columns; Table 7-20 for beam/column joints,
members when subjected to the forces resulting
from the ground motions of the design
and Table 7-21 for slab/column frames.
earthquakes in combination with other loads.
(4)
Expected strength of deformation-
OMFs shall have a design strength, as provided
controlled components shall be the nominal
in the AISC Seismic Provisions, to resist load
flexural strengths determined in accordance with
combinations 4-1 through 4-2 of that document.
Chapter 9 of FEMA 302 with 1.25 fy in lieu of fy
(2) Beam-to-column connections shall be
for the contribution of the reinforcement.
made
by
welds
or
high-strength
bolts.
(5) The lower-bound strength for force-
Connections shall be fully restrained or partially
controlled component shall be taken as the
restrained (Type PR).
applicable nominal strength, Qm, times the
(a) Fully restrained connections. The
appropriate capacity reduction factor, N, in
required flexural strength, Mu, of each beam-to-
accordance with ACI 318.
column connection considered to be part of the
lateral-force-resisting system shall be at least
7-5.
Steel Moment-Resisting Frames.
equal to 1.1RyMp of the beam or column,
a.
General.
whichever is weaker. For pre-engineered steel
structures, Mp is permitted to be taken as the
(1)
Function.
Steel moment-resisting
critical buckling moment of the beam section.
frames have functions and behavior similar to
Welded joints in the connection shall be made
those of concrete moment frames, as discussed in
with filler metal rated to have a Charpy V-notch
Paragraph 7-4a(1).
toughness of 20 ft-lbs (27N-m) at a temperature
of 0 , as determined by ASTM A673. Except
F
(2) Frame types. FEMA 302 prescribes
three types of steel moment frames: Ordinary
for connections of beams to end plates for use in
Moment Frames (OMFs), Intermediate Moment
pre-engineered metal structures, welded joints
Frames (IMFs), and Special Moment Frames
shall be complete penetration welds.
At the
(SMFs). Restrictions regarding the use of these
bottom flange of welds, weld backing shall be
frames are summarized in Table 7-1, which also
removed, the root inspected and repaired, and a
provides the appropriate R value for each
reinforcing fillet added. At the top flange welds,
classification. Design of steel moment frames
backing shall be removed and repaired or shall
shall be in accordance with the provisions of
be attached by means of a continuous fillet weld
AISC Seismic Provisions for Structural Steel
on the edge away from the complete penetration
Buildings.
weld.
Alternately, only connections having a
demonstrated inelastic rotation capability of at
b.
Ordinary Moment Frames (OMFs).
least 0.01 radian, based on tests as described in
(1)
General.
OMFs are expected to
Paragraph 7-5c, shall be permitted to be
withstand limited inelastic deformations in their
7-91
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