Design Considerations for Earthquake Forces - Simplified Design of Reinforced Concrete Buildings - page 306

11.11.2 Example 2 - Building # 1 Alternate (1) Standard Pan Joist

To illustrate the seismic design analysis for moment resisting frames Building 1 alternate (1) will be analyzed
for the north-south direction seismic forces.

Seismic design data

Assuming that the building is located in north Illinois with the maximum considered earthquake spectral
response accelerations for short period (0.2 second) and one second period determined from IBC maps
(2009 IBC Figures 1613.5(1) through 1613.5(14)) as follows:

S s = 0.20 g
S 1 = 0.10 g

Soil site class definition is C

Occupancy category I

Determination of the Seismic Design Category SDC

(1) Based on the values of S s and S 1 and soil site class C, determine the site coefficients F a and F v

from ASCE Tables 11.4-1 and 11.4-2. Notice that linear interpolation is performed.

F a = 1.20
F v = 1.70

(2) Calculate the adjusted maximum considered earthquake spectral response acceleration:

S MS = F a S s = 1.20 0.20 = 0.24g

S M1 = F v S 1 = 1.70 0.10 = 0.17g

(3) Calculate the design earthquake spectral response accelerations:

S DS = 2/3 S MS = 2/3(0.24) = 0.16g
S D1 = 2/3 S M1 = 2/3(0.17) = 0.11g

(4) For S DS = 0.16g ASCE Table 11.6-1 shows that the SDC is A

For S D1 =0.11g ASCE Table 11.6-2 shows that the SDC is B
Use the highest category from both tables
SDC = B

Considering the exception in ASCE 11.6 (see Section 11.2) check the building SDC:

T s = S D1 /S DS = 0.11/0.16 = 0.69 seconds
Building T (see below) = 0.43 < 0.8(T s ) = 0.8(0.69) = 0.55 seconds O.K.