component, i.e., the mode in which the deformation-
b.
When Nonlinear Procedures are Required.
controlled component will first yield, or fail in the
In order to determine whether a building may be
case of a brittle force-controlled component. This
analyzed
with
sufficient
accuracy
by
linear
DCR is termed the critical component DCR. If an
procedures, it is necessary to perform a linear
element is composed of multiple components, then
analysis and then examine the results to determine
the components with the largest computed DCR is
the magnitude and distribution of inelastic demands
the critical component for the element, i.e., this will
on the various components of the primary lateral-
be the first component in the element to yield, or fail.
force-resisting elements.
The magnitude and
The largest DCR for any component in an element at
distribution of inelastic demands are indicated by
a particular story is termed the critical element DCR
demand-capacity ratios (DCRs). DCRs for existing
at that story. If the DCRs computed for all of the
and new building components shall be computed in
critical actions (axial force, moment, shear) of all of
accordance with the equation:
the components (such as beams, columns, wall piers,
braces, and connections) of the primary elements are
Q
DCR = UD
(5-2)
less than 2.0, then linear analysis procedures are
QCE
applicable, regardless of considerations of regularity.
If some computed DCRs exceed 2.0, then linear
where:
methods should not be used if any of the following
QUD = the combined effect of gravity loads
apply:
and earthquake loads
There is an in-plane discontinuity in any
QC
=
the expected strength of the
E
primary element of the lateral-force-resisting system.
component or element at the deformation level under
In-plane discontinuities occur whenever a lateral-
consideration for deformation-controlled actions.
force-resisting element is present in one story, but
does not continue, or is offset, in the story
DCRs should be calculated for each controlling
immediately below.
Figure 5-1 indicates such a
action (such as axial force, moment, and shear) of
condition.
each component. If all of the computed controlling
DCRs for a component is less than or equal to 1.0,
There is an out-of-plane discontinuity in
then the component is expected to respond elastically
any primary element of the lateral-force-resisting
to the earthquake ground shaking being evaluated.
system. An out-of-plane discontinuity exists when
If one or more of the computed DCRs for a
an element in one story is offset relative to the
component is greater than 1.0, then the component is
continuation of that element in an adjacent story, as
expected to respond inelastically to the earthquake
indicated in Figure 5-2.
ground shaking. The largest DCR calculated for a
given component defines the critical action for the
5-4
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