1、ACI 215R-74(Revised 1992/Reapproved 1997)Considerations for Design of Concrete StructuresSubjected to Fatigue LoadingReported by ACI Committee 215John M. HansonChairmanPaul W. AbelesJohn D. AntrimEarl I. Brown, IIJohn N. CernicaCarl E. Ekberg, Jr.*Neil M. HawkinsHubert K. HiisdorfCraig A. BallingerS
2、ecretaryCornie L. HulsbosDon A. LingerEdmund P. Segner, Jr.Surendra P. ShahLaurence E. SvabWilliam J. Venuti* Chairman of ACI Committee 215 at the time preparation of this report was begun.Committee members voting on the 1992 revisions:David W. JohnstonChairmanM. ArockiasamyP.N. BalaguruMark D. Bowm
3、anJohn N. CernicaLuis F. EstenssoroJohn M. HansonNeil M. HawkinsThomas T.C. HsuCraig A. BallingerSecretaryTi HuangLambit KaldMichael E. KregerBasile G. RabbatRaymond S. RollingsSurendra P. ShahLuc R. TaerweWilliam J. VenutiThis report presents information that is intended to aid the practicing engin
4、eerconfronted with consideration of repeated loading on concrete structures. Investi-1.1-Objective and scopegations of the fatigue properties of component materiak+oncrete, reinforcingl.2-Definitionsbars, welded reinforcing mats, and prestressing tendo ns-are reviewed. Applica- 1.3-Standards cited i
5、n this reporttion of this information to predicting the fatigue life of beams and pavements isdiscussed. A significant change in Section 3.1.2 of the 1992 revisions is theChapter 2-Fatigue properties of component materials, pg.increase in the allowable stress range for prestressing steel from 0.04 f
6、pu to215R-20.06 I;,.2.1-Plain concreteKeywords: beams (supports); compressive strength; concrete pavements: cracking (frac-2.2-Reinforcing barsturing); dynamic loads; fatigue (materials); impact; loads (Forces); microcracking; plain 2.3-Welded wire fabric and bar matsconcrete; prestressed concrete;
7、prestressing steel; reinforcedconcrete: reinforcingsteels; 2.4-Prestressing tendonsspecifications; static loads: strains; stresses; structural design; tensile strength; weldedwire fabric; welding; yield strength.CONTENTSChapter 3-Fatigue of beams and pavements, pg. 215R-153.1-Beams3.2-PavementsChapt
8、er l-Introduction, pg. 215R-2ACI Committee 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 bemade in the Project Documents. If items fo
9、und in these doc-uments are desired to be part of the Project Documents theyshould be phrased in mandatory language and incorporatedinto the Project Documents.2 1 5R-1Notation, pg. 215R-19References, pg. 215R-19Appendix, pg. 215R-23ACI 215R-74 (Revised 1992) became effective Nov. 1, 1992.Copyright 0
10、 1992, 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 any electronic ormechanical device, printed or written or oral, or recording for sound or visual repro-duction or for
11、 use in any knowledge or retrieval system or device, unless permission inwriting is obtained from the copyright proprietors.215R-2 ACI COMMITTEE REPORTCHAPTER l-INTRODUCTIONIn recent years, considerable interest has developed in thefatigue strength of concrete members. There are several rea-sons for
12、 this interest. First, the widespread adoption of ulti-mate strength design procedures and the use of higherstrength materials require that structural concrete membersperform satisfactorily under high stress levels. Hence there isconcern about the effects of repeated loads on, for example,crane beam
13、s and bridge slabs.Second, new or different uses are being made of concretefatigue; however, this report does not specifically deal withthese types of loadings.1.3-Standards cited in this reportThe standards and specifications referred to in this docu-ment are listed below with their serial designat
14、ion, includingyear of adoption or revision. These standards are the latesteffort at the time this document was revised. Since some ofthe standards are revised frequently, although generally onlyin minor details, the user of this document may wish to checkdirectly with the committee if it is correct
15、to refer to themembers or systems, such as prestressed concrete railroad latest revision.ties and continuously reinforced concrete pavements. Theseuses of concrete demand a high performance product with an AC I 301-89assured fatigue strength.Third, there is new recognition of the effects of repeated
16、 ACI 318-89loading on a member, even if repeated loading does notcause a fatigue failure. Repeated loading may lead to inclined ASTM A 416-90cracking in prestressed beams at lower than expected loads,or repeated loading may cause cracking in component mater-ials of a member that alters the static lo
17、ad carrying char- ASTM A 421-90acteristics.l.l-Objective and scope ASTM A 615-90This report is intended to provide information that willserve as a guide for design for concrete structures subjectedto fatigue loading. ASTM 722-90However, this report does not contain the type of detaileddesign procedu
18、res sometimes found in guides.Chapter 2 presents information on the fatigue strength of AWS Dl.4-79concrete and reinforcing materials. This information has beenobtained from reviews of experimental investigations reportedin technical literature or from unpublished data made avail-able to the committ
19、ee. The principal aim has been to sum-marize information on factors influencing fatigue strengththat are of concern to practicing engineers.Chapter 3 considers the application of information onconcrete and reinforcing materials to beams and pavements.Provisions suitable for inclusion in a design spe
20、cification arerecommended.An Appendix to this report contains extracts from currentspecifications that are concerned with fatigue.1.2-DefinitionsIt is important to carefully distinguish between static,dynamic, fatigue, and impact loadings. Truly static loading, orsustained loading, remains constant
21、with time. Nevertheless,a load which increases slowly is often called static loading;the maximum load capacity under such conditions is referredto as static strength.Dynamic loading varies with time in any arbitrary manner.Fatigue and impact loadings are special cases of dynamicloading. A fatigue lo
22、ading consists of a sequence of loadrepetitions that may cause a fatigue failure in about 100 ormore cycles.Very high level repeated loadings due to earthquakes orother catastrophic events may cause failures in less than 100cycles. These failures are sometimes referred to as low-cycleSpecifications
23、for Structural Concrete forBuildingsBuilding Code Requirements for Rein-forced ConcreteStandard Specification for Uncoated SevenWire Stress Relieved Steel Strand for Pre-stressed ConcreteStandard Specification for Uncoated StressRelieved Steel Wire for Prestressed Con-creteStandard Specification for
24、 Deformed andPlain Billet Steel Bars for Concrete Rein-forcementStandard Specification for Uncoated HighStrength Steel Bar for Prestressing Con-creteStructuralWelding Code-Reinforcing SteelCHAPTER 2-FATIGUE PROPERTIESOF COMPONENT MATERIALSThe fatigue properties of concrete, reinforcing bars, andpres
25、tressing tendons are described in this section. Much ofthis information is presented in the form of diagrams and al-gebraic relationships that can be utilized for design. However,it is emphasized that this information is based on the resultsof tests conducted on different types of specimens subjecte
26、dto various loading conditions. Therefore, caution should beexercised in applying the information presented in this report.2.1-Plain concrete*2.1.1 General-Plain concrete, when subjected to repeatedloads, may exhibit excessive cracking and may eventually failafter a sufficient number of load repetit
27、ions, even if the maxi-mum load is less than the static strength of a similar speci-men. The fatigue strength of concrete is defined as a fractionof the static strength that it can support repeatedly for agiven number of cycles. Fatigue strength is influenced byrange of loading, rate of loading, ecc
28、entricity of loading, loadhistory, material properties, and environmental conditions.* Dr. Surendra P. Shahsection of the report.was the chairman of the subcommittee that prepared thisFATIGUE LOADING DESIGN CONSIDERATIONS 215R-31.0I- icGs thebottom of the bar was adjacent to the extreme tensile fibe
29、rsin the beam. The smoother zone, with the dull, rubbed ap-pearance, is the fatigue crack. The remaining zone of morejagged surface texture is the part that finally fractured intension after the growing fatigue crack weakened the bar. Itis noteworthy that the fatigue crack did not start from thebott
30、om of the bar. Rather it started along the side of the bar,at the base of one of the transverse lugs. This is a commoncharacteristic of most bar fatigue fractures.Quite a number of laboratory investigations of the fatiguestrength of reinforcing bars have bee n reyears from the United States,18-26Can
31、ada,!?orte d in recentand Japan.35-397;28 Europe,29-34In most of these investigations, the relation-ship between stress range, S, and fatigue life, N, was deter-mined by a series of repeated load tests on bars which wereeither embedded in concrete or tested in air.There is contradiction in the techn
32、ical literature as towhether a bar has the same fatigue strength when tested inair or embedded in a concrete beam. In an investigation31ofhot-rolled cold-twisted bars, it was found that bars embeddedin beams had a greater fatigue strength than when tested inair. However, in another investigation,29t
33、he opposite conclu-sion was reached. More recent Studies28,32indicate that thereshould be little difference in the fatigue strength of bars inair and embedded bars if the height and shape of the trans-verse lugs are adequate to provide good bond between thesteel and concrete.The influence of frictio
34、n between a reinforcing bar andconcrete in the vicinity of a crack has also been considered.32In laboratory tests, an increase in temperature is frequentlyobserved at the location where the fatigue failure occurs.However, rates of loading up to several thousand cycles perminute and temperatures up t
35、o several hundred degrees Care normally not considered to have a significant effect onfatigue strength.400In a statistical analysis41of an inves-tigation of reinforcing bars,266differences in fatigue strengthdue to rates of loading of 250 and 500 cycles per minute werenot significant.It is therefore
36、 believed that most of the data reported ininvestigations in North America and abroad is directly com-parable, even though it may have been obtained under quitedifferent testing conditions.A number of S,-N curves obtained from tests on concretebeams containing straight deformed bars made in NorthAme
37、rica18,21,24-28are shown in Fig. 6. These curves are forbars varying in size from #5 to #ll, with minimum stresslevels ranging from -0.10 to 0.43 of the tensile yield strengthof the bars.Although only about one-third of the total number of S,-Ncurves reported in the indicated references are shown in
38、 Fig.* Dr. John M. Hanson was the chairman of the subcommittee that prepared this sectionof the report.215R-6 ACI COMMITTEE REPORT60 - - 414StressStressRangeRangeS, ksiS, MPa40 -20 - -13801; I IO01 IO10.0Cycles to Failure, N, millionsFig. 6-Stress range-fatigue life curves for reinforcing bars6, the
39、y include the highest and lowest fatigue strength. Thevarying characteristics of these curves suggest that there aremany variables in addition to stress range that influence thefatigue strength of deformed reinforcing bars.Most of the curves in Fig. 6 show a transition from asteeper to a flatter slo
40、pe in the vicinity of one million cycles,indicating that reinforcing bars exhibit a practical fatiguelimit. Fatigue strengths associated with the steeper or flatterpart of the S,-N curves will be referred to as being in thefinite life or long life region, respectively. Because of the lackof sufficie
41、nt data in the long life region, it is noted that manyof the S,-N curves in this region are conjectural.The fatigue strength of the steel in reinforcing bars de-pends upon chemical composition, microstructure, inclusions,and other variables.400However, it has been shown26,28thatthe fatigue strength
42、of reinforcing bars may be only one-halfof the fatigue strength of coupons machined from samples ofthe bars. In addition, reinforcing bar specifications are basedon physical characteristics. Consequently, the variables relatedto the steel composition are of limited concern to practicingstructural en
43、gineers. The variables related to the physicalcharacteristics and use of the reinforcing bars are of greaterconcern. The main variables that have been considered in thetechnical literature are:1. Minimumstress2. Bar size and type of beam3. Geometry of deformations4. Yield and tensile strength5. Bend
44、ing6. WeldingEach of these is discussed in the following sections.2.2.2 Minimum stress -In several investigations,18,21,29it hasbeen reported that the fatigue strength of reinforcing bars isrelatively insensitive to the minimum stress level. However,in two recent investigations,26,28it was concluded
45、 that mini-mum stress level does influence fatigue strength to the extentapproximately indicated by a modified Goodman diagramwith a straight line envelope. This indicates that fatiguestrength decreases with increasing minimum stress level inproportion to the ratio of the change in the minimum stres
46、slevel to the tensile strength of the reinforcing bars.2.2.3 Bar size and type of beam-These two factors are re-lated because bars embedded in concrete beams have a stressgradient across the bar. In design, it is only the stress at themidfibers of the bar that is generally considered. Large barsin s
47、hallow beams or slabs may have a significantly higherstress at the extreme rather than the midfibers of the bar.The effect of bar size is examined in Table 1 using datafrom three investigations. 28y32P36 Since #8 bars or their equi-valent were tested in each of these investigations, the fatiguestren
48、gth of other bar sizes was expressed as a ratio relative tothe fatigue strength of th e #8 bars. For each comparison, thebars were made by the same manufacturer, and they alsowere tested at the same minimum stress level. The fatiguestrength is the stress range causing failure at 2 million ormore cyc
49、les.The tests reported in Reference 32 were on bars subjectedto axial tension. Therefore, there was no effect of straingradient in this data, yet the fatigue strength of the #5 barswas about 8 percent greater than that of the #8 bars.Tests in Reference 28 were on bars in concrete beams.The strain gradients in these beams resulted in stresses at theextreme fibers for the different size bars that were about thesame. Still, an effect of bar size was found that was of aboutthe same order of magnitude.In the tests in Reference 36 the strain gradient was greateracross the #8 bars than
