nonlinear response of the seismic framing.
One
procedure for evaluating the target displacement for
S
1
R= a ⋅
(5-6)
Vy
C0
an individual line of vertical seismic framing is
W
given by Equation 5-5. The fundamental period of
each vertical line of seismic framing, for calculation
where Sa and C0 are defined above, and:
of the target displacement, shall follow the general
procedures described for the Nonlinear Static
Vy = yield strength calculated using results
Procedure; masses shall be assigned to each level of
of Nonlinear Static Procedure, where the nonlinear
the mathematical model on the basis of tributary
force-displacement (i.e., base shear force versus
area. For a building with neither rigid nor flexible
control node displacement) curve of building is
diaphragms
at
each
floor
level,
the
target
characterized by a bilinear relation (Figure 5-3).
displacement shall be calculated using rational
procedures. One acceptable procedure for including
W = total dead load and anticipated live
the effects of diaphragm flexibility is to multiply the
load.
displacement calculated using Equation 5-5 by the
ratio of the maximum displacement at any point on
Coefficient C3 shall be calculated as follows if the
the roof, and the displacement of the center of mass
relation between base shear force and control node
of the roof, both calculated by modal analysis of a
displacement exhibits negative post-yield stiffness.
three-dimensional model of the building using the
design response spectrum. The target displacement
3
so calculated shall be no less than that displacement
α (R - 1)
2
C3 = 1.0 +
(5-7)
given by Equation 5-5, assuming rigid diaphragms at
Te
each floor level. No vertical line of seismic framing
shall be evaluated for displacements smaller than the
where R and Te are defined above, and:
target displacement.
" = ratio of post-yield stiffness to effective
elastic
stiffness,
where
the
nonlinear
force-
5-5.
Nonlinear Dynamic Procedure.
displacement relation is characterized by a bilinear
relation (Figure 5-3).
Under the Nonlinear Dynamic Procedure, design
seismic forces, and the corresponding internal forces
For a building with flexible diaphragms at each floor
and system displacements are determined using an
level, a target displacement shall be estimated for
inelastic response history dynamic analysis.
The
each line of vertical seismic framing. The target
basis, modeling approaches, and acceptance criteria
displacements
shall
be
estimated
using
an
for the Nonlinear Dynamic Procedure are similar to
established procedure that accounts for the likely
those of the Nonlinear Static Procedure. The main
5-17
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