Page 525 - Design of Reinforced Masonry Structures

SHEAR WALLS 7.87

7.10.2 Seismic Design Categories
Every structures in an occupancy category (Occupancy Category I, II, III, and IV) is
assigned a SDC A through F based on consideration of following seismic design parameters
(both must be considered simultaneously):
1. Design, 5 percent damped, spectral acceleration parameter at short periods (0.2s), S
DS
2. Design, 5 percent damped, spectral acceleration parameter at 1-s period, S .
D1
Values of S and S for various occupancy categories are listed in Tables 7.8 and 7.9;
DS D1
each building and structure is assigned more severe of the categories so determined.
TABLE 7.8 Seismic Design Category Based on
Design, 5 Percent Damped, Spectral Acceleration
Parameter at Short Periods, S [7.13]
DS
Occupancy category
I or II III IV
Value of S DS
S DS < 0.167 A A A
0.167 ≤ S DS < 0.33 B B C
0.33 ≤ S DS < 0.5 C C D
D D D
0.5 ≤ S DS

TABLE 7.9 Seismic Design Category Based on Design,
5 Percent Damped, Spectral Acceleration Parameter at a
Period of 1 s, S [7.13]
D1
Occupancy category
I or II III IV
Value of S DS
S D1 < 0.067 A A A
0.067 ≤ S D1 < 0.133 B B C
0.133 ≤ S D1 < 0.20 C C D
D D D
0.20 ≤ S D1
The following exceptions apply to determination of seismic design category as deter-
mined from Tables 7.8 and 7.9:

1. Occupancy Category I, II, and III structures located where the mapped spectral accelera-

tion parameter at 1-s period, S , is greater than or equal to 0.75 shall be assigned Seismic
1
Design Category E.
2. Occupancy Category IV structures located where the mapped spectral acceleration
parameter at 1-s period, S , is equal to or greater than 0.75 (i.e., S ≥ 0.75) shall be
1
1
assigned Seismic Design Category F.
3. Where S is greater than 0.75, seismic design category is permitted to be determined based
1
on considerations of only S as listed in Table 7.8 where all of the following apply:
DS
(a) In each of the two orthogonal directions, the approximate fundamental period of the
structure, T , is less than 0.8T .
a s
(b) In each of the two orthogonal directions, the fundamental period of the structure
used to calculate the story drift is less than T .
s