1、ACI 544.4R-88(Reapproved 2009)Design Considerations for Steel Fiber Reinforced ConcreteReported by ACI Committee 544Shuaib H. AhmadCharles H. Henager, Sr.*M. ArockiasamyP. N. BalaguruClaire BallHiram P. Ball, Jr.Gordon B. Batson*Arnon BenturRobert J. Craig*$Marvin E. Criswell*Sidney FreedmanRichard
2、E. GalerMelvyn A. GalinatVellore GopalaratnamAntonio Jose GuerraLloyd E. HackmanM. Nadim HassounSurendra P. ShahChairmanD. V. ReddyGeorge C. HoffNorman M. HydukRoop L. JindalColin D. JohnstonCharles W. JosifekDavid R. LankardBrij M. MagoHenry N. Marsh, Jr.*Assir MelamedNicholas C. MitchellHenry J. M
3、olloyD. R. MorganA. E. NaamanStanley L. Paul+Seth L. PearlmanV. RamakrishnanJames I. DanielSecretaryThe present state of development of design practices for fiber rein-forced concrete and mortar using steel fibers is reviewed. Mechanicalproperties are discussed, design methods are presented, and typ
4、icalapplications are listed.Keywords: beams (supports;) cavitation; compressive strength; concrete slabs;creep properties; fatigue (materials) ; fiber reinforced concretes; fibers; flexuralstrength; freeze-thaw durability; metal fibers; mortars (material); structural de-sign.CONTENTSChapter 1 -Intro
5、duction, p. 544.4R-1Chapter 2-Mechanical properties used indesign, p. 544.4R-22.1 -General2.2-Compression2.3-Direct tension2.4-Flexural strength2.5-Flexural toughness2.6-Shrinkage and creep2.7-Freeze-thaw resistance2.8-Abrasion/cavitation/erosion resistance2.9-Performance under dynamic loadingACI Co
6、mmittee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in designing, plan-ning, executing, or inspecting construction and in preparingspecifications. Reference to these documents shall not be madein the Project Documents. If items found in these documentsare desired t
7、o be part of the Project Documents they shouldbe phrased in mandatory language and incorporated into theProject Documents.Ralph C. RobinsonE. K. Schrader*Morris Schupack*Shah SomayajiJ. D. SpeakmanR. N. SwamyPeter C. TatnallB. L. TilsenGeorge J. VentaGary L. VondranMethi WecharatanaGilbert R. Willia
8、mson+C. K. WilsonRonald E. WitthohnGeorge Y. WuRobert C. ZellersRonald F. ZolloChapter 3-Design applications, p. 544.4R-83.l-Slabs3.2-Flexure in beams3.3-Shear in beams3.4-Shear in slabs3.5-Shotcrete3.6-Cavitation erosion3.7-Additional applicationsChapter 4-References, p. 544.4R-144.l-Specified and/
9、or recommended references4.2-Cited references4.3-Uncited referencesChapter 5-Notation, p. 544.4R-17CHAPTER 1-INTRODUCTIONSteel fiber reinforced concrete (SFRC) and mortarmade with hydraulic cements and containing fine orfine and coarse aggregates along with discontinuousdiscrete steel fibers are con
10、sidered in this report. Thesematerials are routinely used in only a few types of ap-*Members of the subcommittee that prepared the report.+Co-chairmen of the subcommittee that prepared the report.Deceased.Copyright 0 1988, American Concrete Institute.All rights reserved including rights of reproduct
11、ion and use in any form orby any means, including the making of copies by any photo process, or by anyelectronic or mechanical device, printed, written, or oral, or recording for soundor visual reproduction or for use in any knowledge or retrieval system or de-vice, unless permission in writing is o
12、btained from the copyright proprietors.544.4R-1544.4R-2MANUAL OF CONCRETE PRACTICEplications at present (1988), but ACI Committee 544believes that many other applications will be developedonce engineers become aware of the beneficial proper-ties of the material and have access to appropriate de-sign
13、 procedures. The contents of this report reflect theexperience of the committee with design proceduresnow in use.The concrete used in the mixture is of a usual type,although the proportions should be varied to obtaingood workability and take full advantage of the fibers.This may require limiting the
14、 aggregate size, optimizingthe gradation, increasing the cement content, and per-haps adding fly ash or other admixtures to improveworkability. The fibers may take many shapes. Theircross sections include circular, rectangular, half-round,and irregular or varying cross sections. They may bestraight
15、or bent, and come in various lengths. A con-venient numerical parameter called the aspect ratio isused to describe the geometry. This ratio is the fiberlength divided by the diameter. If the cross section isnot round, then the diameter of a circular section withthe same area is used.The designer may
16、 best view fiber reinforced concreteas a concrete with increased strain capacity, impact re-sistance, energy absorption, and tensile strength. How-ever, the increase in these properties will vary fromsubstantial to nil depending on the quantity and type offibers used; in addition, the properties wil
17、l not increaseat the same rate as fibers are added.Several approaches to designing members with steelfiber reinforced concrete (SFRC) are available that arebased on conventional design methods supplemented byspecial procedures for the fiber contribution. Thesemethods generally modify the internal fo
18、rces in themember to account for the additional tension from thefibers. When supported by full-scale test data, theseapproaches can provide satisfactory designs. The ma-jor differences in the proposed methods are in the de-termination of the magnitude of the tensile stress in-crease due to the fiber
19、s and in the manner in which thetotal force is calculated. Other approaches that havebeen used are often empirical, and they may apply onlyin certain cases where limited supporting test data havebeen obtained. They should be used with caution innew applications, only after adequate investigation.Gen
20、erally, for structural applications, steel fibersshould be used in a role supplementary to reinforcingbars. Steel fibers can reliably inhibit cracking and im-prove resistance to material deterioration as a result offatigue, impact, and shrinkage, or thermal stresses. Aconservative but justifiable ap
21、proach in structuralmembers where flexural or tensile loads occur, such asin beams, columns, or elevated slabs (i.e., roofs, floors,or slabs not on grade), is that reinforcing bars must beused to support the total tensile load. This is becausethe variability of fiber distribution may be such thatlow
22、 fiber content in critical areas could lead to unac-ceptable reduction in strength.In applications where the presence of continuous re-inforcement is not essential to the safety and integrityof the structure, e.g., floors on grade, pavements,overlays, and shotcrete linings, the improvements inflexur
23、al strength, impact resistance, and fatigue perfor-mance associated with the fibers can be used to reducesection thickness, improve performance, or both.ACI 318 does not provide for use of the additionaltensile strength of the concrete in building design and,therefore, the design of reinforcement mu
24、st follow theusual procedure. Other applications provide more free-dom to take full advantage of the improved propertiesof SFRC.There are some applications where steel fibers havebeen used without bars to carry flexural loads. Thesehave been short-span elevated slabs, e.g., a parking ga-rage at Heat
25、hrow Airport with slabs 3 ft-6 in. (1.07 m)square by 2l/2 in. (10 cm) thick, supported on four sides(Anonymous 1971). In such cases, the reliability of themembers should be demonstrated by full-scale loadtests, and the fabrication should employ rigid qualitycontrol.Some full-scale tests have shown t
26、hat steel fibers areeffective in supplementing or replacing the stirrups inbeams (Williamson 1978; Craig 1983; Sharma 1986).Although it is not an accepted practice at present, otherfull-scale tests have shown that steel fibers in combina-tion with reinforcing bars can increase the moment ca-pacity o
27、f reinforced concrete beams (Henager andDoherty 1976; Henage r 1977a).Steel fibers can also provide an adequate internal re-straining mechanism when shrinkage-compensating ce-ments are used, so that the concrete system will per-form its crack control function even when restraintfrom conventional rei
28、nforcement is not provided. Fi-bers and shrinkage-compensating cements are not onlycompatible, but complement each other when used incombination (Paul et al. 1981). Guidance concerningshrinkage-compensating cement is available in ACI223.1R.ASTM A 820 covers steel fibers for use in fiber rein-forced
29、concrete. The design procedures discussed in thisreport are based on fibers meeting that specification.Additional sources of information on design areavailable in a selected bibliography prepared by Hoff(1976-l 982), in ACI publications SP-44 (1974) an d SP-81 (1984), in proceedings of the 1985 U.S.
30、-Sweden jointseminar edited by Shah and Skarendah l (1986), and therecent ACI publication SP-105 edited by Shah an d Bat-son (1987).For guidance regarding proportioning, mixing, plac-ing, finishing, and testing for workability of steel fiberreinforced concrete, the designer should refer t o ACI544.3
31、R.CHAPTER 2-MECHANICAL PROPERTIES USEDIN DESIGN2.1-GeneralThe mechanical properties of steel fiber reinforcedconcrete are influenced by the type of fiber; length-to-diameter ratio (aspect ratio); the amount of fiber; theDESIGN OF STEEL FIBER REINFORCED CONCRETE544.4R-3strength of the matrix; the siz
32、e, shape, and method ofpreparation of the specimen; and the size of the aggre-gate. For this reason, mixtures proposed for use in de-sign should be tested, preferably in specimens repre-senting the end use, to verify the property values as-sumed for design.SFRC mixtures that can be mixed and placed
33、withconventional equipment and procedures use from 0.5 to1.5 volume percent* fibers. However, higher percent-ages of fibers (from 2 to 10 volume percent) have beenused with special fiber addition techniques and place-ment procedures (Lankard 1984). Most properties givenin this chapter are for the lo
34、wer fiber percentage range.Some properties, however, are given for the higher fi-ber percentage mixtures for information in applicationswhere the additional strength or toughness may justifythe special techniques required.Fibers influence the mechanical properties of con-crete and mortar in all fail
35、ure modes (Gopalaratnamand Shah 1987a), especially those that induce fatigueand tensile stress, e.g.,direct tension, bending, impact,and shear. The strengthening mechanism of the fibersinvolves transfer of stress from the matrix to the fiberby interfacial shear, or by interlock between the fiberand
36、matrix if the fiber surface is deformed. Stress isthus shared by the fiber and matrix in tension until thematrix cracks, and then the total stress is progressivelytransferred to the fibers.Aside from the matrix itself, the most important var-iables governing the properties of steel fiber reinforcedc
37、oncrete are the fiber efficiency and the fiber content(percentage of fiber by volume or weight and totalnumber of fibers). Fiber efficiency is controlled by theresistance of the fibers to pullout, which in turn de-pends on the bond strength at the fiber-matrix inter-face. For fibers with uniform sec
38、tion, pullout resis-tance increases with an increase in fiber length; thelonger the fiber the greater its effect in improving theproperties of the composite.Also, since pullout resistance is proportional to in-terfacial surface area, nonround fiber cross sections andsmaller diameter round fibers off
39、er more pullout resis-tance per unit volume than larger diameter round fi-bers because they have more surface area per unit vol-ume. Thus, the greater the interfacial surface area (orthe smaller the diameter), the more effectively the fi-bers bond. Therefore, for a given fiber length, a highratio of
40、 length to diameter (aspect ratio) is associatedwith high fiber efficiency. On this basis, it would ap-pear that the fibers should have an aspect ratio highenough to insure that their tensile strength is ap-proached as the composite fails.Unfortunately, this is not practical. Many investiga-tions ha
41、ve shown that use of fibers with an aspect ratiogreater than 100 usually causes inadequate workabilityof the concrete mixture, non-uniform fiber distribu-tion, or both if the conventional mixing techniques areused (Lankard 1972). Most mixtures used in practice* Percent by volume of the total concret
42、e mixture.(1 psi = 6.695 kPa)- Straight FibersHooked Fibers6000- Enlarged-End FibersCompressiveStress,4000psiCompressive Strain, millionthsFig. 2.1-Stress-strain curves for steel fiber reinforcedconcrete in compression, 3/s -in. (9.5-mm) aggregatemixtures (Shah 1978)employ fibers with an aspect rati
43、o less than 100, andfailure of the composite, therefore, is due primarily tofiber pullout. However, increased resistance to pulloutwithout increasing the aspect ratio is achieved in fiberswith deformed surfaces or end anchorage; failure mayinvolve fracture of some of the fibers, but it is still usu-
44、ally governed by pullout.An advantage of the pullout type of failure is that itis gradual and ductile compared with the more rapidand possibly catastrophic failure that may occur if thefibers break in tension. Generally, the more ductile thesteel fibers, the more ductile and gradual the failure ofth
45、e concrete. Shah an d Rangan (1970) have shown thatthe ductility provided by steel fibers in flexure was en-hanced when the high-strength fibers were annealed (aheating process that softens the metal, making it lessbrittle).An understanding of the mechanical properties ofSFRC and their variation wit
46、h fiber type and amount isan important aspect of successful design. These prop-erties are discussed in the remaining sections of thischapter.2.2-CompressionThe effect of steel fibers on the compressive strengthof concrete is variable. Documented increases for con-crete (as opposed to mortar) range f
47、rom negligible inmost cases to 23 percent for concrete containing 2 per-cent by volume of fiber with e/d = 100, %-in. (19-mm)maximum-size aggregate, and tested with 6 x 12 in. (150x 300 mm) cylinders (Williamson 1974). For mortarmixtures, the reported increase in compressive strengthranges from negl
48、igible (Williamson 1974) to sligh t (Fa-nella and Naaman 1985).Typical stress-strain curves for steel fiber reinforcedconcrete in compression are shown in Fig. 2.1 (Shah etal. 1978). Curves for steel fiber reinforced mortar areshown in Fig. 2.2 and 2. 3 (Fanella and Naaman 1985).In these curves, a s
49、ubstantial increase in the strain atthe peak stress can be noted, and the slope of the de-scending portion is less steep than that of control spec-imens without fibers. This is indicative of substantiallyhigher toughness, where toughness is a measure ofability to absorb energy during deformation, and it canbe estimated from the area under the stress-straincurves or load-deformation curves. The improvedtoughness in compression imparted by fibers is useful in544.4R-4MANUAL OF CONCRETE PRACTICE10000rSmooth Steel FibersCompressiStress,psiR/df= 83( 1 psi16.895 kPa )Tensile 300Stress,psi20010000 50
