ACI 423 3R-2005 Recommendations for Concrete Members Prestressed with Unbonded Tendons《有未粘合预应力钢筋的混凝土构件预应力建议》.pdf

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1、ACI 423.3R-05 supersedes ACI 423.3R-96 and became effective June 14, 2005.Copyright 2005, 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, pr

2、inted, written, or oral, or 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.ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in plan

3、ning,designing, executing, and inspecting construction. Thisdocument is intended for the use of individuals who arecompetent to evaluate the significance and limitations of itscontent and recommendations and who will acceptresponsibility for the application of the material it contains.The American C

4、oncrete Institute disclaims any and allresponsibility for the stated principles. The Institute shall notbe 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 p

5、art of the contract documents, theyshall be restated in mandatory language for incorporation bythe Architect/Engineer.423.3R-1It is the responsibility of the user of this document toestablish health and safety practices appropriate to the specificcircumstances involved with its use. ACI does not mak

6、e anyrepresentations with regard to health and safety issues and theuse of this document. The user must determine theapplicability of all regulatory limitations before applying thedocument and must comply with all applicable laws andregulations, including but not limited to, United StatesOccupationa

7、l Safety and Health Administration (OSHA)health and safety standards.Recommendations for Concrete MembersPrestressed with Unbonded TendonsReported by Joint ACI-ASCE Committee 423ACI 423.3R-05This report is a guide for the design of flexural concrete members in buildingspost-tensioned with unbonded t

8、endons. Suggestions for revisions and additionsto ACI 318 regarding this subject are presented. Consideration is given todetermination of fire endurance, design for seismic forces, and design forcatastrophic loadings, in addition to design for gravity and lateral loads.Recommendations concerning det

9、ails and properties of tendons, protectionagainst corrosion, and construction procedures are presented.Keywords: anchorage (structural); beams (supports); bond (concrete toreinforcement); concrete construction; concrete slabs; cover; cracking(fracturing); earthquake-resistant structures; fire resist

10、ance; flat concreteplates; flat concrete slabs; joints (junctions); loads (forces); post-tensioning;prestressed concrete; prestressing; prestressing steels; shear properties;stresses; structural analysis; structural design; unbonded prestressing.CONTENTSChapter 1Introduction, p. 423.3R-21.1General1.

11、2Objective1.3Scope1.4Notations and definitionsChapter 2Design considerations, p. 423.3R-22.1General2.2Continuous members2.3Corrosion protection2.4Fire resistance2.5Earthquake loadingChapter 3Design, p. 423.3R-63.1General3.2One-way systems3.3Two-way systems3.4Tendon stress at factored load3.5Prestres

12、s losses3.6Average prestress3.7Supporting walls and columns3.8Serviceability requirements3.9Design strength3.10Anchorage zone reinforcementChapter 4Materials, p. 423.3R-154.1Tendons4.2Protection materialsRobert W. Barnes Charles W. Dolan Leslie D. MartinDavid H. SandersSarah L. Billington Martin J.

13、Fradua Gerrard McGuire Thomas C. Schaeffer*Kenneth B. Bondy*William L. Gamble Mark E. Moore Andrea J. SchokkerNed H. Burns Pawan R. Gupta*Antoine Naaman Morris SchupackGregory P. Chacos J. Weston Hall Thomas E. Nehil Richard W. StoneTodd J. Christopherson Mohammad Iqbal Julio A. Ramirez H. Carl Walk

14、erSteven R. Close Paul Johal Carin L. Roberts-Wollmann*Paul ZiaHenry J. Cronin Ward N. Marianos David M. RogowskyBruce W. RussellChairShawn P. GrossSecretary*Subcommittee members involved in updating this report.Deceased.423.3R-2 ACI COMMITTEE REPORT4.3Protection of anchorage zones4.4Concrete coverC

15、hapter 5Construction, p. 423.3R-165.1Construction joints5.2Closure strips5.3Placement of tendons5.4Concrete placement and curing5.5Stressing operations5.6Form removal and reshoring5.7Welding and burning5.8Protection of tendonsChapter 6References, p. 423.3R-186.1Referenced standards and reports6.2Cit

16、ed referencesCHAPTER 1INTRODUCTION1.1GeneralThis report is an update to the previous ACI-ASCECommittee 423 report entitled “Recommendations forConcrete Members Prestressed with Unbonded Tendons(ACI 423.3R-96).” Since the publication of that report andthe four previous reports that it replaced, many

17、previousrecommendations have been incorporated into ACI 318-02.These recommendations have been prepared to provide acomprehensive guide for design, materials, and constructionfor concrete members prestressed with unbonded tendons.Suggested revisions and additions to ACI 318 are alsoincluded in this

18、report.1.2ObjectiveThis report presents recommendations for design, materials,and construction for concrete structures prestressed withunbonded tendons that are commensurate with the safety andserviceability requirements of ACI 318-02.This report is a guide, and practitioners should use theirjudgmen

19、t when applying its recommendations. This reportis generally not intended for reference in a specification or a code.1.3ScopeThe recommendations pertinent to design with unbondedtendons considered in this report include the design of beams,girders, slabs, continuous members, and details and properti

20、esof tendons and anchors and their protection from corrosionduring construction and throughout the life of the structure.The recommendations in this report are not intended forunbonded construction stages of elements using bondedtendons; for multistrand unbonded tendons used as externaltendons; memb

21、ers subject to direct tension, such as tiebacks,cable stays, arch ties, or circumferential tendons for contain-ment structures; or ground-supported post-tensioned slabsfor light residential construction (PTI 2004).1.4Notations and definitionsSymbols are defined in the text. Definitions of terms asus

22、ed in this report follow.anchoragea mechanical device comprising all compo-nents required to anchor the prestressing steel and perma-nently transfer the post-tensioning force from theprestressing steel to the concrete.bonded tendonstendons in which prestressing steel isbonded to concrete either dire

23、ctly or through grouting and,therefore, are not free to move relative to the concrete.couplera device designed to connect ends of two strandstogether, thereby transferring the prestressing force from endto end of the tendon.post-tensioning coatingmaterial used to protect againstcorrosion and reduce

24、friction between prestressing steel andsheathing.prestressing steelhigh-strength steel, most commonly aseven-wire strand, used to impart prestress forces to concrete.sheathinga material encasing prestressing steel toprevent bonding of the prestressing steel with the surroundingconcrete, provide corr

25、osion protection, and contain thecorrosion-inhibiting coating.tendonin post-tensioned applications, the tendon is acomplete assembly consisting of anchorages, prestressingsteel, and sheathing with coating for unbonded applicationsor ducts with grout for bonded applications.unbonded tendontendon in w

26、hich the prestressing steelis prevented from bonding to the concrete and is free to moverelative to the concrete. The prestressing force is perma-nently transferred to the concrete at the tendon ends by theanchorages only.CHAPTER 2DESIGN CONSIDERATIONS2.1GeneralStrength and serviceability limitation

27、s (including stresses)should conform to the provisions of ACI 318-02, but somerecommendations are offered that differ from ACI 318 orrelate to areas not covered by ACI 318-02.2.2Continuous members2.2.1 One-way membersFor slabs or beams continuousover two or more spans with one-way prestressing only,

28、 aloading condition or fire exposure that causes failure of allthe tendons in one span will lead to a loss of prestress andmuch of the load-carrying capacity in the other spans.Consideration should be given to the consequence of such acatastrophic failure in any specific span to the overallstability

29、 of the structural system. ACI 318-02 has respondedto this concern and to other considerations, such as crackwidth limitation, in Section 18.9.2. This section specifiesminimum bonded reinforcement equal to 0.40% of the areaof that part of the cross section between the flexural tensionface and the ce

30、nter of gravity of the gross section. Grade 60(Grade 420) reinforcement should be used for this purpose.This amount of bonded reinforcement is approximatelyequal to the minimum reinforcement requirement fornonprestressed slabs (Section 10.5.4 of ACI 318-02).One-way slabs can also incorporate unbonde

31、d partial lengthtendons, lapped tendons, or tendons with intermediateanchorages that would serve to limit the extent of the loss ofload-carrying capacity. The Uniform Building Code (UBC)required an alternate load-carrying capacity provided bybonded reinforcement of D + 0.25L, with a strength reducti

32、onCONCRETE MEMBERS PRESTRESSED WITH UNBONDED TENDONS 423.3R-3factor of 1.0, for one-way elements post-tensioned withunbonded tendons. Although this is not required by the Interna-tional Building Code (IBC 2003), and has never been requiredby ACI, designers should consider providing it to address the

33、stability considerations mentioned above. Depending on thespan configuration and the loads, the D + 0.25L criterion isoften indirectly satisfied in slabs by the bonded reinforce-ment requirements of Section 18.9.2 of ACI 318-02. TheUBC approach is based on the actual dead and live loadingacting on t

34、he member, which is more direct for stabilityconcerns. In addition, satisfaction of the UBC approachrequires that the reinforcement complies with the require-ments of ACI 318-02 Chapter 12, that is, that it be fullydeveloped. Reinforcing steel required by Section 18.9.2 isnot required to satisfy Cha

35、pter 12; the top and bottom rein-forcement is not even required to have a lap splice (positivemoment bars need only be L/3 centered in the span and nega-tive moment bars need only extend 1/6 the clear span on eachside of the support).In negative moment regions of T-beams or other memberswhere compre

36、ssion width is limited, the amount of reinforce-ment provided is limited (Section 18.8 of ACI 318-02) toavoid the possibility of a compression failure at factored loads.In accordance with Section 18.9.4.3 of ACI 318-02, bondedreinforcement for both beams and slabs should be detailed inaccordance wit

37、h the provisions of Chapter 12 of ACI 318-02,with sufficient development length for the positive and negativemoment bars, to ensure that the bonded reinforcement willfunction as an independent load-carrying system.2.2.2 Two-way membersIn the case of two-way slabs ofthe usual proportions, catastrophi

38、c loading beyond designcapacity in one bay is generally not as critical to other spans asin one-way systems. For two-way slabs, the load-carryingcapacity of the tendons in each direction should be considered.Tests (PTI 1977; Ritz, Marti, and Thurlimann 1975; Burns andHemakom 1977; Hemakom 1975) have

39、 demonstrated thattwo-way flexural behavior of slabs with significant loss ofprestress force still have adequate resistance capacity. Thisfavorable behavior is recognized in ACI 318-02 and in theInternational Building Code (IBC 2003) and some localbuilding codes by a reduction of the amount of bonde

40、d rein-forcement required in comparison with one-way systems.2.3Corrosion protectionUnbonded prestressing tendons should be protected againstcorrosion during fabrication, transit, storage, construction, andafter installation. Section 18.16 of ACI 318-02 indicatesminimum requirements for corrosion pr

41、otection. Moredetailed requirements are found in ACI 423.6. ACI 423.4Rprovides a history of the development of corrosion protectionmethods and a description of problems that can arise due toinadequate corrosion protection systems.ACI 423.6 provides for two levels or degrees of corrosionprotection, w

42、ith additional corrosion protective measuresrequired for tendons used in aggressive environments.Concrete cover for unbonded tendons should be detailedconsidering the factors discussed in Section 4.4. Guidancefor the protection of tendons during storage, transit, andinstallation can be found in the

43、Post-Tensioning Institutepublication “Field Procedures Manual for Unbonded SingleStrand Tendons (PTI 2000a).”Structures exposed to aggressive environments include allstructures subjected to direct or indirect applications ofdeicing chemicals, seawater, brackish water, or spray fromthese sources, str

44、uctures in the immediate vicinity ofseacoasts exposed to salt-laden air, and structures where theanchorages are in direct contact with soil and nonwater-proofed backfilled structures. Stressing pockets andconstruction joints at intermediate anchorages that are notmaintained in a normally dry conditi

45、on after constructionshould also be considered exposed to an aggressive environ-ment. The designer should evaluate the conditions to determineif the environment in which the structure is located isconsidered aggressive in any way. Enclosed buildings (officebuildings, apartment buildings, warehouses,

46、 and manufacturingfacilities) are usually considered to be nonaggressive environ-ments. Attention should be paid to such areas as the locationof stressing-end and intermediate anchors, constructionjoints, locations of planters, balconies, and swimming pools.2.4Fire resistanceFire-resistance ratings

47、can be determined in accordancewith the heat transmission and dimensional provisions ofSection 2.4.1 or by the rational design procedures for deter-mining fire endurance discussed in Section 2.4.2 (Precast-Prestressed Concrete Institute 1989; PTI 1990; ACI 216.1;and ASTM E 119). ASTM E 119 includes

48、a guide for classi-fying construction as restrained or unrestrained. A restrainedmember may develop considerable axial forces due to thelateral stiffness of the supporting elements. This allows themember to arch and significantly improves its ability tosupport load. If the supporting members are too

49、 flexible andcannot restrain the expansion of the member, or are incapableof resisting the axial forces caused by the expansion of themember, the member should be treated as unrestrained.2.4.1 Minimum dimensions for various fire resistiveclassifications (PTI 1990)2.4.1.1 SlabsTo meet minimum heat-transmissionrequirements, that is, a temperature rise of 250 F (140 C)of the unexposed surface, the thickness requirements forconcrete slabs should be the same whether the concrete isplain, reinforced, or prestressed. Table 2.1 gives