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aci 2014
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American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 1
WWW.CONCRETE.ORG/ACI318 1
Chapter 10 - Columns
ACI 318-14:Reorganized for Design
WWW.CONCRETE.ORG/ACI318 2
Columns
• Common sub-headings– 10.1 Scope– 10.2 General– 10.3 Design limits– 10.4 Required strength– 10.5 Design strength– 10.6 Reinforcement limits– 10.7 Reinforcement detailing
American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 2
WWW.CONCRETE.ORG/ACI318 3
Scope of columns:
• Nonprestressed concrete• Prestressed concrete• Composite concrete and steel members• Not in this chapter
– Plain concrete columns → Ch. 14
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
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Connections to other members
• Beam-column and slab-column cast-in-place joints → Ch. 15
• Precast → 16.2• Foundations → 16.3
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
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Column dimensions
• Irregular shapes– Treat like circular
• Oversized columns– Min. effective area = ½ total area– Not allowed in special moment
frames• Columns in walls
– 1.5 in. outside ties
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
Effective area ≥ ½ total area
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Column slenderness• Moment
magnification → 6.6.4• 2nd order analysis →
6.7 • Consider multiple
load cases
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
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Design strength
• φPn > Pu, φMn ≥ Mu → 22.4• φVn > Vu → 22.5• φTn > Tu, → Ch. 9 (if necessary)• Reduction factor, φ → 21.2
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
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Reinforcement limits
• Longitudinal– Minimum Ast = 0.01 Ag– Maximum Ast = 0.08 Ag
• Also applies at splice regions
• Transverse– Required where
Vu > 0.5φVc– Av,min= greater of
• 0.75• 50 ⁄
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
Offset bars from column below
Bars in column above
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Minimum longitudinal bars
Rectangular tiesTriangular ties Spirals or circular hoops
GOOD PRACTICE –use 8 bars in circular arrangements
Bars in circular hoops
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
Circular ties
Prohibited – use of interlocking headed
bars as hoop transverse reinforcement *
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Splices
• Permitted types– Lap– Mechanical– Butt-welded– End-bearing
• Splice length → 25.5
Lap spliceMechanical butt - splice
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
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Ties (25.7.2)10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing • Closed loop
• Clear spacing ≥ 4/3 dagg• Spacing ≤ smallest of:
– 16 db of longitudinal bar– 48 db of tie– Smallest member
dimension• Support for
– Corner bars– Alternate long. bar– > 6 in. clear spacing
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Hoops (25.7.4)
• Closed ties or continuous wound ties
• Seismic hooks at ends• Can be made of several elements
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
Single-piece hoop multi-piece hoop
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Lateral support of longitudinal bars
• Ties or hoops– ½ tie spacing above slab– ½ tie spacing below lowest bars in slab,
drop panel, or shear cap– 3 in. below bottom bars in shallowest
beam • Spirals
– Top of slab– Top of spiral varies per member framing
into column → Table 10.7.6.3.2
10.1 Scope10.2 General10.3 Design limits10.4 Required strength10.5 Design strength10.6 Reinforcement limits10.7 Reinforcement detailing
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Chapter 18 – Earthquake resistant structures
• Beams• Columns
• Beams• Columns• Two-way slabs• Precast structural
walls
• Beams• Columns• Beam-column joints• Moment frames
using precast concrete
• Diaphragms• Members not part
of seismic force resisting system
• Structural walls• Foundations
Ordinary Systems (Min. for SDC B)
Intermediate Systems (Min. for SDC C)
Special Systems (SDC D, E, F)
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Ordinary moment frames
• Section 18.3.3• For ℓu ≤ 5c1, design for Vu = lesser of:
– Shear based on Mn at top and bottom– ΩoE substituted for E
c1
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Intermediate moment frames
• Design all columns for Vu = lesser of:– Shear based on Mn at top
and bottom– ΩoE substituted for E
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• Hoops or spirals required• First hoop at so/2 from the
joint face
so
ℓo
ℓo
Hoop placement
Largest of 1/6 clear span, max. cross section dimension, and 18 in.
Smallest of 8 long. db, 24 hoop db, ½ smallest cross section dimension, and 12 in.
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Columns of special moment frames
• Section 18.7• Dimensional limits
– Smallest dimension ≥ 12 in.– Short side/long side ≥ 0.4
• Min. flexural strength– ∑Mnc ≥ (6/5)∑Mnb, otherwise,
non-participating
Beam
Column
Mnb Mnb
Mnc
Mnc
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Longitudinal reinforcement
• Max. Ast = 0.06 Ag
• Tension lap splice only in center ½ of column and enclosed by transverse reinf. per 18.7.5.2 and 18.7.5.3
Lap splice at mid-height region
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Transverse reinforcement• Trans. reinf. over ℓo
– Spirals or hoops– Crosstie ends alternating– Engage corner and
alternate bars– Spacing of laterally
supported bars, xi ≤ 14 in.
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Confinement in special columns with high axial force or high f’c *
ACI 318-14, 18.7.5.2(f): Where Pu> 0.3Agf’c or f’c > 10,000 psi in columns with rectilinear hoops, every longitudinal bar ... around the perimeter … shall have lateral support provided by the corner of a hoop or by a seismic hook, and the maximum value of hx shall not exceed 8 in.
xi
xi
hx is the largest xi
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• First hoop at so/2 from the joint face
so
ℓo
ℓo
Hoop placement
Largest of 1/6 clear span, max. cross section dimension, and 18 in.
Smallest of 6 long. db, 1/4 smallest cross section dimension, , and 6 in. Need not by less than 4 in.
so
s
s ≤ 6 long. db, 6 in.
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Ch. 18 – Area of ties for special columns *
Where:Kf = concrete strength factor (f’c > 10,000 psi)Kn = confinement effectiveness factor
*
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Shear strength
• Calculate Vu using Mpr at each end of column (125% fy)
• Transverse reinforcement over ℓo calculated assuming Vc = 0 when – Seismic shear ≥ ½ Vu and – Pu ≤ Agf’c / 20
Vu
Vu
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Nonparticipating columns (18.14)
• If design strength not exceeded– Max. Ast = 0.06 Ag– Trans. reinf. meets geometry requirements in
18.7.5.2 (special moment frames)– Vu due to Mpr at both ends– Transverse reinf. over ℓo calculated assume Vc = 0
when • Seismic shear ≥ ½ Vu and • Pu ≤ Agf’c/20
– Hoop at so ≤ 6 long. db, 6 in. entire height– Additional requirements if Pu > 0.35 Po
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Nonparticipating columns (18.14)
• If design strength is exceeded, columns must satisfy – 18.7.4 Special moment frame longitudinal
reinforcement – 18.7.5 Special moment frame transverse
reinforcement– 18.7.6 Special moment frame shear strength
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