ASCE NO – ASCE NO - ABSTRACTasceneworleans.org/wp-content/uploads/2019/11/ACI318-19... · 2019....

ABSTRACT:

This presentation is a chapter by chapter review of ACI 318-19 “Building Code Requirements for Structural Concrete”, released in August 2019 to replace ACI 318-14. Highlighted are the code provisions which the author of this presentation has used most often while engaged in the design of industrial, marine, and commercial reinforced concrete structures. Figures and short example problems illustrating use of the provisions are included. The emphasis is on non-prestressed, non-seismic structures designed by traditional methods.

2

6

CHAPTER 1 – GENERAL

1.1- SCOPE OF

ACI 318

1.3.1 The purpose of this Code is to provide for public health and safety by establishing minimum requirements for strength, stability, durability, and integrity of concrete structures.

7

8

CHAPTER 2 - NOTATION AND TERMINOLOGY

2.2 – NOTATION

a = depth of equivalent rectangular stress block, inchesb = width of compression face of member, inchesc = distance from extreme compression fiber to neutral axis, inchesd = distance from extreme compression fiber to centroid of longitudinal tension reinforcement, inchesh = overall thickness, height, or depth of member, inchesl = span length of beam or one-way slab; clear projection of cantilever, inches.

9

2.3-

TERMINOLOGY

• base of structure – level at which horizontal earthquake ground motions are assumed to be imparted to a building. This level does not necessarily coincide with the ground level.

• Design story drift ratio – relative difference of design displacement between the top and bottom of a story, divided by the story height.

• Load, service – all loads, static or transitory, imposed on a structure or element thereof, during the operation of a facility, without load factors

10

2.3-

TERMINOLOGY

(CONT’D)

• spiral reinforcement –continuously wound reinforcement in the form of a cylindrical helix.

• steel element, brittle – element with a tensile test elongation of less than 14 percent, or reduction in area of less than 30 percent at failure.

11

13

CHAPTER 3 - REFERENCED

STANDARDS

3.2-REFERENCED

STANDARDS 3.2.3 ASCE/SEI 7-16

14

3.2-

REFERENCED

STANDARDS

3.2.4 ASTM A615 and ASTM A706

3.2.5 AWS D1.4

16

17

CHAPTER 4 – STRUCTURAL

SYSTEM REQUIREMENTS

4.4.6-SEISMIC

FORCE-RESISTING

SYSTEM

4.4.6.1 Every structure shall be assigned to a Seismic Design Category in accordance with the general building code.

18

4.4.6-SEISMIC

FORCE-RESISTING

SYSTEM (CONT’D)

4.4.6.2 Structural systems designated as part of the seismic-force-resisting system shall be restricted to those systems designated by the general building code…

19

4.4.6-SEISMIC

FORCE-RESISTING

SYSTEM (CONT’D)

4.4.6.3 Structural systems

assigned to Seismic Design

Category A shall satisfy the

applicable requirements of

this Code. …not required to

be designed in accordance

with Chapter 18.

20

4.4.6-SEISMIC

FORCE-RESISTING

SYSTEM

4.4.6.4 Structural systems

assigned to Seismic Design

Category B, C, D, E, or F shall

satisfy the requirements of

Chapter 18 in addition…

21

22

CHAPTER 5 – LOADS

5.3 – LOAD FACTORS

AND COMBINATIONS

1.4D

1.2D + 1.6L

1.2D +1.0W +1.0L

1.2D + 1.0E +1.0L

0.9D +1.0W

0.9D +1.0E

23

5.3 – LOAD FACTORS

AND COMBINATIONS 5.3.5 If W is “service-level”

use 1.6W in place of 1.0W

24

26

CHAPTER 6 – STRUCTURAL

ANALYSIS

6.2.5. - SLENDERNESS

EFFECTS

6.2.5.1 Slenderness effects

permitted to be neglected

for:

a) Columns not braced

against sidesway if kl/r LE

22

b) Columns braced against

sidesway if kl/r LE 34 +

12(M1/M2) and LE 40

For sway frames, obtain k

from nomograph

27

6.2.5. SLENDERNESS

EFFECTS (CONT’D)

6.2.5.2 r = sqrt( Ig / Ag ) or

0.3 times depth of

rectangular column or 0.25

times the diameter of

circular column

28

6.2.5. SLENDERNESS

EFFECTS (CONT’D)

6.2.5.3 Second order

moments must not exceed

1.4 ( First order moments )

29

6.3.2-T BEAM

GEOMETRY

6.3.2.1 Effective flange

widths nonprestressed

beams:

T beam: Web width plus

each side: minimum

( 8 times slab thickness,

one half clear distance to

adjacent web, one eighth

clear span of beam )

32

6.3.2 T BEAM

GEOMETRY

(CONT’D)

L beam: Web width

plus: minimum( 6 times

slab thickness, one half

clear distance to

adjacent web, one

twelfth clear span of

beam )

33

6.4 – ARRANGEMENT

OF LIVE LOAD

6.4.2 For one-way slabs

and beams:

a) Maximum positive

moment near midspan :

L on alternate spans

b) Maximum negative

moment at support: L

on adjacent spans

35

6.4 – ARRANGEMENT

OF LIVE LOAD

(CONT’D)

6.4.3 For two-way slab

systems.

Moments at least the

values resulting from L

on all panels.

36

6.4 – ARRANGEMENT

OF LIVE LOAD

6.4.3.3 Generally also

check 0.75L

checkerboard for

positive moments,

0.75L adjacent panels

only for negative

moments

37

6.5 – SIMPLIFIED METHOD

OF ANALYSIS FOR

NONPRESTRESSED

CONTINUOUS BEAMS AND

ONE-WAY SLABS

6.5.1 Restrictions on

use: Prismatic

members, uniform

loads, unfactored live

load LE 3 times

unfactored dead load,

at least two spans,

longer of two adjacent

spans not more than 1.2

times shorter span

39


OF ANALYSIS FOR

NONPRESTRESSED


ONE-WAY SLABS (CONT’D)

6.5.2 Design factored moments:

Coefficients* factored uniform

load *clear span squared

• Positive end span moment

with discontinuous end

integral with support : 1/14

• Positive end span moment

with discontinuous end

unrestrained: 1/11

• Positive interior span

moments: 1/16

40


OF ANALYSIS FOR

NONPRESTRESSED



• Negative moment

interior face of exterior

column: 1/16

• Negative moment

exterior face of first

interior support: 1/9 for

2 spans, 1/10 more than

2 spans

• Negative moment face

of other supports: 1/11

41


OF ANALYSIS FOR

NONPRESTRESSED



6.5.3 Moment

redistribution not

allowed for values from

simplified analysis

42


OF ANALYSIS FOR

NONPRESTRESSED


ONE-WAY SLABS

6.5.4 Gravity load

design shears: simple

span values except 15%

higher at exterior face

of first interior support

43

6.6.3 - SECTION

PROPERTIES

A = Gross A

Columns : I = 0.7 * Gross I

Beams: I = 0.35 * Gross I , or 0.7

* Gross I of web for T beams

45

6.6.3 - SECTION

PROPERTIES (CONT’D)

6.6.3.1.2 For factored lateral load

analysis, permitted to use I = 0.5 *

Gross I for all members

46

6.6.4 – SLENDERNESS

EFFECTS, MOMENT

MAGNIFICATION

METHOD

6.6.4.4.1 Stability index Q for a

building story equals: (total

factored vertical load * first order

story drift due to factored story

shear) / (factored story shear *

centerline story height)

47

6.6.4 - SLENDERNESS

EFFECTS, MOMENT

MAGNIFICATION

METHOD

6.6.4.4.2 The critical buckling

load of a member, Euler value :

(9.86 * effective(EI)) / (kL *kL)

48

6.6.4 - SLENDERNESS

EFFECTS, MOMENT

MAGNIFICATION

METHOD

6.6.4.4.4 For lateral load analysis

with no sustained lateral loads:

Effective (EI) = 0.4 Gross EI

(E, ksi from 19.2.2:

57 *sqrt (compressive strength

of concrete, psi)

49

6.6.4.6 – MOMENT

MAGNIFICATION

METHOD: SWAY

FRAMES

6.6.4.6.1 Column end moment =

end moment due to gravity loads

plus moment magnifier times

moment due to lateral loads

51

6.6.4.6 - MOMENT

MAGNIFICATION

METHOD: SWAY

FRAMES (CONT’D)

6.6.4.6.2 Moment magnifier =

1 / (1-Q) GE 1.0

OR:

Moment magnifier = 1 / (1 –

(Sum of all story column vertical

loads / 0.75 * sum of all story

column critical buckling loads)

52

54

CHAPTER 7 – ONE – WAY SLABS

7.2.2 –

MATERIALS

Design properties for

concrete: Chapter 19

Design properties for steel reinforcement: Chapter 20

55

7.3 – DESIGN

LIMITS

7.3.1 Minimum

thickness of solid

nonprestressed one-

way slabs, 60ksi yield

steel reinforcing,

(unless deflections

calculated to be

acceptable)

56

7.3 – DESIGN

LIMITS (CONT’D)

Simply supported: h, inches

GE span,inches /20 span =

centerline or clear???

One end continuous: h GE

span/24

Both ends continuous: h GE

span/28

Cantilever: h GE span/10

57

7.3 – DESIGN

LIMITS (CONT’D)

7.3.3 Reinforcement

strain limit in

nonprestressed slabs:

Must be tension-

controlled, ie tension

strain in extreme

tension steel at failure

must exceed the

tension yield strain plus

0.003.

58

7.3 – DESIGN

LIMITS (CONT’D)

(Note: 22.2.2.1

Maximum strain at the

extreme concrete

compression fiber shall

be assumed equal to

0.003. ie “Failure” in

reinforced concrete is

still considered to be

the moment the first

point reaches a

compression strain of

0.003)

59

7.3 – DESIGN

LIMITS (CONT’D)

(Note: 20.2.2.2: Modulus of

elasticity for nonprestressed bars

and wires shall be permitted to

be taken as 29,000,000psi)

(Note: 22.2.1.2: Strain in

concrete and nonprestressed

reinforcement shall be assumed

proportional to the distance from

the neutral axis.)

(Note: 22.2.2.2: Tensile strength

of concrete shall be neglected in

flexural and axial strength

calculations,)

60

7.3 – DESIGN

LIMITS (CONT’D)

(Note: 21.2.2.1: For deformed

reinforcement the yield strain shall

be the yield stress divided by the

modulus of elasticity. For a yield

strength of 60ksi, it shall be

permitted to take the yield strain as

0.002.)

61

7.3. DESIGN

LIMITS (CONT’D)

7.3.4 Stress limits in prestressed

slabs

Prestressed slabs shall be

classified as Class U, T, or C in

accordance with 24.5.2

Stresses in prestressed slabs

immediately after transfer and at

service loads shall not exceed the

permissible stresses in 24.5.3 and

24.5.4.

63

7.4. REQUIRED

STRENGTH

7.4.2 Factored moment

For slabs built integrally with

supports, face of support

moment can be used as the

design maximum.

7.4.3 Factored shear

For nonprestressed slabs built

integrally with supports,

generally can use the shear at “d”

from support face as the design

maximum.

64

7.5. DESIGN

STRENGTH

Strength reduction factors: 21.2

Nominal moment capacity: 22.3

Nominal shear capacity: 22.5

T beam effective flange designed

as a cantilever

65

7.6

REINFORCEMENT

LIMITS

Tension steel reinforcement area per unit width GE 0.0018h

7.6.3 Minimum shear

reinforcement: Required for slabs

when design shear exceeds

concrete shear capacity

7.6.3.3 If shear reinforcement is

required, minimum values of

9.6.3.4 apply.

67

7.6

REINFORCEMENT

LIMITS (CONT’D)

7.6.4 Minimum shrinkage and

temperature reinforcement: 24.4

(Note: 24.4: Minimum ratio of

deformed shrinkage and

temperature reinforcement area to

gross concrete area is 0.0018.

Maximum spacing 5h or 18inches)

(Note: Placement of minimum

shrinkage and temperature

reinforcement all on the “tension”

side is not required.)

68

7.7.

REINFORCEMENT

DETAILING

Cover: 20.5.1

Development lengths: 25.4

Splices: 25.5

Bundled bars: 25.6

Minimum spacing: 25.2

Maximum spacing

nonprestressed and Class C

prestressed slabs, bonded

reinforcement closest to the

tension face: 24.3

69

7.7

REINFORCEMENT

DETALING

(CONT’D)

Nonprestressed and Class T and C

prestressed slabs with unbonded

tendons, maximum spacing of

deformed longitudinal

reinforcement the lesser of 3h and

18 in.

70

7.7. –

REINFORCEMENT

DETAILING (CONT’D)

7.7.3.1 Calculated tensile or compressive force in reinforcement at each section of the slab shall be developed on each side of that section.

71

7.7

REINFORCEMENT

DETAILING

(CONT’D)

7.7.3.2 Critical locations for development of reinforcement are points of maximum stress and points along the span where bent or terminated tension reinforcement is no longer required to resist flexure

7.7.3.3 Generally must extend

reinforcement “d” or 12 bar

diameters beyond where

needed.

72

7.7

REINFORCEMENT

DETAILING

(CONT’D)

7.7.3.5 Flexural tension reinforcement

shall not be terminated in a tension

zone unless….a) Factored shear ≤ 2/3

shear strength.

7.7.3.8 At least one third of required

maximum positive moment

reinforcement must extend into

“simple” supports. For “other”

supports, one fourth required to extend

6 inches into support. At least one third

of the required negative moment

reinforcement at a support must extend

beyond the point of inflection the

greatest of “d”, 12 bar diameters, or the

clear span/16.73

7.7 -

REINFORCEMENT

DETAILING

(CONT’D)

7.7.7 Structural integrity

reinforcement in cast-in-place

one-way slabs

Minimum ¼ of maximum positive

moment reinforcement shall be

continuous; at non-continuous

supports shall develop the yield

stress at the face of the support.

74

75

Figure - Simple span one-way

slab check

78

CHAPTER 8 – TWO – WAY SLABS

8.1- SCOPE

Scope: a) Solid slabs d) Two-way

joist systems in accordance with

8.8.

79

8.2 - GENERAL

8.2.1 …permitted to be designed

by any procedure satisfying

equilibrium and geometric

compatibility…The direct design

method or the equivalent frame

method is permitted.

Commentary: The direct design

method and the equivalent

frame method are limited in

application to orthogonal frames

subject to gravity loads only.

80

8.2 GENERAL

(CONT’D)

Note: ACI 318-14 Sections 8.10

Direct Design Method and 8.11

Equivalent frame method were

discontinued in ACI 318-19.

8.2.4 A “drop panel” projects

below the slab at least one-

fourth of the adjacent slab

thickness and extends in each

direction from the centerline

of support a distance not less

than one sixth the centerline

span length in that direction.

81

8.3 – DESIGN

LIMITS

8.3.1 Minimum slab thickness

8.3.1.1 Nonprestressed slabs

without interior beams on all

sides, deflections not

calculated and shown

adequate: Without drop

panels – 5 inch minimum

thickness; with drop panels –

4 inch minimum thickness;

and satisfy Table 8.3.1.1.

82

8.3 – DESIGN

LIMITS (CONT’D)

Table 8.3.1.1 for 60 ksi yield

reinforcing, no drop panels,

with edge beams minimum h:

Exterior panels: Long direction

clear span/33

Interior panels: Long direction

clear span/33

83

8.3 – DESIGN

LIMITS (CONT’D)

8.3.3 Reinforcement strain limit

in nonprestressed slabs: Must

be tension-controlled


slabs: Design as Class U with

maximum tensile stress 6

times the sqrt (compressive

strength of concrete)

84

8.4 – REQUIRED

STRENGTH

8.4.1 General

8.4.1.5 A column strip is a design

strip with a width on each

side of the column centerline

equal to the lesser of

0.25(centerline span in

direction being designed) and

0.25(perpendicular span). A

column strip shall include

beams within the strip, if

present.

85

8.4 – REQUIRED

STRENGTH

(CONT’D)

8.4.1.6 A middle strip is a design

strip bounded by two column

strips.

8.4.1.8 For monolithic or fully

composite construction

supporting two-way slabs, a

beam includes that portion of

slab, on each side of the

beam extending a distance

equal to the projection of the

beam above or below the

slab, whichever is greater, but

LE four times the slab

thickness. 86

8.4.2 – FACTORED

MOMENT

8.4.2.1 For slabs built integrally

with supports, maximum

design moments can be taken

as face of support values.

8.4.2.2 Factored slab moment

resisted by column (interior

column with no beams or

capital considered here)

88

8.4.2 – FACTORED

MOMENT

(CONT’D)

8.4.2.2.2 A fraction (0 to 1.0)of the

moment transferred from slab to

column is considered transferred

by flexure (the remainder by

nonsymmetric punching shear

described in 8.4.4.2). The

fraction assumed transferred by

flexure is: 1 / ( 1 +

0.667(sqrt((column dimension in

direction being analyzed + slab

“d” value) / (column dimension

in perpendicular direction + slab

“d” value)

89

8.4.2 – FACTORED

MOMENT

(CONT’D)

8.4.2.2.3 The effective slab width

for resisting this flexure

component is the column

width + 1.5 slab “h” each side

of column

90

8.4.3 – FACTORED

ONE WAY SHEAR

8.4.3 Factored one-way shear –

Generally can use value at “d”

from face of support as the

design value

8.4.4 Factored two-way shear

92

8.4.4.1 – CRITICAL

SECTION

8.4.4.1.1 Slabs shall be evaluated

for two-way shear in the vicinity

of columns, concentrated loads,

and reaction areas at critical

sections in accordance with

22.6.4.

8.4.4.1.2 Slabs reinforced with

stirrups or headed shear stud

reinforcement shall be

evaluated for two-way shear at

critical sections in accordance

with 22.6.4.2.

93


SECTION (CONT’D)

8.4.4.2 Factored two-way shear

stress due to shear and factored

slab moment resisted by the

column

8.4.4.2.3 The factored shear stress

resulting from the eccentric

shear portion of the moment

transfer from slab to column

shall be assumed to vary linearly

about the centroid of the critical

section.

(Commentary gives help with

critical section geometric

property J )94


SECTION (CONT’D)

(Note: 22.6.4.1: For two-way

shear, critical sections shall be

located so that the perimeter

is a minimum but need not be

closer than 0.5d to the

column edge)

95

8.5 – DESIGN

STRENGTH

8.5.1 General

8.5.1.1 For each applicable

factored load combination,

ensure that nominal

capacities multiplied by

capacity reduction factors

exceed the corresponding

effects of the factored loads.

a) Moment at all sections along

the span in each direction

b) Moment in the slab at the

column connection

97

8.5 – DESIGN

STRENGTH

(CONT’D)

c) Shear at all sections along the

span in each direction for

one-way shear

d) Punching shear stress,

including moment transfer

from eccentric shear, at

columns

98

8.5 – DESIGN

STRENGTH

(CONT’D)

8.5.1.2 Capacity reduction factors

from 21.2

8.5.2 Moment

8.5.2.1 Nominal moment

capacity from 22.3

8.5.3 Shear

8.5.3.1.1 For one-way shear 22.5

8.5.3.1.2 For two-way shear 22.6

8.6 – Reinforcement limits :

Minimum flexural reinforcement

near tension face .0018h per unit

width.

99

8.7 –

REINFORCEMENT

DETAILING

8.7.1 General –Cover 20.5.1;

Development length 25.4;

Splice lengths 25.5

8.7.2 Flexural reinforcement

spacing: minimum spacing

25.2, maximum spacing the

lesser of 2h and 18 inches at

critical sections and the lesser

of 3h and 18 inches at other

sections.

8.7.3 Corner restraint in slabs

100

8.7 –

REINFORCEMENT

DETAILING

(CONT’D)

8.7.3.1.2 Reinforcement shall be

provided for a distance in

each direction from the

corner equal to one-fifth the

longer span.

8.7.4 Flexural reinforcement in

nonprestressed slabs

8.7.4.1 Termination of

reinforcement

101

8.7 –

REINFORCEMENT

DETAILING

(CONT’D)

8.7.3.1.2 Reinforcement shall be

provided for a distance in

each direction from the

corner equal to one-fifth the

longer span.


nonprestressed slabs

8.7.4.1 Termination of

reinforcement

102

8.7 –

REINFORCEMENT

DETAILING

(CONT’D)

8.7.4.1.1 For slab supported on

spandrel beam, column, or

wall, reinforcement

perpendicular to

discontinuous edge: Positive

moment reinforcement shall

extend to the edge of slab and

have embedment, straight or

hooked, at least 6 inches.

Negative moment


developed at the face of

support.

103

8.7 –

REINFORCEMENT

DETAILING

(CONT’D)

Figure 8.7.4.1.3 – Minimum

extensions for deformed

reinforcement in two-way

slabs without beams.

Example, without drop panels,

column strip top steel: At

least 50% of required steel at

exterior supports must extend

at least 0.3 of the clear span

beyond the face of support.

104

8.7 –

REINFORCEMENT

DETAILING

(CONT’D)


prestressed slabs

8.7.6 Shear reinforcement –

stirrups

Stirrups permitted as shear

reinforcement; anchorage and

geometry to satisfy 25.7.1;

maximum spacing d/2 in

analyzed span direction, 2d in

perpendicular direction

8.7.7 Shear reinforcement –headed stud

107

8.8 –

NONPRESTRESSED

TWO-WAY JOIST

SYSTEMS

8.8.1 General

Top slab designed to span in two

directions; rib width at least 4

inches all locations; rib depth

not greater than 3.5 times

minimum rib width; clear

spacing between ribs shall not

exceed 30 inches; can

increase section 22.5 shear

strength by 10%; at least one

bottom bar developed at face

of support.

110

111

CHAPTER 9 - BEAMS

9.0 - BEAMS

From Chapter 2: “beam” = member

subjected primarily to flexure

and shear, with or without axial

force or torsion; beams in a

moment frame that forms part

of the lateral-force-resisting

system are predominantly

horizontal members; a girder is a

beam.

112

9.1 - SCOPE

9.1 - Scope: nonprestressed,

prestressed, one-way joists

9.8, deep beams 9.9

9.2 – General

9.2.1 Materials:

Concrete design properties

Chapter 19; steel

reinforcement design

properties Chapter 20;

embedments 20.6

113

9.2 GENERAL

(CONT’D)

9.2.1 Materials:

Concrete design properties

Chapter 19; steel

reinforcement design

properties Chapter 20;

embedments 20.6

9.2.2 Connection to other members:Cast-in-place beam to column and slab to column joints: Chapter 15

114

9.2 - GENERAL

(CONT’D)

Precast concrete construction

force transfer: 16.2

9.2.3 Stability: Spacing of lateral

bracing shall not exceed 50

times the least width of the

compression flange or face.

9.2.3.2 In prestressed beams,

buckling of thin webs and

flanges shall be considered….

115

9.2 - GENERAL

(CONT’D)

9.2.4 T-beam construction

9.2.4.1 In T-beam construction,

flange and web concrete shall

be place monolithically or

made composite in

accordance with 16.4.

9.2.4.2 Effective flange width

shall be in accordance with

6.3.2.

116

9.2- GENERAL

(CONT’D)

9.2.4.3 For T-beam flanges where

the primary flexural slab

reinforcement is parallel to

the longitudinal axis of the

beam, reinforcement in the

flange perpendicular to the

longitudinal axis of the beam

shall be in accordance with

7.5.2.3.

117

9.2 GENERAL

(CONT’D)

9.2.4.4 For torsional design

according to 22.7, the

overhanging flange width

used to calculate section

properties shall satisfy: Not

greater than beam projection

above or below slab, not

greater than 4 times slab

thickness, flanges to be

neglected if they cause

section properties to

decrease.

118

9.3 – DESIGN

LIMITS

9.3.1 Minimum beam depth

9.3.1.1 For nonprestressed

beams not supporting or

attached to partitions or

other construction likely to be

damaged by large deflections,

overall beam depth h shall

satisfy the limits in Table

9.3.3.1, unless the calculated

deflection limits of 9.3.2 are

satisfied.120

9.3 – DESIGN

LIMITS (CONT’D)

Table 9.3.1.1 – Minimum depth of

nonprestressed beams ( for normal

weight concrete and 60ksi yield steel

reinforcement)

Simply supported: L/16

One end continuous: L/18.5

Both ends continuous: L/21

Cantilever: L/8

( L = span = centerline or clear?)

9.3.2 Calculated deflection limits 24.2

121

9.3 – DESIGN

LIMITS (CONT’D)

9.3.3 Reinforcement strain limit

in nonprestressed beams

9.3.3.1 Nonprestressed beams

with factored axial

compression stress less than

0.1 of the compressive

strength shall be tension

controlled in accordance with

Table 21.2.2.

(Note: Previous permission to

have extreme tension strain of

0.004 with a capacity

reduction factor reduced from

0.9 has not been retained.)123

9.3 – DESIGN

LIMITS (CONT’D)


beams

9.3.4.1 Prestressed beams shall

be classified as Class U, T, or C

in accordance with 24.5.2.

9.3.4.2 Stresses in prestressed

beams immediately after

transfer and at service loads

shall not exceed permissible

stresses in 24.5.3 and 24.5.4.

124

9.4 –REQUIRED

STRENGTH

9.4 – Required strength: Load

combinations from Chapter 5;

required strength from

Chapter 6; reactions induced

by prestressing in accordance

with 5.3.11.

9.4.2 Factored moment: For

beams built integrally with

supports, moments at faces of

supports can be used as

design values.

125

9.4 –REQUIRED

STRENGTH

(CONT’D)

9.4.3 Factored shear: Generally can use shear at “d” from support face as maximum design value.

9.4.4 Factored torsion

126

9.5 –DESIGN

STRENGTH

9.5.4.1 When the torsion due to

factored loads is less than the

“Threshold torsion” given in

22.7 multiplied by the

capacity reduction factor

(0.75), it is permitted to

neglect torsional effects;

minimum reinforcement

requirements of 9.6.4 and

detailing requirements of

9.7.5 and 9.7.6.3 need not be

satisfied.

9.5.4.2 Nominal torsion capacity:

22.7

127

9.5 – DESIGN

STRENGTH

(CONT’D)

9.5.4.3 Longitudinal and

transverse reinforcement

required for torsion shall be

added to that required for

shear, moment, and axial

force.

128

9.6 –

REINFORCEMENT

LIMITS

9.6.1 Minimum flexural

reinforcement in

nonprestressed beams

9.6.1.1 A minimum area of

flexural reinforcement shall

be provided at every section

where tension reinforcement

is required by analysis.

129

9.6 –

REINFORCEMENT

LIMITS (CONT’D)

9.6.1.2 The minimum area of

tension side reinforcement

shall be the larger of

a) 3sqrt(concrete compressive

strength)(beam web

width)(beam “d”) / yield

stress of reinforcing steel

b) 200 (beam web width) (beam

“d”) / yield stress of

reinforcing steel

(Transition point is concrete

compression strength of

4444psi)

130

9.6 –

REINFORCEMENT

LIMITS (CONT’D)

9.6.2 Minimum flexural

reinforcement in prestressed

beams

9.6.2.1 For beams with bonded

prestressed reinforcement,

the areas of nonprestressed

and prestressed tension

reinforcement must be

adequate to develop a

factored moment at least 1.2

times the beam cracking

moment.

131

9.6.3 – MINIMUM SHEAR

REINFORCEMENT

9.6.3.1 For nonprestressed

beams, a minimum area of

shear reinforcement must

generally be provided

wherever the factored beam

shear exceeds

0.75sqrt(concrete

compressive strength)(width

of beam web)(“d”)

132

9.6.3 – MINIMUM SHEAR

REINFORCEMENT

Exceptions: Beam “h” LE 10

inches; T-beam “h” LE 24

inches and LE the greater of

2.5 times flange thickness or

0.5 times beam web width;

one-way joist systems defined

in 9.8

Note: No exception for footings

and pilecaps.

133

9.6.3 – MINIMUM

SHEAR

REINFORCEMENT

9.6.3.2 For prestressed beams

the threshold factored shear

is 0.5( 0.75)(Nominal shear

capacity of prestressed

concrete)

9.6.3.4 Minimum area of shear

reinforcement where torsion

can be neglected,

nonprestressed:

0.75sqrt(concrete compressive

strength)(beam web

width)(stirrup spacing)/steel

yield stress

But use a concrete compressive

strength at least 4444psi.134

9.6.4 – MINIMUM

TORSIONAL

REINFORCEMENT

9.6.4.1 A minimum area of

torsional reinforcement shall

be provided in all regions

where the torsion due to

factored loads exceeds 0.75

times the threshold torsion

from 22.7.

9.6.4.2 If torsional reinforcement is required, the minimum stirrup areas are similar to those for shear alone, however, only exterior legs of the stirrups are counted.

135

9.6.4 – MINIMUM

TORSIONAL

REINFORCEMENT

9.6.4.3 If torsional reinforcement is

required, there is a minimum

area of longitudinal

reinforcement required:

5 sqrt(concrete compressive

strength)(Concrete area of

torsion beam)/yield stress

reinforcement

- (required area of transverse

torsion reinforcement per unit

length of beam)(perimeter of

outer torsion stirrups) , where

the required area of torsion

reinforcement per unit length

need not be taken as less than

25(beam web width)/steel

yield stress 136

9.7 –

REINFORCEMENT

DETAILING

9.7.1 General: Concrete cover

20.5.1; Development lengths

25.4; Splices 25.5; bundled

bars 25.6

9.7.2 Reinforcement spacing:

Minimum spacing 25.2

137

9.7 –DETAILING

(CONT’D)

9.7.1 General: Concrete cover

20.5.1; Development lengths

25.4; Splices 25.5; bundled

bars 25.6


Minimum spacing 25.2

9.7.2.3 For nonprestressed and

Class C prestressed beams with

“h” greater than 36 inches,

longitudinal skin reinforcement

shall be uniformly distributed

on both sides of the beam for a

distance 0.5h from the tension

face, minimum spacing

according to 24.3.2138

9.7.3 –FLEXURAL

REINFORCEMENT IN

NONPRESTRESSED

BEAMS

9.7.3.1 Calculated tensile or

compressive force in

reinforcement at each section

of the beam shall be

developed on each side of

that section.

9.7.3.2 Critical locations for

development of

reinforcement are points of

maximum stress and points

along the span where bent or

terminated tension

reinforcement is no longer

required to resist flexure.

140

9.7.3 –FLEXURAL

REINFORCEMENT IN

NONPRESTRESSED

BEAMS

9.7.3.3 Reinforcement shall

extend beyond the point at

which it is no longer required

to resist flexure for a

distance equal to the greater

of “d” and 12 bar diameters,

except at supports of simply-

supported spans and at free

ends of cantilevers.

141

9.7.3 –FLEXURAL

REINFORCEMENT IN

NONPRESTRESSED

BEAMS

9.7.3.4 Continuing flexural

tension reinforcement shall

extend at least its

development length beyond

the point where bent or

terminated tension

reinforcement is no longer

required to resist flexure.

142

9.7.3 –FLEXURAL

REINFORCEMENT IN

NONPRESTRESSED

BEAMS (CONT’D)

9.7.3.5 Flexural tension

reinforcement shall not be

terminated in a tension zone

unless (a), (b), or (c) is

satisfied:

(a) Shear due to factored loads LE

0.667(0.75)(Nominal shear

capacity) at the cutoff point

(b) (c)

143

9.7.3.8 –

TERMINATION OF

REINFORCEMENT

9.7.3.8.1 At simple supports, at

least one-third of the


reinforcement shall extend

along the beam bottom into

the support at least 6 inches,

except for precast beams

where such reinforcement

shall extend at least to the

center of the bearing length.

145

9.7.3.8 –

TERMINATION OF

REINFORCEMENT

(CONT’D)

9.7.3.8.2 At other supports, at least one-fourth of the maximum positive moment reinforcement shall extend along the beam bottom into the support at least 6 inches and if the beam is part of the primary later-load-resisting system, shall be anchored to develop the steel yield stress in tension at the face of the support.

146

9.7.3.8 –TERMINATION

OF REINFORCEMENT

(CONT’D)

9.7.3.8.3 At simple supports and

points of inflection, the bar

diameter of positive moment

tension reinforcement shall

be limited such that the

development length of the

bar satisfies (a) or (b), unless

reinforcement terminates

beyond the support

centerline with a standard

hook or equivalent:

147


OF REINFORCEMENT

(CONT’D)

(a) Bar development length LE 1.3( Nominal moment capacity/ Shear due to factored loads) +la , if end of reinforcement is confined by a compressive reaction, or(b) Bar development length LE ( Nominal moment capacity / Shear due to factored loads) + la, if not.La is the embedment length beyond the center of support or point of inflection, limited to the greater of “d” and 12 bar diameters

148


OF REINFORCEMENT

(CONT’D)

9.7.3.8.4 At least one-third of the

negative moment

reinforcement at a support

shall have an embedment

length beyond the point of

inflection at least the greatest

of “d”, 12 bar diameters, or

the clear span/16.

149

9.7.4 –FLEXURAL

REINFORCEMENT IN

PRESTRESSED

BEAMS

9.7.4.3.1 Post-tensioned

anchorage zones shall be

designed and detailed in


9.7.4.3.2 Post-tensioning

anchorages and couplers shall

be designed and detailed in


151

9.7.5 – LONGITUDINAL

TORSIONAL

REINFORCEMENT

9.7.5.1 If torsional reinforcement is

required, longitudinal torsional


distributed around the

perimeter of closed stirrups that

satisfy 25.7.1.6 or hoops with a

spacing not greater than 12

inches. The longitudinal

reinforcement shall be inside

the stirrup or hoop, and at least

one longitudinal bar or tendon

shall be placed in each corner.

152

9.7.5 – LONGITUDINAL

TORSIONAL

REINFORCEMENT

(CONT’D)

9.7.5.2 Longitudinal torsional

reinforcement shall have a

diameter at least 0.042 times the

transverse reinforcement spacing,

but not less than 3/8 inch.

9.7.5.3 Longitudinal torsion

reinforcement shall extend for a

distance of at least (torsion beam

width + “d”) beyond the point

required by analysis.

9.7.5.4 Longitudinal torsional

reinforcement shall be developed

at the face of the support at both

ends of the beam.

153

9.7.6 –

TRANSVERSE

REINFORCEMENT

9.7.6.1 General: Details in


9.7.6.2 Shear

9.7.6.2.1 If required, shear


provided using stirrups,

hoops, or longitudinal bent

bars.

154

9.7.6 –

TRANSVERSE

REINFORCEMENT

Table 9.7.6.2.2 – Revised from

ACI 318-14 to include “Across

width” limits

For locations along beam where

required nominal shear

capacity of shear

reinforcement LE

4sqrt(concrete compressive

strength)(beam web

width)(“d”)

155

9.7.6 – TRANSVERSE

REINFORCEMENT

(CONT’D)

Leg spacing “s” LE 24 inches

along length or across width

and:

Nonprestressed: Along length s

LE 0.5d; across width s LE d

Prestressed: Along length s LE

.75h; across width s LE 1.5h

156


REINFORCEMENT

(CONT’D)

For locations along beam where

required nominal shear

capacity of shear reinforcement

GT 4sqrt(concrete compressive

strength)(beam web

width)(“d”) :

Leg spacing “s” LE 12inches along

length or across width and:

Nonprestressed: Along length s

LE 0.25d; across width s LE

0.5d

Prestressed: Along length s LE

.375h; across width s LE 0.75h

157

9.7.6.3 – TORSION

9.7.6.3.1 If required, transverse


be closed stirrups satisfying

25.7.1.6 or hoops.

9.7.6.3.2 Transverse torsional

reinforcement shall extend a

distance of at least ( torsion

beam width + d) beyond the

point required by analysis.

159

9.7.6.3 – TORSION

(CONT’D)

9.7.6.3.3 Spacing of transverse


not exceed the lesser of

0.125 times the perimeter of

the torsion stirrup or 12

inches.

9.7.6.4 Lateral support of

compression reinforcement

(Note: This is the “Beam”

Chapter.)

160

9.7.6.4 –

LATERAL SUPPORT

OF COMPRESSION

REINFORCEMENT

9.7.6.4.1 Transverse


provided throughout the

distance where longitudinal

compression reinforcement is

required…

161

9.7.6.4 –

LATERAL SUPPORT OF

COMPRESSION

REINFORCEMENT

(CONT’D)

9.7.6.4.2,3,4 Same rules as for

column ties given in 25.7.2:

#3 for #10 or smaller, # 4 for

#11 or larger; spacing along

beam LE 16 longitudinal bar

diameters and LE 48 tie bar

diameters; every corner and

every alternate compression

bar enclosed by tie angle LE

135 degrees and every

unsupported bar not more

than 6 inches clear each side

to a supported bar.162

9.7.7 – STRUCTURAL

INTEGRITY

REINFORCEMENT IN

CAST-IN-PLACE BEAMS

9.7.7.1 For perimeter beams: (a)

At least one-quarter


reinforcement and at least

two bars continuous, (b) At

least one-sixth negative

moment reinforcement at

support and at least two bars

continuous; (c) At least

minimum closed stirrups in

accordance with 25.7.1.6

along the entire clear span of

the beam.

163


INTEGRITY

REINFORCEMENT IN

CAST-IN-PLACE BEAMS

(CONT’D)

9.7.7.2 For other than perimeter

beams, structural integrity

reinforcement shall be in

accordance with (a) OR (b): (a) At

least one-quarter and two bars of


reinforcement continuous, (b)

Minimum stirrups entire clear

span.

164


INTEGRITY

REINFORCEMENT IN

CAST-IN-PLACE BEAMS

(CONT’D)

9.7.7.3 Longitudinal integrity

reinforcement shall pass

through the region bounded

by the longitudinal

reinforcement of the column.

165


INTEGRITY

REINFORCEMENT IN

CAST-IN-PLACE BEAMS

(CONT’D)

9.7.7.4 At noncontinuous

supports, develop the

tension yield stress of

integrity reinforcement at

face of support.

9.7.7.5 Splice bottom steel

near support and top steel

near midspan.

166


INTEGRITY

REINFORCEMENT IN

CAST-IN- PLACE BEAMS

(CONT’D)

9.7.7.6 Use mechanical or

welded splices in accordance

with 25.5.7 or Class B tension

lap splices in accordance with

25.5.2 (Class B is the higher

strength, 1.3 times

development length)

167

9.8 – NONPRESTRESSED

ONE-WAY JOIST SYSTEMS

9.8.1 General: Regularly spaced

(LE 30inches) ribs at least 4

inches wide with rib depth

not greater than 3.5 times the

minimum width, top slab

“one-way”, can increase

concrete shear strength 10%,

at least one bottom bar

tension developed into

supports.

168

9.9 – DEEP BEAMS

9.9.1 General: A “deep beam” is

loaded on one face and

supported on the other and

has a clear span less than 4h.

9.9.1.2 ….nonlinear distribution

of longitudinal strain over the

depth of the beam.

9.9.1.3 The strut-and-tie

method in accordance with

Chapter 23 is deemed to

satisfy 9.9.1.2

169

9.9.2 – DIMENSIONAL

LIMITS

7.5sqrt(concrete compressive

strength)(beam web width)(d)

GE [ maximum shear

due to factored loads] ?

( Shear at support face?)

170

9.9.3 – REINFORCEMENT

LIMITS

9.9.3.1 Distributed reinforcement

along the side faces of deep

beams shall be at least that

required in (a) and (b):

(a) The area of distributed

reinforcement perpendicular

to the longitudinal axis of the

beam shall be at least

0.0025bws, where s is the

spacing of the distributed

transverse reinforcement.

171

9.9.3 – REINFORCEMENT

LIMITS (CONT’D)

(b) The area of distributed reinforcement

parallel to the longitudinal axis of the

beam shall be at least 0.0025bws2,

where s2 is the spacing of the

distributed longitudinal reinforcement.

9.9.4 Reinforcement detailing: Concrete

cover 20.5.1; minimum spacing

longitudinal reinforcement 25.2;

spacing of (a) above LE 0.2d and LE 12

inches; at simple supports bottom

steel to develop the tension yield

stress; at interior supports top bars

must be continuous- no splices, and

bottom bars can be continuous or

splices with reinforcement from the

adjacent span.172

174

CHAPTER 10 - COLUMNS

10.2 – GENERAL

From Chapter 2, “column” = member,

usually vertical or predominantly

vertical, used primarily to support

axial compression load, but can

also resist moment, shear, or

torsion. Columns used as part of a

lateral-force-resisting system resist

combined axial load, moment, and

shear.

10.2 - General: Concrete design

properties Chapter 19; Steel

reinforcement Chapter 20;

Embedments 20.6; Joints for cast-

in-place concrete Chapter 15;

Joints for precast concrete 16.2;

Column connections to

foundations 16.3.175

10.3 – DESIGN LIMITS

10.3.1 Dimensional limits

10.3.1.1 For columns with a

square, octagonal, or other

shaped cross section, it shall

be permitted to base gross

area considered, required

reinforcement, and design

strength on a circular section

with a diameter equal to the

least lateral dimension of the

actual shape.

176

10.3 – DESIGN LIMITS

10.3.1.2 For columns with cross

sections larger than required

by consideration of loading, it

shall be permitted to base

gross area considered,

required reinforcement, and

design strength on a reduced

effective area, not less than

one-half the total area. This

provision shall not apply to

columns in special moment

frames or…

177

10.4 – REQUIRED

STRENGTH

Factored load combinations from Chapter 5; analysis procedures Chapter 6

178

10.5 – DESIGN STRENGTH

10.5.1 General: Nominal

strengths times appropriate

capacity reduction factors

from 21.2 must exceed effects

of factored loads; check axial

force, moment, shear, and

torsion and interaction.

179

10.5 – DESIGN STRENGTH

10.5.2 Axial force and moment:

Nominal capacities in


10.5.3 Shear: Nominal capacity in

accordance with22.5.

10.5.4 Torsion: If torsion due to

factored loads exceeds the

threshold torsion of 22.7

multiplied by the capacity

reduction factor (0.75 for

torsion), torsion shall be

considered in accordance

with Chapter 9.

180

10.6 – REINFORCEMENT

LIMITS

10.6.1 Minimum and maximum

longitudinal reinforcement: For

nonprestressed columns and for

prestressed columns with after

loss prestress less than 225psi,

area of longitudinal

reinforcement shall be between

one and eight percent of the

gross column area.

10.6.2 Minimum shear reinforcement: Required where shear due to factored loads exceeds half the design shear strength of the concrete; A v GE 0.75sqrt(f’c)(bw)(s)/ fyt , with f’c GE 4444psi

184


DETAILING

10.7.1 General: Cover 20.5.1;

Development 25.4; Bundled

bars 25.6.


Minimum spacing 25.2.

10.7.3 Longitudinal

reinforcement: Minimum 4

bars enclosed within

rectangular or circular ties;

minimum 6 bars enclosed by

spirals or in special moment

frames.

185


DETAILING (CONT’D)

10.7.4 Offset bent longitudinal

reinforcement: Transition

maximum slope 1:6; use

dowels if column face offset

exceeds 3 inches.

10.7.5 Splices of longitudinal

reinforcement: Lap,

mechanical, butt-welded, or

end bearing; if tension splice

required, generally Class B.

186


REINFORCEMENT

10.7.6.1 General: Ties 25.7.2;

Spirals 25.7.3; Hoops 25.7.4;

longitudinal reinforcement

laterally supported in

accordance with 10.7.6.2,

10.7.6.3.

10.7.6.5 Shear: If required, shear


provided using ties, hoops, or

spirals; maximum spacing by

Table 10.7.6.5.2 – similar to

beams for along length limits,

no across width limits.

187

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