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1/58Winter 2013 |PCI Journal2

The American Concrete Institute (ACI) has published

Building Code Requirements orStructural Con-

crete (ACI 318-11) and Commentary (ACI 318R-

11).1 ACI 318-11 has been adopted by the 2012Interna-

tional Building Code (IBC).2 Thus, whenever the 2012 IBCis adopted by a local jurisdiction, as it will be by the State

o Caliornia on January 1, 2014, ACI 318-11 will be law

within that jurisdiction.

Although the changes rom ACI 318-083 to ACI 318-11 are

not as extensive or as substantive as those rom ACI 318-

054 to ACI 318-08, some o the changes in the latest cycle

have signicant eects on the design and construction o

concrete structures.

Chapter 1:

General Requirements

In section 1.1.4, ACI 332-04Residential Code Require-

ments or Structural Concrete5 has been updated to

ACI 332-10.6

In commentary sections R1.1.8.1 and R.1.1.8.2, two

standards published by the Steel Deck Institute (SDI) are

reerenced: Standard or Non-Composite Steel Floor Deck

(ANSI/SDI NC-2010)7 and Standard or Composite Steel

Floor Deck(ANSI/SDI C1.0-2006).8 The rst document

reers to ACI 318 or the design and construction o the

structural concrete slab. The second document reers to the

This paper summarizes the signicant changes made since the

publication o the 2008 Building Code Requirements for Struc-

tural Concrete (ACI 318-08) and Commentary (ACI 318R-08)

that are refected in the 2011 edition o the code.

Changes aecting conventionally reinorced concrete as well

as precast, prestressed concrete, including posttensioned

concrete, are enumerated.

The changes to Appendix D: Anchoring to Concrete, are

particularly important and are o major interest to the precast/

prestressed concrete industry. These are described in detail.

Significant changesfrom the 2008 to the 2011

edition of ACI 318

S. K. Ghosh


2/58 14PCI Journal|Winter 2013

Specifcation or Steel Welded Wire Reinorcement, Plain,

or Concrete,24 ASTM A496 Standard Specifcation or

Steel Wire, Deormed, or Concrete Reinorcement,25 and

ASTM A497 Standard Specifcation or Steel Welded Wire

Reinorcement, Deormed, or Concrete26 have been com-

bined into ASTM A1064 Standard Specifcation or Steel

Wire and Welded Wire Reinorcement, Plain and Deormed,

or Concrete.27

This change is refected in the denition owelded wire reinorcement in section 2.2 o ACI 318-11.

Chapter 3: Materials

Section 3.2.1 now reers to slag cement, rather than

ground-granulated blast-urnace slag, because ASTM

has changed the title o ASTM C989 to Standard Specif-

cation or Slag Cement or Use in Concrete and Mortars.28

ASTM A615 Standard Specifcation or Deormed and

Plain Carbon Steel Bars or Concrete Reinorcement29 and

ASTM A706 Standard Specifcation or Low-Alloy Steel

Deormed and Plain Bars or Concrete Reinorcement30

(section 3.5.3.1) have both added Grade 80 reinorce-

ment, which has a minimum yield strength o 80,000 psi

(550 MPa). The use o this reinorcement is not permitted

by section 21.1.5 in special moment rames and special

structural walls. Available data were judged to be insu-

cient to conrm applicability o existing code provisions

to special moment rames and special structural walls

reinorced with steel having yield strength higher than

60,000 psi (410 MPa).

Section 3.5.3.2 o ACI 318-08 required that or bars with

y exceeding 60,000 psi, the yield strength shall be taken asthe stress corresponding to a strain o 0.35 percent. ACI

denesy as specied yield strength o reinorcement. The

same section in ACI 318-11 requires that or bars withy

less than 60,000 psi, the yield strength shall be taken as the

stress corresponding to a strain o 0.5 percent, and or bars

withy at least 60,000 psi, the yield strength shall be taken

as the stress corresponding to a strain o 0.35 percent.

This denition o yield strength overrides the one pre-

scribed in ASTM A615, A706, A995, and A996.

Section 3.5.3.8 permits the use o zinc and epoxy dual-

coated reinorcing bars conorming to ASTM A1055Standard Specifcation or Zinc and Epoxy Dual-Coated

Steel Reinorcing Bars.31

Section 3.5.9 now requires ASTM A970 headed deormed

bars to conorm to Annex A1 Requirements or Class

HA Head Dimensions. The commentary explains that the

limitation to Class HA head dimensions rom Annex A1

o ASTM A970 is due to a lack o test data or headed

deormed bars that do not meet Class HA dimensional

requirements. While ACI 318-11 reerences ASTM A970-

09,22 ACI 318-08 reerenced ASTM A970-06,32 which did

not have an Annex A1. ACI 318 required that obstructions

appropriate portions o ACI 318 or the design and con-

struction o the concrete portion o the composite assembly.

Design Manual or Composite Decks, Form Decks, and

Roo Decks,9 published by SDI, is also reerenced. ACI 318

previously reerenced Standard or the Structural Design o

Composite Slabs (ANSI/ASCE 3)10 or the design o com-

posite slabs and Standard Practice or the Construction and

Inspection o Composite Slabs(ANSI/ASCE 9)

11

or guide-lines on the construction o composite steel deck slabs.

In commentary section R1.1.9.1, the reerences have

been updated rom the 200512 to the 201013 ASCE 7/SEI

standardMinimum Design Loads or Buildings and Other

Structures, rom the 200614 to the 200915 edition o the

International Building Code, and rom the 200616 to the

200917 edition o the National Fire Protection Association

(NFPA) 5000Building Construction and Saety Code.

These newer editions have been added to Table R1.1.9.1,

Correlation between Seismic-Related Terminology in Mod-

el Codes. The ollowing sentence has been added at the

end o commentary section R1.1.9.1: The model building

codes also speciy overstrength actors, 0, that are related

to the seismic-orce-resisting system used or the structure

and used or the design o certain elements.

Section 1.1.10 states that ACI 318 does not govern the

design and construction o tanks and reservoirs. Section

R1.1.10 now tells the user that guidance or the design and

construction o cooling towers and circular prestressed

concrete tanks is ound in the reports o ACI committees

334 Concrete Shell Design and Construction,18 350 Envi-

ronmental Engineering Concrete Structures,19 372 Tanks

Wrapped with Wire or Strand,20 and 373 Tanks with Inter-nal Tendons.21 This is an expanded version o commentary

section R19.1.1 o ACI 318-08, which has been moved to

chapter 1 o ACI 318-11.

Section 1.2 now requires Type, size, and location o

anchors, and anchor installation and qualication require-

ments in accordance with D.9 to be shown in contract

documents.

Chapter 2:Notations and Definitions

The denition or headed deormed bars in ACI 318-08

contained a number o requirements or the head. The de-

nition now reers to section 3.5.9, which in turn reerences

Annex A1 Requirements or Class HA Head Dimensions

o ASTM A970 Standard Specifcation or Headed Steel

Bars or Concrete Reinorcement.22

Denitions have been added or vertical wall segment and

wall pier.

ASTM A82 Standard Specifcation or Steel Wire, Plain,

or Concrete Reinorcement,23

ASTM A185 Standard



Chapter 6: Formwork,Embedments, andConstruction Joints

Design drawings and specications has been changed

to contract documents in sections 6.1.1 and 6.4.7. Other

than that, there are no changes in this chapter.

Chapter 7:Details of Reinforcement

In section 7.7.6, which addresses corrosive environments

and other severe exposure, amount o concrete protec-

tion shall be suitably increased has been changed to the

concrete cover shall be increased as deemed necessary and

specied by the licensed design proessional.

In section 7.10.4.5, which is about splicing o spiral reinorce-

ment, the use o deormed zinc-coated (galvanized) bars, plain

zinc-coated (galvanized) bars, and zinc-and-epoxy dual-coat-

ed deormed bars as spiral reinorcement is now recognized.

A new section 7.10.5.4 has been added, and it reads:

Where longitudinal bars are located around the perimeter

o a circle, a complete circular tie shall be permitted. The

ends o the circular tie shall overlap by not less than 6 in.

[150 mm] and terminate with standard hooks that engage a

longitudinal column bar. Overlaps at ends o adjacent cir-

cular ties shall be staggered around the perimeter enclosing

the longitudinal bars. Figure1 illustrates the requirement.

In sections 7.12.3.2 through 7.12.3.5, new requirements

have been added concerning temperature and shrinkagereinorcement in posttensioned slabs. These requirements

dene the gross area o beam and slab sections to be used

or determining the eective prestress. A gure has been

added to the commentary to better illustrate the intentions

o the provision. Figure2 is an adaptation o the commen-

tary gure. The primary reason or this code change was

to clearly discourage the practice o providing all o the

required shrinkage and temperature reinorcement in the

beam web with none in the slab between beams.

Chapter 8: Analysis

and DesignGeneralConsiderations

There are no changes in this chapter.

Chapter 9: Strength andServiceability Requirements

The design load combinations in section 9.2 have been

revised to be ully consistent with those o ASCE/SEI

7-10.13 That standard has converted wind loads tostrength

level and changed the wind load actor in strength design

rom 1.6 to 1.0.

and interruptions o the bar deormations, i any, shall not

extend more than 2db rom the bearing ace o the head (db

is the nominal diameter o bar).

Chapter 4:Durability Requirements

It is required in Table 4.2.1 that percent sulate by massin soil be determined by ASTM C1580 Standard Test or

Water-Soluble Sulate in Soil33 and that concentration o

dissolved sulates in water in parts per million (ppm) be

determined by ASTM D516 Standard Test Method or

Sulate Ion in Water34 or ASTM D4130 Standard Test

Method or Sulate Ion in Brackish Water, Seawater, and

Brine.35

Section R4.5.1 says that ACI 222R-01 Protection o Met-

als in Concrete against Corrosion36 has adopted chloride

limits, test methods, and construction types and condi-

tions that are slightly dierent rom those in ACI 318, as

shown in Table R4.3.1. It also says that ACI 201.2R-08

Guide to Durable Concrete37 has adopted these same

limits by reerring to ACI 222R-01.

Chapter 5: Concrete Quality,Mixing, and Placing

For the purpose o establishing standard deviation or

test records, a test record obtained less than 12 months

beore a submittal was acceptable under ACI 318-08.

The 12-month limit has now been extended to 24 months

in ACI 318-11 section 5.3.1.1.

ACI 318-08 required documentation showing that

proposed concrete mixture proportions will produce an

average compressive strength equal to or greater than

the required average compressive strength to consist o

one or more eld strength test record(s) or trial mixtures

not more than 12 months old. The 12-month limit has

now been extended to 24 months in ACI 318-11 section

5.3.3.

Section 5.6.1 now requires the testing agency perorm-

ing acceptance testing o concrete to have minimum

prociency in compliance with ASTM C1077 StandardPractice or Laboratories Testing Concrete and Con-

crete Aggregates or Use in Construction and Criteria

or Laboratory Evaluation.38 Also, all reports o accep-

tance tests are required to be provided to the licensed

design proessional, contractor, concrete producer, and

when requested, to the owner and the building ocial.

Commentary section R5.6.5 now claries that the in-

structions or investigation o low-strength test results

are applicable only or evaluation o in-place strength at

the time o construction. Strength evaluation o existing

structures is covered in chapter 20.



concrete, bw is web width, and dis distance rom extreme

compression ber to centroid o longitudinal tension

reinorcement. It now requires Vu to be less than or equal

to 10 fc

' bwd, where Vu is actored shear orce at section

and is strength reduction actor. Section 11.7.4, requiring

distributed reinorcement along the sides o deep beams

to be not less than that required in 11.7.4.1 and 11.7.4.2 is

The less common loadssel-straining loads T, fuid

pressure F, and horizontal earth pressureHhave been

removed rom the basic load combinations. They are now

covered in sections 9.2.3, 9.2.4, and 9.2.5, respectively.

Chapter 10:Flexure and Axial Loads

Lateral buckling shall be considered has been deleted

rom section 10.7.1 because it is not a meaningul or en-

orceable requirement. Also, section 10.7.4 o ACI 318-08

has been deleted because it contained shear reinorcement

requirements in a chapter devoted to fexure and axial

loads.

Commentary section R10.10.2 has added the ollowing

text: Several methods have been developed to evaluate

slenderness eects in compression members that are sub-

ject to biaxial bending. A review o some o these methods

is presented in Reerence 10.34.39

Chapter 11: Shear and Torsion

Section 11.7 on deep beams has undergone several

changes. Section 11.7.2 now reads: Deep beams shall be

designed either by taking into account nonlinear distribu-

tion o strain or by appendix A. In all cases, minimum

distribution reinorcement shall be provided in accordance

with 11.7.4. The rst sentence is rewritten or clarity.

The second sentence is an addition. Section 11.7.3 used to

require Vn not to exceed 10 fc' bwd, where Vn is nominal

shear strength, fc

' is specied compressive strength o

Figure 2. Gross area or determining eective prestress. Source: Adapted by permission rom ACI, Building Code Requirements for Structural Concrete (ACI 318-11)

and Commentary (ACI 318R-11)(2011), Fig. R7.12.3(a). Note: L1 = clear slab span on let side o beam; L2 = clear slab span on right side o beam. 1 in. = 25.4 mm;1 t = 0.305 m.

Figure 1. Circular tie confguration per section 7.10.5.4. Note: 1 in. = 25.4 mm.



new. In section 11.7.4.2,the area o shear reinorce-

ment parallel to the longitudinal axis o the beam is

now required to be not less t han 0.0025bws2, where

s2 is the center-to-center spacing o the longitudinal

shear reinorcement. The 0.0025 was 0.0015 in ACI

318-08. The ormer section 11.7.6, which permitted

provision o reinorcement satisying A.3.3 instead

o the minimum horizontal and vertical reinorce-ment speciied in 11.7.4 (now 11.7.4.1) and 11.7.5

(now 11.7.4.2) has been deleted.

Commentary section R11.7 has been rewritten to re-

lect these changes and to explain some o them. The

last sentence in section R11.7.4 now reads: Tests

have shown that vertical shear reinorcement (per-

pendicular to the longitudinal axis o the member) is

more eective or member strength than horizontal

shear reinorcement (parallel to the longitudinal

axis o the member) in a deep beam, but the speci-

ied minimum reinorcement in both directions is

required to control the growth and width o diagonal

cracks. This explains the increase in the amount o

the minimum horizontal shear reinorcement as well

as the deletion o ormer section 11.7.6.

Chapter 12: Developmentand Splices of Reinforcement

The actor used to modiy development length based

on reinorcement coating e given in section 12.2.4(b),

applicable in ACI 318-08 to epoxy-coated bars and

wires, has now been made applicable to zinc-and-epoxy

dual-coated bars.

Part o commentary section R12.6 Development o

Headed and Mechanically Anchored Deormed Bars in

Tension has been rewritten to relect the change dis-

cussed under chapter 3, item 5.

In 2011, the excess reinorcement actor or headed

bars in section 12.6.2 was removed rom the code. The

excess reinorcement actorAs required/As provided, (where

As required is area o nonprestressed longitudinal tension

reinorcement required andAs provided is area o nonpre-

stressed longitudinal tension reinorcement provided)applicable to deormed bars without heads, is not

applicable or headed bars where orce is transerred

through a combination o bearing at the head and bond

along the bar.

Chapter 13:Two-Way Slab Systems

In slabs with shear heads and in lit-slab construction,

structural integrity reinorcement is now required to have

Class B, rather than Class A, tension lap splices or me-

chanical or welded splices satisying section 12.14.3.

Chapter 14: Walls

Commentary section R14.8.4 reerences ASCE 7 Appen-

dix C: Serviceability Considerations. The text has been

updated to be consistent with ASCE/SEI 7-10.

Chapter 15: Footings


Chapter 16: Precast Concrete

There are only minor revisions to this chapter.

Chapter 17: CompositeConcrete Flexural Members


Chapter 18:Prestressed Concrete

The permissible stress o 0.82py (wherepy is specied

yield strength o prestressing steel) but not greater than

0.74pu (wherepu is specied tensile strength o prestress-

ing steel) in prestressing steel immediately upon prestress

transer in section 18.5.1 has been eliminated based on

practical experience with posttensioned concrete members.

Commentary section R18.5.1 is now considerably shorter

and much more direct.

The ormulas or estimating riction loss in posttension-

ing tendons have been eliminated rom section 18.6.2.1 asbeing textbook material. That section now simply states:

The required eective prestress orce shall be indicated

in the contract documents. Table R18.6.2, giving riction

coecients or posttensioning tendons or use in the de-

leted ormulas, has also been eliminated. Section 18.6.2.2

now reads: Computed riction loss shall be based on

experimentally determined wobble and curvatureriction

coecients. Section 18.6.2.3 says: The prestress orce

and riction losses shall be veried during tendon stressing

operations as specied in 18.20.

Commentary section R18.7.2 has been expanded toprovide guidance on the value op or various types o

prestressing reinorcement. The pterm in Eq. (18-1)

refects the infuence o the stress-strain properties o di-

erent types o prestressing reinorcement on the value o

ps

, stress in prestressing steel at nominal fexural strength.

Commentary section R18.9.3.2 now claries how to

compute the minimum bonded reinorcement correspond-

ing to resultant tensile orceNc in positive moment areas.

In chapter 2, the denition oNc now makes it clear that

it includes the combined eects o all service loads and

eective prestress.



Chapter 19: Shells and FoldedPlate Members


Chapter 20: StrengthEvaluation of Existing

StructuresThere are no changes in this chapter.

Chapter 21: Earthquake-Resistant Structures

In sections 21.1.4.1 and 21.1.5.1, reerences to special

structural walls and coupling beams have now been

changed to special structural walls, and all components o

special structural walls including coupling beams and wall

piers. This is in view o the inclusion o wall pier provi-

sions in section 21.9 o ACI 318-11.

ACI 318-08 section 21.1.5.2 requireddeormed reinorce-

ment resisting earthquake-induced fexure, axial orce, or

both to comply with ASTM A706,40 except that ASTM

A61541 grades 40 and 60 reinorcement were permitted

subject to two supplementary requirements. ACI 318-11

requires the ASTM A706 reinorcement to be Grade 60.

This is in order to exclude the new Grade 80 reinorcement

that has been added to ASTM A706.

Section 21.3.3 o ACI 318-08 provided two choices or the

calculation o the required shear strength o a column o an

intermediate moment rame. It could be calculated as thesum o the shear associated with the development o nominal

moment strength at each restrained end o the clear span and

the shear calculated or actored gravity loads. Alternatively,

it could be calculated as the maximum shear obtained rom

design load combinations that includeE(whereEis eects

o earthquake or related internal moments and orces), with

Eassumed to be twice that prescribed by the legally adopted

general building code or earthquake-resistant design. In the

new section 21.3.3.2 o ACI 318-11, the multiplier o two

has been increased to the overstrength actor o the interme-

diate moment rame 0, which is three. The multiplier o

two was determined to be unconservative.

In ACI 318-08 section 21.5.3.2, the spacing o hoops

within the region o potential plastic hinging at each end

could not exceed the smallest o the ollowing:

d/4

8 times the diameter o the smallest longitudinal bars

24 times the diameter o the hoop bars

12 in. (300 mm)

In ACI 318-11 section 21.5.3.2, item (b) has been changed

to six times the diameter o the smallest primary fexural

reinorcing bars, excluding longitudinal skin reinorce-

ment required by section 10.6.7. Item (c) has been deleted.

Item (d) now is 6 in. (150 mm). For deeper beams, this is a

signicant decrease in the spacing o connement rein-

orcement in the regions o potential plastic hinging. It is

intended to improve connement in these regions.

Section 21.5.3.3 has been expanded to read as ollows:

Where hoops are required, primary fexural reinorcing

bars closest to the tension and compression aces shall

have lateral support conorming to 7.10.5.3 or 7.10.5.4.

The spacing o transversely supported fexural reinorcing

bars shall not exceed 14 in. [360 mm]. Skin reinorcement

required by 10.6.7 need not be laterally supported.

A new section 21.6.3.2 has been added, requiring thatin

columns with circular hoops, the minimum number o

longitudinal bars be six.

For a special shear wall or which special boundary ele-

ments were required, section 21.9.6.4(e) stated: Hori-

zontal reinorcement in the wall web shall be anchored

to developy within the conned core o the boundary

element. The requirement has now been expanded as

ollows: Horizontal reinorcement in the wall web shall

extend to within 6 in. [150 mm] o the end o the wall.

Reinorcement shall be anchored to developy in tension

using standard hooks or heads. Where the conned bound-

ary element has sucient length to develop the horizontal

web reinorcement andAvy/s (whereAv is area o shear

reinorcement within spacing s, and s is center-to-centerspacing o shear reinorcement) o the web reinorcement

is not greater thanAshyt/s (whereAsh is total cross-sectional

area o transverse reinorcement (including crossties)

within spacing s and perpendicular to dimension bc,yt is

the specied yield strength o transverse reinorcement,

and bc is cross-sectional dimension o member core mea-

sured to the outside edges o the transverse reinorcement

composing areaAsh) o the boundary element transverse

reinorcement parallel to the web reinorcement, it shall

be permitted to terminate the web reinorcement without a

standard hook or head. Figure3 illustrates this.

Door and window openings in shear walls oten lead to

narrow vertical wall segments, many o which have been

dened as wall piers in the IBC2 and in the Uniorm Build-

ing Code (UBC)42 beore it. Wall pier provisions are now

included or the rst time in the new section 21.9.8 o ACI

318-11. The dimensions dening wall piers are given in

section 2.2.

Shear ailures o wall piers have been observed in previous

earthquakes. The intent o section 21.9.8 is to prescribe

detailing that would result in sucient shear strength o

wall piers so that ailure will be fexure governed, rather



Chapter 22:Structural Plain Concrete

A new section 22.2.4 has been added, requiring that modi-

cation actor or lightweight concrete in chapter 22 be

in accordance with section 8.6.1.

Appendix A:Strut-and-Tie Models

There are no changes in this appendix.

Appendix B: AlternativeProvisions for Reinforcedand Prestressed ConcreteFlexural and CompressionMembers

There are no changes in this appendix.

Appendix C: Alternative Loadand Strength ReductionFactors

The alternative strength design load combinations in sec-tion C.9.2.2 have been revised to be ully consistent with

those o ASCE/SEI 7-10.13 That standard has converted

wind loads tostrength level and changed the wind load

actor in strength design to 1.0.

Appendix D:Anchoring to Concrete

The onerous nature o seismic design imposed by ACI 318-

08 section D.3.3 on anchors in Seismic Design Category

(SDC) C or higher is alleviated and the seismic design o

anchors is made considerably more reasonable. Where

than shear governed. The provisions apply to wall piers

considered part o the seismic orceresisting system.

Provisions or wall piers not considered part o the

seismic orceresisting system are given in section

21.13.

Wall piers having (w/bw) 2.5 (where w is the length

o the entire wall or wall segment or wall pier con-

sidered in the direction o the shear orce) behave

essentially as columns. Section 21.9.8.1 requires them

to be detailed like columns. Alternative requirements

are provided or wall piers having (w/bw) > 2.5. The

design shear orce determined according to section21.6.5.1 may be unrealistically large in some cases.

As an alternative, section 21.9.8.1(a) permits the de-

sign shear orce to be determined using load combi-

nations in which the earthquake load eect has been

ampliied to account or member overstrength.

Wall piers at the edge o a wall are addressed in section

21.9.8.2. Under in-plane shear, inclined cracks can

propagate into segments o the wall directly above and

below the wall pier. Shear ailure within the adja-

cent wall segments can occur unless suicient rein-

orcement is provided in the adjacent wall segments(Fig. R21.9.8).

A new Table R21.9.1 in the commentary eectively

summarizes the new requirements.

Commentary section R21.10.3 has been expanded to

reerence ACIRequirements or Design o a Special

Unbonded Post-Tensioned Precast Shear Wall Satisy-

ing ACI ITG-5.1 and Commentary (ACI ITG-5.2-09),43

which deines design requirements or one type o spe-

cial structural walls constructed using precast concrete

and unbonded posttensioned tendons.

Figure 3. Development o wall horizontal reinorcement in confned boundary element. Note: fy= specifed yield strength o reinorcement; fyt= specifed yield

strength o transverse reinorcement; d= development length in tension o deormed bar, deormed wire, plain and deormed welded wire reinorcement, or preten-

sioned strand; dh= development length in tension o deormed bar or deormed wire with a standard hook, measured rom critical section to outside end o hook

(straight embedment length between critical section and start o hook [point o tangency] plus inside radius o bend and one bar diameter); dt= development length

in tension o headed deormed bar, measured rom the critical section to the bearing ace o the head; s= center-to-center spacing o shear reinorcement.

1 in. = 25.4 mm.



c. Design or the maximum tension orce that can be

transmitted by a nonyielding attachment (section

D.3.3.4.3(c)).

d. Design or the maximum tension orce obtained rom

design load combinations involvingE, withEin-

creased by 0(section D.3.3.4.3(d)).

For an anchor or a group o anchors subject to shear, three

options similar to b, c, and d have been made available.

Unlike ACI 318-08, ductile anchor ailure in shear is not

an option anymore.

As in ACI 318-08, in calculation o the design strength o

an anchor or a group o anchors subject to the seismic de-

sign requirements or tension, concrete-governed strength

is multiplied by a actor o 0.75, while steel-governed

strength is not (section D.3.3.4.4). However, or anchors

subject to the seismic design requirements or shear, ACI

318-11 does not impose this 0.75 actor on the concrete-

governed strengths anymore.

In ACI 318-08 and earlier editions, the steel strength and

pullout strength o anchors in tension and the steel strength

in shear o a group o anchors were calculated based on

the strength o a single anchor multiplied by the number

o anchors in the group. Unless the anchors are all loaded

equally, this can lead to a situation where the most highly

stressed anchor could ail beore reaching the calculated

capacity o the group. In ACI 318-11, Table D.4.1.1 pre-

scribes how to compute the strength o an anchor group

depending on the ailure mode and based on the most

highly stressed anchor.

The maximum anchor diameter or which the provisions

o sections D.5.2 and D.6.2 can be applied to calculate the

concrete breakout strength in tension and shear, respec-

tively, has been increased rom 2 to 4 in. (50 to 100 mm)

(section D.4.2.2). This expansion is based on the results

rom new tests conducted using larger-diameter anchors.

However, a new Eq. (D-34) has also been introduced or

an upper-bound value o basic concrete breakout strength

in shear or a single anchor Vb to account or the larger-

diameter anchors.

ACI 318-08 also imposed a 25 in. (635 mm) limitation

on the anchor embedment depth or the calculation o

concrete breakout strength using the provisions o appen-

dix D. This limitation was eectively removed by section

1908.1.10 o the 2009 IBC.15 ACI 318-11 does not have

this limitation anymore.

An adhesive anchor is dened in section D.1 as a post-

installed anchor, inserted into hardened concrete with an

anchor hole diameter not greater than 1.5 times the anchor

diameter, that transers loads to the concrete by bond

between the anchor and the adhesive, and bond between

the tension component o the strength-level earthquake

orce applied to the anchor or group o anchors is equal to

or less than 20% o the total actored anchor tensile orce

determined rom the same load combination, the seismic

design requirements o section D.3.3 to prevent a brittle

tension ailure o anchors simply do not apply anymore

(section D.3.3.4.1). Similarly, where the shear component

o the strength-level earthquake orce applied to the anchoror group o anchors is equal to or less than 20% o the total

actored anchor shear orce determined rom the same load

combination, the seismic design requirements o section

D.3.3 to prevent a brittle shear ailure o anchors simply do

not apply anymore (section D.3.3.5.1).

Where the seismic component o the total actored tension

demand on an anchor or a group o anchors exceeds 20%,

the ollowing our options have been made available:

a. Ensure ailure o ductile steel anchor ahead o the

brittle ailure o concrete (section D.3.3.4.3(a)). In

other words, the strength o ductile steel anchors needs

to be smaller than the strengths calculated rom vari-

ous concrete ailure modes. In ACI 318-08, this check

was based on the design strengths o anchors deter-

mined rom the considerations o steel anchor ailure

and concrete ailure under tension. In ACI 318-11, this

check is made less onerous in two ways:

Theductilitycheckistobeperformednowbased

on the nominal strengths associated with ductile

steel anchor and concrete ailure modes. This is

easier to satisy than a check based on design

strengths because the -actors applied to concreteailure modes are smaller than that applied to steel

anchor ailure.

InACI318-08,theconcretefailurestrengths

were reduced by a actor o 0.75. In ACI 318-11,

or the purpose o this ductility check, the 0.75

actor is replaced by a actor o 1.2 on the steel

strength. This is equivalent to applying a actor

o1/1.2 = 0.83 on the concrete strengths, an 11%

increase rom beore.

In addition, this ductility check now involves the newconcept o a stretch length: a minimum unbonded

length o 8 times the diameter o the anchor to ensure

an adequate ductile rotational capacity o the connec-

tion or proper energy dissipation. The stretch length

can be provided outside o concrete by using an an-

chor chair (Fig.4) or by debonding part o the anchor

within concrete.

b. Design the anchor or the maximum tension orce that

can be transmitted by a ductile metal attachment ater

considering the overstrength and strain hardening o

the attachment (section D.3.3.4.3(b)).



tion and during the anchor service lie and can be obtained

or cracked and uncracked concrete rom tests perormed

and evaluated in accordance with ACI 355.4-11,Accep-

tance Criteria or Qualifcation o Post-Installed Adhesive

Anchors in Concrete.44 Alternatively, the minimum values

given in Table D.5.5.2 can be used, provided the condi-

tions outlined in section D.5.5.2 and in Table D.5.5.2 are

satised.

Miscellaneous items

The term design drawings and specications has been

replaced with contract documents throughout ACI 318-

11. Lateral reinorcement and lateral ties have been

replaced with transverse reinorcement and transverse

ties, respectively.

Acknowledgments

Signicant help rom Pro Dasgupta and Jason Ericksen o

S. K. Ghosh Associates Inc. with this paper is grateully

acknowledged.

References

1. ACI (American Concrete Institute) Committee 318.

2011.Building Code Requirements or Structural

Concrete (ACI 318-11) and Commentary (ACI 318R-

11). Farmington Hills, MI: ACI.

2. ICC (International Code Council). 2012.International

Building Code. Washington, DC: ICC.

3. ACI Committee 318. 2008.Building Code Require-

ments or Structural Concrete (ACI 318-08) and Com-

mentary (ACI 318R-08). Farmington Hills, MI: ACI.

the adhesive and the concrete(Fig.5). The method o

calculating nominal strength o adhesive anchors in bond

ailure is provided, along with requirements or testing and

evaluation o adhesive anchors or use in cracked concrete

or subject to sustained loads. Failure modes postulated or

other anchors apply to adhesive anchors as well, except

that the calculation o strength in anchor pullout is replaced

by the evaluation o adhesive bond strength in accordance

with section D.5.5. The provisions or adhesive anchors

include criteria or overhead anchors, seismic design

requirements, installation and inspection requirements,

and certication o adhesive anchor installers. Separately,

a certication program has been established jointly by ACIand the Concrete Reinorcing Steel Institute. Characteristic

bond stress o adhesive anchors depends on the installation

method and use conditions anticipated during construc-

Figure 4. Use o anchor chair or providing stretch length. Photo courtesy o J.

Silva, Hilti North America.

Figure 5.Adhesive anchor and bond ailure o adhesive anchor. Photo courtesy o Rol Eligehausen, University o Stuttgart.



19. ACI Committee 350. 2006. Code Requirements or

Environmental Engineering Concrete Structures and

Commentary. ACI 350-06. Farmington Hills, MI: ACI.

20. ACI Committee 372. 2003.Design and Construction

o Circular Wire- and Strand-Wrapped Prestressed

Concrete Structures. ACI 372R-03. Farmington Hills,

MI: ACI.

21. ACI Committee 373. 1997.Design and Construc-

tion o Circular Prestressed Concrete Structures with

Circumerential Tendons. ACI 373R-97. Farmington

Hills, MI: ACI.

22. ASTM Subcommittee A01.05. 2009. Standard Speci-

fcation or Headed Steel Bars or Concrete Reinorce-

ment including Annex A1 Requirements or Class HA

Head Dimensions. ASTM A970/A970M-09. West

Conshohocken, PA: ASTM International.


fcation or Steel Wire, Plain, or Concrete Reinorce-

ment. ASTM A82/A82M-07. West Conshohocken, PA:

ASTM International.

24. ASTM Subcommittee A01.05. 2007. Standard Specif-

cation or Steel Welded Wire Reinorcement, Plain, or

Concrete. ASTM A185/ A185-07. West Conshohock-

en, PA: ASTM International.

25. ASTM Subcommittee A01.05. 2007. Standard

Specifcation or Steel Wire, Deormed, or Concrete

Reinorcement. ASTM A496/A496M-07. West Con-shohocken, PA: ASTM International.


fcation or Steel Welded Wire Reinorcement, De-

ormed, or Concrete. ASTM A497/A497M-07. West

Conshohocken, PA: ASTM International.


cation or Steel Wire and Welded Wire Reinorcement,

Plain and Deormed, or Concrete. ASTM A1064/

A1064M-10. West Conshohocken, PA: ASTM Interna-

tional.

28. ASTM Subcommittee C09.27. 2009. Standard Speci-

fcation or Slag Cement or Use in Concrete and Mor-

tars. ASTM C989/C989M-09a. West Conshohocken,

PA: ASTM International.


cation or Deormed and Plain Carbon-Steel Bars or

Concrete Reinorcement. ASTM A615/A615M-09b.

West Conshohocken, PA: ASTM International.



mentary (ACI 318R-05). Farmington Hills, MI: ACI.

5. ACI Committee 332. 2004.Residential Code Require-


mentary. Farmington Hills, MI: ACI.

6. ACI Committee 332. 2010.Residential Code Require-


mentary. Farmington Hills, MI: ACI.

7. SDI (Steel Deck Institute). 2010. Standard or Non-

Composite Steel Floor Deck. ANSI/SDI NC-2010. Fox

River Grove, IL: SDI.

8. SDI. 2006. Standard or Composite Steel Floor Deck.

ANSI/SDI C1.0-2006. Fox River Grove, IL: SDI.

9. SDI. 2007.Design Manual or Composite Decks, Form

Decks, and Roo Decks. No. 31. Fox River Grove, IL:

SDI.

10. ASCE (American Society o Civil Engineers). 1994.

Standard or the Structural Design o Composite

Slabs. ANSI/ASCE 3-91. Reston, VA: ASCE.

11. ASCE. 1994. Standard Practice or the Construction

and Inspection o Composite Slabs. ANSI/ASCE 9-91.

Reston, VA: ASCE.

12. SEI (Structural Engineering Institute). 2005.Minimum

Design Loads or Buildings and Other Structures.ASCE 7-05. Reston, VA: ASCE.

13. SEI. 2010.Minimum Design Loads or Buildings and

Other Structures. ASCE 7-10. Reston, VA: ASCE.

14. ICC. 2006.International Building Code. Washington,

DC: ICC.

15. ICC. 2009.International Building Code. Washington,

DC: ICC.

16. NFPA (National Fire Protection Association). 2006.Building Construction and Saety Code. NFPA 5000.

Quincy, MA: NFPA.

17. NFPA. 2009.Building Construction and Saety Code.

NFPA 5000. Quincy, MA: NFPA.

18. ACI Committee 334. 1991.Reinorced Concrete

Cooling Tower ShellsDesign and Construction. ACI

334.2R-91. Farmington Hills, MI: ACI.



42. ICBO (International Conerence o Building O-

cials). 1997. Uniorm Building Code. Whittier, CA:

ICBO.

43. ACI Innovation Task Group 5. 2009.Requirements or

Design o a Special Unbonded Post-Tensioned Precast

Shear Wall Satisying and Commentary. ACI ITG-5.2-

09.Farmington Hills, MI: ACI.

44. ACI Committee 355. 2011.Acceptance Criteria or

Qualifcation o Post-Installed Adhesive Anchors in

Concrete and Commentary. ACI 355.4-11.Farmington

Hills, MI: ACI.

Notation

As provided = area o nonprestressed longitudinal tension rein-

orcement provided

As required = area o nonprestressed longitudinal tension rein-

orcement required

Ash = total cross-sectional area o transverse reinorce-

ment (including crossties) within spacing s and

perpendicular to dimension bc

Av = area o shear reinorcement within spacing s

bc = cross-sectional dimension o member core

measured to the outside edges o the transverse

reinorcement composing areaAsh

bw = web width

d = distance rom extreme compression ber to

centroid o longitudinal tension reinorcement

db = nominal diameter o bar

E = eects o earthquake or related internal moments

and orces

fc' = specied compressive strength o concrete

ps = stress in prestressing steel at nominal fexuralstrength

pu = specied tensile strength o prestressing steel

py = specied yield strength o prestressing steel

y = specied yield strength o reinorcement

yt = specied yield strength o transverse reinorcement

F = fuid pressure


fcation or Low-Alloy Steel Deormed and Plain Bars

or Concrete Reinorcement. ASTM A706/A706M-

09b. West Conshohocken, PA: ASTM International.

31. ASTM Subcommittee A01.05. 2010. Standard

Specifcation or Zinc and Epoxy Dual-Coated Steel

Reinorcing Bars. ASTM A1055/A1055M-10. WestConshohocken, PA: ASTM International.


fcation or Headed Steel Bars or Concrete Reinorce-

ment. ASTM A970/A970M-06. West Conshohocken,

PA: ASTM International.

33. ASTM Subcommittee C09.69. 2009. Standard Test

or Water-Soluble Sulate in Soil. ASTM C1580/

C1580M-09. West Conshohocken, PA: ASTM Interna-

tional.

34. ASTM Subcommittee D19.05. 2007. Standard

Test Method or Sulate Ion in Water. ASTM D516/

D516M-07. West Conshohocken, PA: ASTM Interna-

tional.

35. ASTM Subcommittee D19.05. 2008. Standard Test

Method or Sulate Ion in Brackish Water, Seawater,

and Brine. ASTM D4130/D4130M-08. West Con-

shohocken, PA: ASTM International.

36. ACI Committee 222. 2001. Protection o Metals in

Concrete Against Corrosion (ACI 222R-01). Farming-

ton Hills, MI: ACI.

37. ACI Committee 201. 2008. Guide to Durable Concrete

(ACI 201.2R-08). Farmington Hills, MI: ACI.

38. ASTM Subcommittee C09.98. 2010. Standard Prac-

tice or Laboratories Testing Concrete and Concrete

Aggregates or Use in Construction and Criteria or

Laboratory Evaluation. ASTM C1077/C1077M-10.


39. Furlong, R. W.; Hsu, C.-T. T.; and Mirza, S. A. 2004.

Analysis and Design o Concrete Columns or BiaxialBendingOverview. ACI Structural Journal 101 (3):

413423.


fcation or Low-Alloy Steel Deormed and Plain Bars

or Concrete Reinorcement. ASTM A706/A706M-

06A. West Conshohocken, PA: ASTM International.


fcation or Deormed and Plain Carbon-Steel Bars

or Concrete Reinorcement. ASTM A615/A615M-07.




H = horizontal earth pressure

w = length o entire wall or length o wall segment or

wall pier considered in direction o shear orce

d = development length in tension o deormed bar,

deormed wire, plain and deormed welded wire

reinorcement, or pretensioned strand

dh = development length in tension o deormed bar

or deormed wire with a standard hook, mea-

sured rom critical section to outside end o hook

(straight embedment length between critical

section and start o hook [point o tangency] plus

inside radius o bend and one bar diameter)

dt = development length in tension o headed de-

ormed bar, measured rom the critical section to

the bearing ace o the head

L1 = clear slab span on let side o beam

L2 = clear slab span on right side o beam

Nc = resultant tensile orce in positive moment

s = center-to-center spacing o shear reinorcement

s2 = center-to-center spacing o longitudinal shear

reinorcement

T = sel-straining loads

Vb = concrete breakout strength in shear or a single

anchor

Vn = nominal shear strength

Vu = actored shear orce at section

p = infuence o dierent types o prestressing rein-

orcement on the value ops

= modication actor or lightweight concrete

= strength reduction actor

e = actor used to modiy development length based

on reinorcement coating

0 = overstrength actor



About the author

S. K. Ghosh, PhD, FPCI, heads

his own consulting practice, S. K.Ghosh Associates Inc., in Palatine,

Ill., and Aliso Viejo, Cali. He was

ormerly director o Engineering

Services, Codes, and Standards at

the Portland Cement Association

in Skokie, Ill. Ghosh specializes in the analysis and

design, including wind- and earthquake-resistant

design, o reinorced and prestressed concrete struc-

tures. He is active on many national technical commit-

tees and is a member o American Concrete Institute

(ACI) Committee 318 Standard Building Code, the

Masonry Standards Joint Committee, and the ASCE 7

Standard Committee (Minimum Design Loads or

Buildings and Other Structures). He is a ormer

member o the Boards o Direction o ACI and the

Earthquake Engineering Research Institute.

Abstract

Signicant changes made since the publication o

the 2008Building Code Requirements or Structural


08) that are refected in the 2011 edition o the code

are summarized. Changes aecting conventionallyreinorced concrete as well as precast, prestressed

concrete, including posttensioned concrete, are enu-

merated. The changes to Appendix D: Anchoring to

Concrete are particularly important and are o major

interest to the precast/prestressed concrete industry.

Keywords

ACI 318, code, structural concrete.

Review policy

This paper was reviewed in accordance with the

Precast/Prestressed Concrete Institutes peer-review

process.

Reader comments

Please address any reader comments to journal@pci

.org or Precast/Prestressed Concrete Institute, c/o PCI

Journal, 200 W. Adams St., Suite 2100, Chicago, IL

60606. J


14/58

3PCI Journal|Special Supplement

Significant

changes

to the ACI318-08

appendixes

relative

to precast/prestressed

concreteS. K. Ghosh

Significant changes have been made since American

Concrete Institute (ACI) Committee 318 published

the 2005Building CodeRequirements for Structural


05).1 Changes to the appendixes in the new 2008 edition2

are summarized in this paper. The rest of the changes

were covered in a three-part series of articles in special

members-only supplements.

The intent of this article is to provide a summary of

significant changes affecting conventionally reinforced

concrete, precast concrete, and prestressed concrete

(including post-tensioned concrete). This information

should be useful to building officials, design engineers,

practitioners, and the academic community.

Changes to chapters 1 through 8 of ACI 318-08 were

discussed in the MarchApril 2008 issue of the PCI

Journal in part 1 of the aforementioned article series.

Changes to chapters 9 through 20 were discussed in part

2 of this series in the supplement to the MayJune 2008

issue. Changes to chapter 21 were discussed in part 3

of the article series in a supplement to the September

October 2008 issue.

ACI 318-08 will be the reference document for con-crete design and construction in the 2009 edition of the

Editors quick points

n This paper describes changes rom the 2005 edition to the

2008 edition o ACI 318, Building Code Requirements for

Structural Concrete and Commentary. Specifcally, changes

to the appendixes are discussed.

n ACI 318 underwent a major revision with this version.

n Changes aecting conventionally reinorced concrete and

provisions aecting precast/prestressed concrete, includingpost-tensioned concrete, are enumerated.


15/58

Special Supplement |PCI Journal

tension, or 3ca1 from one or more adjacent anchors when

subjected to shear. The distance from the center of an

anchor shaft to the edge of concrete in one direction is

represented by ca1. ACI 318-08 also added to the defini-

tion, only those anchors susceptible to the particular

failure mode under investigation shall be included in the

group.

An important new term, anchorreinforcement, is de-

fined as reinforcement used to transfer the full design

load from the anchors into the structural member. New

sections D.5.2.9 and D.6.2.9 contain provisions concern-

ing anchor reinforcement.

ACI 318-05 defined supplementary reinforcement as

reinforcement proportioned to tie a potential concrete

failure prism to the structural member. ACI 318-08 has

revised the supplementary reinforcement definition to

read, reinforcement that acts to restrain the potential

concrete breakout but is not designed to transfer the fulldesign load from the anchors into the structural mem-

ber. The second part of the revised definition clearly

indicates that supplementary reinforcement is not anchor

reinforcement.

Section D.3.3 of ACI 318-05 reads, When anchor de-

sign includes seismic loads, the additional requirements

of D.3.3.1 through D.3.3.5 shall apply. This wording

has now changed to when anchor design includes earth-

quake forces for structures assigned to Seismic Design

Category C, D, E, or F, the additional requirements of

D.3.3.1 through D.3.3.6 shall apply. There are two dif-

ferences:

Section D.3.3.6 has been added.

The applicability of the ACI 318-05 provision

included seismic design category (SDC) B, which is

no longer the case.

The change in the SDC matters for section D.3.3.1 only

because subsequent ACI 318-05 language restricted

the applicability of sections D.3.3.2 through D.3.3.5 to

structures assigned SDC C, D, E, or F.

Section D.3.3.2 of ACI 318-08 specifically requires that

pullout strengthNp and steel strength of the anchor in

shear Vsa shall be based on the results of the ACI 355.2

Simulated Seismic Tests. This specific requirement was

not part of ACI 318-05.

Section D.3.3.3 has undergone an important change.

While the section in ACI 318-05 required that the

design strength of anchors shall be taken as 0.75Nn

and 0.75Vn, the ACI 318-08 section requires that theanchor design strength associated with concrete failure

International Building Code (IBC),3 which will continue

to reference ASCE 7-05,Minimum Design Loads for

Buildings and Other Structures.4

All section and chapter numbers used in this paper refer

to those of ACI 318-08 unless otherwise noted.

Appendix A: Strut-and-TieModels

No significant changes were made to this appendix.

Appendix B: AlternativeProvisions for Reinforcedand Prestressed ConcreteFlexural and CompressionMembers

Changes were made in section B.8.4, Redistribution

of Moments in Continuous Nonprestressed FlexuralMembers, that parallel changes in section 8.4, Redis-

tribution of Moments in Continuous Flexural Members.

Section 8.4 was discussed in part 1 of the ACI 318-08

article series.

Appendix C: AlternativeLoad and Strength ReductionFactors

No significant changes were made to this appendix.

Appendix D: Anchoring toConcrete

The three significant changes in Appendix D are the

following:

new definitions of reinforcement types that cross

the concrete breakout surface

new requirements on how seismic loads are handled

for anchors

provisions that were added to the concrete breakout

design of anchorages for lightweight concrete

ACI 318-05 defined an anchor group as a number of

anchors of approximately equal effective embedment

depth with each anchor spaced at less than three times

its embedment depth [3hef] from one or more adjacent

anchors. This definition considered anchors subject to

tension but not anchors subject to shear. This deficiency

has now been corrected. The 318-08 definition reads, a

number of anchors of approximately equal effective em-

bedment depth with each anchor spaced at less than 3heffrom one or more adjacent anchors when subjected to


16/58


reinforcement is not required. However, the arrange-

ment of supplementary reinforcement should generally

conform to that of the anchor reinforcement shown in

Fig. RD.5.2.9 and RD.6.2.9 (b). Full development is not

required [of the supplemental reinforcement].

The descriptions of conditions A and B in section D.4.4

were editorially modified for greater clarity. The de-

scriptions now read, Condition A applies where supple-

mentary reinforcement is present except for pullout and

pryout strengths. Condition B applies where supple-

mentary reinforcement is not present, and for pullout or

pryout strength.

A distinction is now made between the effective cross-

sectional area of anchor in tensionAse,Nand the effec-

tive cross-sectional area of anchor in shearAse,V. In ACI

315-05, there was only the effective cross-sectional area

of anchorAse. The change is reflected in ACI 318-08 Eq.(D-3), (D-19), and (D-20).

modes shall be taken as 0.75Nn and 0.75Vn. The

variables ,Nn, and Vn represent the strength reduction

factor, the nominal strength in tension, and the nominal

shear strength, respectively. By making the seismic

reduction apply only to concrete failure modes, it is

significantly more difficult to meet the requirements

of section D.3.3.4 when anchors subjected to seismic

forces in structures assigned to SDC C, D, E, or F haveto be governed by the strength of a ductile steel element.

Section D.3.3.4 of ACI 318-05 waived the ductile

anchor failure requirement if section D.3.3.5 could be

satisfied. The same section in ACI 318-08 waives the

ductile failure requirement if either section D.3.3.5 or

section D.3.3.6 can be satisfied.

The 2006 IBC section 1908.1.16 modified ACI 318-05

section D.3.3.5 to read, Instead of D.3.3.4 . . . speci-

fied in D.3.3.3, or the minimum design strength of the

anchors shall be at least 2.5 times the factored forcestransmitted by the attachment. The 2006 IBC includes

the text of ACI 318-05 section D.3.3.5 with the addition

of or the minimum design strength of the anchors shall

be at least 2.5 times the factored forces transmitted by

the attachment. In other words, ductile anchor failure

was declared unnecessary if the anchorage was overde-

signed for concrete breakout.

This concept has been adopted into section D.3.3.6

of ACI 318-08 with the wording, as an alternative to

D.3.3.4 [ductile anchor failure] and D.3.3.5 [yielding in

the attachment], it shall be permitted to take the design

strength of the anchors as 0.4 times the design strength

determined in accordance with D.3.3.3. For anchors of

stud-bearing walls, the 0.4 factor may be taken as 0.5.

Because ACI 318 is a material standard, the committee

did not feel comfortable modifying the design load, as

the 2006 IBC had done. It was decided instead, in effect,

to modify the strength reduction factor. A 0.4 multiplier

on is equivalent to a 2.5 multiplier on the design load.

Section D.3.4 concerning anchors embedded in light-

weight concrete is differentbut mostly in appearance,

not really in substance.

An important sentence has been added to section

D.4.2.1: Where anchor reinforcement is provided in

accordance with D.5.2.9 and D.6.2.9, calculation of the

concrete breakout strength in accordance with D.5.2 and

D.6.2 is not required. This sentence was added because

anchor reinforcement is reinforcement that carries all of

the design load when breakout failure occurs.

The commentary concerning supplementary rein-

forcement has changed in section RD.4.4. Importantnew points are, An explicit design of supplementary

Figure 1.Anchor reinforcement for tension.

Source: Reprinted by permission from Building Code Requirements for Struc-

tural Concrete (ACI 318-08) and Commentary (ACI 318R-08)(Farmington Hills,

MI: ACI, 2008), p. 426, Fig. RD.5.2.9.


17/58


Commentary section RD.5.1.2 reproduces an equation

from American National Standards Institute (ANSI)/

American Society of Mechanical Engineers (ASME)

B1.1, Unified Inch Screw Threads (UN and UNR Thread

Form)5 forAse,Nof threaded bolts. Commentary section

RD.6.1.2 reproduces an equation from ANSI/ASME

B1.1 forAse,Vfor threaded bolts. The two equations are

identical. The difference in the value obtained from the

two equations is evident for postinstalled mechanical an-chors, particularly torque-controlled expansion anchors

with a tapered conical shape at the bottom. Approved

postinstalled anchors give both effective areas in the

product approval. In most cases, the areas provided are

the same as those given by the equations in the ACI 318-

08 commentary.

In Eq. (D-7) for basic concrete breakout strength, a

lightweight concrete factor was introduced.

An important new section, D.5.2.9, has been added to

ACI 318-08. This section reads, Where anchor rein-

forcement is developed in accordance with Chapter 12

on both sides of the breakout surface, the design strength

of the anchor reinforcement shall be permitted to be

used instead of the concrete breakout strength in deter-

mining Nn. A strength reduction factor of 0.75 shall be

used in the design of the anchor reinforcement.

Figure 3. Edge reinforcement and anchor reinforcement for shear.



MI: ACI, 2008), p. 435, Fig. RD.6.2.9(b).

Figure 2. Hairpin anchor reinforcement for shear.



MI: ACI, 2008), p. 435, Fig. RD.6.2.9(a).


18/58


An important new commentary section RD.5.2.9 states

that for conditions where the factored tensile force

exceeds the concrete breakout strength of the anchor(s)

or where the breakout strength is not evaluated, the

nominal strength can be that of anchor reinforcement.

The commentary includes Fig. RD.5.2.9, which is help-

ful and is reproduced in this paper as Fig. 1.

The variable d0, which represents the outside diameter or

shaft diameter of a headed stud, headed bolt, or hooked

bolt of ACI 318-05, has been replaced with dain ACI

318-08. This change is reflected in Eq. (D-16) for pull-

out strength in tension and in section D.8.3.

The lightweight concrete factor is introduced in Eq.

(D-17) for the concrete side-face blowout strength of a

single anchor in tension and in Eq. (D-18) for the con-

crete side-face blowout strength of a group of anchors in

tension.

A new modification factor h,Vhas been added to Eq.

(D-21) and (D-22) for concrete breakout strength of an-

chors in shear. The factor is defined by Eq. (D-29) and is

for anchors located in a concrete member in which

ha < 1.5ca1 and ha is the thickness of the member in

which an anchor is located, measured parallel to anchor

axis.

The lightweight concrete factor is also introduced into

Eq. (D-24) and (D-25) for the basic concrete breakout

strength in shear.

Paralleling section D.5.2.9, another important new sec-

tion, D.6.2.9, has been added to ACI 318-08. It reads,

Where anchor reinforcement is either developed in ac-

cordance with Chapter 12 on both sides of the breakout

surface, or encloses the anchor and is developed beyond

the breakout surface, the design strength of the anchor

reinforcement shall be permitted to be used instead of

the concrete breakout strength in determining Vn. A

strength reduction factor of 0.75 shall be used in the

design of the anchor reinforcement. New commentary

section RD.6.2.9 explains the provision. It includes Fig.

RD. 6.2.9(a) and RD.6.2.9(b), which are reproduced in

this paper as Fig. 2 and 3, respectively.

Summary and conclusion

Significant and substantial changes have been made in

appendix D of ACI 318-08. The other appendixes had

no or only minor changes. Changes to appendix D in

ACI 318-08 have been summarized and discussed in this

paper on significant changes from ACI 318-05 to ACI

318-08.

The changes to appendix D are few in number but are

quite substantive in nature. Anchor design strength as-

sociated with steel failure is no longer to be reduced by

an additional 0.75 factor. Also, there are new provisions

that clearly define the role of anchor reinforcement,

which is designed to carry the entire anchorage load

once breakout failure in tension or shear occurs.

References

1. American Concrete Institute (ACI) Committee 318.

2005.Building Code Requirements for Structural

Concrete (ACI 318-05) and Commentary (ACI

318R-05). Farmington Hills, MI: ACI.


ments for Structural Concrete (ACI 318-08) and

Commentary (ACI 318R-08). Farmington Hills,

MI: ACI.

3. International Code Council (ICC). 2009.Interna-

tional Building Code. Washington, DC: ICC.

4. Structural Engineering Institute. 2005.Minimum

Design Loads for Buildings and Other Structures

(ASCE 7-05). Reston, VA: American Society of

Civil Engineers.

5. American Society of Mechanical Engineers

(ASME). 1989. Unified Inch Screw Threads (UN

and UNR Thread Form). American National Stan-

dards Institute (ANSI)/ASME B1.1. Fairfield, NJ:

ASME.

Notation

Ase = effective cross-sectional area of anchor (ACI

318-05)

Ase,N = effective cross-sectional area of anchor in tension

Ase,V = effective cross-sectional area of anchor in shear

ca1 = distance from the center of an anchor shaft to

the edge of concrete in one direction (if shear is

applied to the anchor, ca1 is the maximum edge

distance)

ca2 = distance from the center of an anchor shaft to the

edge of concrete in the direction perpendicular to

ca1, in.

d0 = outside diameter of anchor or shaft diameter of

headed stud, headed bolt, or hooked bolt (ACI

318-05)


19/58


Nn = nominal strength in tension

Np = pullout strength in tension of a single anchor in

cracked concrete

V = shear force

Vn = nominal shear strength

Vsa = nominal strength in shear of a single anchor

or group of anchors as governed by the steel

strength

= lightweight concrete factor

= strength reduction factor

h,V = factor used to modify shear strength of anchors

located in concrete members with ha < 1.5ca1

da = outside diameter of anchor or shaft diameter of

headed stud, headed bolt, or hooked bolt

ha = thickness of member in which an anchor is lo-

cated, measured parallel to anchor axis

hef = effective embedment depth of anchor

ld = development length in tension of deformed bar,

deformed wire, plain and deformed welded-wire

reinforcement, or pretensioned strand, in.

ldh = development length in tension of deformed bar

or deformed wire with a standard hook, mea-

sured from critical section to outside end of hook

(straight embedment length between critical

section and start of hook [point of tangency] plus

inside radius of bend and one bar diameter), in.

N = tensile force

About the author

S. K. Ghosh, PhD, FPCI,

is president of S. K.

Ghosh Associates Inc. in

Palatine, Ill.

Synopsis

Significant changes were made since Ameri-

can Concrete Institute (ACI) Committee 318

published the 2005Building Code Require-

ments for Structural Concrete (ACI 318-05)

and Commentary (ACI 318R-05). The changes

in the appendixes of the 2008 edition are sum-

marized in this article. In addition to changes

affecting conventionally reinforced concrete,

provisions affecting precast/prestressed con-

crete, including post-tensioned concrete, are

enumerated.

Keywords

ACI 318, code, structural concrete.

Reader comments

Please address any reader comments to PCI

Journal editor-in-chief Emily Lorenz at

[email protected] or Precast/Prestressed Con-

crete Institute, c/o PCI Journal, 209 W. Jackson

Blvd., Suite 500, Chicago, IL 60606. J


20/58

SPCI Journal|Special Supplement

Editors quick points

n This second of three papers describes the changes from the

2005 edition to the 2008 edition of ACI 318,Building Code

Requirements for Structural Concrete and Commentary, for

chapters 9 through 20.

nACI 318 underwent a major revision with this version.

n Part 3 will follow in a subsequent issue of the PCI Journal.

Significant

changes

to ACI 318-08

relative

to precast/

prestressed

concrete:

Part 2S. K. Ghosh

Significant changes have been made since American Con-

crete Institute (ACI) Committee 318 published the 2005

Building CodeRequirements for Structural Concrete (ACI

318-05) and Commentary (ACI 318R-05).1 The changes in

the new 2008 edition2 are summarized in this paper.

The intent of this article is to provide a summary of

significant changes affecting conventionally reinforced

concrete, precast concrete, and prestressed concrete (in-

cluding post-tensioned concrete). This information should

be useful to building officials, design engineers, practitio-

ners, and the academic community. Changes to chapters 1

through 8 of ACI 318-08 were discussed in part 1 of this

article series, published as a member supplement to the

MarchApril 2008 issue of the PCI Journal. Changes to

chapter 9 through 20 of ACI 318-08 are discussed in this

part 2 of the article series. Changes to chapter 21 and the

appendices will be discussed in part 3, which will appear

in a subsequent issue of the PCI Journal.

ACI 318-08 will be the reference document for concrete

design and construction in the 2009 edition of theInter-

national Building Code (IBC),3 which will continue to

reference ASCE 7-05.4

All section and chapter numbers used in this paper refer to

those of ACI 318-08 unless otherwise noted.


21/58

Special Supplement |PCI Journal4

Members. The slenderness provisions are reorganized to

reflect current practice where second-order effects are

considered primarily using computer analysis techniques,

while the style of presentation used by ACI 318 since 1971

is retained. The moment magnifier method is also retained

as an alternate procedure.

Section 10.10.1 permits slenderness effects to be neglected

"for compression members not braced against sidesway

when:

klu

r! 22

"

and

"for compression members braced against sidesway

when:

klu

r! 34"12 M1

M2

#$%

&'(! 40"

where

k = effective length factor

lu

= unsupported length

r = radius of gyration

M1

= smaller factored end moment

2

= larger factored end moment

M1/M

2= positive if a compression member is bent in

single curvature

A new feature permits a compression member to be con-

sidered braced against sidesway when bracing elements

have a total stiffness, resisting lateral movement of that

story, of at least 12 times the gross stiffness of the columns

within the story.

Section 10.10.2 requires that when slenderness effects are

not neglected as permitted by section 10.10.1, the design

of compression members, restraining beams, and other

supporting members be based on the factored forces and

moments from a second-order analysis satisfying [section]

10.10.3, 10.10.4, or 10.10.5.

Section 10.10.3 is titled Nonlinear Second-Order Analy-

sis, section 10.10.4 contains requirements for elastic

second-order analysis, and section 10.10.5 details mo-

ment magnification procedure. The members being

discussed are also required to satisfy sections 10.10.2.1and 10.10.2.2. Section 10.10.2.1 requires that second-order

effects in compression members, restraining beams, or

Chapter 9: Strength andServiceability Requirements

The new commentary section, R9.2.1(a), provides valuable

and much-needed clarification. It points out that the load-

factor modification of section 9.2.1(a) is different from the

ive-load reduction based on the loaded area that is typi-

cally allowed in the legally adopted general building code.The live-load reduction in the code adjusts the nominal

oadL. The lesser load factor in section 9.2.1(a) reflects the

reduced probability of the joint occurrence of maximum

values of multiple transient loads at the same time. The

reduced live loads specified in the legally adopted general

building code can be used simultaneously with the 0.5 load

factor specified in section 9.2.1(a).

In section 9.3.2.2, the strength-reduction factor for spi-rally reinforced columns was increased from 0.70 to 0.75.

Commentary section R9.3.2 notes that this increase is part-

y due to the superior performance of spirally reinforcedcolumns when subjected to excessive loads or extreme

excitations5 and is partly due to new reliability analyses.6

The -factor modifications of section 9.3.4(a)(c) arenow also applicable to structures that rely on intermediate

precast concrete structural walls to resist earthquake effects

n seismic design categories (SDC) D, E, or F. Previously,

the modifications applied only to structures that rely on

special moment frames or special structural walls to resist

earthquake effects.

In section 9.3.5, the -factor for plain concrete was in-creased from 0.55 to 0.60. As stated in commentary section

R9.3.5, this is partly due to recent reliability analysis and a

statistical study of concrete properties.6

The first paragraph of section R9.3.4 of ACI 318-05 was

eliminated. In section R9.4, it is clarified that the maxi-

mum specified yield strength of nonprestressed reinforce-

mentfy

in section 21.1.5 is 60,000 psi (420 MPa) in special

moment frames and special structural walls.

Chapter 10: Flexureand Axial Loads

For a compression member with a cross section larger than

required by considerations of loading, section 10.8.4 permits

the minimum reinforcement to be based on a reduced effec-

tive areaAgnot less than one-half the total area. ACI 318-05

used to state that the provision does not apply in regions of

high seismic risk. ACI 318-08 now states that this provision

does not apply to special moment frames or special structural

walls designed in accordance with chapter 21.

The most significant change in chapter 10 is a rewritingof sections 10.10 through 10.13 of ACI 318-05 into the

new section 10.10, Slenderness Effects in Compression


22/58


other structural members not exceed 40% of the moment

due to first-order effects. Section 10.10.2.2 requires that

second-order effects be considered along the length of

compression members. This can be done using the non-

sway moment magnification procedure outlined in section

10.10.6.

Section 10.10.4 on elastic second-order analysis includes

new equations (10-8) and (10-9), which provide more-

refined values ofEIconsidering axial load, eccentricity,

reinforcement ratio, and concrete compressive strength, as

presented in the two Khuntia and GhoshACI Structural

Journal articles.7,8

Commentary section R10.13.8, Tie Reinforcement around

Structural Steel Core, which was section R10.16.8 in ACI

318-05, used to state:

Concrete that is laterally confined by tie bars is likely

to be rather thin along at least one face of a steel core

section. Therefore, complete interaction between the

core, the concrete, and any longitudinal reinforcement

should not be assumed. Concrete will probably separate

from smooth faces of the steel core. To maintain the

concrete around the structural steel core, it is reason-

able to require more lateral ties than needed for ordi-

nary reinforced concrete columns. Because of probable

separation at high strains between the steel core and the

concrete, longitudinal bars will be ineffective in stiffen-

ing cross sections even though they would be useful in

sustaining compression forces.

This text has now been replaced with, Research hasshown that the required amount of tie reinforcement

around the structural steel core is sufficient for the longi-

tudinal steel bars to be included in the flexural stiffness of

the composite column.9

Chapter 11: Shearand Torsion

The revisions to achieve a consistent treatment of light-

weight concrete throughout ACI 318 (see discussion

of section 8.6 in Significant Changes to ACI 318-08

Relative to Precast/Prestressed Concrete: Part 110) have

led to the deletion of section 11.2 of ACI 318-05. The

revisions to ACI 318 also affect several of the equations

in chapter 11. Those equations are found in sections 11.2,

Shear Strength Provided by Concrete for Nonprestressed

Members; 11.3, Shear Strength Provided by Concrete

for Prestressed Members; 11.5.1, Threshold Torsion;

11.5.2, Calculation of Factored Torsional Moment; 11.9,

Provisions for Walls; and 11.11, Provisions for Slabs

and Footings.

In addition, in section 11.6.4.3 (11.6 is the section on

shear friction), = 0.85 for sand-lightweight concrete waschanged to Otherwise, shall be determined based onvolumetric proportions of lightweight and normalweight

aggregates as specified in [section] 8.6.1, but shall not

exceed 0.85. Although the equations in the sections noted

previously have different appearances, there have not been

any significant changes related to the shear strength of

structural members made of lightweight concrete.

Significant changes were made to the list of members in sec-

tion 11.4.6.1 for which minimum shear reinforcement is not

required where Vu exceeds 0.5Vc. Solid slabs, footings, andjoists are excluded from the minimum shear-reinforcement

Figure 1. Stud rails are used as slab shear reinforcement. Photo courtesy of Decon U.S.A. Inc.


23/58


lines of headed shear stud reinforcement.

Both the amount of shear assigned to the concrete Vc

and

the nominal shear strength Vn

= Vc

+ Vsare permitted to be

larger for headed stud assemblies than for other forms of

slab or footing shear reinforcement at 3 fc' b

odand

8 fc

' bod, respectively. Section 11.11.5.1 clarifies that in

the calculation ofVd=A

vf

yd/s,A

vis equal to the cross-sec-

tional area of all the shear reinforcement on one peripheralline that is approximately parallel to the perimeter of the

column section, where s is the spacing of the peripheral

lines of headed shear stud reinforcement.

Commentary section R11.11.5.1 clarifies that when there

is unbalanced moment transfer, the design must be based

on stresses. The maximum shear stress due to a combina-

tion ofVu

and the fraction of unbalanced moment vM

u

should not exceed vn, where v

nis taken as the sum of

3 fc

' andAvf

yt/(b

os).

The specified spacings between peripheral lines of shearreinforcement [Fig. 2] are justified by experiments.18

Commentary section R11.11.5.2 cautions that the clear

spacing between the heads of the studs should be adequate

to permit placing of the flexural reinforcement.

Chapter 12: Developmentand Splices ofReinforcement

A new section 12.1.3 was added. The section specifi-

cally calls designers attention to the structural-integrity

requirements in section 7.13. There was concern within

ACI Committee 318 that many designers were simply not

aware of these requirements, though they have existed

since the 1989 edition of ACI 318.

In all of the equations for development length of deformed

bars and deformed wire in tension and compression, in

sections 12.2.2 and 12.2.3, respectively, the lightweight-

aggregate factor was moved from the numerator to thedenominator. At the same time, in section 12.2.4(d), =1.3 was replaced by shall not exceed 0.75 unlessf

ctis

specified (see [section] 8.6.1). All of this is consistent

with the definition of in section 8.6 and is explainedclearly in commentary section R12.2.4.

Before ACI 318-08, Eq. (12-2) for Ktr

included the yield

strength of the transverse reinforcementfyt. The current ex-

pression assumes thatfyt

= 60 ksi (414 MPa) and includes

only the area and the spacing of the transverse reinforce-

ment and the number of bars being developed or lap

spliced. This is because tests have shown that transverse

reinforcement rarely yields during bond failure.

By far the most significant change in chapter 12 is theintroduction of section 12.6, Development of Headed and

Mechanically Anchored Deformed Bars in Tension. The

requirement because there is a possibility of load sharing

between weak and strong areas. Section 11.4.6.1, under

item (a), has now clarified that the slabs must be solid. Based

on experimental evidence,11 a new limit on the depth of hol-

low-core units was established in item (b) of section 11.4.6.1.

Research has shown that deep, lightly reinforced one-way

slabs and beams, particularly if constructed with high-

strength concrete, or concrete with a small coarse aggre-gate size, may fail at shear demands less than V

ccomputed

using Eq. (11-3) especially when subjected to concentrated

loads.1214 Because of this, the exclusion for certain beam

types in 11.4.6.1(e) is restricted to cases in which the total

depth h does not exceed 24 in.

Commentary section R11.4.6.1 further advises that for

beams wheref

c' is greater than 7000 psi, consideration

should be given to providing minimum shear reinforcement

when h is greater than 18 in. and Vu

is greater than 0.5Vc.

The new exception in item (f) in section 11.4.6.1 provides

a design alternative to the use of shear reinforcement, asdefined in section 11.4.1.1, for members with longitudinal

flexural reinforcement in whichf

c' does not exceed 6000

psi, h is not greater than 24 in., and Vu

does not exceed

2 fc' b

wd. Fiber-reinforced concrete beams with hooked

or crimpled steel fibers in dosages greater than or equal to

100 lb/yd3 (59 kg/m3) have been shown through laborato-

ry tests to exhibit shear strengths larger than 3.5 fc' b

wd.15

Commentary section R11.4.6.1(f) points out that the use

of steel fibers as shear reinforcement is not recommended

when corrosion of fiber reinforcement is of concern.

In section 11.6.5, the upper limit on the nominal shear-fric-

tion strength Vn

was significantly increased for both mono-

lithically placed concrete and concrete placed against inten-

tionally hardened concrete. Commentary section R11.6.5

points out that the increase is justified in view of test data.16,17

Section 11.6.5 now clarifies that if a lower-strength concrete

is cast against a higher-strength concrete, the value off

c'

used to evaluate Vn

must be thef

c' for the lower-strength con-

crete. The increase in the upper limit on the nominal shear-

friction strength is also reflected in section 11.8.3.2.1 (part of

section 11.8, Provisions for Brackets and Corbels).

One of the most significant changes in chapter 11 is the

addition of code requirements to permit the use of headed

stud assemblies as shear reinforcement in slabs and foot-

ings (section 11.11.5). Using shear stud assemblies, as

shear reinforcement in slabs and footings, requires specify-

ing the stud shank diameter, the spacing of the studs, and

the height of the assemblies for the particular applications

(Fig. 1). Tests18 have shown that vertical studs mechani-

cally anchored as close as possible to the top and bottom of

slabs are effective in resisting punching shear. . . . Com-

pared with a leg of a stirrup having bends at the ends, a stud

head exhibits smaller slip, and thus results in smaller shearcrack widths. The improved performance results in larger

limits for shear strength and spacing between peripheral


24/58


bearing strength provisions of [section] 10.4.19,20 Appendix

D contains provisions for headed anchors related to the

individual failure modes of concrete breakout, side-face

blowout, and pullout, all of which were considered in the

formulation of [section] 12.6.2. The restriction that the

concrete must be normalweight, the maximum bar size of

no. 11, and the upper limit of 60,000 psi onfy

are based on

test data.21

Commentary Fig. R12.6(a) shows the length of headed

deformed bar ldt

measured from the critical section to the

bearing face of the head, which is given in section 12.6.2

for developing headed deformed bars.

use of headed deformed bars is attractive as an alternative

to hooked bar anchorages in regions where reinforcement

is heavily congested.

The term development, as used in section 12.6, indicates

that the force in the bar is transferred to the concrete

through a combination of a bearing force at the head and

bond forces along the bar. The term anchorage, as used in

section 12.6, indicates that the force in a bar is transferredto the concrete through bearing of the head alone.

Commentary section R12.6 states that the provisions for

headed deformed bars were written with due consideration

of the provisions for anchorage in Appendix D and the

Figure 2. Typical arrangements are shown for headed shear-stud reinforcement and critical sections. Reproduced with permission from ACI 318-08 Figure R11.11.5.


25/58


from the face of the column that is equal to the thickness

of the projection below the slab soffit.

In section 13.3, what used to be called special reinforce-

mentis now called corner reinforcement. Corner reinforce-

ment is now required at exterior corners of slabs support-

ed by edge walls or where one or more edge beams have a

value off

greater than 1.0.

New, useful commentary is provided in section R13.3.6.

In section 13.3.8.5, column core was replaced by region

bounded by the longitudinal reinforcement of the column.

Section 13.5.3.3 on transfer of unbalanced moments to col-

umns was editorially rewritten for clarity. Two substantive

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