PCA Education Foundation
2015 Professors’ Workshop
July 21, 2015
_________________________________________________________
Seismic Details for Reinforced
Concrete Buildings
David A. Fanella, Ph.D., S.E., P.E.
TGRWA, LLC
2
Permitted
Not
Permitted
3

Sections of Chapter 18 to be satisfied
according to SDC
4
4
5
6

Beams of Ordinary Moment Frames (ACI 18.3)
Minimum 2 continuous longitudinal bars at both
top and bottom faces
 Area of continuous bottom bars at least 25% of
total area of bottom bars


Bars anchored to develop fy in tension at the face
of support
7
7

Columns
 Shear strength requirements for columns in ordinary
moment frames (ACI 18.3.3)
▪ If clear height is less than or equal to 5 times the column dimension
in the direction of analysis, column must be designed for the lesser
of the shear forces in ACI 18.3.3(a) and 18.3.3(b)
(a) Shear associated with development of 𝑀𝑛 at each end due to
reverse curvature bending
(b) Maximum shear obtained from design load combinations that
include 𝐸 with Ω𝑜 𝐸 substituted for 𝐸
8
9
10

Beams of Intermediate Moment Frames
 Summary of requirements (ACI 18.4.2)
▪ Flexure
▪ Confinement
▪ Shear
11

Beams of Intermediate Moment Frames
 Flexural requirements
12
13

Beams of Intermediate Moment Frames
 Confinement requirements
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15
Hoops
16

Beams of Intermediate Moment Frames
 Shear requirements
▪ Two methods
▪ Method 1
 Factored shear force is determined based on factored gravity
loads and the development of the nominal moment strength of
the section at both ends of the member
17
18

Beams of Intermediate Moment Frames
 Shear requirements
▪ Two methods
▪ Method 2
 Factored shear force is obtained from the design load
combinations that include E where E is assumed to be twice that
prescribed by the building code
19

Two-way slabs without beams (ACI 18.4.5)
 May be considered part of the seismic-force-
resisting system in buildings assigned to SDC B and
C
20
21

Two-way slabs without beams
 Two-way shear
▪ Shear caused by factored gravity loads limited to
22

Columns of Intermediate Moment Frames
 Summary of requirements (ACI 18.4.3)
▪ Transverse reinforcement
▪ Shear strength
23

Columns of Intermediate Moment Frames
 Transverse reinforcement
24
25

Columns of Intermediate Moment Frames
 Transverse reinforcement requirements for
columns supporting discontinued stiff members
26
27

Columns of Intermediate Moment Frames
 Shear strength
▪ Same two methods required for beams except instead of
2E in Method 2, E is to be increased by Wo
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29

Beams of Special Moment Frames
 Summary of requirements (ACI 18.6)
▪ General
▪ Flexure
▪ Splices
▪ Transverse reinforcement
▪ Shear
30

Beams of Special Moment Frames
 General requirements
▪ Factored axial force
▪ Geometric requirements
31
32

Beams of Special Moment Frames
 Flexural requirements
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34

Beams of Special Moment Frames
 Lap splice requirements
35
36

Beams of Special Moment Frames
 Transverse reinforcement requirements
▪ Vc = 0 when both of the following occur:
▪ Earthquake-induced shear force ≥ Vu/2
▪ Pu < Agf’c/20
37
38

Beams of Special Moment Frames
 Shear requirements
39
40

Columns of Special Moment Frames
 Summary of requirements (ACI 18.7)
▪ General
▪ Flexure
▪ Longitudinal reinforcement
▪ Transverse reinforcement
▪ Shear
41

Columns of Special Moment Frames
 General requirements
▪ Geometric constraints
42
43

Columns of Special Moment Frames
 Minimum flexural strength
▪ Columns must have sufficient strength so that they will
not yield prior to the beams at the beam-column joints
44
45
46
47

Columns of Special Moment Frames
 Minimum flexural strength
▪ If minimum flexural strength is not satisfied
▪ Lateral strength and stiffness of the columns framing into the joint
are to be ignored when determining the strength and stiffness of
the structure
▪ Columns must satisfy the provisions of ACI 18.14
48

Columns of Special Moment Frames
 Longitudinal reinforcement requirements
49
50

Columns of Special Moment Frames
 Transverse reinforcement requirements
51
𝑷𝒖 ≤ 𝟎. 𝟑𝑨𝒈 𝒇′𝒄
𝒇′𝒄 ≤ 𝟏𝟎 𝐤𝐬𝐢
52
𝑷𝒖 > 𝟎. 𝟑𝑨𝒈 𝒇′𝒄
𝒇′𝒄 > 𝟏𝟎 𝐤𝐬𝐢
53
54
55

Columns of Special Moment Frames
 Shear requirements
▪ Shear forces associated with development of Mpr acting
at the ends of the member associated with the range of
Pu
▪ Maximum shear force may be limited by the probable
flexural strengths of the beams framing into the joint
56
57
58
First Floor Column
59

Joints of Special Moment Frames
 Summary of requirements (ACI 18.8)
▪ General
▪ Transverse reinforcement
▪ Shear
▪ Development length of bars in tension
60

Joints of Special Moment Frames
 General requirements
▪ Joint forces are calculated using a stress of 1.25fy in the
beam longitudinal reinforcement passing through the
joint
▪ Column dimension parallel to the beam reinforcement
must be greater than or equal to 20 times the diameter
of the largest longitudinal bar in the beam for normal
weight concrete (26 times for lightweight concrete)
61

Joints of Special Moment Frames
 Transverse reinforcement
▪ For members framing into all 4 sides of a joint
▪ Transverse reinforcement may be taken as 50% of that required
for the column
▪ Spacing is permitted to be increased to 6 in.
62
63

Joints of Special Moment Frames
 Transverse reinforcement
▪ For less than full joint confinement
▪ Provide column transverse reinforcement through joint
64
65

Joints of Special Moment Frames
 Shear strength Vn
▪ For joints confined on all four faces……
▪ For joints confined on three faces or on two opposite
faces……
▪ For all other joints……
66
67

Joints of Special Moment Frames
 Shear force
▪ Shear force in joint = column shear force – (sum of the
tensile force in the top beam reinforcement and the
compressive force at the top of the beam on the
opposite face of the column)
▪ Stress in reinforcement = 1.25fy
68
𝑉𝑐𝑜𝑙
+ + 𝑀−
𝑀𝑝𝑟
𝑉𝑒,1 + 𝑉𝑒,2 × 𝑐1 2
𝑝𝑟
=
+
ℓ𝑐
ℓ𝑐
69
70
71

Joints of Special Moment Frames
 Development length of bars in tension
▪ Straight bars
72
73

Special Structural Walls
 Summary of requirements (ACI 18.10)
▪ Reinforcement
▪ Shear strength
▪ Flexure and axial loads
▪ Boundary elements
74

Special Structural Walls
 Reinforcement requirements
▪
▪
▪
▪ Minimum reinforcement per ACI 11.6
▪ Maximum spacing = 18 in.
75

Special Structural Walls
 Reinforcement requirements
▪
▪ Two curtains of reinforcement must be provided
76

Special Structural Walls
 Shear strength
▪
≤ 8𝐴𝑐𝑣 𝑓𝑐′
▪
77

Special Structural Walls
 Flexure and axial loads
▪ Design in accordance with ACI 22.4
78

Special Structural Walls
 Wall segments
79
80

Special Structural Walls
 Boundary elements
▪ Two design approaches
▪ ACI 18.10.6.2 (displacement-based)
▪ ACI 18.10.6.3
81

Special Structural Walls
 ACI 18.10.6.2
▪ Applicable to
▪ Walls or wall piers that are effectively continuous in cross-section
over the entire height
▪ Walls with one critical section for flexure and axial loads
82
83

Special Structural Walls
 ACI 18.10.6.3
▪ Applicable to essentially all walls
84
85

Special Structural Walls
 Boundary elements
▪ Detailing requirements where boundary elements are
required (ACI 18.10.6.4)
86
87
88
89

Special Structural Walls
 Boundary elements
▪ Detailing requirements where boundary elements are
not required (ACI 18.10.6.5)
90
91

Coupling Beams
 ACI 18.10.7
92
93

Coupling Beams
 ℓ𝑛 ℎ ≥ 4
▪ Satisfy requirements of ACI 18.6 for beams of special
moment frames
 ℓ𝑛 ℎ < 2 and 𝑉𝑢 ≥ 2𝜆 𝑓𝑐′ 𝐴𝑐𝑤
▪ Two intersecting groups of diagonally placed bars
symmetrical about the midspan of the coupling beam
▪ 𝑉𝑛 = 2𝐴𝑣𝑑 𝑓𝑦 sin 𝛼 ≤ 10 𝑓𝑐′ 𝐴𝑐𝑤
94
95
96
97

Wall Piers
 Vertical wall segment within a structural wall
 Bounded horizontally by two openings or by an
opening and an edge
 Length to wall thickness ℓ𝑤 /𝑏𝑤 ≤ 6
 Clear height to horizontal length ℎ𝑤 /ℓ𝑤 ≥ 2
98
99

Wall Piers
 ACI 18.10.8
 Must satisfy the special moment frame
requirements for columns
▪ ACI 18.7.4, 18.7.5 and 18.7.6
 Alternatively, where
ℓ𝑤
𝑏𝑤
≥ 2.5
▪ Must satisfy (a) through (f) of ACI 18.10.8.1
100

Structural Diaphragms
 Summary of requirements (ACI 18.12)
▪ Minimum thickness
▪ Reinforcement
▪ Flexural strength
▪ Shear strength
101

Foundations
 Summary of requirements (ACI 18.13)
▪ Footings, foundation mats, and pile caps
▪ Grade beams and slabs-on-ground
▪ Piles, piers, and caissons
102

Foundations
 Footings, foundation mats, and pile caps
103
104

Foundations
 Grade beams
105
106

Foundations
 Grade beams
▪ Grade beams that are part of a mat foundation that
resists flexural stresses from columns that are part of the
SFRS must conform to the provisions of ACI 18.6 for
flexural members of special moment frames
107

Foundations
 Slab-on-ground
▪ For slabs-on-ground that are part of the SFRS (acts as a
diaphragm that holds the structure together at the
ground level and minimizes the effects of out-of-phase
ground motion)
▪ Design and detail per ACI 18.12 for diaphragms
108

Foundations
 Piles, piers, and caissons
109
110

Members not Designated as Part of the SFRS
 Summary of requirements (ACI 18.14)
▪ Members where combined bending moments and shear forces due
to factored gravity loads and design displacements are less than or
equal to the design moment and shear strengths
▪ Members where combined bending moments and shear forces due
to factored gravity loads and design displacements exceed the
design moment and shear strengths, or if induced moments are not
calculated
▪ Slab-column connections of two-way slabs without beams and wall
piers
111

Members not Designated as Part of the SFRS
 Beams
▪ Induced bending moments and shear forces are less than
or equal to the design moment and shear strengths
112
113

Members not Designated as Part of the SFRS
 Beams
▪ Induced bending moments and shear forces exceed the
design moment and shear strengths
▪ Induced bending moments and shear forces are not
calculated
114
115

Members not Designated as Part of the SFRS
 Columns
▪ Induced bending moments and shear forces are less than
or equal to the design moment and shear strengths
116
117

Members not Designated as Part of the SFRS
 Columns
▪ Induced bending moments and shear forces exceed the
design moment and shear strengths
▪ Induced bending moments and shear forces are not
calculated
▪ Detailing requirements are essentially the same as those
for columns in special moment frames
118

Members not Designated as Part of the SFRS
 Two-way slabs without beams
▪ Where Δ𝑥 ℎ𝑠𝑥 ≥ 0.035 − 1 20 𝑣𝑢𝑔 𝜙𝑣𝑐 or
Δ𝑥 ℎ𝑠𝑥 > 0.005
▪ Provide slab shear reinforcement conforming to ACI 8.7.6
(stirrups) or ACI 8.7.7 (headed studs) supplying a nominal shear
strength 𝑣𝑠 ≥ 3.5 𝑓𝑐′
119

Members not Designated as Part of the SFRS
 Wall Piers
▪ Must satisfy the requirements of ACI 18.10.8
120