 809-07
30 November 1998
For periods less than or equal to, T0 the design spectral acceleration, Sa shall be (FEMA 302, Equation
4.1.2.6-1):
SDS
S a = 0.6
T + 0.4SDS
(Eq C-5)
T0
For periods greater than or equal to T0 and less than or equal to TS, the design spectral response
acceleration , Sa, shall be taken as equal to SDS.
For periods greater than TS, the design spectral response acceleration, Sa, shall be (FEMA 302, Equation
4.1.2.6-3):
S D1
Sa =
(Eq C-6)
T
Where:
T = the fundamental period of the structure in seconds.
T0 = 0.2SD1/SDS.
TS = SD1/SDS.
C3. SEISMIC DESIGN CATEGORY. Each structure shall be assigned a seismic design category based
on their Seismic Use Group and design response coefficients, SDS and SD1 as indicated in the tables
below (from FEMA 302 Tables 4.2.1a and 4.2.1b):
Table C-3a Seismic Design Category Based on Short Period
Response Accelerations
Value of SDS
Seismic Use Group
I
II
III
SDS < 0.167g
A
A
A
0.167g ≤ SDS < 0.33g
B
B
C
0.33g ≤ SDS < 0.50g
C
C
D
0.50g ≤ SDS
D
D
D
Table C-3b Seismic Design Category Based on 1 Second Period
Response Accelerations
Value of SDS
Seismic Use Group
I
II
III
SD1 < 0.067g
A
A
A
0.067g ≤ SD1 < 0.133g
B
B
C
0.133g ≤ SD1 < 0.20g
C
C
D
0.20g ≤ SD1
D
D
D
0.75g ≤ 1
E
E
F
S
C4. STRUCTURAL CONFIGURATION AND REDUNDANCY. FEMA 302, Section 5.2.3 and 5.2.4
presents guidance on structural configurations and redundancy. Diaphragms are considered flexible if
the maximum lateral deformation of the diaphragm exceeds twice the average story drift of the
associated story (FEMA 302, 5.2.3.1).
A reliability factor, ρ, shall be defined for all structures based on the extent of structural redundancy in
the lateral-force-resisting system. For structures in Seismic Design Categories A, B and C, the value for
C-3
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