and strain-hardened special segment.
Special
hinge
will
be
formed
during
inelastic
truss moment frames shall have a design strength
deformation of the intermediate moment frame.
to resist the applicable load combinations of the
d.
Special Moment Frames (SMFs).
AISC Seismic Provisions as modified by the
Special
moment
frames
are
expected
to
following
added
requirements.
withstand significant inelastic deformation when
subjected to the forces resulting from the
(2)
Special segment.
Each horizontal
motions of the design earthquake in combination
truss that is part of the moment frame shall have
with other loads. Special moment frames shall
a special segment located within the middle one-
conform to all of the requirements for IMFs,
half length of the truss. The length of the special
except:
segment shall range from 0.1 to 0.5 times the
truss span length. The length-to-depth ratio of
(1) Cyclic test results of the beam/column
any panel in the special segment shall be limited
connection must demonstrate inelastic rotation
to a maximum of 1.5 and a minimum of 0.67.
capacity of at least 0.03 radian.
The second
All panels within a special segment shall be
exceptions in Paragraph 7-5c(2) shall not apply
either Vierendeel or X braced, not a combination
to SMFs.
thereof. Where diagonal members are used in
the special segment, they shall be arranged in an
(2)
Circular sections shall have an
X pattern separated by vertical members. Such
outside-wall-diameter-to-thickness
ratio
not
diagonal members shall be interconnected at
exceeding 1300/Fy (250/Fy for Fy in MPa).
points of crossing.
The interconnection shall
Rectangular tubes shall have an out-to-out width-
have a design strength adequate to resist a force
to-wall thickness b/t not exceeding 110/Fy (21/Fy
at least equal to 0.25 times the diagonal member
for Fy in MPa).
nominal tensile strength.
Bolted connections
e.
Special Truss Moment Frames (STMFs).
shall not be used for web members within the
special segment.
Splicing of chord members
(1)
General.
Special truss moment
shall not be permitted within the special
frames, as shown in Figure 7-44, shall be
segment, nor within panel length from the
designed so that when subjected to earthquake
ends of the special segment.
Axial forces in
loading, yielding will occur in specially designed
diagonal web members due to factored dead plus
segments of the truss girders which are part of
live loads acting within the special segment shall
the lateral-force-resisting system. Such trusses
not exceed 0.03 FyAg.
shall be limited to span length between column
not to exceed 60 feet (18m), and overall depth
(3) Special segment nominal strength. In
not to exceed 6 feet (1.8m). The columns and
the fully yielded state, the special segment shall
truss segments outside of the special segments
develop vertical nominal shear strength through
shall be designed to remain elastic under the
the nominal flexural strength of the chord
forces that can be generated by the fully yielded
7-101
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