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.
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
addition to the requirements of OMFs.
yielding in the confined concrete regions of the
beam or girder elements, the design process
General design requirements.
consists of two phases.
The first phase
basic concept of SMFs is to provide inelastic
establishes the beam sizes and capacities needed
to resist the specified factored gravity and
Columns must, therefore, be
Then, with the
stronger than the flexural capacity of the girders,
known girder strengths and some preliminary
reinforcing bar anchorage capacity capable of
developing the full flexural yield level in the
joints, and establishes the column flexural
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
and column sections, along with closely spaced
in the regions of potential flexural yielding.
(1) Response modification factors, R, for
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.
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-
16 for beam/column joints; and Table 7-17 for
(d) Reinforcing bar splices and straight
(3) Modeling parameters and numerical
acceptance criteria for nonlinear procedures are
developing the strain-hardened yield of the
provided in Table 7-18 for beams; in Table 7-19