stage, internal forces and elastic and plastic
bilinear
relation
are
sensitive
to
the
target
deformations of all components are calculated.
displacement.
(e) The loading process is continued until
(i) Once the target displacement is known,
unacceptable performance is detected or a roof
the accumulated forces and deformations at this
displacement is obtained that is larger than the
displacement of the control node should be used to
maximum displacement specified in Paragraph 5-
evaluate the performance of components and
4e(1). Unacceptable performance may be defined as
elements.
excessive drift of the building, or the undesirable
response or failure of critical components or
1.
For deformation-controlled actions
elements.
(e.g., flexure in beams), the deformation demands
are compared with the maximum permissible values
(f) The forces and deformations from all
given in Chapter 7.
previous loading stages are accumulated to obtain
the total forces and deformations (elastic and plastic)
2.
For force-controlled actions (e.g.,
of all components at all loading stages.
shear in beams), the lower-bound strength capacity is
compared with the force demand.
Capacities are
Note:
given in Chapters 7 through 10.
Steps (c) through (f) can be performed
systematically with a nonlinear computer analysis
(j) If either (a) the force demand in force-
program using an event-by-event strategy, or an
controlled actions, components, or elements, or (b)
incremental
analysis
with
predetermined
the deformation demand in deformation-controlled
displacement increments in which iterations are
actions,
components,
or
elements,
exceeds
performed to balance internal forces.
permissible values by more than 10 percent, then the
action, component, or element is deemed to violate
(g) The displacement of the control node
the performance criterion.
versus first story (base) shear at various loading
stages is plotted as a representative nonlinear
(k)
When the demand exceeds the
response diagram of the structure. The changes in
permissible capacity of the components or elements
slope of this curve are indicative of the yielding of
as described in Step (j) above, the mathematical
various components.
model of the building shall be redesigned to provide
additional strength and/or rigidity to the deficient
(h) The control node displacement versus
components or elements, and the pushover procedure
base shear curve is used to estimate the target
shall be repeated, as necessary.
Similarly, if the
displacement,
as
described
in
the
following
evaluation indicates that a number of components or
paragraph. Note that this step may require iteration
elements are overdesigned by a factor of 10 percent
if the yield strength and stiffnesses of the simplified
5-13
Previous Page
