ACI 318, depending on the magnitude of the moment
means that a frame meeting the minimum strength
induced in those members when subjected to the
requirements of this manual will survive a major
calculated displacements in FEMA 302. When the
earthquake only if it can yield and sustain cyclic
effects of lateral displacement are not explicitly
inelastic deformations without essential loss of lateral
checked, the provisions of Section 21.7.3 shall apply.
resistance and vertical load capacity. Since normal
building
materials
have
very
limited
energy-
d.
Ordinary Moment Frames (OMF) are
absorbing capacity in the elastic range of action, it
reinforced concrete moment frames conforming to
follows that what is needed is a large energy capacity
the provisions of ACI 318, exclusive of Appendix A.
in the inelastic range. The term "ductility" is used to
denote this property. Providing a ductile seismic
frame will allow the structure to sustain tolerable, and
(1) Flexural members of OMF' forming part
s
in many cases, repairable damage, instead of
of a seismic-force-resisting system shall be designed
suffering
catastrophic
failure.
The
energy
in accordance with Section 7.13.2 of ACI 318, and at
and
structural
response
least two main flexural reinforcing bars shall be
(deformation) of moment-resisting frames depend
provided continuously top and bottom throughout the
upon the types of members, connections (joints), and
beams through, or developed within, exterior
materials of construction used.
The behavior of
columns or boundary elements.
joints is a critical factor in the ability of building
frames to resist high-intensity cyclic loading.
(2) Columns of OMFs having a clear height-
to-maximum plan dimension ratio of 5 or less shall
(3)
Mechanical and welded splices.
See
be designed for shear in accordance with Section
Paragraph 7-2a(3) for revisions to ACI 318
21.8.3 of ACI 318.
provisions regarding mechanical and welded splices
in reinforcement.
Intermediate Moment Frames (IMFs) are
e.
frames conforming to the requirements of Sections
b.
Classification of Concrete Moment-Resisting
21.1, 21.2.1.1, 21.2.1.2, 21.2.2.3, and 21.8 of ACI
Frames.
FEMA 302 classifies concrete moment-
318, in addition to the requirements of OMFs. Flat-
resisting frames as Ordinary Moment Frames (OMF),
plate or two-way slabs are permitted for the beam
Intermediate Moment Frames (IMF), or Special
elements of IMFs.
These slab systems have a
Moment Frames (SMF). Restrictions regarding the
potential for a brittle mode of punching shear failure
use
of
the
various
frame
classifications
are
at the column supports due to gravity load combined
summarized in Table 7-1, which also provides the
with the eccentric shear caused by moment
appropriate R value for each classification.
transferred from the slab to the column. In order to
prevent punching shear failure under the maximum
c.
Nonseismic Frames.
Frame members
expected earthquake deformation, the slab shall be
assumed not to contribute to lateral resistance shall
designed in accordance with Section 21.8 of ACI
be detailed according to Section 21.7.2 or 21.7.3 of
7-69
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