Structural Concrete - Hassoun

20.2 Seismic Design Category 803
Step 6. Using Eq. 20.1a determine design spectral response acceleration coefficient for short periods,
S DS , and using Eq. 20.1b determine spectral response acceleration coefficient for 1-s
period, S D1 .
Step 7. Determine SDC according to Section 20.2.4. Utilize Tables 20.5 and 20.6.
Example 20.1
Determine seismic design category for a minor storage facility building in San Francisco on soft rock.
Solution
1. According to Table 20.1, minor storage facilities buildings are classified in risk category I.
2. S S = 2.02 g (Fig. 20.1a)
S 1 = 0.60 g (Fig. 20.2b)
3. According to the Table 20.4, a site with soft rock is considered to be class C.
4. According to the Table 20.2 for the site class C and S S = 2.02 > 1.25, F a = 1.0.
According to Table 20.3 for site class C and S 1 = 0.60 > 0.5, F v = 1.3.
5. S MS = F a S S = (1.0)(2.02) = 2.02 g (Eq. 20.2a)
S M1 = F v S 1 = (1.3)(0.60) = 0.78 g (Eq. 20.2b)
6. S DS = 2 S 3 MS = 2 (2.02) =1.35 g (Eq. 20.1a)
3
S D1 = 2 S 3 M1 = 2 (0.78) =0.52 g
3
(Eq. 20.1b)
7. According to Table 20.5 for S DS = 1.35 g > 0.50 g, risk category I, and since S 1 < 0.75 g, therefore
SDC is category D.
8. According to Table 20.6 for S D1 = 0.52 g > 0.20 g, risk category I, and since S 1 < 0.75 g, therefore
SDC is category D.
Therefore, seismic design category D is assigned to the structure.
Example 20.2
Determine seismic design category for a hospital building in Oakland, California, on soft clay soil.
Solution
1. According to Table 20.1, hospital buildings are classified in the risk category IV.
2. S S = 2.08 g (Fig. 20.1a)
S 1 = 0.92 g (Fig. 20.2b)
3. According to Table 20.4, the site class for soft soil is E.
4. According to the Table 20.2, for the site class E and S S = 2.08 > 1.25, F a = 0.9.
According to the Table 20.3, for the site class E and S 1 = 0.92 > 0.5, F v = 2.4.
5. S MS = F a S S = (0.9)(2.08) = 1.87 g (Eq. 20.2a)
S M1 = F v S 1 = (2.4)(0.92) = 2.21 g (Eq. 20.2b)
6. S DS = 2 S 3 MS = 2 (1.87) =1.25 g (Eq.20.1a)
3
S D1 = 2 S 3 M1 = 2 (2.21) =1.47 g (Eq.20.1b)
3
7. According to Section 20.2.4, for S DS = 1.25 g > 0.50 g, risk category IV, and since S 1 > 0.75 g,
SDC is category F.
8. According to Section 20.2.4, for S D1 = 1.47 g > 0.20 g, risk category IV, and since S 1 > 0.75 g,
SDC is class F.
Therefore, seismic design category F is assigned to the structure.