Civil Engineering Reference
In-Depth Information
11.5
EARTHQUAKE FORCES
The IBC code requires a structural analysis procedure to determine the magnitude and distribution of
earthquake forces. The permitted analysis procedure for certain structures depends on the seismic design
category and the structure characteristics (Occupancy Catagory, structural irregularity, height, and location).
The 2009 IBC refers to ASCE 7-05
11.2
(Minimum Design Loads for Buildings and other Structures) for the
permitted analysis procedures for different structures (ASCE Table 12.6.1). Therefore, the provisions of
ASCE 7-05 will be used from here on. For structures assigned to SDC A, the structure must be analyzed for
the effects of static lateral forces applied independently in each of two orthogonal directions. In each direction,
the static lateral forces at all levels must be applied simultaneously. The lateral force considered at each floor
level is equal to one percent (1%) of the portion of the total dead load of the structure,
D
, assigned to that level.
Table 11-1 Permitted Building Systems for Different SDC (ASCE Table 12.2-1)
gy
(
)
SDC
Basic Seismic Force Resisting System
R
C
d
ABCDE
F
Bearing Wall
Special Reinforced Concrete
Shearwall
160 ft
160 ft
100 ft
5
5
Ordinary Reinforced Concrete
Shearwall
4
4
Building
Frame
Special Reinforced Concrete
Shearwall
160 ft
160 ft
100 ft
6
5
Ordinary Reinforced Concrete
Shearwall
5
4.5
Moment Resisting Frame
Special Frame
8
5.5
Intermediate Frame
5
4.5
Ordinary Frame
3
2.5
Dual System
Special
Shearwall
7
5.5
With Special
Moment Frame
Ordinary
Shearwall
6
5
Special
Shearwall
160 ft
100 ft
100 ft
6.5
5
With
Intermediate
Moment Frame
Ordinary
Shearwall
5.5
4.5
Permitted with the indicated height limit (if any)
Not permitted
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