Special moment frames are reinforced concrete frames designed to resist earthquakes through flexural, axial, and shearing actions. They have additional proportioning and detailing requirements compared to intermediate or ordinary moment frames to improve seismic resistance. This includes the strong column weak beam design where the sum of the flexural strengths of the columns at a joint must exceed 120% of the sum of the flexural strengths of the beams to ensure plastic hinges form in the beams before the columns. Proper hinge reinforcement is also required to allow hinges to undergo large rotations without losing strength.

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Dr Youssef Hammida
Seismic Design Special
Moment Frames
Strong Column Weak Beam

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Reinforced concrete special moment frames
are used as part of seismic force-resisting systems in buildings that
are designed to resist earthquakes.
Beams, columns, and beam-column joints
in moment frames are proportioned and detailed to resist
flexural, axial, and shearing actions that result as a building
sways through multiple displacement cycles during strong
earthquake ground shaking.

4. 4
Special proportioning and detailing requirements result in a frame
capable of resisting strong earthquake shaking without significant
loss of stiffness or strength.
These moment-resisting frames are called “Special
Moment Frames” because of these additional requirements,
which improve the seismic resistance in comparison with less
stringently detailed Intermediate and Ordinary Moment Frames.

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columnsweak beam behavior, shear failures of-strong columnTo ensure
M interaction diagram shows-, moment capacity. The Pmust be precluded
.this range of axial loads for an example column

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The important aspects of joint design are ensuring proper bar development
and precluding shear failures in the joint. This can be accomplished
through proper detailing of hoop reinforcement and bar ho

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‫اﻟﻘﺺ‬ ‫ﺑﺎﺟﮫﺎد‬ ‫اﻟﻌﺎﻣﻮد‬ ‫اﻧﮫﯿﺎر‬

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he important aspects of joint design are ensuring proper bar development
and precluding shear failures in the join
)‫اﻟﻌﺎﻣﻞ‬R‫ﻟﻠﻌﺰوم‬ ‫ﻣﻘﺎوﻣﺔ‬ ‫اطﺎرات‬ (

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(R)‫ﺣﻤﺎﻟﺔ‬ ‫ﻗﺼﯿﺔ‬ ‫ﺟﺪران‬
‫ھﺒﻜﻠﻲ‬ ‫ﺑﻨﺎء‬ ‫ﻗﺼﯿﺔ‬ ‫ﺟﺪران‬

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‫اطﺎرات+ﺟﺪران‬ ‫ﻣﺸﺘﺮك‬ ‫ﺗﻔﺎﻋﻞ‬
‫ﻋﺰﻣﯿﺔ‬ ‫اطﺎرات‬‫و‬‫اﻟﻤﻨﺎط‬ ‫ﺷﺪة‬‫ق‬‫اﻟﺰﻟﺰاﻟﯿﺔ‬

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three types of frames: ordinary, intermediate, and special.
Ordinary moment frames have very few requirements in ACI 318
‫ﻧ‬‫اﻟزﻟزاﻟﯾﺔ‬ ‫اﻟﻣﻧطﻖ‬ ‫وﺷدة‬ ‫اﻟﻘﺻﻲ‬ ‫اﻟﺟدار‬ ‫وع‬

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‫اﻟﺼﻨﻊ‬ ‫ﻣﺴﯿﻘﺔ‬ ‫ﻗﺼﯿﺔ‬ ‫ن‬ ‫ﺟﺪرا‬

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‫ا‬‫ﻟﻠﻌﺰم‬ ‫ﻣﻘﺎوﻣﺔ‬ ‫ﺧﺎﺻﺔ‬ ‫طﺎرات‬
‫اﻟﻀﻌﯿﻒ‬ ‫واﻟﺠﺎﺋﺰ‬ ‫اﻟﻘﻮي‬ ‫اﻟﻌﺎﻣﻮد‬
strong column-weak beam design is required for special moment frames For a
system with strong columns and weak beams, a mechanism is created when ALL
beams on ALL stories yield (much more seismic energy dissipated prior to
collapse).
Special Moment Frames

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 To ensure that the beams develop plastic hinges before the columns.
 the sum of the flexural strengths of the columns at a joint must
exceed 120% of the sum of the flexural strengths of the beams.
 This requirement protects against premature development of a story
mechanism
‫اﻟﻌﺎﻣﻮد‬ ‫ﻣﻊ‬ ‫اﻟﺠﺎﺋﺰ‬ ‫اﺗﺼﺎل‬ ‫ﻋﻘﺪة‬ ‫ﺗﺤﻘﯿﻘﺎت‬
1-‫اﻟﺠﻮاﺋﺰ‬ ‫ﻓﻲ‬ ‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬ ‫ﺗﺸﻜﻞ‬
2-= ‫اﻷﻋﻤﺪة‬ ‫ﻋﺰوم‬ ‫ﻣﺠﻤﻮع‬1.2‫ﻋﺰوم‬ ‫ﻣﺠﻤﻮع‬
‫اﻟﺘﻼﻗﻲ‬ ‫ﻋﻘﺪة‬ ‫ﻓﻲ‬ ‫اﻟﺤﻮاﺋﺰ‬

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‫اﻟﺠﻮاﺋﺰ‬ ‫ﻓﻲ‬ ‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬ ‫ﺗﺸﻜﻞ‬ ‫ﻣﺘﻄﻠﺒﺎت‬
to ensure proper hinge development. The hinges must be able to form and
then undergo large rotations and load reversals without significant
reduction in strength
1-‫اﻟﻠﺪﻧﺔ‬ ‫اﻟﻤﻨﻄﻘﺔ‬ ‫ﻓﻲ‬ ‫اﻟﻌﻨﺎﺻﺮ‬ ‫ﻋﻤﻞ‬ ‫واﺳﺘﻤﺮار‬ ‫واﻟﻤﻤﻄﻮﻟﯿﺔ‬ ‫اﻟﻤﻄﺎوﻋﺔ‬ ‫ﺗﺤﻘﯿﻖ‬
2-‫اﻟﻤﻔﺼﻞ‬ ‫ﺗﺸﻜﻞ‬‫ﻣﻘ‬ ‫وﺗﺸﻘﻖ‬ ‫ﻛﺒﯿﺮة‬ ‫دوراﻧﺎت‬ ‫ﻣﻊ‬ ‫اﻟﻠﺪن‬‫اﻟﺨﺮﺳﺎﻧﺔ‬ ‫ﻄﻊ‬‫ﻣﻦ‬
‫اﻟﺘﺼﻤﯿﻢ‬ ‫ﻣﻘﺎوﻣﺔ‬ ‫ﻓﻲ‬ ‫اﻟﺰﻳﺎدة‬ ‫دون‬ ‫اﻟﻤﺘﻨﺎوﺑﺔ‬ ‫اﻟﺤﻤﻮﻻت‬ ‫ﺗﺄﺛﯿﺮ‬‫اﻟﺘﺴﻠﯿﺢ‬ ‫وﻣﻘﺎطﻊ‬

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‫طﺎﻗﺔ‬ ‫ﻣﻦ‬ ‫ﺟﺰء‬ ‫واﻣﺘﺼﺎص‬ ‫وﺗﺸﺘﯿﺖ‬ ‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬ ‫ﺗﺸﻜﻞ‬
‫اﻟﺰﻟﺰال‬
‫اﻟﻤﻔﺼﻞ‬ ‫ﺗﺸﻜﻞ‬ ‫ﺣﯿﺚ‬‫واﺳﺘﻤﺮار‬ ‫اﻟﻠﺪن‬‫ﻳﺸﺘﺖ‬ ‫اﻟﻠﺪﻧﺔ‬ ‫اﻟﻤﻨﻄﻘﺔ‬ ‫ﻓﻲ‬ ‫اﻟﻌﻤﻞ‬
‫ﻗﺴﻢ‬‫ﻣﻘﺎ‬ ‫اﻟﺰﻟﺰال‬ ‫طﺎﻗﺔ‬ ‫ﻣﻦ‬ ‫ﻛﺒﯿﺮ‬‫ﺑ‬‫اﻟﻠﺪﻧﺔ‬ ‫واﻟﺘﺸﻮھﺎت‬ ‫اﻻﻧﺘﻘﺎﻻت‬ ‫زﻳﺎدة‬ ‫ﻞ‬‫دون‬
‫اﻟﻌﻨﺎﺻﺮ‬ ‫وﺗﺴﻠﯿﺢ‬ ‫ﻣﻘﻄﻊ‬ ‫ﻓﻲ‬ ‫زﻳﺎدة‬ ‫او‬ ‫اﻟﺘﺼﻤﯿﻢ‬ ‫ﻣﻘﺎوﻣﺔ‬ ‫ﻓﻲ‬ ‫زﻳﺎدة‬
‫وﻧﻘﺮﻳﺒﺎ‬‫ان‬‫ﻗﯿﻤﺔ‬ ‫ﻧﻔﺲ‬ ‫ﺗﻌﺎدل‬ ‫اﻟﺰﻟﺰال‬ ‫ﻗﻮة‬ ‫ﻣﻦ‬ ‫اﻟﻤﺸﺘﺘﺔ‬ ‫اﻟﻄﺎﻗﺔ‬ ‫ﻗﯿﻤﺔ‬
) ‫اﻟﻤﻘﺎوﻣﺔ‬ ‫زﻳﺎدة‬ ‫ﻋﺎﻣﻞ‬ ‫ﻣﻦ‬ ‫اﻟﺘﺼﻌﯿﺪ‬R(
‫ﺣﯿﺚ‬ ‫وﻛﻤﯿﺜﺎل‬) ‫ﻗﯿﻤﺔ‬ ‫ﻟﺪﻳﻨﺎ‬ ‫ﻋﺎدﻳﺔ‬ ‫اطﺎرات‬ ‫ﺣﺎل‬ ‫ﻓﻲ‬R=(4
) ‫ﺗﺼﺒﺢ‬ ‫ﻟﻠﻌﺰم‬ ‫ﻣﻘﺎوم‬ ‫ﺧﺎص‬ ‫اطﺎر‬ ‫ﺣﺎل‬ ‫وﻓﻲ‬R= (8
=‫ﻗﯿﻤﻨﻪ‬ ‫ﻣﺎ‬ ‫واﻣﺘﺼﺎص‬ ‫ﺗﺸﺘﯿﺖ‬ ‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬ ‫وﻋﻠﻰ‬8/4=2
‫ﻗﻮة‬ ‫ﺿﻌﻒ‬ ‫اي‬‫اﻟﻤﻔﺼﻞ‬ ‫ﻳﺸﺘﺘﮫﺎ‬ ‫ان‬ ‫ﻳﺠﺐ‬ ‫اﻟﻘﺎﻋﺪي‬ ‫اﻟﻘﺺ‬
‫اﻟﻠﺪن‬‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬ ‫ﺗﻄﺒﯿﻖ‬ ‫طﺮﻳﻘﺔ‬ ‫ﺳﻤﯿﺖ‬ ‫ھﺬا‬ ‫وﻋﻠﻰ‬‫ﺑﺎﻟﻨﻈﺮﻳﺔ‬
‫اﻟﺰﻟﺰاﻟﯿﺔ‬ ‫اﻻﻗﺘﺼﺎدﻳﺔ‬
‫اﻟﻘﺎﻋﺪى‬ ‫اﻟﻘﺺ‬ ‫ﻗﻮة‬ ‫ﻧﺼﻒ‬ ‫ﻋﻠﻰ‬ ‫ﺗﻘﺮﻳﺒﺎ‬ ‫اﻟﺒﻨﺎء‬ ‫ﻧﺼﻤﻢ‬ ‫ﺣﯿﺚ‬
‫اﻟﺰﻟﺰال‬ ‫ﻗﻮة‬ ‫ﻛﺎﻣﻞ‬ ‫وﻟﯿﺲ‬
‫و‬‫اﻷول‬ ‫اﻟﻨﺼﻒ‬‫اﻟﺰﻟﺰال‬ ‫ﻗﻮة‬ ‫ﻣﻦ‬‫ﻳﺼﻤﻤ‬‫ﻊ‬‫اﻟﻤﺮﻧﺔ‬ ‫اﻟﻤﻨﻄﻘﺔ‬ ‫ﻓﻲ‬ ‫واﻟﺘﺴﻠﯿﺢ‬ ‫اﻟﻤﻘﻄﻊ‬
‫واﻟﻨﺼﻒ‬‫ﺗ‬ ‫ﻳﻘﻮم‬ ‫اﻵﺧﺮ‬‫ﺑﻤﻘﺎوﻣﺘﻪ‬ ‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬ ‫ﺸﻜﻞ‬‫وﺗﺸﺘﯿﺘﻪ‬‫ﻳﻀﺎف‬ ‫ﻻ‬ ‫و‬‫اي‬
‫ﻟﺘﺴﻠﯿﺢ‬ ‫او‬ ‫اﻟﻤﻘﻄﻊ‬ ‫ﻓﻲ‬ ‫زﻳﺎدة‬‫اﻟﺰﻟﺰاﻟﯿﺔ‬ ‫اﻟﺤﻤﻮﻟﺔ‬ ‫زﻳﺎدة‬ ‫ﻣﻘﺎﺑﻞ‬
‫ﻟﻜﻦ‬‫ﻳﺒﻘﻰ‬‫ﻧﺸﻜﻞ‬‫ﻣﻘﻄﻊ‬ ‫ﺗﺸﻘﻖ‬ ‫ﻣﻌﻨﺎه‬ ‫اﻟﻠﺪن‬ ‫اﻟﻤﻔﺼﻞ‬‫اﻟﺨﺮﺳﺎﻧﺔ‬ ‫ﺑﯿﺘﻮن‬
‫اﻟﺒﻨﺎء‬ ‫ﺧﺎرج‬ ‫ﻟﻠﻨﺰوح‬ ‫اﻟﺴﻜﺎن‬ ‫ﺗﺠﺒﺮ‬ ‫ﻗﺪ‬ ‫وﺿﺎرة‬ ‫ﻛﺒﯿﺮة‬ ‫اﻧﺸﺎﺋﯿﺔ‬ ‫ﺗﺸﻘﻘﺎت‬‫واﻋﺎدة‬
.‫اﻧﺸﺎﺋﯿﺎ‬ ‫وﺗﺄھﯿﻠﻪ‬ ‫ﺗﺪﻋﯿﻤﻪ‬

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parabolic distribution in the concrete, and some compressive stress in the top
steel. Upon spalling, the stress distribution changes, The compression block of
the concrete moves lower in the cross section, and the stresses in the
compression steel are greatly increased.

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Under reverse load applications, hinge development affects both the top and
bottom faces of beams. This leads to bidirectional cracking and spalling of
cover on the top and bottom of the beam
 beam longitudinal reinforcement requirements per ACI 318.
 The reinforcement ratio limits insure a tension controlled failure mode
in bending and reduce congestion of reinforcing steel.
 Continuous bars in the top and bottom are required due to reversal
of seismic motions and variable live load.
 Splice locations and transverse reinforcement are specified because
lap splices are unreliable and cover concrete will spall.

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At low loads the section is uncracked and an analysis using uncracked

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Shear Design
Seismic induced energy in special moment resisting frames is expected to be
dissipated through flexural yielding of members. During inelastic response,
however, the members should be protected against premature brittle shear
failure. This is ensured by providing sufficient shear capacity to resist seismic
design shear forces. Seismic design shear Ve in plastic hinge regions is
associated with maximum inelastic moments that can develop at the ends of
members when the longitudinal tension reinforcement is in the strain hardening
range (assumed to develop 1.25 fy)
Fig. 6-1 Internal forces in a reinforced concrete section at probable
moment resistance
Figure 6-1 illustrates the internal forces of a sectM pr for a rectangular section
with tension reinforcement can be obtained from Seismic 3.
This design aid provides values for coefficient Kpr, which is used to solve the
following equation:ion that develop at probable moment resistance.

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Once Mpr is obtained, the seismic design shear can be computed from the
equilibrium of forces shown in Seismic 4.
within the plastic hinge region (lengthcThe contribution of concrete to shear, V
equal to twice the member depth at each end) may be negligibly small upon the
.ion of hinge due to the deterioration of concreteformat
half or more of-to onewithin the hinging region is equaleTherefore, when V
the maximum required shear strength, and the factored axial compression
should be ignoredcV/ 20,cf’gincluding earthquake effects is less than A
)= 0ccompletely in design (V

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.
Strong-Column Weak-Beam Concept

32. 32
‫ﻟدﻧﺔ‬ ‫ﻣﻔﺎﺻل‬ ‫ﺗﺷﻛل‬ ‫ﺣﺎل‬ ‫ﻓﻲ‬ ‫ﺧﺎص‬ ‫ھو‬ ‫اﻟﻌطﺎﻟﺔ‬ ‫ﺗﺧﻔﯾض‬
‫ﻋﺎدﯾﺔ‬ ‫اطﺎرات‬ ‫ﺣﺎل‬ ‫ﻓﻲ‬‫ﻣﺗﺷﻘﻖ‬ ‫ﻏﯾر‬ ‫اﻟﻣﻘطﻊ‬ ‫ﯾﻛون‬uncracked
‫اﻟﻣروﻧﺔ‬ ‫ﻣﺟﺎل‬ ‫ﻓﻲ‬= ‫اﻟﻌﻧﺎﺻر‬ ‫ﻟﻛل‬ ‫اﻋﺗﺑﺎر‬ ‫وﯾﻣﻛن‬0.7–0.8

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ASCE 7 - 12.2.5.5 outlines requirements where special moment
frames extend through below-grade floors, as shown in Figure
4-2. The restraint and stiffness of the below-grade diaphragms
and basement walls needs to be considered.
In this condition the columns would be modeled as continuous elements
downto the footing.
Thetypeof rotational restraint at the column
base will not have a significant effect on the behavior of the
moment frame. Large forces are transferred through the grade
level diaphragm to the basement walls, which are generally very
stiff relative to the special moment frame

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Design Strong colum Weak Beam
When a building sways during an earthquake, the distribution of
damage over height depends on the distribution of lateraldrift.
If the building has weak columns, drift tends to concentrate
in one or a few stories (Figure 3-1a), and may exceed the drift
capacity of the columns.
On the other hand, if columns provide a stiff and strong spine over the
building height, drift will be more uniformly distributed (Figure 3-1c),
and localized damage
will be reduced.
Additionally, it is important to recognize that the columns in a given
story support the weight of the entire building above those columns,
whereas the beams only support the gravity loads of the floor of which
they form a part; therefore, failure of a column is of greater
consequence than failure of a beam.

35. 35
Recognizing this behavior, building codes specify that
columns be stronger than the beams that frame into them. This strong-
column/weak-beam principle is fundamental to achieving safe behavior
of frames during strong earthquake ground shaking.
Figure 3-1 - Design of special moment frames aims to avoid the story
mechanism (a) and instead achieve either an intermediate mechanism (b)
or a beam mechanism (c).
.

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40. 40

41. 41
Seismic Design Aids

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-‫اﻟﻌﺎﻣود‬ ‫ﻋرض‬‫اﻟﺟﺎﺋز‬ ‫ﻋرض‬ ‫ﻣن‬ ‫أﻛﺑر‬
-‫اﻟﻌﺎﻣود‬ ‫ﺗﺳﻠﯾﺢ‬ ‫ﯾوﺿﻊ‬‫ﺻب‬ ‫ﻗﺑل‬‫اﻟﺳﻘف‬ ‫ﺑﻼطﺔ‬
‫اﻟﻠدن‬ ‫اﻟﻣﻔﺻل‬ ‫ﻣﻧطﻘﺔ‬ ‫ﻣﺎﺑﻌد‬ ‫اﻟﻌﺎﻣود‬ ‫ﻓﻲ‬ ‫اﻟﻘﺿﺑﺎن‬ ‫وﺻل‬
‫ﺣﺑث‬ ‫اﻟﻌﺎﻣود‬ ‫ﻣﻧﺗﺻف‬ ‫ﻓﻲ‬ ‫اﻟوﺻل‬ ‫وﯾﻔﺿل‬M=0

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elevation and plan views of cast-in-place concrete frame
buildings

56. 56
Plan views of steel moment-frame buildings

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-sheet Excel-design beams frame‫ﻛﻣرات‬ ‫ﺗﺻﻣﯾم‬
‫واﻟزﻻزل‬ ,‫ﻟﻠﻌزوم‬ ‫ﻣﻘﺎوم‬ ‫اطﺎر‬
beams-design.xls
https://usc.academia.edu/
design beams frame - sheet Excel- ‫اطﺎر‬ ‫ﻛﻣرات‬ ‫ﺗﺻﻣﯾم‬
‫واﻟزﻻزل‬ ,‫ﻟﻠﻌزوم‬ ‫ﻣﻘﺎوم‬
Reinforced concrete special moment frames are used as part of
seismic force-resisting systems in buildings that are designed to
resist earthquakes. Beams, columns, and beam-column joints in
moment frames are proportio... more abstract.

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Dr youssef Hammida