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1、ACI 421.1R-08 Reported by Joint ACI-ASCE Committee 421 Guide to Shear Reinforcement for Slabs Guide to Shear Reinforcement for Slabs First Printing June 2008 ISBN 978-0-87031-280-9 American Concrete Institute Advancing concrete knowledge Copyright by the American Concrete Institute, Farmington Hills
2、, MI. All rights reserved. This material may not be reproduced or copied, in whole or part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of ACI. The technical committees responsible for ACI committee reports and standards strive t
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9、uding but not limited to, United States Occupational Safety and Health Administration (OSHA) health and safety standards. Order information: ACI documents are available in print, by download, on CD-ROM, through electronic subscription, or reprint and may be obtained by contacting ACI. Most ACI stand
10、ards 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 U.S.A. Phone:248-848-3700 Fax:248-848-3701 www.concrete.org ACI 421.1R-08 supersedes ACI 421.1R-99 and was a
11、dopted and published June 2008. Copyright 2008, 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 electronic or mechanical device, printed, written, or oral, or recording f
12、or sound or visual reproduction or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. 421.1R-1 ACI Committee Reports, Guides, Manuals, Standard Practices, and Commentaries are intended for guidance in planning, designing,
13、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 material it contains. The American Concrete Ins
14、titute 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 desired by the Architect/Engineer to be a part of
15、 the contract documents, they shall be restated in mandatory language for incorporation by the Architect/Engineer. Guide to Shear Reinforcement for Slabs Reported by Joint ACI-ASCE Committee 421 ACI 421.1R-08 Tests have established that punching shear in slabs can be effectively resisted by reinforc
16、ement consisting of vertical rods mechanically anchored at the top and bottom of slabs. ACI 318 sets out the principles of design for slab shear reinforcement and makes specific reference to stirrups, headed studs, and shearheads. This guide reviews other available types and makes recommendations fo
17、r their design. The application of these recommendations is illustrated through numerical examples. Keywords: column-slab connection; concrete flat plate; headed shear studs; moment transfer; prestressed concrete; punching shear; shear stresses; shearheads; slabs; two-way slabs. CONTENTS Chapter 1In
18、troduction and scope, p. 421.1R-2 1.1Introduction 1.2Scope 1.3Evolution of practice Chapter 2Notation and definitions, p. 421.1R-2 2.1Notation 2.2Definitions Chapter 3Role of shear reinforcement, p. 421.1R-3 Chapter 4Punching shear design equations, p. 421.1R-4 4.1Strength requirement 4.2Calculation
19、 of factored shear stress vu 4.3Calculation of shear strength vn 4.4Design procedure Chapter 5Prestressed slabs, p. 421.1R-9 5.1Nominal shear strength Chapter 6Tolerances, p. 421.1R-10 Chapter 7Requirements for seismic-resistant slab-column connections, p. 421.1R-10 Chapter 8References, p. 421.1R-10
20、 8.1Referenced standards and reports 8.2Cited references Appendix ADetails of shear studs, p. 421.1R-12 A.1Geometry of stud shear reinforcement A.2Stud arrangements A.3Stud length Appendix BProperties of critical sections of general shape, p. 421.1R-13 Appendix CValues of vc within shear-reinforced
21、zone, p. 421.1R-14 Simon Brown*Amin Ghali*James S. Lai*Edward G. Nawy Pinaki R. ChakrabartiHershell GillMark D. MarvinEugenio M. Santiago William L. GambleNeil L. Hammill*Sami H. MegallyStanley C. Woodson Ramez B. Gayed*Mahmoud E. Kamara* *Subcommittee members who prepared this report. The committee
22、 would like to thank David P. Gustafson for his contribution to this report. Theodor Krauthammer* Chair 421.1R-2ACI COMMITTEE REPORT Appendix DDesign examples, p. 421.1R-17 D.1Interior column-slab connection D.2Edge column-slab connection D.3Corner column-slab connection D.4Prestressed slab-column c
23、onnection CHAPTER 1INTRODUCTION AND SCOPE 1.1Introduction In flat-plate floors, slab-column connections are subjected to high shear stresses produced by the transfer of the internal forces between the columns and the slabs. Section 11.11.3 of ACI 318-08 allows the use of shear reinforcement for slab
24、s and footings in the form of bars, as in the vertical legs of stirrups. ACI 318 emphasizes the importance of anchorage details and accurate placement of the shear reinforcement, especially in thin slabs. Section 11.11.5 of ACI 318-08 permits headed shear stud reinforcement conforming to ASTM A1044/
25、A1044M. A general procedure for evaluation of the punching shear strength of slab-column connections is given in Section 11.11 of ACI 318-08. Shear reinforcement consisting of vertical rods (studs) or the equivalent, mechanically anchored at each end, can be used. In this report, all types of mechan
26、ically anchored shear reinforcement are referred to as “shear stud” or “stud.” To be fully effective, the anchorage should be capable of developing the specified yield strength of the studs. The mechanical anchorage can be obtained by heads or strips connected to the studs by welding. The heads can
27、also be formed by forging the stud ends. 1.2Scope Recommendations in this guide are for the design of shear reinforcement in slabs. The design is in accordance with ACI 318. Numerical design examples are included. 1.3Evolution of practice Extensive tests (Dilger and Ghali 1981; Andr 1981; Van der Vo
28、et et al. 1982; Mokhtar et al. 1985; Elgabry and Ghali 1987; Mortin and Ghali 1991; Dilger and Shatila 1989; Cao 1993; Brown and Dilger 1994; Megally 1998; Birkle 2004; Ritchie and Ghali 2005; Gayed and Ghali 2006) have confirmed the effectiveness of mechanically anchored shear reinforcement, such a
29、s shown in Fig. 1.1, in increasing the strength and ductility of slab-column connections subjected to concentric punching or punching combined with moment. Stud assemblies consisting of either a single-head stud attached to a steel base rail by welding (Fig. 1.1(a) or double-headed studs mechanicall
30、y crimped into a nonstructural steel channel (Fig. 1.1(b) are specified in ASTM A1044/ A1044M. Figure 1.2 is a top view of a slab that shows a typical arrangement of shear reinforcement (stirrup legs or studs) in the vicinity of an interior column. ACI 318 requires that the spacing g between adjacen
31、t stirrup legs or studs, measured on the first peripheral line of shear reinforcement, be equal to or less than 2d. Requirement for distances so and s are given in Chapter 4. CHAPTER 2NOTATION AND DEFINITIONS 2.1Notation Ac= area of concrete of assumed critical section Av= cross-sectional area of sh
32、ear reinforcement on one peripheral line parallel to perimeter of column section bo= length of perimeter of critical section cb,ct= clear concrete cover of reinforcement to bottom and top slab surfaces, respectively cx,cy= size of rectangular column measured in two orthogonal span directions D= diam
33、eter of stud or stirrup d= effective depth of slab; average of distances from extreme compression fiber to centroids of tension reinforcements running in two orthogonal directions db= nominal diameter of flexural reinforcing bars fc= specified compressive strength of concrete fct= average splitting
34、tensile strength of light- weight-aggregate concrete fpc= average value of compressive stress in concrete in two directions (after allowance for all prestress losses) at centroid of cross section Fig. 1.1Stud assemblies conforming to ASTM A1044/ A1044M: (a) single-headed studs welded to a base rail;
35、 and (b) double-headed studs crimped into a steel channel. Fig. 1.2Top view of flat plate showing arrangement of shear reinforcement in vicinity of interior column. SHEAR REINFORCEMENT FOR SLABS421.1R-3 fyt= specified yield strength of shear reinforce- ment g= distance between adjacent stirrup legs
36、or studs, measured in a parallel direction to a column face h= overall thickness of slab Jc= property of assumed critical section (Eq. (4-4), defined by ACI 318 as “analogous to polar moment of inertia” Jx,Jy= property of assumed critical section of any shape, equal to d multiplied by second moment
37、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 section ls= overall specified height of headed stud assembly including anchors (Fig. 1.1,
38、 Eq. (6-1) lx,ly= projections of assumed critical section on principal axes x and y lx1,ly1= lengths of sides in x and y directions of critical section at d/2 from column face lx2,ly2= lengths of sides in x and y directions of critical section at d/2 outside outermost legs of shear reinforcement Mux
39、,Muy= factored unbalanced moments transferred between slab and column about centroidal principal axes x and y of assumed critical section Mux,Muy= factored unbalanced moment about the centroidal nonprincipal x or y axis MuOx,MuOy= factored unbalanced moment about x or y axis through columns centroid
40、 O n= number of studs or stirrup legs per line running in x or y direction s= spacing between peripheral lines of shear reinforcement so= spacing between first peripheral line of shear reinforcement and column face Vp= vertical component of all effective prestress forces crossing the critical sectio
41、n Vu= factored shear force vc= nominal shear strength provided by concrete in presence of shear reinforcement, psi (MPa) vn= nominal shear strength at critical section, psi (MPa) vs= nominal shear strength provided by shear reinforcement, psi (MPa) vu= maximum shear stress due to factored forces, ps
42、i (MPa) x,y= coordinates of point on perimeter of shear- critical section with respect to centroidal axes x and y x,y= coordinates of point on perimeter of shear- critical section with respect to centroidal nonprincipal axes x and y = distance between column face and critical section divided by d s=
43、 dimensionless coefficient equal to 40, 30, and 20, for interior, edge, and corner columns, respectively = ratio of long side to short side of column cross section p= constant used to compute vc in prestressed slabs vx,vy= factor used to determine unbalanced moment about the axes x and y between sla
44、b and column that is transferred by shear stress at assumed critical section = modification factor reflecting the reduced mechanical properties of lightweight concrete, all relative to normalweight concrete of the same compressive strength = strength reduction factor = 0.75 2.2Definitions drop panel
45、thickened structural portion of a flat slab in the area surrounding a column, as defined in Chapter 13 of ACI 318-08. The plan dimensions of drop panels are greater than shear capitals. For flexural strength, ACI 318 requires that drop panels extend in each direction from the centerline of support a
46、 distance not less than 1/6 the span length measured from center-to-center of supports in that direction. ACI 318 also requires that the projection of the drop panel below the slab be at least 1/4 the slab thickness. flat plateflat slab without column capitals or drop panels. shear capitalthickened
47、portion of the slab around the column with plan dimensions not conforming with the ACI 318 requirements for drop panels. shear-critical sectioncross section, having depth d and perpendicular to the plane of the slab, where shear stresses should be evaluated. Two shear-critical sections should be con
48、sidered: 1) at d/2 from column periphery; and 2) at d/2 from the outermost peripheral line of shear reinforcement (if provided). stud shear reinforcement (SSR)reinforcement conforming to ASTM A1044/A1044M and composed of vertical rods anchored mechanically near the bottom and top surfaces of the sla
49、b. unbalanced momentsum of moments at the ends of the columns above and below a slab-column joint. CHAPTER 3ROLE OF SHEAR REINFORCEMENT Shear reinforcement is required to intercept shear cracks and prevent them from widening. The intersection of shear reinforcement and cracks can be anywhere over the height of the shear reinforcement. The strain in the shear reinforcement is highest at that intersection. Effective anchorage is essential, and its location should be as close as possible to the structural members outer surfaces.
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