1、Recommendations for Concrete Members Prestressed with Single- Strand Unbonded Tendons Reported by Joint ACI-ASCE Committee 423 ACI 423.3R-17First PrintingJuly 2017 ISBN: 978-1-945487-70-5 Recommendations for Concrete Members Prestressed with Single-Strand Unbonded Tendons Copyright by the American C
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11、ds and committee reports are gathered together in the annually revised ACI Manual of Concrete Practice (MCP). American Concrete Institute 38800 Country Club Drive Farmington Hills, MI 48331 Phone: +1.248.848.3700 Fax: +1.248.848.3701 www.concrete.orgThis report provides information for the design of
12、 flexural concrete members in buildings post-tensioned with single-strand unbonded tendons. The report is intended to complement the commentary in ACI 318 and to provide suggestions for revisions and addi- tions to ACI 318. Consideration is given to design for gravity and lateral loads, determinatio
13、n of fire endurance, design for seismic forces, and design for catastrophic loadings. Recommendations concerning details and properties of tendons, protection against corrosion, and construction procedures are presented. Keywords: concrete slabs; cracking; fire resistance; joints; punching shear; un
14、bonded post-tensioning. CONTENTS CHAPTER 1INTRODUCTION, p. 2 1.1General, p. 2 1.2Objective, p. 2 1.3Scope, p. 2 CHAPTER 2NOTATION AND DEFINITIONS, p. 2 2.1Notation, p. 2 2.2Definitions, p. 3 CHAPTER 3MEMBER DESIGN, p. 3 3.1General, p. 3 3.2One-way systems, p. 3 3.3Two-way systems, p. 4 3.4Beams, p.
15、8 3.5Effects of supporting walls and columns on prestress forces, p. 9 CHAPTER 4ANCHORAGE ZONES, p. 10 4.1Anchorage zone reinforcement, p. 10 Carin L. Roberts-Wollmann, Chair Amy M. Reineke Trygestad, Secretary ACI 423.3R-17 Recommendations for Concrete Members Prestressed with Single-Strand Unbonde
16、d Tendons Reported by Joint ACI-ASCE Committee 423 Theresa M. Ahlborn Rashid Ahmed * Robert W. Barnes Florian G. Barth Asit N. Baxi * Roger J. Becker Charles W. Dolan * James P. Donnelly Pierre Esselinck Martin J. Fradua William L. Gamble Harry A. Gleich Pawan R. Gupta William M. Hale H. R. Trey Ham
17、ilton III Carol Hayek * Mohammad Iqbal Donald P. Kline * Larry B. Krauser Jason J. Krohn Theodore L. Neff Sami H. Rizkalla James Rogers Brandon Ross Bruce W. Russell Thomas C. Schaeffer * Richard W. Stone Miroslav Vejvoda Jeffrey S. V olz H. Carl Walker Zuming Xia Paul Zia Consulting Members Kenneth
18、 B. Bondy * Robert N. Bruce Jr. Ned H. Burns Chunsheng “Steve” Cai Steven R. Close Henry J. Cronin Jr. Ward N. Marianos Jr. Hani Melhem Antoine E. Naaman Thomas E. Nehil Andrea J. Schokker * Subcommittee members involved in updating this report. ACI Committee Reports, Guides, and Commentaries are in
19、tended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the mat
20、erial it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desir
21、ed by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer. ACI 423.3R-17 supersedes ACI 423.3R-05 and was adopted and published July 2017. Copyright 2017, American Concrete Institute. All rights reser
22、ved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduction or for use in any knowledge or retrieval system or device, un
23、less permission in writing is obtained from the copyright proprietors. 1CHAPTER 5SEISMIC DESIGN, p. 11 5.1Earthquake loading, p. 11 CHAPTER 6DESIGN CONSIDERATIONS, p. 13 6.1General, p. 13 6.2Design strength, p. 13 6.3Tendon stress at factored load, p. 13 6.4Prestress losses, p. 14 6.5Average prestre
24、ss, p. 14 6.6Serviceability requirements, p. 15 6.7Continuous members, p. 15 6.8Corrosion protection, p. 15 6.9Fire resistance, p. 16 CHAPTER 7MATERIALS, p. 18 7.1Tendons, p. 18 7.2Protection materials, p. 18 7.3Protection of anchorage zones, p. 18 7.4Concrete cover, p. 18 CHAPTER 8CONSTRUCTION, p.
25、19 8.1Construction joints, p. 19 8.2Closure strips, p. 19 8.3Placement of tendons, p. 19 8.4Concrete placement and curing, p. 19 8.5Stressing operations, p. 20 8.6Form removal and reshoring, p. 21 8.7Welding and burning, p. 21 8.8Protection of tendons, p. 21 CHAPTER 9REFERENCES, p. 21 Authored docum
26、ents, p. 21 CHAPTER 1INTRODUCTION 1.1General Since the publication of previous ACI 423.3R reports, many of their recommendations have been incorporated into ACI 318. All references to ACI 318 refer to ACI 318-14 unless specifically noted. The recommendations in this report have been prepared to prov
27、ide a comprehensive guide for design, materials, and construction for concrete members prestressed with single-strand unbonded tendons. Suggested revisions and additions to ACI 318 are also included in this report. Mandatory language used in this report reflects requirements in ACI 318. 1.2Objective
28、 This report presents recommendations for design, mate- rials, and construction for concrete structures prestressed with unbonded tendons that are commensurate with the strength, serviceability, and safety requirements of ACI 318. Practitioners should use their judgment when applying the recommendat
29、ions of this report. This report is not intended for reference in a specification or a code. 1.3Scope Recommendations pertinent to design with single-strand unbonded tendons considered in this report include the design of slabs, beams, and continuous members; details and properties of tendons and an
30、chors; and protection from corrosion during construction and throughout the life of the structure. The recommendations in this report are not intended for unbonded construction stages of elements using bonded tendons; for multistrand unbonded tendons used as external tendons; for members subject to
31、direct tension, such as tiebacks, cable stays, arch ties, or circumferential tendons for containment structures; or for ground-supported post- tensioned slabs for light residential construction. CHAPTER 2NOTATION AND DEFINITIONS 2.1Notation A b= net bearing plate area. in. 2(mm 2 ) A b = maximum are
32、a of the portion of the concrete anchorage surface that is geometrically similar to and concentric with the area of the anchorage, in. 2(mm 2 ) A c = cross-sectional area of the slab, perpendicular to the slab edge, between the center of the exterior span and the slab edge, in. 2(mm 2 ) A cf= larger
33、 of gross cross-sectional areas of the slab- beam strips of the two orthogonal equivalent frames intersecting at the column, in. 2(mm 2 ) A ps= area of prestressed longitudinal tension reinforce- ment, in. 2(mm 2 ) A s,min= minimum bonded reinforcement in negative moment areas of two-way systems b =
34、 width of compression face of member, in. (mm) b f= total flange width b n= effective overhang flange width for normal forces, in. (mm) b o= perimeter of critical section for two-way shear in slabs, in. (mm) b w= effective flange width for normal forces at post- tension anchor, in. (mm) d p= distanc
35、e from extreme compression fiber to centroid of prestressing reinforcement, in. (mm) E s= modulus of elasticity of prestressing reinforcement, psi (MPa) f ci = strength of concrete at time of initial prestress, psi (MPa) f cp= permissible concrete compressive stress, psi (MPa) f pc= compressive stre
36、ss in concrete, after allowance for all prestress losses, at centroid of cross section resisting externally applied loads or at junction of web and ange where the centroid lies within the ange, psi (MPa); in a composite member, f pcis the resultant compressive stress at centroid of composite section
37、, or at junction of web and ange where the centroid lies within the ange, due to both prestress and moments resisted by precast member acting alone, psi (MPa) American Concrete Institute Copyrighted Material www.concrete.org 2 CONCRETE MEMBERS PRESTRESSED WITH SINGLE-STRAND UNBONDED TENDONS (ACI 423
38、.3R-17)f ps= stress in prestressing reinforcement at nominal flexural strength, psi (MPa) f ps= stress in post-tensioned tendons at nominal strength at high temperatures, psi (MPa) f pu= specified tensile strength of prestressing reinforce- ment, psi (MPa) f pu= tensile strength of tendons at high t
39、emperatures, psi (MPa) f se= effective stress in prestressing reinforcement, after allowance for all prestress losses, psi (MPa) f y= specified yield stress of reinforcement, psi (MPa) h = slab thickness, in. (mm) L = span length of beam or one-way slab; clear projec- tion of cantilever, in. (mm) =
40、length of tendon, in. (mm) M = total applied static moment (unfactored), lb-in. (kN-m) M tq += retained midspan moment, lb-in. (kN-m) M t1 = retained negative moment capacity at Column 1, lb-in. (N-m) M t2 = retained negative moment capacity at Column 2, lb-in. (N-m) N c= resultant tensile force act
41、ing on the portion of the concrete cross section that is subjected to tensile stresses due to the combined effects of service loads and effective prestress, lb (N) P = average force in the prestressing reinforcement, lb (N) V p= vertical component of effective prestress forces crossing the critical
42、section v c= stress corresponding to nominal two-way shear strength provided by concrete, psi (MPa) v cw= nominal shear stress provided by concrete where diagonal cracking results from high principal tensile stress in web, lb (N) w = uniformly distributed load, plf (kN/m) s= constant used to calcula
43、te V cin slabs, lb (MPa) = tendon elongation, in. (mm) = strength reduction factor = modification factor to reflect the reduced mechan- ical properties of lightweight concrete p= ratio of A psto bd p 2.2Definitions ACI provides a comprehensive list of definitions through an online resource, “ACI Con
44、crete Terminology,” https:/ www.concrete.org/store/productdetail.aspx?ItemID=CT16. Definitions provided herein complement that source. encapsulated tendona tendon that is completely enclosed in a watertight covering from end to end, including anchorages, sheathing, post-tensioning coating, sleeves,
45、and an encapsulation cap over the strand tail at each end. post-tensioning coatingmaterial between prestressing reinforcement and sheathing used to protect against corro- sion and reduce friction. prestressing reinforcementstrand, wire, or bar tensioned to impart forces to the concrete. sheathingmat
46、erial encasing prestressing reinforcement to prevent bonding of the prestressing reinforcement with the surrounding concrete, to provide corrosion protection, and to contain the corrosion-inhibiting coating. CHAPTER 3MEMBER DESIGN 3.1General The design provisions of ACI 318 apply to the contents of
47、this chapter, but some recommendations are offered that complement those of ACI 318. Significant changes were made in ACI 318-02, ACI 318-08, ACI 318-11, and ACI 318-14 that impact the design of prestressed concrete members and unify the design approach for prestressed and nonprestressed members. AC
48、I 318 limits for flexural rein- forcement and moment redistribution are specified in terms of the net tensile strain in the extreme tension reinforcement t . Prestressed members are grouped into three design cate- gories: uncracked (U), transition (T), and cracked (C). Each category is defined accor
49、ding to the maximum calculated flexural tensile stress under service load conditions. For C members, there is no upper limit on calculated flexural tensile stresses under service loads, and any combination of stressed and unstressed reinforcement is permitted. Service- ability requirements related to C and T members are given in ACI 318. 3.2One-way systems One-way slabs are addressed in ACI 318-14 Chapter 7. The chapter organization provides design limits, required strength, required design strengt
