(e)
Details illustrating the above
318. Details illustrating these requirements are
requirements are presented in Figure 7-33
presented in Figures 7-27 through 7-32.
through 7-40.
f.
Special Moment Frames (SMFs) are
(2) The two phases of design. With the
frames conforming to the requirements of
design concept that inelastic behavior and energy
Sections 21.1 through 21.5 of ACI 318, in
dissipation are to be restricted to flexural
addition to the requirements of OMFs.
yielding in the confined concrete regions of the
beam or girder elements, the design process
(1)
General design requirements.
The
consists of two phases.
The first phase
basic concept of SMFs is to provide inelastic
establishes the beam sizes and capacities needed
energy dissipation by flexural yielding in the
to resist the specified factored gravity and
girder elements.
Columns must, therefore, be
seismic load combinations.
Then, with the
stronger than the flexural capacity of the girders,
known girder strengths and some preliminary
and all elements must have shear resistance and
column sizes, the second phase proportions the
reinforcing bar anchorage capacity capable of
shear resistance of the girders, columns, and
developing the full flexural yield level in the
joints, and establishes the column flexural
girders.
In order to provide the girder yield
strengths such that all of these elements are able
mechanism, the design provisions require:
to resist the effects of a strain-hardened flexural
yielding in the beams along with unfactored
(a) Compact proportions for the girder
gravity loads.
and column sections, along with closely spaced
seismic ties or hoops for confinement of concrete
Acceptance Criteria.
g.
in the regions of potential flexural yielding.
(1) Response modification factors, R, for
(b)
Column
interaction
flexural
Performance Objective 1A, for concrete frames
capacity greater than 6/5 times the value required
in various structural systems are provided in
to develop girder yield.
Table 7-1.
(c)
Girder, column, and joint shear
(2) Modification factors, m, for enhanced
capacity greater than shears induced by gravity
performance objectives are provided in Table 7-
loads and the strain-hardened flexural capacity of
14 for beams; Table 7-15 for columns; Table 7-
the girders.
16 for beam/column joints; and Table 7-17 for
slab/column frames.
(d) Reinforcing bar splices and straight
(3) Modeling parameters and numerical
and
hooked
bar
anchorages
capable
of
acceptance criteria for nonlinear procedures are
developing the strain-hardened yield of the
provided in Table 7-18 for beams; in Table 7-19
girder steel.
for
7-70
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