exist if the ratio of the average shear DCR for any
structure and for any performance objective, with the
story to that for an adjacent story in the same
following exceptions and limitations:
direction exceeds 125 percent. The average DCR for
a story may be calculated by the equation:
The use of the nonlinear static procedure in
this document is required for those structures in
Seismic Use Groups II and III with the structural
n
∑ DCR V
i
i
characteristics described in Paragraph 5-4b, unless
1
(5-3)
=
n
DCR
specific instructions to the contrary are received from
∑
Vi
the cognizant design authority.
1
where:
The procedure is not recommended for use
with wood-frame structures.
DCR = the average DCR for the story
The procedure should not be used for
DCRI = the critical action DCR for element
structures
in
which
higher-mode
effects
are
i
significant unless a linear elastic dynamic procedure
is also performed.
To determine if higher-mode
VI = the total calculated lateral shear force
effects are significant, a modal response spectrum
in an element i due to earthquake response,
analysis shall be performed for the structure using
assuming that the structure remains elastic
sufficient modes to capture 90 percent mass
participation, and a second modal response spectrum
n = the total number of elements in the
analysis shall be performed considering only the first
story.
mode participation.
Higher-mode effects shall be
considered significant if the shear in any story
There
is
a
severe
torsional
strength
calculated from the analysis with 90 percent mass
irregularity present in any story. A severe torsional
participation
exceeds
130
percent
of
the
strength irregularity may be deemed to exist in a
corresponding
story
shear
from
the
analysis
story when the diaphragm above the story is not
considering only the first mode response. A linear
flexible, and the ratio of the critical element DCRs
elastic dynamic procedure may be performed to
for primary elements on one side of the center of
supplement the nonlinear static procedure for
resistance in a given direction for a story, to those on
structures with significant higher-mode effects, in
the other side of the center of resistance for the story,
which case the acceptance criteria values for
deformation-controlled actions (m values) in Chapter
exceeds 1.5.
7 may be increased by a factor of 1.3.
c.
Limitations on Use of the Procedure. The
nonlinear static procedure may be used for any
5-8
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