(2)
Actions and Deformations.
With the
deformations
by
subtraction
of
the
yield
procedures
as
described
in
Paragraph
5-4,
deformations, 2 y.
compliance with the performance objective requires
compliance with the global displacement criteria for
i. For beams:
the structure as a whole, and the local deformation
criteria for individual structural elements.
ZFye l b
(6-7)
2y=
6EI b
(a) Global displacement. The displacement
for the control node of the structure in the
ii. For columns:
force/displacement plot (i.e., pushover analysis) must
equal or exceed the target displacement, δ described
t,
ZFyelc
P
1 -
(6-8)
2y=
6EIc Pye
in Paragraph 5-4f. Story drifts shall not exceed the
values indicated in Table 6-1.
where:
(b)
Deformation-controlled
actions.
Primary and secondary components shall have
Z = Plastic section modulus, in3 (mm3).
expected deformation capacities not less than the
deformations derived from the pushover analysis
Fye = Expected yield strength, psi (kPa), as
when the target displacement, δ is attained.
defined in the AISC Seismic provisions.
t,
Modeling parameters and numerical acceptance
criteria are provided for each performance objective
Moment of inertia of beams, in4
Ib =
for the structural systems described in Chapters 7
(mm4).
through 10. The acceptance criteria are provided in
Ic = Moment of inertia of columns, in4
or deformation ratios ) /) y, as depicted in Figure 6-2.
(mm4).
1.
Steel moment and braced frames.
lb = Beam length, in (mm).
Acceptance criteria are provided in terms of either
plastic rotations of ratios or plastic rotations to yield
lc = Column length, in (mm).
rotations.
Figure 6-3 illustrates the definition of
chord rotation for frame beams and columns. If it is
P = Axial force in the columns, kips (kN).
assumed that the total chord rotation, 2 , (elastic plus
plastic rotation) is defined by the interstory drift,
Pye = Expected axial yield strength, Ag Fye
) /h, then the interstory drift ratio becomes a
kips (kN).
convenient parameter to monitor the inelastic
6 - 10
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