effective lateral stiffness, *K*e, and the yield strength,

displacement of the control node is compared with

the

target

displacement,

a

displacement

that

characterizes the effects of earthquake shaking.

effective lateral stiffness shall be taken as the secant

stiffness calculated at a base shear force equal to 60

(3) Lateral load patterns. Lateral loads shall

percent of the yield strength.

The effective

fundamental period *T*e shall be calculated as:

be applied to the building in profiles that

approximately bound the likely distribution of inertia

forces in an earthquake.

For three-dimensional

(5-4)

analysis, the horizontal distribution should simulate

the distribution of inertia forces in the plane of each

floor diaphragm.

For both two- and three-

where:

dimensional analysis, the vertical distributions of

lateral load shall be selected from one of the

elastic fundamental period (in

following two options:

seconds) in the direction under consideration

calculated by elastic dynamic analysis

A lateral-load pattern represented by

values of *C*VX given in Equation 5.3.4-1 of FEMA

302, which may be used if more than 75 percent of

in the direction under consideration

the total mass participates in the fundamental mode

in the direction under consideration.

effective lateral stiffness of the

building in the direction under consideration.

A lateral-load pattern proportional to the

story inertia forces consistent with the story shear

See Figure 5-3 for further information.

distribution calculated by combination of modal

responses using (1) response spectrum analysis of the

(5)

Analysis of three-dimensional models.

building including a sufficient number of modes to

Static lateral forces shall be imposed on the three-

capture 90 percent of the total mass; and (2) the

dimensional mathematical model corresponding to

appropriate ground-motion spectrum.

the mass distribution at each floor level. The effects

of

accidental

torsion

shall

be

considered.

(4)

Period determination.

The effective

Independent analysis along each principal axis of the

fundamental period *T*e in the direction under

three-dimensional mathematical model is permitted

consideration shall be calculated using the force-

unless multi-directional evaluation is required, as

displacement

relationship

of

the

Nonlinear

prescribed in Section 5.2.6.3.1 of FEMA 302.

Procedure.

The nonlinear relation between base

shear and displacement of the target node shall be

replaced with a bilinear relation to estimate the

5-10

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