Structural Concrete - Hassoun

794 Chapter 20 Seismic Design of Reinforced Concrete Structures
Table 20.2 Values of Site Coefficient, F a a [Table 1613.3.3(1) of IBC 2012]
Mapped Spectral Response Acceleration at Short Periods
Site Class S S
≤ 0.25 S S
= 0.50 S S
= 0.75 S S
= 1.00 S S
≥ 1.25
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.2 1.2 1.1 1.0 1.0
D 1.6 1.4 1.2 1.1 1.0
E 2.5 1.7 1.2 0.9 0.9
F Noteb Note b Note b Note b Note b
a Use straight-line interpolation for intermediate values of mapped spectral response acceleration at short period, S s
.
b Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine appropriate
values, or in accordance with Section 11.4.7 of ASCE 7.
Table 20.3 Values of Site Coefficient, F v a [Table 1613.3.3(2) of IBC 2012]
Mapped Spectral Response Acceleration at 1-Second Period
Site Class S 1
≤ 0.1 S 1
= 0.2 S 1
= 0.3 S 1
= 0.4 S 1
≥ 0.5
A 0.8 0.8 0.8 0.8 0.8
B 1.0 1.0 1.0 1.0 1.0
C 1.7 1.6 1.5 1.4 1.3
D 2.4 2.0 1.8 1.6 1.5
E 3.5 3.2 2.8 2.4 2.4
F Note b Note b Note b Note b Note b
a Use straight-line interpolation for intermediate values of mapped spectral response acceleration at 1-s period, S 1
.
b Site-specific ground motion procedures in accordance with Section 11.4.7 of ASCE 7.
3. For periods T s < T ≤ T L , the design spectral response acceleration, S a , shall be determined as
S a = S D1
T
4. For periods greater than T L , S a shall be taken as
(20.7)
S a = S D1T L
T 2 (20.8)
where T L is the long-period transition period(s) shown in Fig. 20.2a and 20.2b (conterminous
United States), Fig. 20.2c (region 1), Fig. 20.2d (Alaska), Fig. 20.2e (Hawaii). Fig. 20.2f (Puerto
Rico, Culebra, Vieques, St. Thomas, St. John, and St. Croix), and Fig. 20.2g (Guam and Tutuila).
20.2.4 Determination of Seismic Design Category (SDC)
Structures shall be assigned SDCs, which are classified as A, B, C, D, E, and F and are determined
from Tables 20.5 and 20.6. These have no relation to the site class types that are also named A, B,