effective lateral stiffness, Ke, and the yield strength,
displacement of the control node is compared with
Vy, of the building as indicated in Figure 5-3. The
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 Te 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
Ki
Te = Ti
(5-4)
analysis, the horizontal distribution should simulate
Ke
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
Ti =
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 CVX given in Equation 5.3.4-1 of FEMA
Ki = elastic lateral stiffness of the building
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.
Ke =
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 Te 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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