taken as the maximum of the sum of the shears in any

two adjacent columns, in the plane of a moment

All buildings shall be assigned a Seismic Design

frame, divided by the story shear.

For columns

Category based on their assigned Seismic Use Group

common

to

two

bays

with

moment-resisting

and their applicable spectral acceleration coefficients,

connections on opposite sides at the level under

consideration, 70 percent of the shear in that column

structure shall be assigned to the more severe Seismic

may be used in the column shear summation. For

Design Category in accordance with Table 4-2a or

shear walls, rmax x shall be taken as equal to the shear

Table 4-2b. The category designations are used in

in the most heavily loaded wall or wall pier

FEMA 302 to determine permissible structural

multiplied by 10/*l*w (the metric equivalent is 3.3 (*l*w),

systems, limitations on height and irregularity, and

where *l*w is the wall or wall pier length in feet (m),

coefficients related to overstrength and drift.

divided by the story shear. For dual systems, rmax x

shall be taken as the maximum value as defined

FEMA 302 prescribes a reliability factor, *D*, to be

above considering all lateral-load-resisting elements

in the story. The lateral loads shall be distributed to

assigned to all buildings based on the extent of

elements based on relative rigidities considering the

structural redundancy inherent in the lateral-force-

interaction of the dual system. For dual systems, the

resisting system. The value of *D *may be taken as 1.0

value of *D *need not exceed 80 percent of the value

for buildings in Seismic Design Categories A, B, C.

calculated above.

For buildings in Seismic Design Categories D, E, and

F, *D *shall be taken as the largest of the values of

diaphragm level immediately above the story.

accordance with the following equation:

The metric equivalent of Equation 4-1 is:

6.1

20

(4-1)

where Ax is in square meters.

where:

The value of *D *need not exceed 1.5, which is

permitted to be used for any structure. The value of *D*

shall not be taken as less than 1.0.

resisted by the single element carrying the most shear

force in the story to the total story shear, for a given

direction of loading. For braced frames, the value of

systems in any direction comprised solely of special

moment frames, the lateral-force-resisting system

most heavily loaded brace element divided by the

shall be configured such that the value of *D *calculated

For moment frames, rmax x shall be

story shear.

in accordance with this section does not exceed 1.25.

4-5

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