Original PDF Flash format guide-to-shear-reinforcement-for-slabs  


Guide To Shear Reinforcement For Slabs

ACI 421.1R-08
Guide to Shear Reinforcement for Slabs
Reported by Joint ACI-ASCE Committee 421
Theodor Krauthammer*
Chair
Simon Brown*
Amin Ghali*
James S. Lai*
Edward G. Nawy
Pinaki R. Chakrabarti
Hershell Gill
Mark D. Marvin
Eugenio M. Santiago
William L. Gamble
Neil L. Hammill*
Sami H. Megally
Stanley C. Woodson
Ramez 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.
Tests have established that punching shear in slabs can be effectively
Chapter 4—Punching shear design equations,
resisted by reinforcement consisting of vertical rods mechanically
p. 421.1R-4
anchored at the top and bottom of slabs. ACI 318 sets out the principles of
4.1—Strength requirement
design for slab shear reinforcement and makes specific reference to stirrups,
4.2—Calculation of factored shear stress vu
headed studs, and shearheads. This guide reviews other available types
4.3—Calculation of shear strength v
and makes recommendations for their design. The application of these
n
recommendations is illustrated through numerical examples.
4.4—Design procedure
Keywords: column-slab connection; concrete flat plate; headed shear
Chapter 5—Prestressed slabs, p. 421.1R-9
studs; moment transfer; prestressed concrete; punching shear; shear
5.1—Nominal shear strength
stresses; shearheads; slabs; two-way slabs.
Chapter 6—Tolerances, p. 421.1R-10
CONTENTS
Chapter 1—Introduction and scope, p. 421.1R-2
Chapter 7—Requirements for seismic-resistant
1.1—Introduction
slab-column connections, p. 421.1R-10
1.2—Scope
1.3—Evolution of practice
Chapter 8—References, p. 421.1R-10
8.1—Referenced standards and reports
Chapter 2—Notation and definitions, p. 421.1R-2
8.2—Cited references
2.1—Notation
2.2—Definitions
Appendix A—Details of shear studs, p. 421.1R-12
A.1—Geometry of stud shear reinforcement
Chapter 3—Role of shear reinforcement, p. 421.1R-3
A.2—Stud arrangements
A.3—Stud length
ACI Committee Reports, Guides, Manuals, Standard
Practices, and Commentaries are intended for guidance in
Appendix B—Properties of critical sections of
planning, designing, executing, and inspecting construction.
general shape, p. 421.1R-13
This document is intended for the use of individuals who are
competent to evaluate the significance and limitations of its
Appendix C—Values of v
content and recommendations and who will accept
c within shear-reinforced
responsibility for the application of the material it contains.
zone, p. 421.1R-14
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
ACI 421.1R-08 supersedes ACI 421.1R-99 and was adopted and published June 2008.
Copyright © 2008, American Concrete Institute.
documents. If items found in this document are desired by the
All rights reserved including rights of reproduction and use in any form or by any
Architect/Engineer to be a part of the contract documents, they
means, including the making of copies by any photo process, or by electronic or
shall be restated in mandatory language for incorporation by
mechanical device, printed, written, or oral, or recording for sound or visual reproduction
or for use in any knowledge or retrieval system or device, unless permission in writing
the Architect/Engineer.
is obtained from the copyright proprietors.
421.1R-1
421.1R-2
ACI COMMITTEE REPORT
Appendix D—Design examples, p. 421.1R-17
D.1—Interior column-slab connection
D.2—Edge column-slab connection
D.3—Corner column-slab connection
D.4—Prestressed slab-column connection
CHAPTER 1—INTRODUCTION AND SCOPE
1.1—Introduction
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 slabs
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
Fig. 1.1—Stud assemblies conforming to ASTM A1044/
permits headed shear stud reinforcement conforming to
A1044M: (a) single-headed studs welded to a base rail; and
ASTM A1044/A1044M. A general procedure for evaluation
(b) double-headed studs crimped into a steel channel.
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 mechanically 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 also be formed by
forging the stud ends.
1.2—Scope
Fig. 1.2—Top view of flat plate showing arrangement of
Recommendations in this guide are for the design of shear
shear reinforcement in vicinity of interior column.
reinforcement in slabs. The design is in accordance with
ACI 318. Numerical design examples are included.
CHAPTER 2—NOTATION AND DEFINITIONS
2.1—Notation
1.3—Evolution of practice
A
Extensive tests (Dilger and Ghali 1981; Andrä 1981; Van
c
= area of concrete of assumed critical section
A
der Voet et al. 1982; Mokhtar et al. 1985; Elgabry and Ghali
v
= cross-sectional area of shear reinforcement
on one peripheral line parallel to perimeter of
1987; Mortin and Ghali 1991; Dilger and Shatila 1989; Cao
column section
1993; Brown and Dilger 1994; Megally 1998; Birkle 2004;
bo
= length of perimeter of critical section
Ritchie and Ghali 2005; Gayed and Ghali 2006) have
cb,ct
= clear concrete cover of reinforcement to
confirmed the effectiveness of mechanically anchored shear
bottom and top slab surfaces, respectively
reinforcement, such as shown in Fig. 1.1, in increasing the
cx,cy
= size of rectangular column measured in two
strength and ductility of slab-column connections subjected
orthogonal span directions
to concentric punching or punching combined with moment.
D
= diameter of stud or stirrup
Stud assemblies consisting of either a single-head stud
d
= effective depth of slab; average of distances
attached to a steel base rail by welding (Fig. 1.1(a)) or
from extreme compression fiber to centroids
double-headed studs mechanically crimped into a nonstructural
of tension reinforcements running in two
steel channel (Fig. 1.1(b)) are specified in ASTM A1044/
orthogonal directions
A1044M. Figure 1.2 is a top view of a slab that shows a
db
= nominal diameter of flexural reinforcing bars
typical arrangement of shear reinforcement (stirrup legs or
fc′
= specified compressive strength of concrete
studs) in the vicinity of an interior column. ACI 318 requires
fct
= average splitting tensile strength of light-
that the spacing g between adjacent stirrup legs or studs,
weight-aggregate concrete
measured on the first peripheral line of shear reinforcement,
fpc
= average value of compressive stress in
be equal to or less than 2d. Requirement for distances so and
concrete in two directions (after allowance for
s are given in Chapter 4.
all prestress losses) at centroid of cross section