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

WWW.CONCRETE.ORG/ACI318 4

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 3

WWW.CONCRETE.ORG/ACI318 5

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

WWW.CONCRETE.ORG/ACI318 6

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 4

WWW.CONCRETE.ORG/ACI318 7

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

WWW.CONCRETE.ORG/ACI318 8

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 5

WWW.CONCRETE.ORG/ACI318 9

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 *

WWW.CONCRETE.ORG/ACI318 10

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 6

WWW.CONCRETE.ORG/ACI318 11

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

WWW.CONCRETE.ORG/ACI318 12

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 7

WWW.CONCRETE.ORG/ACI318 13

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

WWW.CONCRETE.ORG/ACI318 14

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)

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 8

WWW.CONCRETE.ORG/ACI318 15

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

WWW.CONCRETE.ORG/ACI318 16

Intermediate moment frames

• Design all columns for Vu = lesser of:– Shear based on Mn at top

and bottom– ΩoE substituted for E

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 9

WWW.CONCRETE.ORG/ACI318 17

• 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.

WWW.CONCRETE.ORG/ACI318 18

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 10

WWW.CONCRETE.ORG/ACI318 19

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

WWW.CONCRETE.ORG/ACI318 20

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.

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 11

WWW.CONCRETE.ORG/ACI318 21

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

WWW.CONCRETE.ORG/ACI318 22

• 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.

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 12

WWW.CONCRETE.ORG/ACI318 23

Ch. 18 – Area of ties for special columns *

Where:Kf = concrete strength factor (f’c > 10,000 psi)Kn = confinement effectiveness factor

*

WWW.CONCRETE.ORG/ACI318 24

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

American Concrete Institute © 2015. All rights reserved. No part of this publication may be reproduced, copied, distributed, or transmitted in any form. 13

WWW.CONCRETE.ORG/ACI318 25

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

WWW.CONCRETE.ORG/ACI318 26

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