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1、ACI 215R-74 (Revised 1992/Reapproved 1997) Considerations for Design of Concrete Structures Subjected to Fatigue Loading Reported by ACI Committee 215 John M. Hanson Chairman Paul W. Abeles John D. Antrim Earl I. Brown, II John N. Cernica Carl E. Ekberg, Jr.* Neil M. Hawkins Hubert K. Hiisdorf Craig
2、 A. Ballinger Secretary Cornie L. Hulsbos Don A. Linger Edmund P. Segner, Jr. Surendra P. Shah Laurence E. Svab William 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. Johnston Chairman M. Arockiasam
3、y P.N. Balaguru Mark D. Bowman John N. Cernica Luis F. Estenssoro John M. Hanson Neil M. Hawkins Thomas T.C. Hsu Craig A. Ballinger Secretary Ti Huang Lambit Kald Michael E. Kreger Basile G. Rabbat Raymond S. Rollings Surendra P. Shah Luc R. Taerwe William J. Venuti This report presents information
4、that is intended to aid the practicing engineer confronted with consideration of repeated loading on concrete structures. Investi- 1.1-Objective and scope gations of the fatigue properties of component materiak+oncrete, reinforcing l.2-Definitions bars, welded reinforcing mats, and prestressing tend
5、ons-are reviewed. Applica- 1.3-Standards cited in this report tion of this information to predicting the fatigue life of beams and pavements is discussed. A significant change in Section 3.1.2 of the 1992 revisions is the Chapter 2-Fatigue properties of component materials, pg. increase in the allow
6、able stress range for prestressing steel from 0.04 fpu to 215R-2 0.06 I;,. 2.1-Plain concrete Keywords: beams (supports); compressive strength; concrete pavements: cracking (frac- 2.2-Reinforcing bars turing); dynamic loads; fatigue (materials); impact; loads (Forces); microcracking; plain 2.3-Welde
7、d wire fabric and bar mats concrete; prestressed concrete; prestressing steel; reinforcedconcrete: reinforcingsteels; 2.4-Prestressing tendons specifications; static loads: strains; stresses; structural design; tensile strength; welded wire fabric; welding; yield strength. CONTENTS Chapter 3-Fatigue
8、 of beams and pavements, pg. 215R-15 3.1-Beams 3.2-Pavements Chapter l-Introduction, pg. 215R-2 ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in designing, plan- ning, executing, or inspecting construction and in preparing specifications. Reference to
9、these documents shall not be made in the Project Documents. If items found in these doc- uments are desired to be part of the Project Documents they should be phrased in mandatory language and incorporated into the Project Documents. 21 5R-1 Notation, pg. 215R-19 References, pg. 215R-19 Appendix, pg
10、. 215R-23 ACI 215R-74 (Revised 1992) became effective Nov. 1, 1992. Copyright 0 1992, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device,
11、 printed or written or oral, or recording for sound or visual repro- duction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS E
12、mployees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 01:27:37 MSTNo reproduction or networking permitted without license from IHS -,-,- 215R-2 ACI COMMITTEE REPORT CHAPTER l-INTRODUCTION In recent years, considerable interest has developed in the fatigue strength of concrete members
13、. There are several rea- sons for this interest. First, the widespread adoption of ulti- mate strength design procedures and the use of higher strength materials require that structural concrete members perform satisfactorily under high stress levels. Hence there is concern about the effects of repe
14、ated loads on, for example, crane beams and bridge slabs. Second, new or different uses are being made of concrete fatigue; however, this report does not specifically deal with these types of loadings. 1.3-Standards cited in this report The standards and specifications referred to in this docu- ment
15、 are listed below with their serial designation, including year of adoption or revision. These standards are the latest effort at the time this document was revised. Since some of the standards are revised frequently, although generally only in minor details, the user of this document may wish to ch
16、eck directly with the committee if it is correct to refer to the members or systems, such as prestressed concrete railroad latest revision. ties and continuously reinforced concrete pavements. These uses of concrete demand a high performance product with an ACI 301-89 assured fatigue strength. Third
17、, there is new recognition of the effects of repeated ACI 318-89 loading on a member, even if repeated loading does not cause a fatigue failure. Repeated loading may lead to inclined ASTM A 416-90 cracking in prestressed beams at lower than expected loads, or repeated loading may cause cracking in c
18、omponent mater- ials of a member that alters the static load carrying char- ASTM A 421-90 acteristics. l.l-Objective and scope ASTM A 615-90 This report is intended to provide information that will serve as a guide for design for concrete structures subjected to fatigue loading. ASTM 722-90 However,
19、 this report does not contain the type of detailed design procedures sometimes found in guides. Chapter 2 presents information on the fatigue strength of AWS Dl.4-79 concrete and reinforcing materials. This information has been obtained from reviews of experimental investigations reported in technic
20、al literature or from unpublished data made avail- able to the committee. The principal aim has been to sum- marize information on factors influencing fatigue strength that are of concern to practicing engineers. Chapter 3 considers the application of information on concrete and reinforcing material
21、s to beams and pavements. Provisions suitable for inclusion in a design specification are recommended. An Appendix to this report contains extracts from current specifications that are concerned with fatigue. 1.2-Definitions It is important to carefully distinguish between static, dynamic, fatigue,
22、and impact loadings. Truly static loading, or sustained loading, remains constant with time. Nevertheless, a load which increases slowly is often called static loading; the maximum load capacity under such conditions is referred to as static strength. Dynamic loading varies with time in any arbitrar
23、y manner. Fatigue and impact loadings are special cases of dynamic loading. A fatigue loading consists of a sequence of load repetitions that may cause a fatigue failure in about 100 or more cycles. Very high level repeated loadings due to earthquakes or other catastrophic events may cause failures
24、in less than 100 cycles. These failures are sometimes referred to as low-cycle Specifications for Structural Concrete for Buildings Building Code Requirements for Rein- forced Concrete Standard Specification for Uncoated Seven Wire Stress Relieved Steel Strand for Pre- stressed Concrete Standard Spe
25、cification for Uncoated Stress Relieved Steel Wire for Prestressed Con- crete Standard Specification for Deformed and Plain Billet Steel Bars for Concrete Rein- forcement Standard Specification for Uncoated High Strength Steel Bar for Prestressing Con- crete StructuralWelding Code-Reinforcing Steel
26、CHAPTER 2-FATIGUE PROPERTIES OF COMPONENT MATERIALS The fatigue properties of concrete, reinforcing bars, and prestressing tendons are described in this section. Much of this information is presented in the form of diagrams and al- gebraic relationships that can be utilized for design. However, it i
27、s emphasized that this information is based on the results of tests conducted on different types of specimens subjected to various loading conditions. Therefore, caution should be exercised in applying the information presented in this report. 2.1-Plain concrete* 2.1.1 General-Plain concrete, when s
28、ubjected to repeated loads, may exhibit excessive cracking and may eventually fail after a sufficient number of load repetitions, 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 fraction of the static strength that
29、 it can support repeatedly for a given number of cycles. Fatigue strength is influenced by range of loading, rate of loading, eccentricity of loading, load history, material properties, and environmental conditions. * Dr.Surendra P. Shah sectionof the report. was the chairman of the subcommittee tha
30、t prepared this Copyright American Concrete Institute Provided by IHS under license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 01:27:37 MSTNo reproduction or networking permitted without license from IHS -,-,- FATIGUE LOADING DESIGN CONSIDERATIONS 21
31、5R-3 1.0 I- icGs the bottom of the bar was adjacent to the extreme tensile fibers in the beam. The smoother zone, with the dull, rubbed ap- pearance, is the fatigue crack. The remaining zone of more jagged surface texture is the part that finally fractured in tension after the growing fatigue crack
32、weakened the bar. It is noteworthy that the fatigue crack did not start from the bottom of the bar. Rather it started along the side of the bar, at the base of one of the transverse lugs. This is a common characteristic of most bar fatigue fractures. Quite a number of laboratory investigations of th
33、e fatigue strength of reinforcing bars have been re years from the United States,18-26 Canada, !?orted in recent and Japan.35-39 7;28 Europe,29-34 In 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
34、bars which were either embedded in concrete or tested in air. There is contradiction in the technical literature as to whether a bar has the same fatigue strength when tested in air or embedded in a concrete beam. In an investigation31 of hot-rolled cold-twisted bars, it was found that bars embedded
35、 in beams had a greater fatigue strength than when tested in air. However, in another investigation,29 the opposite conclu- sion was reached. More recent Studies28,32 indicate that there should be little difference in the fatigue strength of bars in air and embedded bars if the height and shape of t
36、he trans- verse lugs are adequate to provide good bond between the steel and concrete. The influence of friction between a reinforcing bar and concrete in the vicinity of a crack has also been considered.32 In laboratory tests, an increase in temperature is frequently observed at the location where
37、the fatigue failure occurs. However, rates of loading up to several thousand cycles per minute and temperatures up to several hundred degrees C are normally not considered to have a significant effect on fatigue strength.400In a statistical analysis41 of an inves- tigation of reinforcing bars,266dif
38、ferences in fatigue strength due to rates of loading of 250 and 500 cycles per minute were not significant. It is therefore believed that most of the data reported in investigations in North America and abroad is directly com- parable, even though it may have been obtained under quite different test
39、ing conditions. A number of S,-N curves obtained from tests on concrete beams containing straight deformed bars made in North America18,21,24-28are shown in Fig. 6. These curves are for bars varying in size from #5 to #ll, with minimum stress levels ranging from -0.10 to 0.43 of the tensile yield st
40、rength of the bars. Although only about one-third of the total number of S,-N curves reported in the indicated references are shown in Fig. * Dr. John M. Hanson was the chairman of the subcommittee that prepared this section of the report. Copyright American Concrete Institute Provided by IHS under
41、license with ACI Licensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/05/2007 01:27:37 MSTNo reproduction or networking permitted without license from IHS -,-,- 215R-6 ACI COMMITTEE REPORT 60 - 414 Stress Stress Range Range S, ksi S, MPa 4 0 - 2 0 - -138 01; IIO 01IO 10.0 Cycl
42、es to Failure, N, millions Fig. 6-Stress range-fatigue life curves for reinforcing bars 6, they include the highest and lowest fatigue strength. The varying characteristics of these curves suggest that there are many variables in addition to stress range that influence the fatigue strength of deform
43、ed reinforcing bars. Most of the curves in Fig. 6 show a transition from a steeper to a flatter slope in the vicinity of one million cycles, indicating that reinforcing bars exhibit a practical fatigue limit. Fatigue strengths associated with the steeper or flatter part of the S,-N curves will be re
44、ferred to as being in the finite life or long life region, respectively. Because of the lack of sufficient data in the long life region, it is noted that many of the S,-N curves in this region are conjectural. The fatigue strength of the steel in reinforcing bars de- pends upon chemical composition,
45、 microstructure, inclusions, and other variables.40 0However, it has been shown26,28 that the fatigue strength of reinforcing bars may be only one-half of the fatigue strength of coupons machined from samples of the bars. In addition, reinforcing bar specifications are based on physical characterist
46、ics. Consequently, the variables related to the steel composition are of limited concern to practicing structural engineers. The variables related to the physical characteristics and use of the reinforcing bars are of greater concern. The main variables that have been considered in the technical lit
47、erature are: 1.Minimum stress 2. Bar size and type of beam 3. Geometry of deformations 4. Yield and tensile strength 5.Bending 6.Welding Each of these is discussed in the following sections. 2.2.2 Minimum stress-In several investigations,18,21,29 it has been reported that the fatigue strength of rei
48、nforcing bars is relatively insensitive to the minimum stress level. However, in two recent investigations,26,28 it was concluded that mini- mum stress level does influence fatigue strength to the extent approximately indicated by a modified Goodman diagram with a straight line envelope. This indica
49、tes that fatigue strength decreases with increasing minimum stress level in proportion to the ratio of the change in the minimum stress level 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 stress gradient across the bar. In design, it is only the stress at the midfibers of the bar that is generally considered. Large bars in shallow beams or sl