1、ACI 408R-03 became effective September 24, 2003.Copyright 2003, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by anymeans, including the making of copies by any photo process, or by electronic ormechanical device, printed, written, or oral, o
2、r recording for sound or visual reproductionor for use in any knowledge or retrieval system or device, unless permission in writingis obtained from the copyright proprietors.1ACI Committee Reports, Guides, Manuals, and Commentariesare intended for guidance in planning, designing, executing,and inspe
3、cting construction. This document is intended for theuse of individuals who are competent to evaluate thesignificance and limitations of its content and recommendationsand who will accept responsibility for the application of thematerial it contains. The American Concrete Institute disclaimsany and
4、all responsibility for the stated principles. The Instituteshall not be liable for any loss or damage arising therefrom.Reference to this document shall not be made in contractdocuments. If items found in this document are desired by theArchitect/Engineer to be a part of the contract documents, they
5、shall be restated in mandatory language for incorporation bythe Architect/Engineer.Bond and Development of StraightReinforcing Bars in TensionReported by ACI Committee 408ACI 408R-03(Reapproved 2012)The performance of reinforced concrete structures depends on adequatebond strength between concrete a
6、nd reinforcing steel. This report describesbond and development of straight reinforcing bars under tensile load. Bondbehavior and the factors affecting bond are discussed, including concretecover and bar spacing, bar size, transverse reinforcement, bar geometry,concrete properties, steel stress and
7、yield strength, bar surface condition,bar casting position, development and splice length, distance betweenspliced bars, and concrete consolidation. Descriptive equations and designprovisions for development and splice strength are presented and com-pared using a large database of test results. The
8、contents of the databaseare summarized, and a protocol for bond tests is presented.Test data and reliability analyses demonstrate that, for compressivestrengths up to at least 16,000 psi (110 MPa), the contribution of concretestrength to bond is best represented by the compressive strength to the 1/
9、4power, while the contribution of concrete to the added bond strengthprovided by transverse reinforcement is best represented by compressivestrength to a power between 3/4 and 1.0. The lower value is used inproposed design equations. These values are in contrast with the squareroot of compressive st
10、rength, which normally is used in both descriptiveand design expressions. Provisions for bond in ACI 318-02 are shown to beunconservative in some instances; specifically, the 0.8 bar size factor forsmaller bars should not be used and a -factor for bond is needed toprovide a consistent level of relia
11、bility against bond failure. Descriptiveequations and design procedures developed by Committee 408 that provideimproved levels of reliability, safety, and economy are presented. The ACICommittee 408 design procedures do not require the use of the 1.3 factorfor Class B splices that is required by ACI
12、 318.Keywords: anchorage; bond; concrete; deformed reinforcement; develop-ment length; reinforced concrete; reinforcement; relative rib area; splice;stirrup; tie.CONTENTSPreface, p. 408R-2Chapter 1Bond behavior, p. 408R-31.1Bond forcesbackground1.2Test specimens1.3Details of bond response1.4Notation
13、John H. Allen Rolf Eligehausen Roberto T. Leon*Stavroula J. PantazopoulouAtorod Azizinamini Fernando E. Fagundo LeRoy A. LutzMax L. PorterGyorgy L. Balazs Anthony L. FelderSteven L. McCabe Julio A. RamirezJoAnn Browning*Robert J. FroschJohn F. McDermott John F. SilvaJames V. Cox Bilal S. Hamad*Denis
14、 Mitchell Jun Zuo*Richard A. DeVries*Neil M. Hawkins*Members of the subcommittee who prepared this report.Members of the editorial subcommittee.David Darwin*ChairAdolfo B. Matamoros*Secretary408R-2 ACI COMMITTEE REPORTChapter 2Factors affecting bond, p. 408R-92.1Structural characteristics2.2Bar prop
15、erties2.3Concrete properties2.4SummaryChapter 3Descriptive equations, p. 408R-253.1Orangun, Jirsa, and Breen3.2Darwin et al.3.3Zuo and Darwin3.4Esfahani and Rangan3.5ACI Committee 4083.6ComparisonsChapter 4Design provisions, p. 408R-294.1ACI 3184.2ACI 408.34.3Recommendations by ACI Committee 4084.4C
16、EB-FIP Model Code4.5Structural reliability and comparison of designexpressionsChapter 5Database, p. 408R-385.1Bar stresses5.2DatabaseChapter 6Test protocol, p. 408R-396.1Reported properties of reinforcement6.2Concrete properties6.3Specimen properties6.4Details of test6.5Analysis method6.6Relative ri
17、b areaChapter 7References, p. 408R-417.1Referenced standards and reports7.2Cited referencesAppendix ASI equations, p. 408R-47PREFACEThe bond between reinforcing bars and concrete has beenacknowledged as a key to the proper performance of reinforcedconcrete structures for well over 100 years (Hyatt 1
18、877).Much research has been performed during the interveningyears, providing an ever-improving understanding of thisaspect of reinforced concrete behavior. ACI Committee 408issued its first report on the subject in 1966. The reportemphasized key aspects of bond that are now well under-stood by the d
19、esign community but that, at the time, repre-sented conceptually new ways of looking at bond strength.The report emphasized the importance of splitting cracks ingoverning bond strength and the fact that bond forces did notvary monotonically and could even change direction inregions subjected to cons
20、tant or smoothly varying moment.Committee 408 followed up in 1979 with suggested provi-sions for development, splice, and hook design (ACI408.1R-79), in 1992 with a state-of-the-art report on bondunder cyclic loads (ACI 408.2R-92), and in 2001 with designprovisions for splice and development design
21、for high relativerib area bars (bars with improved bond characteristics) (ACI408.3-01). This report represents the next in that line,emphasizing bond behavior and design of straight reinforcingbars that are placed in tension.For many years, bond strength was represented in terms ofthe shear stress a
22、t the interface between the reinforcing barand the concrete, effectively treating bond as a materialproperty. It is now clear that bond, anchorage, development,and splice strength are structural properties, dependent notonly on the materials but also on the geometry of the reinforcingbar and the str
23、uctural member itself. The knowledge base onbond remains primarily empirical, as do the descriptiveequations and design provisions. An understanding of theempirical behavior, however, is critical to the eventualdevelopment of rational analysis and design techniques.Test results for bond specimens in
24、variably exhibit largescatter. This scatter increases as the test results fromdifferent laboratories are compared. Research since 1990indicates that much of the scatter is the result of differencesin concrete material properties, such as fracture energy andreinforcing bar geometry, factors not norma
25、lly considered indesign. This report provides a summary of the current stateof knowledge of the factors affecting the tensile bondstrength of straight reinforcing bars, as well as realisticdescriptions of development and splice strength as a functionof these factors. The report covers bond under the
26、 loadingconditions that are addressed in Chapter 12 of ACI 318;dynamic, blast, and seismic loading are not covered.Chapter 1 provides an overview of bond behavior,including bond forces, test specimens, and details of bondresponse. Chapter 2 covers the factors that affect bond,discussing the impact o
27、f structural characteristics as well asbar and concrete properties. The chapter provides insight notonly into aspects that are normally considered in structuraldesign, but into a broad range of factors that controlanchorage, development, and splice strength in reinforcedconcrete members. Chapter 3 p
28、resents a number of widelycited descriptive equations for development and splicestrength, including expressions recently developed by ACICommittee 408. The expressions are compared for accuracyusing the test results in the ACI Committee 408 database.Chapter 4 summarizes the design provisions in ACI
29、318,ACI 408.3, the 1990 CEB-FIP Model Code, as well as designprocedures recently developed by Committee 408. Thedesign procedures are compared for accuracy, reliability,safety, and economy using the ACI Committee 408 database.The observations presented in Chapters 3 and 4 demonstratethat fc1/4 provi
30、des a realistic representation of the contributionof concrete strength to bond for values up to at least16,000 psi (110 MPa), while fc3/4 does the same for theeffect of concrete strength on the increase in bond strengthprovided by transverse reinforcement. This is in contrast to, which is used in mo
31、st design provisions. The comparisonsin Chapter 4 also demonstrate the need to modify the designprovisions in ACI 318 by removing the bar size g factor of0.8 for small bars and addressing the negative impact onbond reliability of changing the load factors while maintainingfcBOND AND DEVELOPMENT OF S
32、TRAIGHT REINFORCING BARS IN TENSION 408R-3the strength reduction factor for tension in the transitionfrom ACI 318-99 to ACI 318-02. Design proceduresrecommended by ACI Committee 408 that provide bothadditional safety and economy are presented. Chapter 5describes the ACI Committee 408 database, while
33、 Chapter 6presents a recommended protocol for bond tests. Theexpressions within the body of the report are presented ininch-pound units. Expressions in SI units are presented inAppendix A.A few words are appropriate with respect to terminology.The term bond force represents the force that tends to m
34、ovea reinforcing bar parallel to its length with respect to thesurrounding concrete. Bond strength represents themaximum bond force that may be sustained by a bar. Theterms development strength and splice strength are,respectively, the bond strengths of bars that are not splicedwith other bars and o
35、f bars that are spliced. The termsanchored length, bonded length, and embedded length areused interchangeably to represent the length of a bar overwhich bond force acts; in most cases, this is the distancebetween the point of maximum force in the bar and the endof the bar. Bonded length may refer to
36、 the length of a lapsplice. Developed length and development length are used inter-changeably to represent the bonded length of a bar that is notspliced with another bar, while spliced length and splice lengthare used to represent the bonded length of bars that are lappedspliced. When used in design
37、, development length and splicelength are understood to mean the “length of embeddedreinforcement required to develop the design strength ofreinforcement at a critical section,” as defined in ACI 318.CHAPTER 1BOND BEHAVIORIn reinforced concrete construction, efficient and reliableforce transfer betw
38、een reinforcement and concrete isrequired for optimal design. The transfer of forces from thereinforcement to the surrounding concrete occurs for adeformed bar (Fig. 1.1) by: Chemical adhesion between the bar and the concrete; Frictional forces arising from the roughness of the inter-face, forces tr
39、ansverse to the bar surface, and relative slipbetween the bar and the surrounding concrete; and Mechanical anchorage or bearing of the ribs against theconcrete surface.After initial slip of the bar, most of the force is transferredby bearing. Friction, however, especially between theconcrete and the
40、 bar deformations (ribs) plays a significantrole in force transfer, as demonstrated by epoxy coatings,which lower the coefficient of friction and result in lowerbond capacities. Friction also plays an important role forplain bars (that is, with no deformations), with slip-inducedfriction resulting f
41、rom transverse stresses at the bar surfacecaused by small variations in bar shape and minor, thoughsignificant, surface roughness. Plain bars with suitably lowallowable bond stresses were used for many years forreinforced concrete in North America and are still used insome regions of the world.When
42、a deformed bar moves with respect to thesurrounding concrete, surface adhesion is lost, while bearingforces on the ribs and friction forces on the ribs and barrel ofthe bar are mobilized. The compressive bearing forces on theribs increase the value of the friction forces. As slipincreases, friction
43、on the barrel of the reinforcing bar isreduced, leaving the forces at the contact faces between theribs and the surrounding concrete as the principal mechanism offorce transfer. The forces on the bar surface are balanced bycompressive and shear stresses on the concrete contactsurfaces, which are res
44、olved into tensile stresses that canresult in cracking in planes that are both perpendicular andparallel to the reinforcement, as shown in Fig. 1.2(a) and1.2(b). The cracks shown in Fig. 1.2(a), known as Goto(1971) cracks, can result in the formation of a conical failuresurface for bars that project
45、 from concrete and are placed intension. They otherwise play only a minor role in theanchorage and development of reinforcement. The trans-verse cracks shown in Fig. 1.2(b) form if the concrete coveror the spacing between bars is sufficiently small, leading tosplitting cracks, as shown in Fig. 1.2(c
46、). If the concretecover, bar spacing, or transverse reinforcement is sufficientto prevent or delay a splitting failure, the system will fail byshearing along a surface at the top of the ribs around the bars,resulting in a “pullout” failure, as shown in Fig. 1.2(d). It iscommon, for both splitting an
47、d pullout failures, to observecrushed concrete in a region adjacent to the bearing surfacesof some of the deformations. If anchorage to the concrete isadequate, the stress in the reinforcement may become highenough to yield and even strain harden the bar. Tests havedemonstrated that bond failures ca
48、n occur at bar stresses upto the tensile strength of the steel.From these simple qualitative descriptions, it is possible tosay that bond resistance is governed by: The mechanical properties of the concrete (associatedwith tensile and bearing strength); The volume of the concrete around the bars (re
49、lated toconcrete cover and bar spacing parameters); The presence of confinement in the form of transversereinforcement, which can delay and control crackpropagation; The surface condition of the bar; and The geometry of the bar (deformation height, spacing,width, and face angle).A useful parameter describing bar geometry is the so-called relative rib area Rr, illustrated in Fig. 1.3, which is theratio of the bearing area of the bar deformations to theFig. 1.1Bond force transfer mechanisms.408R-4 ACI COMMITTEE REPORTshearing area betwee
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