Design Considerations for Earthquake Forces - Simplified Design of Reinforced Concrete Buildings - page 307

The SDC can be determined based on Table 11.6-1 and the building assigned SDC A. This will reduce the
seismic forces drastically. For illustrative purposes only this building example will continue using SDC B.

Table 11-1 shows that the building frame system with ordinary frame can be used for SDC B.

Fundamental Period

The approximate natural period of the structure can be calculated as follows:

T = C t h n x

For moment resisting frame system C t = 0.016 and x = 0.9

T = 0.016(39) 0.9 = 0.43 second (also T can be obtained from Fig. 11-8)

Seismic Response Coefficient:

S D1
R
I

C s =

⎛
⎜

⎞
⎟

T

For ordinary moment resisting frame system the modification factor R = 3 Table 11-1 (ASCE Table 9.5.2.2).
The occupancy importance factor I E = 1 (2003 IBC Table 1604.85).

0.11
3
1

C s =

0.43 =

0.087

⎛ ⎞

⎜ ⎟

C s should not be taken less than:

C s = 0.01

C s need not exceed:

S DS
R
I

0.16
3
1

C s = = = 0.053

⎛
⎜

⎞
⎟

⎛ ⎞

⎜ ⎟

Use C s = 0.053