ACI 421.1R-2008 Guide to Shear Reinforcement for Slabs (Incorporating Errata 02 23 2015)《抗剪钢筋》.pdf

1、ACI 421.1R-08Reported by Joint ACI-ASCE Committee 421Guide to Shear Reinforcementfor SlabsGuide to Shear Reinforcement for SlabsFirst printingErrata as of 02/23/15ISBN 978-0-87031-280-9Copyright by the American Concrete Institute, Farmington Hills, MI. All rights reserved. This materialmay not be re

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10、ual ofConcrete Practice (MCP).American Concrete Institute38800 Country Club DriveFarmington Hills, MI 48331U.S.A.Phone: 248-848-3700Fax: 248-848-3701www.concrete.orgACI 421.1R-08 supersedes ACI 421.1R-99 and was adopted and published June 2008.Copyright 2008, American Concrete Institute.All rights r

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15、neer.Guide to Shear Reinforcement for SlabsReported by Joint ACI-ASCE Committee 421ACI 421.1R-08Tests have established that punching shear in slabs can be effectivelyresisted by reinforcement consisting of vertical rods mechanicallyanchored at the top and bottom of slabs. ACI 318 sets out the princi

16、ples ofdesign for slab shear reinforcement and makes specific reference to stirrups,headed studs, and shearheads. This guide reviews other available typesand makes recommendations for their design. The application of theserecommendations is illustrated through numerical examples.Keywords: column-sla

17、b connection; concrete flat plate; headed shearstuds; moment transfer; prestressed concrete; punching shear; shearstresses; shearheads; slabs; two-way slabs.CONTENTSChapter 1Introduction and scope, p. 421.1R-21.1Introduction1.2Scope1.3Evolution of practiceChapter 2Notation and definitions, p. 421.1R

18、-22.1Notation2.2DefinitionsChapter 3Role of shear reinforcement, p. 421.1R-3Chapter 4Punching shear design equations,p. 421.1R-44.1Strength requirement4.2Calculation of factored shear stress vu4.3Calculation of shear strength vn4.4Design procedureChapter 5Prestressed slabs, p. 421.1R-95.1Nominal she

19、ar strengthChapter 6Tolerances, p. 421.1R-10Chapter 7Requirements for seismic-resistant slab-column connections, p. 421.1R-10Chapter 8References, p. 421.1R-108.1Referenced standards and reports8.2Cited referencesAppendix ADetails of shear studs, p. 421.1R-12A.1Geometry of stud shear reinforcementA.2

20、Stud arrangementsA.3Stud lengthAppendix BProperties of critical sections of general shape, p. 421.1R-13Appendix CValues of vcwithin shear-reinforced zone, p. 421.1R-14Simon Brown*Amin Ghali*James S. Lai*Edward G. NawyPinaki R. Chakrabarti Hershell Gill Mark D. Marvin Eugenio M. SantiagoWilliam L. Ga

21、mble Neil L. Hammill*Sami H. Megally Stanley C. WoodsonRamez B. Gayed*Mahmoud E. Kamara*Subcommittee members who prepared this report.The committee would like to thank David P. Gustafson for his contribution to this report.Theodor Krauthammer*Chair421.1R-2 ACI COMMITTEE REPORTAppendix DDesign exampl

22、es, p. 421.1R-17D.1Interior column-slab connectionD.2Edge column-slab connectionD.3Corner column-slab connectionD.4Prestressed slab-column connectionCHAPTER 1INTRODUCTION AND SCOPE1.1IntroductionIn flat-plate floors, slab-column connections are subjectedto high shear stresses produced by the transfe

23、r of the internalforces between the columns and the slabs. Section 11.11.3 ofACI 318-08 allows the use of shear reinforcement for slabsand footings in the form of bars, as in the vertical legs ofstirrups. ACI 318 emphasizes the importance of anchoragedetails and accurate placement of the shear reinf

24、orcement,especially in thin slabs. Section 11.11.5 of ACI 318-08permits headed shear stud reinforcement conforming toASTM A1044/A1044M. A general procedure for evaluationof the punching shear strength of slab-column connections isgiven in Section 11.11 of ACI 318-08.Shear reinforcement consisting of

25、 vertical rods (studs) orthe equivalent, mechanically anchored at each end, can beused. In this report, all types of mechanically anchored shearreinforcement are referred to as “shear stud” or “stud.” To befully effective, the anchorage should be capable of developingthe specified yield strength of

26、the studs. The mechanicalanchorage can be obtained by heads or strips connected tothe studs by welding. The heads can also be formed byforging the stud ends.1.2ScopeRecommendations in this guide are for the design of shearreinforcement in slabs. The design is in accordance withACI 318. Numerical des

27、ign examples are included.1.3Evolution of practiceExtensive tests (Dilger and Ghali 1981; Andr 1981; Vander Voet et al. 1982; Mokhtar et al. 1985; Elgabry and Ghali1987; Mortin and Ghali 1991; Dilger and Shatila 1989; Cao1993; Brown and Dilger 1994; Megally 1998; Birkle 2004;Ritchie and Ghali 2005;

28、Gayed and Ghali 2006) haveconfirmed the effectiveness of mechanically anchored shearreinforcement, such as shown in Fig. 1.1, in increasing thestrength and ductility of slab-column connections subjectedto concentric punching or punching combined with moment.Stud assemblies consisting of either a sin

29、gle-head studattached to a steel base rail by welding (Fig. 1.1(a) ordouble-headed studs mechanically crimped into a nonstructuralsteel channel (Fig. 1.1(b) are specified in ASTM A1044/A1044M. Figure 1.2 is a top view of a slab that shows atypical arrangement of shear reinforcement (stirrup legs ors

30、tuds) in the vicinity of an interior column. ACI 318 requiresthat the spacing g between adjacent stirrup legs or studs,measured on the first peripheral line of shear reinforcement,be equal to or less than 2d. Requirement for distances soands are given in Chapter 4.CHAPTER 2NOTATION AND DEFINITIONS2.

31、1NotationAc= area of concrete of assumed critical sectionAv= cross-sectional area of shear reinforcementon one peripheral line parallel to perimeter ofcolumn sectionbo= length of perimeter of critical sectioncb,ct= clear concrete cover of reinforcement tobottom and top slab surfaces, respectivelycx,

32、cy= size of rectangular column measured in twoorthogonal span directionsD = diameter of stud or stirrupd = effective depth of slab; average of distancesfrom extreme compression fiber to centroidsof tension reinforcements running in twoorthogonal directionsdb= nominal diameter of flexural reinforcing

33、 barsfc = specified compressive strength of concretefct= average splitting tensile strength of light-weight-aggregate concretefpc= average value of compressive stress inconcrete in two directions (after allowance forall prestress losses) at centroid of cross sectionFig. 1.1Stud assemblies conforming

34、 to ASTM A1044/A1044M: (a) single-headed studs welded to a base rail; and(b) double-headed studs crimped into a steel channel.Fig. 1.2Top view of flat plate showing arrangement ofshear reinforcement in vicinity of interior column.SHEAR REINFORCEMENT FOR SLABS 421.1R-3fyt= specified yield strength of

35、 shear reinforce-mentg = distance between adjacent stirrup legs or studs,measured in a parallel direction to a columnfaceh = overall thickness of slabJc= property of assumed critical section (Eq. (4-4),defined by ACI 318 as “analogous to polarmoment of inertia”Jx,Jy= property of assumed critical sec

36、tion of anyshape, equal to d multiplied by secondmoment of perimeter about x- or y-axis,respectively (Appendix B)Jxy= d times product of inertia of assumed shear-critical section about nonprincipal axes x and y(Eq. (B-11)l = length of segment of assumed critical sectionls= overall specified height o

37、f headed studassembly including anchors (Fig. 1.1, Eq. (6-1)lx,ly= projections of assumed critical section onprincipal axes x and ylx1,ly1= lengths of sides in x and y directions of criticalsection at d/2 from column facelx2,ly2= lengths of sides in x and y directions of criticalsection at d/2 outsi

38、de outermost legs of shearreinforcementMux,Muy= factored unbalanced moments transferredbetween slab and column about centroidalprincipal axes x and y of assumed critical sectionMux,Muy= factored unbalanced moment about thecentroidal nonprincipal x or y axisMuOx,MuOy= factored unbalanced moment about

39、 x or y axisthrough columns centroid On = number of studs or stirrup legs per linerunning in x or y directions = spacing between peripheral lines of shearreinforcementso= spacing between first peripheral line of shearreinforcement and column faceVp= vertical component of all effective prestressforce

40、s crossing the critical sectionVu= factored shear forcevc= nominal shear strength provided by concretein presence of shear reinforcement, psi (MPa)vn= nominal shear strength at critical section, psi(MPa)vs= nominal shear strength provided by shearreinforcement, psi (MPa)vu= maximum shear stress due

41、to factored forces,psi (MPa)x,y = coordinates of point on perimeter of shear-critical section with respect to centroidal axesx and yx,y = coordinates of point on perimeter of shear-critical section with respect to centroidalnonprincipal axes x and y = distance between column face and criticalsection

42、 divided by ds= dimensionless coefficient equal to 40, 30, and20, for interior, edge, and corner columns,respectively = ratio of long side to short side of columncross sectionp= constant used to compute vcin prestressed slabsvx,vy= factor used to determine unbalanced momentabout the axes x and y bet

43、ween slab andcolumn that is transferred by shear stress atassumed critical section = modification factor reflecting the reducedmechanical properties of lightweight concrete,all relative to normalweight concrete of thesame compressive strength = strength reduction factor = 0.752.2Definitionsdrop pane

44、lthickened structural portion of a flat slab inthe area surrounding a column, as defined in Chapter 13 ofACI 318-08. The plan dimensions of drop panels are greaterthan shear capitals. For flexural strength, ACI 318 requiresthat drop panels extend in each direction from the centerlineof support a dis

45、tance not less than 1/6 the span lengthmeasured from center-to-center of supports in that direction.ACI 318 also requires that the projection of the drop panelbelow the slab be at least 1/4 the slab thickness.flat plateflat slab without column capitals or drop panels.shear capitalthickened portion o

46、f the slab around thecolumn with plan dimensions not conforming with the ACI318 requirements for drop panels.shear-critical sectioncross section, having depth d andperpendicular to the plane of the slab, where shear stressesshould be evaluated. Two shear-critical sections should beconsidered: 1) at

47、d/2 from column periphery; and 2) at d/2from the outermost peripheral line of shear reinforcement (ifprovided).stud shear reinforcement (SSR)reinforcementconforming to ASTM A1044/A1044M and composed ofvertical rods anchored mechanically near the bottom and topsurfaces of the slab.unbalanced momentsu

48、m of moments at the ends of thecolumns above and below a slab-column joint.CHAPTER 3ROLE OF SHEAR REINFORCEMENTShear reinforcement is required to intercept shear cracksand prevent them from widening. The intersection of shearreinforcement and cracks can be anywhere over the height ofthe shear reinfo

49、rcement. The strain in the shear reinforcementis highest at that intersection.Effective anchorage is essential, and its location should beas close as possible to the structural members outer surfaces.This means that the vertical part of the shear reinforcementshould be as tall as possible to avoid the possibility of crackspassing above or below it. When the shear reinforcement isnot as tall as possible, it may not intercept all inclined shearcracks. Anchorage of shear reinforcement in slabs isachieved by mechanical ends (heads)