ACI 421 3R-2015 Guide to Design of Reinforced Two-Way Slab Systems.pdf

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1、Guide to Design of Reinforced Two-Way Slab SystemsReported by Joint ACI-ASCE Committee 421ACI 421.3R-15First PrintingOctober 2015ISBN: 978-1-942727-56-9Guide to Design of Reinforced Two-Way Slab SystemsCopyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This mate

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11、l of Concrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331Phone: +1.248.848.3700Fax: +1.248.848.3701www.concrete.orgThis guide presents analysis methods, design procedures, slab reinforcement and detailing practices, and strength and service-ability co

12、nsiderations, as well as information for the resistance to lateral forces for slab-column frames. It also covers the design for flexure and shear and torsion, as well as the effect of openings. Both two-way nonprestressed slabs and post-tensioned slabs are included.Keywords: analysis method; deflect

13、ion; direct design; flat plates; flat slabs; post-tension; reinforcement; shear; shearhead; slab-column frame; two-way slabs.CONTENTSCHAPTER 1INTRODUCTION AND SCOPE, p. 21.1Introduction: history of two-way slab system, p. 21.2Scope, p. 2CHAPTER 2NOTATION AND DEFINITIONS, p. 22.1Notation, p. 22.2Defi

14、nitions, p. 3CHAPTER 3ANALYSIS METHODS, p. 43.1General, p. 43.2Analysis methods, p. 43.3Finite element analysis, p. 103.4Yield-line theory, p. 113.5Strip method analysis, p. 11CHAPTER 4DESIGN PROCEDURES, p. 114.1General, p. 114.2Gravity loading, p. 124.3Flexural design, p. 124.4Two-way action slab s

15、hear, p. 124.5Critical section, p. 124.6Openings in slab systems, p. 124.7Unbalanced moments, p. 134.8Shear strength, p. 144.9Post-tensioned slabs, p. 14CHAPTER 5SLAB REINFORCEMENT AND DETAILING, p. 145.1General, p. 145.2Slabs without beams, p. 155.3Corner reinforcement, p. 155.4Slab with drop panel

16、, p. 165.5Column strip reinforcement, p. 165.6Middle strip reinforcement, p. 165.7Bent bars, p. 165.8Slab shear reinforcement, p. 17Mustafa A. Mahamid,*ChairACI 421.3R-15Guide to Design of Reinforced Two-Way Slab SystemsReported by Joint ACI-ASCE Committee 421Simon J. BrownPinaki R. ChakrabartiWilli

17、am L. GambleRamez Botros GayedAmin GhaliHershell GillNeil L. HammillMahmoud E. Kamara*Theodor KrauthammerJames S. Lai*Faris A. MalhasMark D. MarvinSami Hanna MegallyMichael C. MotaEdward G. Nawy*Daniel ReiderAly SaidEugenio M. SantiagoMyoungsu Shin*Matthew SmithYing TianAmy M. Reineke TrygestadStanl

18、ey C. Woodson_*Authors and editorial team.Consulting MembersEugene Paul HollandJ. Leroy HulseySidney H. SimmondsACI Committee Reports, Guides, and Commentaries are intended for guidance in planning, designing, executing, and inspecting construction. This document is intended for the use of individua

19、ls who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall

20、 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 desired by the Architect/Engineer to be a part of the contract documents, they shall be restated in mandatory language for incorporation by

21、the Architect/Engineer.ACI 421.3R-15 was adopted and published October 2015.Copyright 2015, American Concrete InstituteAll 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 electronic or mechanical device,

22、 printed, written, or oral, or recording for sound or visual reproduc-tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors.15.9Post-tensioned slabs, p. 185.10Bonded reinforcement in post-tensioned slabs, p. 18CHAPTER

23、6SERVICEABILITY CONSIDERATIONS, p. 196.1Minimum slab thickness, p. 196.2Deflection analysis, p. 206.3Crack control in reinforced two-way action struc-tural slabs and plates, p. 21CHAPTER 7DESIGN OF SLAB-COLUMN FRAMES UNDER LATERAL FORCES, p. 217.1General, p. 217.2Analysis of slab-column frames under

24、 lateral forces, p. 227.3Arrangement of reinforcement in slabs for interme -diate moment frames, p. 227.4Slab-column frames not designated as part of the seismic-force-resisting system, p. 237.5Transfer of moments to column, p. 24CHAPTER 8REFERENCES, p. 24Authored documents, p. 24APPENDIX AEXCERPT B

25、UILDING CODE PROVISIONS, p. 25A.1Direct design method (ACI 318-14, Section 8.10), p. 25A.2Equivalent frame method (ACI 318-14, Section 8.11), p. 27CHAPTER 1INTRODUCTION AND SCOPE1.1Introduction: history of two-way slab systemTwo-way flat slab construction in the United States evolved, and was invent

26、ed and patented, in the early 1900s (Cohen and Heun 1979). Early two-way flat slab construc-tion was built and subjected to load tests in place and scaled models were later tested in laboratories. While the amount of reinforcement in slab construction varied dramatically, flat slab systems were foun

27、d to be economical for heavy live load occupancy. As the number of flat slab projects increased steadily worldwide, design rules were established and formalized (Sozen and Seiss 1963).Prior to the 1950s, two-way waffle slabs and two-way flat slabs were designed and constructed with column capitals a

28、nd some with drop panels. The hollow tile and concrete slab is a type of waffle slab that dates back to at least 1918 (Gamble et al. 1964). Column capitals were used to increase slab shear strength and drop panels to reduce the flexural reinforcement over columns, which allowed for thinner slabs. In

29、 the post-1970s era, field labor to construct form-work for column capitals and drop panels became costly; the introduction of reusable forms led to construction of flat plates, which are two-way flat slabs without column capitals or drop panels.The lift-slab system for multistory construction was p

30、opular in the 1960s and 70s, but is no longer commonly used. The slabs were cast in a stack at ground level, post-tensioned, and then lifted to their final elevations using jacks lifting on steel collars embedded in the slabs.Draped post-tensioning can be designed to balance part of the gravity load

31、s. Combining unbonded post-tensioned tendons and nonprestressed reinforcement results in reduced slab thickness. In addition, the use of nonprestressed rein-forcement supplements prestressed tendons to meet the required nominal strength and control slab cracking.1.2ScopeThe performance record of var

32、ious two-way slab systems is well established based on results of extensive tests and practical construction improvements in the twentieth century. The ACI Building Code permits design of slab systems, both nonprestressed and post-tensioned, based directly on funda-mental principles of structural me

33、chanics that satisfy equilib-rium and compatibility. This guide provides classic solutions based on linearly elastic continuum, as well as prescriptive procedures used in common practice for analysis and design of slab systems. The fundamental principles in this guide are applicable to all planar st

34、ructural slab systems subjected to gravity loads and, in certain conditions, those combined with lateral forces.This guide addresses recommended practice in the selec-tion and distribution of flexural reinforcement, and guide-lines to transmit loads from slabs to columns by flexure, torsion, and she

35、ar. Detailing practices for post-tensioned two-way slabs are found in ACI 423.3R-05. This guide also discusses aspects and parameters where two-way slabs without beams are incorporated in ordinary or intermediate moment frames with ductile detailing and toughness.While two-way slab systems have more

36、 than 100 years of service history, various practical refinements and research programs continue to develop new materials and technolo-gies that support sustainable construction of two-way slabs.CHAPTER 2NOTATION AND DEFINITIONS2.1NotationAcf= larger gross cross-sectional area of the slab-column str

37、ips in the two orthogonal equivalent frames intersecting at a column in a two-way slab, ft2(m2)Asb= area of reinforcement through the column core used as integrity reinforcementb1= dimension of the critical section bomeasured in the direction of the span for which moments are deter-mined, in. (mm)b2

38、= dimension of the critical section bomeasured in the direction perpendicular to b1, in. (mm)be= effective slab width, in. (mm)bo= perimeter of critical section at d/2 from face of support, in. (mm)C = cross-sectional constant to define torsional proper-ties of slab and beamc1= dimension of rectangu

39、lar or equivalent rectangular column, capital, or bracket measured in the direc-American Concrete Institute Copyrighted Material www.concrete.org2 GUIDE TO DESIGN OF REINFORCED TWO-WAY SLAB SYSTEMS (ACI 421.3R-15)tion of the span for which moments are being deter-mined, in. (mm)c2= dimension of rect

40、angular or equivalent rectangular column, capital, or bracket measured in the direc-tion perpendicular to c1, in. (mm)ct= distance from the interior face of the column to slab edge measured parallel to c1, but not exceeding c1, in. (mm)d = distance from extreme compression fiber to the centroid of t

41、ension reinforcement, in. (mm)Ecb= modulus of elasticity of beam concrete, psi (MPa)Ec= modulus of elasticity of slab concrete, psi (MPa)fc = specified compressive strength of concrete, psi (MPa)fpc= average compressive stress in the two directions at centroid of concrete cross section after allowin

42、g for all prestress losses, psi (MPa)fy= specified yield stress of reinforcement, psi (MPa)g = distance between adjacent stirrup legs or studs, measured in a parallel direction to a column faceh = slab thickness, in. (mm)Ib= moment of inertia of gross section of beam about centroidal axis, in.4(mm4)

43、Is= moment of inertia of gross section of slab about centroidal axis defined for calculating fand t, in.4(mm4)Kc= stiffness of columns based on moment of inertia at any cross section outside the jointKec= stiffness of equivalent columnKFP= modification factor accounting for reduction in joint confin

44、ement at exterior connectionsKt= torsional stiffness1= length of span in direction that moments are being determined, measured center-to-center of supports, in. (mm)2= length of span in direction perpendicular to 1, measured center-to-center of supports, in. (mm)3= distance measured from the column

45、centerline to the edge of the slab, in. (mm)n= length of clear span measured face-to-face of supports, in. (mm)t= span of member under load test, taken as the shorter span for two-way slab systems, in. (mm); span is the smaller of: a) distance between centers of supports; and b) clear distance betwe

46、en supports plus thickness h of member.Mo= total factored static moment, in.-lb (kNm)Msc= portion of slab factored moment balanced by support moment, in.-lb (kNm)Nc= resultant tensile force acting on the portion of the concrete cross section that is subjected to tensile stresses due to the combined

47、effects of service loads and effective prestress, lb (N)qDu= factored dead load per unit area, lb/ft2(kPa)qLu= factored live load per unit area, lb/ft2(kPa)qu= factored load per unit area, lb/ft2(kPa)x = shorter overall dimension of rectangular part of cross section, in. (mm)y = longer overall dimen

48、sion of rectangular part of cross section, in. (mm)Vc= nominal shear strength provided by concrete, lb (N)Vp= vertical component of all effective prestress forces crossing the critical section, lb (N)Vse= unfactored shear force, but not less than twice the unfactored dead load shear, lb (N)Vug= fact

49、ored shear force on the slab critical section for two-way action due to gravity loads, lb (N)f= ratio of flexural stiffness of beam section to flex-ural stiffness of a width of slab bounded laterally by centerlines of adjacent panels (if any) on each side of the beamfm= average value of ffor all beams on edges of a panelf1= fin direction of 1f2= fin direction of 2s= constant used to compute Vcin slabs = ratio of long side-to-short side of the column, concentrated load, or reaction areap= factor used to com