Hinge Development
• Tightly Spaced Hoops
– Provide confinement to increase concrete streng
and usable compressive strain
– Provide lateral support to compression bars to
prevent buckling
– Act as shear reinforcement and preclude shear
failures
– Control splitting cracks from high bar bond stress
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Hinge Development
Before
spalling
After
spalling
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Hinge Development
Bidirectional cracki
Spalled cover
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Beam Longitudinal Reinforcement
200 0.025
fy
At least 2 bars continuous
top & bottom
Joint face Mn+ not less than
Min. Mn+ or Mn- not less tha
25% max. Mn at joint face
Splice away from hinges a
enclose within hoops or sp
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Beam Transverse Reinforcement
Closed hoops at hinging re
with “seismic” hook
135º hook, 6dh 3” extens
Maximum spacing of hoop
d/4 8db 24dh 12”
Longitudinal bars on perim
tied as if column bars
2h
min Stirrups elsewhere, s d
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Beam Shear Strength
1.2D + 1.0L + 0.2S
Mpr1 Mpr2
Mpr Mn w
fs 1.25 fy ,
Ve1 n Ve2
Mpr1 Mpr 2 wu n
Ve Ve by analysis
n 2
If earthquake-induced 1
Ve
shear force 2
then Vc = 0
'
A fg c
and Pu
20
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Beam-Column Joint
Vcol
Vj T C Vc
T C
T 1.25 fy A s, top
Vj
C 1.25 fy A s, bo
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Beam-column Joint
20
Vn 15 f 'c A j
12
• Vn often controls size of columns
• Coefficient depends on joint confinement
• To reduce shear demand, increase beam d
• Keep column stronger than beam
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Column Longitudinal Reinforcemen
M nc1
0.01 0.
M nb1 M nb2
Mnc 1.2
(strong column-weak b
M nc2
Mnc based on factored axial force,
consistent with direction of lateral forc
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Column Transverse Reinforcement
Potential Hinging Region
Spirals Hoops
Ag f 'c f 'c Ag
s 0.45 1 Ash 0.3 sbc
Ach f yt f yt Ach
and and
f 'c f 'c
0.12 Ash 0.09 sbc
s
f yt f yt
Ag = gross area of column
Ach = area confined within the hoops
bc = trans. dimension of column core, center to center of outer le
s = hoop spacing
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Column Transverse Reinforcement
Potential Hinging Region
hx hx
14 h x
so 4
3
Spacing shall not exceed the smallest of:
b/4 or 6 db or so (4” to 6”)
Distance between legs of hoops or crossties, hx 14
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Potential Hinge Region
• For columns supporting stiff members such as
walls, hoops are required over full height of colu
if
f 'c A g
Pe
10
• For shear strength- same rules as beams (concr
shear strength is neglected if axial load is low a
earthquake shear is high)
• Lap splices are not allowed in potential plastic
hinge regions
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Splice in Hin
Region
Terminatin
bars
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of SMF:
Potential Hinge Region
clear height
o 6
18"
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Topic Overview
• Concrete and reinforcement behavior
• Reference standards
• Requirements by Seismic Design Catego
– Moment resisting frames
– Shear walls
• Other topics
• Design Examples
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Performance Objectives
• Special R/C shear walls
– Resist axial forces, flexure and shear
– Boundary members
• Where compression stress/strain is large, ma
capacity
– Development of rebar in panel
– Ductile coupling beams
• Ordinary R/C shear walls
– No seismic requirements, Ch. 21 does not apply
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Design Philosophy
• Flexural yielding will occur in predetermi
flexural hinging regions
• Brittle failure mechanisms will be preclud
– Diagonal tension
– Sliding hinges
– Local buckling
– Shear failures in coupling beams
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
General Requirements
w
t = parallel to shear
= perpendicular
hw to shear plane
Shear plane, Acv =
web thickness
length of wall
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
General Requirements
• and t not less than 0.0025
unless
Vu Acv f 'c
then per Sec.14.3
• Spacing not to exceed 18 in.
• Reinforcement contributing to Vn
shall be continuous and distributed
across the shear plane
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
General Requirements
• Two curtains of reinforcing required
if:
Vu 2 Acv f 'c
• Design shear force determined from
lateral load analysis
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
General Requirements
• Shear strength:
Vn Acv c f 'c t fy
c = 3.0 for hw/ w 1.5
c = 2.0 for hw/ w 2.0
Linear interpolation between
• Walls must have reinforcement in tw
orthogonal directions
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
General Requirements
• For axial load and flexure, design like a
column to determine axial load – moment
interaction P
M
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
Boundary Elements
For walls with a high
compression demand
at the edges – specia
boundary elements
are required
Widened end with confine
Extra confinement and/or
longitudinal bars at end
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318: Overview of Special Walls
Boundary Elements
Two options for determining need for boun
elements
• Strain-based: Determined using wall
deflection and associated wall curvature
• Stress-based: Determined using maximu
extreme fiber compressive
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318, Overview of Special Walls
Boundary Elements—Strain
• Boundary elements are required if:
w
c
600 u
hw
u = Design displacement
c = Depth to neutral axis from strain
compatibility analysis with loads
causing u
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318-05, Overview of Walls:
Boundary Elements—Strain
• Where required, boundary elements mus
extend up the wall from the critical sectio
distance not less than the larger of:
w or Mu/4Vu
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318-05: Overview of Walls
Boundary Elements—Stress
• Boundary elements are required where th
maximum extreme fiber compressive stre
calculated based on factored load effects
linear elastic concrete behavior and gros
section properties, exceeds 0.2f’c
• Boundary element can be discontinued
where the compressive stress is less tha
0.15f’c
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318-05: Overview of Walls
Boundary Elements—Detailing
• Boundary elements must extend horizont
not less than the larger of c/2 or c-0.1 w
• In flanged walls, boundary element must
include all of the effective flange width an
least 12 in. of the web
• Transverse reinforcement must extend in
the foundation
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
ACI 318-05: Overview of Walls
Coupling Beams
Requirements based on aspect ratio and shear dem
n /h 4 Design as Special
Moment Frame bea
n /h 2 and Vu 4 f 'c Acw Reinforce with 2
intersecting groups
diagonal bars
Other cases Standard or diago
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
Topic Overview
• Concrete and reinforcement behavior
• Reference standards
• Requirements by Seismic Design Catego
– Moment resisting frames
– Shear walls
• Other topics
• Design Examples
Instructional Materials Complementing FEMA P-751, Design Examples Reinforc
