ACI 355.1R-91
(Reapproved 1997)
STATE-OF-THE-ART REPORT ON
ANCHORAGE TO CONCRETE
Reported by ACI Committee 355
Harry A. Chambers
Secretary
Patrick J. Creegan
Chairman
Edwin A. Burdette
Robert W. Cannon
Peter J. Carrato
Peter D. Courtois
Rolf Eligehausen
Raymond R. Funk
C. Raymond Hays
Paul R. Hollenbach
Gerard B. Hassehvander
Harry B. Lancelot III*
Douglas D. Lee
Alexander Makitka, Jr.
Donald F. Meinheit
Richard S. Orr
Moorman L Scott
George A. Senkiw
Harry Wiewel
Jim L Williams
Richard E. Wollmershauser
*Committee Chairman during the formative years of this report.
For the first time concrete anchoring knowledge based on worldwide test programs is presented in a state-of-the-art document. Performance
of different anchor types, including cast-in-place, grouted, expansion, torque-controlled, chemical (adhesive), and undercut anchors is presented
in both uncracked and cracked concrete. Failure modes in tension and shear, spacing and edge distance, group performance, and load
displacements are offered. The effect of loading conditions for structural supports, column bases, and pipe supports as well as base plate
flexibility, how load is transferred to anchors, and ductility are discussed. Design criteria and existing code requirements, both domestic and
foreign, are presented.
KEYWORDS: Adhesive anchors; anchorages; anchors; anchor groups; base plates; bolts; cast-in-place anchors; chemical anchors; code
requirements; combined loads; compression zone; concrete; cracked concrete; creep; deformation; design criteria; drilling; ductility;
dynamic loads; edge distance; embedment; expansion anchors; failure modes; fatigue loads; fasteners; flexible base plates; grouting; loads;
load transfer; load-displacement; post-installed anchors; preload; pullout; seismic loads; shear loads; slip; spacing; spalling; static loads;
stiffness; studs; structural design; tensile strength; tension loads; tension zone; temperature; torque; torque-controlled anchors; ultimate
strength; undercut anchor, yield strength.
FORWARD
This state-of-the-art report on anchorage to concrete is the first of a two-volume project being undertaken
by ACI Committee 355. The second volume, currently being developed, is a design manual. This first
volume includes no design aids or procedures, per se, but with emphasis on behavior will serve as the guide
for preparation of the second volume.
Committee 355 is working with Committees 349 and 318 toward the objective of including the subject of
anchorage to concrete in ACI 318-95.
ACI Committee Reports, Guides, Standard Practices, and
Commentaries are intended for guidance in designing,
planning, executing, or inspecting construction, and in
preparing specifications. Reference to these documents shall
not be made in the Project Documents. If items found in
these documents are desired to be a part of the Project
Documents, they should be phrased in mandatory language
and incorporated into the Project Documents.
ACI 355.1R-91 became effective JuIy 1, 1991.
Copyright 0 1991, 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 any electronic or mechanical device, printed or 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 is
obtained from the copyright proprietors.
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355.1R-2
MANUAL OF CONCRETE PRACTICE
TABLE OF CONTENTS
Chapter 1-Introduction, p 355.1R-2
1.1 Purpose
1.2 Significance of the subject
1.3 Scope
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Chapter 2-Types of anchoring devices,
p 355.1R-2
2.1
2.2
2.3
2.4
2.5
Introduction
Scope
Anchor systems
Cast-in-place systems
Post-installed systems
Chapter 3-Behavior of anchors, p 355.1R-9
3.1
3.2
3.3
3.4
Introduction
Behavior of anchors in uncracked concrete
Behavior of anchors in cracked concrete
Behavior of cast-in-place anchor bolts in
uncracked concrete piers
3.5 References
Chapter 4-Design considerations,
p 355.1R-53
4.1 Introduction
4.2 Functional requirements
4.3 Materials
4.4 Design basis
4.5 Construction practices
4.6 References
Chapter 5-Construction considerations,
p 355.1R-60
5.1 Introduction
5.2 Shop drawings/submittals
5.3 Tolerances
5.4 Installation of anchors
5.5 Inspection
5.6 Grouting
5.7 Field problems
Chapter 6-Requirements in existing codes
and specifications, p 355.1R-66
6.1 Introduction
6.2 Existing codes and specifications
6.3 Application and development of codes
6.4 References
Appendix A-Conversion factors, p 355.1R-71
Appendix B-Notations, p 355.1R-71
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CHAPTER 1 -INTRODUCTION
1.1-Purpose
The purpose of this document is to summarize
the current state of the art in anchorage to
concrete.
1.2-Significance of the subject
To date, anchorage to concrete has received
little attention in structural codes. Emphasis has
been primarily on the tensile and shear capacities
of anchorage devices. As designs became more
sophisticated and analyses more exacting, more
emphasis was placed on the transfer of loads
through single anchors and anchor systems. It was
recognized that performance of anchors controlled
these load transfers, and that generally, failure
modes at ultimate anchor capacities were
important. There were no definitive design codes
or anchorage performance criteria on which
designers and installers could rely. Subsequently,
a myriad of approaches were developed.
1.3-Scope
This state-of-the-art report summarizes anchor
types and provides an overview of anchor performance and failure modes under various loading
conditions in both uncracked and cracked concrete.
It covers design and construction
considerations and summarizes existing requirements in codes and specifications. References are
given for further review.
CHAPTER 2 -TYPES OF ANCHORING
DEVICES
2.1-Introduction
There are many types of devices used for
anchoring structures or structural members to
concrete. The design of anchorages, involving the
selection and positioning of these devices has been
based on the Engineer’s experience and judgment,
private test data, manufacturers’ data, and existing
(sometimes obsolete) code requirements. It is
proposed to promote a design of anchorages that
more consistently reflects the performance
potential of each type of anchor.
2.2-Scope
This report relates to the most widely used
types of anchor, in sizes ranging from 1/4 in. (6.35
mm) to 2 l/2 in. (63.5 mm) in diameter. Included
for consideration are only those devices which can
generally be considered bolt and insert-type
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ANCHORAGE TO CONCRETE
anchors. Excluded from consideration are shear
lugs, structural shapes, powder actuated fasteners,
light plastic or lead inserts, hammer driven
concrete nails, screw driven systems, and cables.
These are excluded because there is a paucity of
test data regarding their performance. The
anchors included in this report are either
commercially available or may be fabricated.
2.3-Anchor Systems
According to present practice, there are two
broad groups of anchoring systems: cast-in-place
systems (anchors installed before the concrete is
cast) and post-installed systems (anchors installed
in holes drilled after the concrete has been cast
and cured). Table 2.1 identifies these two groups
of anchors.
Table 2.1 -Types of anchors in concrete
Cast-in-place systems
Embedded, nonadjustable
Common bolts
Hooked "J" & "L" bolts
Threaded rod
Reinforcing steel
Threaded inserts
Stud-welded plates
Bolted connections
Adjustable anchors
Fig. 2.1
Fig. 2.2
Fig. 2.3
Fig. 2.4
Fig. 2.5
Fig. 2.6
Fig. 2.7
Fig. 2.8
Post-installed systems
Bonded anchors
Grouted anchors
Headed bolts or anchor
Fig. 2.9
Chemical anchors
With threaded rod
With reinforcing steel
Fig. 2.10
Fig. 2.11
Expansion anchors
Torque-controlled
Heavy-duty sleeve anchor
Sleeve anchor
Shell expansion anchor
Wedge anchor
Rock/concrete expansion
anchor
Fig. 2.12
Fig. 2.13
Fig. 2.14
Fig. 2.15
Deformation controlled
Drop-in anchor
Self-drilling anchor
Stud anchor
Fig. 2.17
Fig. 2.18
Fig. 2.19
Undercut
With predrilled under-cut
hole
Self undercutting
2.4-Cast-in-place systems
2 . 4 . 1 - Embedded Anchors, Non Adjustable - These anchors may have an end
attachment, such as a coil loop, head, nut, or
plate, which will enhance anchorage properties
and develop full potential strength by means of
bond, and/or bearing, or both. Typical examples
of these anchors are:
Common bolts
- structural steel bolts
placed with the head into
the concrete. (Fig. 2.1)
Hooked
"J" or "L" bolts
-bent, smooth or deformed
threaded bars. Have been
known to straighten out in
pull-out tests. (Fig. 2.2)
Threaded rod
- straight threaded rod,
usually with coarse
threads. (Fig. 2.3)
Reinforcing steel - Stock or trade-name reinforcing bar (Fig. 2.4)
wire form or internally
Threaded inserts
threaded ferrule inserts,
or coils, usually manufactured with internal or
external threads, with wire
loop struts. Headed
anchors made from
smooth or reinforcing
steel bar also fall into this
category. (Fig. 2.5)
Stud welded plates - steel plates which have
smooth bent hooked bars,
deformed bars, or headed
stud anchors. (Fig. 2.6)
2.4.2 Bolted connections-These anchors consist
of headed bolts, as embedded or throughconnectors. (Fig. 2.7).
Plastic
Fig. 2.16
L Steel
plate
Fig. 2.20
Fig. 2.20
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Fig. 2.7-Bolted connections
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355.1R4
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D
P
Washer tack welded
.
Note
Fig. 2.1- Common bolts
-
: E i t h e r ' J ' o r ' L ' ’ b o I ts c a n
be
made
from plain or threaded rod
Fig. 2.2-J- and L-bolts (not recommended)
.
b
v
*
Fig. 2.4 -Reinforcing steel
Fig. 2.3 - Threaded rod
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ANCHORAGE TO CONCRETE
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a
*
.
‘X
..
v
*
B
.
Fig. 2.5 - Threaded inserts
We I d
Fig. 2.6 - Stud- welded plates
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2.4.3 Adjustable anchors-Adjustable anchors
can be adjusted for lateral position or depth (Fig.
2.8). They are normally used for attaching large
machines or equipment bases. On thin floor slabs,
the anchor bolt often goes through the concrete to
develop the required anchor capacity. When the
floor slab or foundation is very thick, the anchor
can develop full capacity and still be embedded in
the concrete. After the equipment or machine
base is installed and leveled, grout is used to fill
the void around the anchor. The anchor then acts
similar to a cast-in-place anchor.
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.
P
-
4
Fig. 2.8-Adjustable anchors
2.5-Post-installed s y s t e m s
These anchors are installed in a hole drilled in
the cured concrete. There are two basic groups of
post-installed systems: bonded and expansion.
2.5.1-Bonded anchors
2.5.1.1 Grouted anchors-Grouted anchors are
headed or headless bolts or threaded rods. They
are set in predrilled holes with portland cement
and sand grout or other commercially available
premixed grout. (Fig. 2.9)
2.5.1.2 Chemical anchors-Chemical anchors
are usually threaded rods (Fig. 2.10) or deformed
bars (Fig. 2.11) which are bonded in place with
two-part chemical compounds of polyesters,
vinylesters, or epoxies.
The chemicals are
available in four forms: glass capsules, plastic
cartridges, tubes, or bulk.
Glass capsules are inserted into the drilled hole,
and then broken by the anchor rod when it is rotated and hammered into place, thereby mixing
two components to cause a chemical reaction.
The plastic cartridges are used with a dispenser
and a mixing nozzle which mixes the two parts,
initiating a chemical reaction while installing the
compound into the drilled hole. The anchor rod
is then inserted into the hole completing the
installation. The setting time is dependent on
temperature, varying from a few minutes at 90o F
up to several hours at 30o F.
The tube or “sausage” type contains two
components which are mixed by kneading the
tube, placing the mixture into the hole, and finally,
inserting the anchor rod into the hole.
The bulk systems predominantly use epoxies,
which are either premixed in a pot and used
immediately, or pumped through a mixer and
injected into the hole. The anchor is installed
immediately afterward. Epoxies can be formulated to set up quickly or slowly (up to 36 hr
curing time).
*
in
.v
chemical
or
from capsule
Fig. 2.10-Chemical anchor with threaded rod
n
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ANCHORAGE TO CONCRETE
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2.5.2 Expansion anchors-Expansion anchors
are designed to be inserted into predrilled holes
and then expanded by either tightening the nut
(torque controlled expansion anchor, Sections
2.5.2.1 to 2.5.2.5), hammering the anchor
(deformation controlled expansion anchor,
Sections 2.5.2.6 to 2.5.2.8), or expanding into an
undercut in the concrete (undercut anchors,
Section 2.5.2.9). These anchors transfer the
tension load from the bolt to the concrete by
expansion pressures or forces through friction
and/or keying against the side of the drilled hole.
They often are supplied with a bolt, nut, and
The following sections describe the
washer.
various types of expansion anchors.
2.5.2.1 Heavy duty, torque controlled sleeve
anchor-This type of anchor consists of a bolt or
threaded rod with nut and washer on one end and
a cone on the embedded end, (Fig. 2.12). Around
the cone is a heavy expansion sleeve. Above the
sleeve is a collapsible mechanism, sometimes made
of plastic. A spacer sleeve extends to the surface
of the drilled hole. The anchor is set by tightening the bolt head or nut which draws the cone
up through the expansion sleeve, expanding it
against the side of the drilled hole. The anchor
develops its tensile capacity by means of a combination of keying into the concrete and high
friction between the sleeve and concrete. The
spacer sleeve aids in increasing the shear capacity.
Tensile capacity depends on the strength of the
bolt and its depth of embedment.
BEFORE
TORQUING
AFTER
TORQUING
355.1R-7
2.5.2.2 Sleeve anchors- The sleeve anchor
consists of a steel stud, an expansion sleeve usually
made of sheet metal, and a nut and washer (Fig.
2.13). The bottom of the steel stud has a
uniformly tapered mandrel which has the same
diameter at the end as the expansion sleeve. The
entire length of the bolt below the washer is
enclosed in a section or sections of the steel
tubing. The bottom of the expansion sleeve is slit
longitudinally to provide for expansion. When the
nut is tightened, the tapered mandrel moves into
and expands the sleeve which in turn bears against
the wall of the hole. This anchor is used for
medium and light holding requirements.
.
.
Fig. 2.13 - Sleeve anchor
2.5.2.3 Shell expansion anchors - The shell
expansion anchor, (Fig. 2.14) is available in two
types. One type consists of a two-piece shell held
together by steel tabs with a tapered, internally
threaded end plug. The second type consists of a
two-piece shell section with two tapered steel
cones, one at the top end and one at the bottom,
which are held together by a steel spring at the
center. The bottom cone is internally threaded to
accept a bolt or stud. By torquing the fastener
into the anchor, the steel cones expand the shell
to bear against the wall of the hole.
by
Single-acting
(shell
expanded
single wedge nut)
Double acting
expanded
(shel
by opposing wedge)
Fig. 2.14 - Shell expansion anchor
Fig. 2.12 - Heavy-duty, torque-controlled sleeve
anchor
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2.5.2.4 Wedge anchors-The wedge anchor,
(Fig. 2.15) consists of a steel stud bolt with a nut
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MANUAL OF CONCRETE PRACTICE
and washer. The bottom of the steel stud has a
uniform tapered mandrel around which is positioned an expandable steel clip or separate steel
When the nut is
wedges with protrusions.
tightened, the clip or steel wedges ride up on the
tapered mandrel, wedging between the mandrel
and the wall of the hole.
AFTER
TORQUING
BEFORE
TORQUING
2.5.2.6 Drop-in anchors-The drop-in anchor
consists of a steel shell and an internal steel
expander plug (Fig. 2.17). The anchor is internally
threaded at the top end while the internal end is
machined to a uniform taper, matching the shape
of the steel plug inside the anchor. The lower
portion of the shell is slit longitudinally into equal
segments to allow the anchor to expand when the
internal plug is hammered with a setting tool. By
hammering the plug into the shell, the lower
portion of the shell expands to bear against the
wall of the hole.
BEFORE
AFTER
Fig. 2.15- Wedge anchor
2.5.2.5 Rock/concrete expansion anchor-The
rock/concrete expansion anchor, (Fig. 2.16) consists of a stud bolt that is threaded on the top end
for a hex nut. The bottom end consists of a large
mechanical expansion anchor. To set the expansion anchor, the stud bolt is rotated in a clockwise
direction. Grouting is optional down the center of
the bolt to fill the annular space between the rod
and the drilled hole for corrosion protection.
Grout hole
Threaded rob
Nut
Air tube
Plate
Fig. 2.17-Drop-in anchor
2.5.2.7 Self-drilling anchors-The self-drilling
anchor, (Fig. 2.18) consists of a steel shell and a
tapered steel end plug. The bottom of the shell
has teeth for cutting its own hole in the concrete.
The top of the shell is internally threaded to
accept a bolt or stud. The bottom of the shell is
expanded by hammer drilling the anchor over the
steel plug. The plug expands the bottom of the
shell which bears against the wall of the drilled
hole.
BEFORE
AFTER
Hollow bar
Grout hole
Thrust rl
Mal leable
e shell
Fig. 2. I6 - Rock/concrete expansion anchor
(grouted)
b
0.
Fig. 2.18 -Self-drilling anchor
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355.1R-9
2.5.2.8 Stud anchors -The stud anchor consists of a steel stud, threaded at the top end, and
has a drilled hole with longitudinal slits at the
bottom end, which accepts a tapered steel plug
(Fig. 2.19). The top of the threaded section is
raised to provide a surface for hammering. By
hammering the top of the stud, the tapered plug
expands the bottom end of the bolt causing it to
bear against the wall of the hole.
BEFORE
b
.
v
-
’ .
.
t
.
.v
Q
AFTER
V
*
.
BEFORE
.
4
.
.
n
.
D
V
v
v-
4
Q
A
AFTER
.
.
bolt and tapered cone are drawn up into the
expansion sleeve, keeping the bottom of the
expansion sleeve in the undercut.
A .b
I
.
V’
Fig. 2.19 - Stud anchor
2.5.2.9 Undercut anchors-There are two
primary designs of undercut anchors available
(Fig. 2.20). They all operate by keying and
bearing against an undercut in the concrete at the
bottom of the drilled hole. They cause little or no
expansion force in the concrete, but generate high
tensile-loading capacities.
The first type requires a second drilling
operation to create an undercut at the bottom of
the first drilled hole. The anchor is installed with
the bottom of the expansion sleeve at the undercut. When the nut is tightened, the tapered
expander plug expands the bottom of the steel
expansion sleeve into the undercut.
The second type cuts its own undercut at the
bottom of the drilled hole. A sleeve is hammered
by a rotary hammer drill with a special setting
tool. The bottom of the expansion sleeve is driven
over a cone at the bottom of the hole. The
bottom of the expansion sleeve has a sharp edge
which, on expansion, cuts its own undercut into
the wall of the hole. By tightening the nut, the
Fig. 2.20 - Undercut anchor
CHAPTER 3-BEHAVIOR
3.1 - Introduction
Understanding anchor behavior is necessary in
specifying the appropriate anchorage for a given
application. This includes an understanding of
failure modes and strengths as well as loaddisplacement and relaxation characteristics of
various anchor types. This chapter covers anchor
behavior in uncracked concrete and in cracked
concrete.
Anchors are primarily loaded through
attachments to the embedded anchor. The
loading can be in tension and shear or
combinations of tension and shear (Fig. 3.1).
They may also be subjected to bending depending
on the details of shear transfer through the
attachment. The behavior of anchors in tension is
of primary importance and will be discussed first.
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OF ANCHORS
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MANUAL OF CONCRETE PRACTICE
combined tension
and shear loading
tension loading
[ shear
loading
bending
Fig. 3.1 -Possible loadings of anchors
By far, most anchor testing to date has been
performed in uncracked concrete. While cracking
occurs in almost all concrete, testing in uncracked
concrete provides the basis for understanding
anchor behavior.
The various types of anchors have different displacement characteristics depending on preload,
load transfer mechanism, and failure mode. Fig.
3.3(a)-3.3(c) present three load-displacement
graphs. Fig. 3.3(a) gives the characteristic curves
for headed and undercut anchors while Fig. 3.3(b)
presents curves for torque-controlled, drop-in, and
self-drilling expansion anchors. Fig. 3.3(c) gives
load displacement curves for adhesive anchors.
The displacements shown represent the displacement (slip) of the embedded anchor and the deformation of the concrete as well as the deformation of the anchor.
When a preload is applied to an anchor,
typically by tightening the nut to a prescribed
moment torque, the displacement caused by an
externally applied load is affected. The preloaded
3.2-Behavior of anchors in uncracked
concrete
3.2.1 Load-displacement behavior and failure
modes under tension loading- The five primary
failure modes of anchors in tension are (Fig. 3.2):
(a) Steel failure
(b) Pull-out failure
(c) Concrete splitting failure
(d) Concrete cone failure
(e) Spacing and edge cone failure
a) steel failure
d) concrete cone failure
b) pull-out failure
c) concrete splitting failure
e) spacing and edge cone failure
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Fig. 3.2 - Typical failure modes of anchors loaded in tension
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ANCHORAGE TO CONCRETE
load F [kN]
l o a d F [kN]
0
4
6
8
10
Displacement s [mm]
Fig. 3.3(a) - Typical load-displacement relationships
of headed and undercut anchors (from Rehm,
Eligehausen, and Mallee 1988)
2
I I
Iine
anchor type
6
8
4
d i s p l a c e m e n t s [mm]
bolt diameter anchorage depth
mm
mm
I
Fig. 3.3(b) - Typical load-displacement relationships
of expansion anchors under tension loading (from
Eligehausen and Pusill-Wachtsmuth 1982)
d i s p l a c e m e n t [mm]
Fig. 3.3(c)- Typical load-displacement behavior of chemical anchors under tension and shear loading (from
Eligehausen and Pusill- Wachtsmuth 1982)
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anchor shows little displacement with increasing
external loading until the preload in the anchor
(and resulting clamping force on the concrete) is
overcome. The preload has no effect on the ultimate static tensile capacity of the anchorage, but
significantly reduces the anchor total displacement.
In the case of steel failure (Fig. 3.3(a), Line 3)
the ductility depends on the relationship between
tensile strength and yield strength of the steel and
the anchor length. Inelastic displacements of
headed anchors due to concrete deformations
under the head may be expected at relatively low
loads unless preloaded. Increasing the bearing
area under the head may reduce inelastic displacements but will have little influence on the failure
load [compare Lines 1 and 2 in Fig. 3.3(a)].
Headed anchors that fail due to fracture of the
concrete will exhibit a brittle failure (Fig. 3.3(b),
line 2).
The behavior of drop-in anchors is dependent
on the magnitude of the expansion force created
in setting the anchor. When expanded properly
during installation, high expansion forces are
induced and the load displacement curve may
remain almost linear up to failure [Fig. 3.3(b),
Line 2).
The expansion force, at installation, of torquecontrolled expansion anchors is smaller than that
of drop-in anchors and, therefore, the displacements are larger for equal loads. If the external
load exceeds the preloading force in the bolt
generated by the torquing during installation, the
spreading cone is pulled further into the sleeve,
leading to increased displacement. At failure the
deformations are much larger than for comparable
drop-in anchors [Fig. 3.3(b)].
Self-drilling anchors show larger displacements
in the total load range than torque-controlled
expansion and drop-in anchors [Fig. 3.3(b)]. This
happens because load transfer is mainly by
mechanical interlock which causes high pressure
on the concrete and large concrete deformations.
The displacement behavior of undercut anchors
depends primarily on the bearing area (undercut
area) and the installation torque. Therefore
relatively large deformations may be expected with
some undercut anchors while others exhibit elastic
behavior well above service load [Fig. 3.3(a)].
Adhesive anchors exhibit elastic behavior up to
nearly maximum load [Fig. 3.3(c)]. While the
load-displacement curves of adhesive anchors
exhibit relatively low coefficients of variation in
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comparison to torque-controlled expansion and
drop-in anchors, the bond strengths vary considerably depending on the adhesive component
mix used and the installation procedure.
Under working loads all categories of anchors
should behave elastically with little additional
displacement after installation.
However, at
ultimate load a plastic behavior and in the case of
cyclic loading only a limited strength degradation
is desired. Fig. 3.3(a)-3.3(c) show that the actual
load-displacement behavior of the currently
available expansion, undercut, adhesive, and
headed anchors differs somewhat from this plastic
behavior.
Under sustained loads displacements will
increase with time due to creep of concrete in the
highly stressed load transfer area (bearing area in
the case of headed or undercut anchors, contact
area in the case of expansion anchors, bonded
area in the case of adhesive or grouted anchors).
As an example, in Fig. 3.4 (see Seghezzi and
Vollmer, 1982) the displacements of a torquecontrolled expansion anchor loaded with a
constant tensile force corresponding to approximately 70 percent of the static ultimate strength,
are plotted as a function of load duration on a
double logarithmic scale. It can be seen that the
displacement velocity (tangent to the
displacement-time curve) decreases with increasing
time and, therefore, the displacements approach a
limiting final value. The increase in displacements
is smaller for lower sustained loads. If the load is
increased after a sustained load test, the displacement curve is rather steep until it reaches the
static envelope which is followed thereafter. Failure load and displacement at maximum load are
not negatively influenced by a previous sustained
load smaller than about 70 to 80 percent of the
static failure load.
10*
10
10 2
Duration [Days]
Fig. 3.4 -Increase of displacement during sustained
loading
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ANCHORAGE TO CONCRETE
In principle, the same behavior is valid for
cyclic loadings with up to 1 x lo6 load repetitions
and an upper load (where the cyclic load ranges
between an upper and lower value, both of which
are tension) smaller than about 50 percent of the
static failure load (provided no fatigue failure of
the bolt occurs). For higher upper loads the displacements may increase significantly and a fatigue
failure of the concrete might occur (Rehm,
Eligehausen, and Mallee 1988).
Sustained and cyclic loadings in the workingload range have the same influence on displacements and ultimate loads of headed anchors
as for expansion and undercut anchors.
3.2.2 Relaxation -If headed anchors are preloaded, the initial force induced in the anchor is
reduced with time due to creep of the highly
stressed concrete under the anchor head. The
final value of the tension force in the anchor
depends primarily on the value of bearing stresses
under the head, the concrete deformation and the
anchorage depth. In typical cases the value of
that final force will approach 40 to 80 percent of
the initial preload (40 percent for short anchors,
80 percent for long anchors).
Torque-controlled expansion anchors are
usually preloaded by tightening the nut during
installation. This preload is essential for the
proper performance of such anchors. In a typical
installation, locally high concrete stresses are
created around the embedded anchor wedges or
expansion devices as the anchor is preloaded.
Creep of concrete under these high stresses results
in a slight movement of the embedded anchor,
and in turn, in a reduction in the load in the bolt.
Fig. 3.5 shows a typical load-relaxation test
(Burdette, Perry, and Funk 1987). Preload is
plotted as a function of time. The shape of the
curve is essentially the same for all anchors
(including headed anchors).
There is an
exponential drop-off of load immediately after the
applied tension is released, followed by a
continued gradual diminishing of the load over an
indefinite period. It is estimated that the final
preload will be about 40 to 60 percent of the
initial value. This is confirmed by other test data
(Seghezzi and Vollmer 1982, and Wagner-Grey
1976). After retorquing the anchors, the process
of load relaxation starts again, however, the final
value of the preload is increased (Fig. 3.6).
Retorquing even a short time after anchor installation can be effective (Wagner-Grey 1976).
355.1R-13
I
0
0
20
30
40
50
60
70
Time [Days]
Fig. 3.5 -Reduction of preload as a function of time
(after Burdette, Perry, and Funk 1987)
1
i
I
.I
Torque Controlled Expansion Anchor M12
0
0
2,5
I
I
5,0
7,5
I
10
12,5
Time [h]
Fig. 3.6 -Influence of retorquing on the final value
of preload (from Seghezzi and Vollmer 1982)
Chemical anchors are usually preloaded by
applying a predefined torque. Because of the high
stresses in the adhesive bond, the preload force in
the anchor declines faster and the final value is
less than for torque-controlled expansion and
headed anchors.
Long-term relaxation and creep has been
Four Ml6
investigated in several studies.
diameter polyester anchors tested at loads of 25,
30, 38, and 40 kN (6, 7, 8.5, and 9 kips), showed
displacements still increasing after 5 years, but
ranging from 0.090 to 0.140 mm (0.0036 to 0.056
in.)(Elfgren, Anneling, Eriksson, and Granlund
1988). Creep tests were also performed on 26
Ml6 anchors for 3 years at various loads and
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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I
I
I
10
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MANUAL OF CONCRETE PRACTICE
environmental conditions. At allowable working
loads of 15 kN (3.4 kips), anchors tested indoors
showed small creep, 0.10 to 0.40 mm (0.004 to
0.016 in.). However, anchors tested outdoors
exhibited continually increasing creep. Those
tested indoors at 30- and 45- kN (7 and 10 kips),
loads exhibited continually increasing creep. A 4
month test on epoxy anchors showed creep less
than 0.009 in. (0.2 mm) (Wiewel 1989).
The U.S. Army Corps of Engineers performed
creep tests on polyester and epoxy anchors,
subjecting the anchors to 60 percent of the anchor
steel yield strength for 6 months. Cement and
epoxy grouted specimens exhibited low slippage,
0.0013 to 0.0008 in. (0.03 to 0.02 mm), while
polyester anchors exhibited approximately 30 times
as much movement, 0.008 to 0.024 in. (0.2 to 0.6
mm) (Best, Floyd, and McDonald 1989).
3.2.3 Ultimate strength in tension
3.2.3.1 Steel failure -The strength of anchor
steel controls failure when the embedment of the
anchor is sufficient to preclude concrete failure
and when the spreading forces are sufficiently high
(expansion anchors) or the bearing area is sufficiently large (headed and undercut anchors) to
preclude an anchor slip failure. The failure mode
[Fig. 3.2(a)] is rupture of the anchor steel with
ductility dependent on the type of anchor steel
and embedment length. The ultimate strength can
be determined from Eq. 3.1.
F u = 4 x f,,, lb
(3 .1)
where
As = tensile stress area, in.*
f ut = ultimate tensile strength of steel, psi
For given material properties and anchor
dimensions this case defines the upper limit for
the tensile-load-carrying capacity.
Fig. 3.7 shows a comparison of the failure loads
of headed anchors measured in tests to the values
predicted by Eq. 3.1. Because the theoretical
failure load was calculated with the nominal steel
strength, the ratios of actual to predicted tensile
capacity are larger than one.
number
of
specimens
10 STEEL FAILURE
5-
Fig. 3.7-Ratio of actual to predicted tensile capacity
according to Eq. (3.1) for steel failure (after Klingner
and Mendonca 1982)
3.2.3.2 Concrete cone failure -When the
embedment of an anchor or group of anchors is
insufficient to develop the tensile strength of the
anchor steel, a pullout cone failure of the concrete
[see Fig. 3.2(d)] is the principal failure mode.
When the spacing of anchors or location of an
edge [Fig. 3.2(e)] interferes with the development
of the full cone strength of an anchor, its capacity
will be reduced.
The angle of the failure cone, measured from
the axis of the anchor, varies along the failure
surface and shows considerable scatter. In ACI
349, Appendix B, ACI Committee 349,1985) the
angle of the failure cone of headed and expansion
anchors is assumed as 45’. According to Cannon*,
in the case of expansion anchors the angle varies
from about 60’ for short embedments (Id ( 2 in)
to 45O for 1, 2 6 in. According to Rehm,
Eligehausen, and Mallee 1988, the angle varies
between approximately 50° and 60”, (mean value
5S”) and tends to decrease with increasing
anchorage depth.
The following formulas have been developed to
describe behavior of headed studs, expansion, and
undercut anchors.
*Cannon, Robert W., correspondence to ACI
Committee 355, Nov.
1986.
Cannon, Robert W., correspondence to ACI Committee 355, Sept.
1988.
This correspondence is filed at ACI
ACI headquarters and is available
at cost of reproduction and handling at time of request.
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
355.1R-14
ANCHORAGE TO CONCRETE
ACI 349, Appendix B, limits the tensile capacity
of
of the cone failure of an anchor, or wup
.
anchors, to a uniform stress of 4 +d$ (psi) on
the stress cone surface of the anchors.
(3.2)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
strength reduction factor
0.85 for uncracked concrete
= 0.65 in zone of potential
cracking
A = the summation of the projected
areas (in.2) of individual stress
cones minus the areas of overlap and of any area, or areas,
cut off by intersecting edges.
Note: Other reductions are made based on
member thickness relative to embedment and the
area of fabricated anchor heads (see Fig. 3.8).
ACI 349 has no requirements for minimum
center-to-center spacing of single anchors or
anchors belonging to a group.
Fig. 3.9 shows the frequency diagram of the
ratio of actual to Predicted tensile capacity of
headed anchors.
Theoretical capacity was
calculated according to Eq. (3.2). The tests were
described by Klingner and Mendonca (1982a), and
were evaluated by Cannon*.
Tested were
individual anchors with large and small edge
distances and anchor groups.
In all tests a
concrete cone failure occurred.
If an anchor is installed too close to an edge,
the anchor will fail before developing the concrete
cone strength. Therefore, for headed anchors,
ACI 349 requires that the minimum edge distance
m to the center of the anchor be sufficient to
prevent a side cone failure.
The following
equation is suggested in the ACI 349 Commentary
for determining this minimum value.
m
, in.
(3.3)
where
D = anchor diameter, in.
F = ultimate tensile strength of anchor, psi
f 'c = compressive strength of concrete, psi
If this requirement cannot be satisfied, stirrup
or tie reinforcement should be provided.
Cannon+ found that for embedments less than
6 in., ACI 349 becomes increasingly conservative
with decreasing embedment. He has proposed a
modification to Eq. (3.3) to provide a better fit to
test data. For embedments less than 6 in., this
modification would increase the angle of the
failure cone, measured from the axis of the
anchor.
(3 3
For 1, c 3 in.: cy = 62 - 1.1 (l#, deg
For ld 2 3 in. but < 6 in.: (Y = 45 + 0.79 (6-ld) ,
(3 . 5)
deg
With respect to the minimum edge distance he
reported the results of tests which indicated a
direct relationship between anchor load and side
cone failure.** He suggested Eq. (3.6) instead of
Eq. (3.3) as a more correct lower bound for the
edge distance for headed anchors:
-A Frequency [%]
n = 45 tests
5i = 1,14
v = 26 O/o
20
355.1
R-1 5
m
10
F ut = ASTM-specified tensile strength of the
anchor bolt, kips
1,5
2,0
2,5
Fu,test /Fu,pred
Fig. 3.9 -Ratio of actual to predicted tensile capacity
of headed anchors according to Eq. (3.2) (from
Cannon, 1984 **)
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*Cannon, private correspondence, 1988, previously cited (see
footnote p 14).
+Cannon, private correspondence, 1986, previously cited (see
footnote p 14).
**Cannon, Robert W., Letter to ACI 355, “Comparison of Testing
Edge Conditions and Anchor Spacing with Predictions”, Dec. 1984.
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*EFFECTIVE STRESS AREA,
Ld
I41
B
*EFFECTIVE STRESS
AREA
A t
L
\L DEDUCT AREA
OF ANCHOR HEADS
EFFECTIVE STRESS
AREA
P L A N
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
*REDUCE BY THE TOTAL BEARING AREA OF THE ANCHOR STEEL.
Pd
Pd
t
t
L
J
(a+2Ld-2h)
. A) Effective stress area for anchorage pullout
EFFECTIVE
STRESS
AREA
.
STRESS AREA REDUCTION FOR LIMITED DEPTH (Ar)
Ar= (a+2Ld-2h)(b+2Ld-2h)
*REDUCE BY THE TOTAL BEARING AREA OF THE ANCHOR STEEL
B) Stress area reduction for I imited depth A
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Fig. 3.8-ACI 349 method for determining effective stress areas
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ANCHORAGE TO CONCRETE
The average failure load for a side cone
(bursting) failure is given as:
where
F,
= 15m
f
- kips
(3.7)
35cCo’
m = actual edge distance, in.
For expansion
and undercut anchors,
Eligehausen, Fuchs, and Mayer (1987 and 1988),
derived Eq. (3.8a) from 287 test series with single
anchors with large edge distances showing
concrete cone failure.
(3.8a)
mm (1 9/16 to 20 l/2 in.) and concrete strengths
f’, = 20 to 50 N/mm2 (2900 psi to 7150 psi). Fig.
3.11 shows a histogram of the ratio of measured to
predicted failure load.
The average failure loads given in Eq. (3.8) can
only be obtained if the distances between anchors
are large enough so that concrete cones do not
overlap each other. Assuming an angle of the
failure cone cy = 55o the critical distance is
approximately three times the embedment depth.
The failure load of a two-point fastening results
in:
F ul
‘d
f’,
= average ultimate load, N
depth (see Fig. 3.10), mm
= average compressive strength of concrete cylinders (6 by 12 in.) at time of
testing, N/mm2
(3.9)
G = xcr x F,,
where
where
Fu
355.1R-17
= embedment
ultimate failure load, single
anchor, from Eq. (3.8)
=
& = 1 +a/a,,it I 2
(3.10)
where
a
= distance between center of
anchors
a crit = critical distance between center
of anchors
= 31,, where 1d is the depth of
embedment.
Results of an additional 196 tests on headed
studs showed a similar relationship (from Rehm,
Eligehausen, and Mallee 1988).
FIA4
xai
(3.8b)
= %a1
x Xd
=
ai(acd 5
1 +
x Fur
2
where
In the original equation the concrete strength
was measured on cubes with a side length of 200
mm (8 in.). Eq. (3.8a) and (3.8b) assume f 'c
(cylinder) = 0.82 f 'cc (cube).
The tests with expansion, undercut and headed
studs included anchorage depths from 40 to 525
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a.I = spacing in direction i
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(3.11)
(3.12)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Fig. 3.10 -Illustration of embedment depth as used
in Eq. (3.8a) and (3.86)
Eq. (3.9) leads to the x-method for calculating
the ultimate capacity of multiple anchor fastenings. For the calculation of the ultimate load of
quadruple fastenings the xa factors can be derived
separately for both directions and combined in
product form as follows.
355.1R-18
MANUAL OF CONCRETE PRACTICE
40
Frequency [%]
n = 196 individual tests
si= 1 0 0
v= 1 4 %
30
I
20
10
0.5
1.0
$,
1.5
2.0
0.5
1.0
Fu, test
test ’ %,pred
1.5
/Fu, pred
Fig. 3.11 (a) -Ratio of acutual to predicted tensile
capacity for concrete cone failure of individual
expansion and undercut anchors away from edges
according to Eq. (3.8a). (from Rehm, Eligehausen,
and Mallee 1988, and Eligehausen, Fuchs, and
Mayer 1987 and 1988)
Fig. 3.11(b) -Ratio of actual to predicted tensile
capacity for concrete cone failure of individual
headed anchors away from edges according to Eq.
(3.86). (from Rehm, Eligehausen, and Mallee 1988)
Fig. 3.12 shows the capacity of quadruple
fastenings for headed studs, expansion and
undercut anchors as a function of the ratio of
anchor spacing to embedment depth as measured
in tests and calculated according to Eq. (3.11).
Eq. (3.9) and (3.11) can also be extended for
multiple anchorages with any number of anchors
in any spacing by setting the value of ai as the
distance atot between the outer anchors, and the
x0- value is limited to xa I n with n = number of
anchors in one direction. This is provided that the
spacings between the individual anchors are
smaller than acrit = 31, and the anchor plate is
sufficiently stiff to assure an even distribution of
tension forces to all anchors (see Rehm,
Eligehausen, and Mallee 1988). The X-method
can also be extended to take account of load
eccentricities (Riemann 1985).
Fig. 3.13 shows the ratio of actual to predicted
tensile capacity of groups of headed studs. In the
tests the number of anchors was varied between 4
and 36, the spacing of the outer anchors between
100 and 875 mm and the spacing of the individual
anchors between 0.541, and 2.2&. The groups
were loaded by a concentric tension load which
was equally distributed to all anchors.
Eq. (3.13) covers the influence of edge distances, a,, smaller than critical:
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Fu* = a& * Fy
(3.13)
Xa?n = 0.3 + 0.7 am/a,crit S 1
(3.14)
a m,crit
Fu
=
=
critical distance from free edge
1.5 1d
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
where
=
‘ actual embedment length
= ultimate failure load, single anchor
to be taken from Eq. (3.8)
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355.1R-19
5.0
0
I
I
FE according to eqn. ( 3.8 )
4.0
O
I
8
0
3.0
2.0
1.0
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Fig. 3.12-Ratio of actual failure load of a group of anchors to the predicted value for an individual anchor as
a function of the ratio of anchor spacing to embedment depth (from Rehm, Eligehausen, and Mallee 1988)
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MANUAL OF CONCRETE PRACTICE
I
_.
l-
,
L
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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ANCHORAGE TO CONCRETE
Fig. 3.14 shows a comparison of test results with
the theoretical values according to Eq. (3.13). It
should be noted, however, that minimum distances
from the free edge are necessary for headed studs
in order to allow proper concreting and avoid
local spalling of concrete.
Minimum edge
distances for expansion and undercut anchors are
necessary to avoid splitting of concrete during
installation and expansion of the anchors.
If anchors are located in a corner [see Fig.
3.15(b,)], the factors xarn are calculated separately
for each direction and then the two x-factors are
multiplied.
355.1R-21
Bode and Roik (1987), evaluated data of 106
tests with headed studs to arrive at Eq. (3.15).
F” = 12r,3/2(1 + d&,) 8, N
(3.15)
where
F,
1d
d,
f’,
=
=
=
=
average failure load, N
embedment length, mm
head diameter, mm
concrete cylinder strength
at time of testing, N/mm2
Fig. 3.16 compares the measured failure loads
of headed studs with the values according to Eq.
Roik (1987), assume the critical
spacing of neighboring headed
a cl+ = 41,
(3.16)
Fig. 3.15 - Typical failure modes of anchors Loaded
in shear (from Rehm, Eligehausen, and Mallee
1988)
kN
TU’k lN/mmz I
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
mean value
50
75 100 125 150
h [mm]
Fig. 3.16 - Measured failure loads compared to Eq. 3.15 (where p, = concrete splitting strength) (from Bode and
Roik 1987)
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
.50
o Anchor
0
.00
/
. 00
studs,
concrete break-out
l Headed studs,
local concrete failure
( blow -out)
I
/
L
.50
1.00
1.50
Fig. 3.14-Ratio of actual failure load of an individual anchor close to the edge to the predicted value for an
anchor with large edge distance (from Rehm,
Eligehausen, and Mallee 1988)
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1.75
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
355.1R-23
With respect to the influence of free edges (see
Fig, 3.15) they consider the critical distance
beyond which there is no significant influence on
load as being in the case of one free
ati1 IJ 1.21,
and in the case of two or more free edges:
acit.2
5 21,
For distances from center of headed stud to the
free edge(s) which are smaller than the critical
distance according to Eq. (3.17) and (3.18), they
fou d that the assumption of a linear decrease of
ulti ate failure load in proportion to the ratio of
act”al distance/critical distance gives a lower
bound of their test results, in much the same
ner as shown in Fig. 3.14.
raestrup, Nielson, Jense, and Bach (1976), give
the predicted failure load as:
FM
= 0.21 x 2; (1 + d,ll&f$ N (3.19)
Eq. (3.19) was deduced by applying the theory
of plasticity to headed studs embedded in
co rrete. The failure load is assumed to be
pronI ortional to the concrete compressive strength.
3.2.3.3 Pullout (slip) of the anchor- Slip
failure occurs [Fig. 3.2(b)] with expansion anchors
when the expansion force is too small to develop
either the strength of the anchor steel or a shear
cone failure of the concrete. This is a typical
failure mode for wedge anchors at moderate to
deep embedments in lower strength concrete
where the crushing of the concrete at the wedges
allows the bolt to “pull through”. The cause may
also be due to an oversize hole. Slip failure may
also occur in low strength concrete due to
deformation of the wall of the hole.
The testing of wedge bolt expansion anchors by
Hanks (1973), clearly demonstrated that the
primary failure mode for individual anchor tests
(uninhibited by edge conditions) was either cone
failure of the concrete or anchor slip depending
on the depth of anchor for a given size. Only 10
of 464 tension tests indicated any cracking
associated with a cone failure. The line of
demarcation between shear cone failure and slip
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failure was approximately six bolt diameters.
Under conditions of poor workmanship in the
field (e.g., oversize holes) slip failure may occur at
a much smaller embedment depth than ld = 6D.
Slip failure may also occur with bonded and
adhesive anchors of insufficient embedment to
develop the strength of the anchor steel or to
cause a concrete cone failure.
Torque-controlled wedge anchors, which fail by
slip, generally fail by slipping the expansion cone
past the wedges. This failure mode may also
occur with sleeve anchors. However, in some case
anchors may fail by pulling the whole anchor
(including expansion sleeve) out of the hole.
Torque-controlled expansion anchors may also slip
to a critical depth and fail the concrete.
Deformation-controlled expansion anchors (e.g.,
drop-in anchors) have a fixed expansion and may
slip to a critical depth and then fail the concrete.
The slip failure load is dependent on the
coefficient of friction between the sliding surfaces
and on the spreading force at failure which is a
function of the critical expansion force producing
failure and the deformability of the concrete which
varies with hole depth and concrete properties.
All of these factors may vary with anchor type,
manufacturer, and installation. The spreading
force and thus the slip load of drop-in anchors
decreases significantly with increasing diameter of
the drilled hole with respect to the diameter of the
anchor.
Theoretically the slip failure load F, could be
calculated from Eq. (3.20).
Fit = ps
(3.20)
where
I, = coefficient of friction
S = spreading force
The coefficient of friction depends mainly on
the roughness and cleanliness of the drilled hole
and of the surface of the expansion sleeve or
wedge as well as on the spreading pressure. From
Wagner-Grey (1976), the factor p for torque
controlled expansion anchors is in the range of 0.2
to 0.3 and for drop-in anchors is approximately
0.35. The difficulty in using Eq. (3.20) lies in
properly estimating the spreading force, since
complex mechanics are involved. For this reason
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MANUAL OF CONCRETE PRACTICE
the profession relies on test data. However,
equations for estimating of the spreading force are
given by Wagner-Grey (1976).
Because of the large variability of the spreading
forces and the coefficient of friction, Eq. (3.20)
gives only an approximate estimate of the pullout
load (see Eligehausen, and Pusill-Wachtsmuth
1982). Furthermore, in important applications it
is advisable to test expansion anchors, which
typically fail by slip at specified embedments, in
design strength job concrete to confirm slip
characteristics.
For pullout failures of a chemical anchor, the
bond between the wall of the drilled hole and the
mortar is critical (see Sell 1973). Assuming a
uniform bond stress distribution along the
anchorage length, the bond strength is in the order
of 1300 psi (9 MPa) with a coefficient of variation
of 10 to 15 percent for polyester and vinylester
chemical anchors. This value is for a concrete
compressive strength of 3000 psi (21 MPa) and an
embedment of about nine anchor diameters. The
bond strength increases approximately with the
square root of the concrete strength.
The pullout capacity of chemical anchors
increases with increasing embedment depth:
however, after about nine anchor diameters the
increase is not proportional to embedment. This
is due to the high bonding effect resulting in high
load transfer to the concrete at the top of the
anchorage. The bond stress is no longer uniform,
and if the tensile load is sufficiently high, the
failure initiates with a concrete failure in the
upper portion of the concrete and then the bond
fails in the remainder of the embedment.
For headed anchors local failure in front of the
head will occur when the pressure on the concrete
is larger than about 12f’, to 15f’, (Rehm, Eligehausen, and Mallee, 1988). This type of failure is
somewhat similar to a pullout failure.
3.2.3.4 Splitting failure of concrete -This
failure mode will occur only if the dimensions of
the concrete are too small, the anchors are placed
too close to an edge or too close to each other
[Fig. 3.2(c)], or the expansion forces are too high.
The failure load is usually smaller than for a
concrete cone failure.
Torque-controlled expansion and deformationcontrolled anchors (e.g., drop-in and self-drill
anchors are the type anchor most likely to
experience splitting failure due to the high lateral
thrust required to resist sliding by friction on the
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steel wedges. Deformation-controlled expansion
anchors generate higher spreading forces and
require larger edge distances than torquecontrolled expansion and undercut anchors.
The capacity of expansion anchors which fail by
splitting of the concrete has been evaluated by
Pusill-Wachtsmuth (1982), using theoretical
considerations. It was assumed that splitting
occurs when the tensile stresses averaged over a
critical area reach the concrete tensile strength.
The size of this area was found by evaluating the
results of tests with concentrated loads and of
tests with thick concrete rings subjected to a
constant inner pressure. According to this theory,
the necessary side cover or spacing to preclude a
splitting failure before reaching the concrete cone
failure load must be about 1.751d or 3.51,, respectively. For drop-in anchors a side cover m I 31d
was recommended. The validity of this evaluation
was checked by relatively few test results.
With respect to the minimum edge distance
Cannon* has proposed the following criteria to
preclude a splitting failure occuring at a load
lower than the capacity for concrete cone failure
or pullout failure:
m = D(11.4 - 0.92& in.
where
(3.21)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
355.1R-24
= minimum edge distance
= anchor bolt diameter, in.
= embedment depth to the bottom of the
ld
anchor, in
Eq. (3.21) is valid for anchor spacings s L 2 in.
:
If side cover or spacings of anchors are too
small, splitting cracks may occur during installation
of anchors. This possibility is greater for drop-in
anchors and for self-drilling anchors than for
torque-controlled expansion anchors because of
the higher initial spreading forces. The minimum
edge distance and the minimum spacing to avoid
splitting during installation, as recommended by
Rehm, Eligehausen, and Mallee (1988), are based
on many tests and are given in Table 3.1 for the
different types of anchors.
*Cannon, Private correspondence previously cited Dec. 1984
(see footnote p 14).
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ANCHORAGE TO CONCRETE
355.1R-25
Table 3.1 -Minimum edge distance and minimum spacing to avoid splitting failure
Torque-controlled expansion anchors
with one cone (recent design)
Mihimum edge distance m / 1d to avoid
splitting during installation
1.0
2.0
Minimum center-to-center spacing a / 1d
to avoid splitting during installation
1.0
1.0
3.2.4 Load-displacement behavior and failure
modes in shear-For anchors with an applied
preload, the initial friction forces between the
baseplate and the concrete have to be overcome
by the shear load before there is initial anchor
movement (Fig. 3.17). The baseplate slides and
the anchor moves to the side of the hole in the
second stage of behavior. The third stage of loaddisplacement behavior is a pressure loading
against the top surface of the concrete and a
surface spa1l of the concrete at the edge of the
hole. Depending on edge distance and anchor
embedment, the failure may be by shearing of the
anchor (for deep embedments) with or without a
concrete spa11 preceding the steel failure [Fig.
3.15(a)] or by shearing of the concrete (concrete
failure) in the case of anchors loaded near an
edge [Fig. 3.15(b1), (b2), (b3)].
Shear loading generally produces larger
displacements than tension loading [see Fig.
3.3(c)]. This can be attributed to the bending of
the anchor rod and the deformation of the
concrete in the direction of loading. This is
especially true if the anchor is not flush with the
concrete at the hole opening (e.g., when the
concrete is spalled during drilling). For cast-inplace anchors, the behavior will depend on the
type of anchorage used, the embedment and the
steel strength.
The distribution of shear from the attachment
to anchors of a group depends on the details of
the anchors to the attachment connection and on
overcoming the frictional resistance of the
attachment. The frictional resistance depends on
surface conditions, the existing preload (if any) in
the anchors and the compressive forces applied
Copyright American Concrete Institute
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No reproduction or networking permitted without license from IHS
Drop-in anchors
I
3.0
I
through the attachment as a result of direct loads
or applied moments. The connection details
concern the treatment of connecting surfaces and
the fit and manner of connecting the anchors to
the attachment.
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Undercut anchors
Onset of bearing
crushing in the concrete
lip of loading plate into
bearing on anchor stud
Load transfered by
friction to embedment
. ~~~
0
.50
r
10
r
1.5 0
Deformatlon
Fig. 3.17- Typical load-displacement curve for
wedge anchor in shear from Meinheit and
Heidbrink 1985)
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-7
20
355.1R-26
MANUAL OF CONCRETE PRACTICE
3.2.5 Ultimate strength in shear
3.2.5.1 Steel failure - Steel failure usually occurs
after relatively large displacements and is most
common for deep embedments, lower strength
steels and large edge distances. The failure load
depends on the steel area and the steel strength
and is given by Eq. (3.22).
number
of specimens
x
I
”
0,: 0.65-4
I
= N A,f,, lb
(3.22)
where the factor N takes account of the steel
“shear” strength and has the range 0.6 to 0.7
[Klingner and Mendonca, (1982b)], A, is the tensile stress area (as defined in Eq. (3.1)) and f,t is
the ultimate tensile strength.
Eligehausen and Fuchs (1988), propose the
value N = 0.6 on the basis of an evaluation of
230 tests.
3.2.5.2 Concrete failure -Concrete failures will
exhibit two modes; (1) blow out cones due to edge
proximity (Fig. 3.15) and (2) concrete spa11
followed by a possible anchor pullout or steel
failure away from an edge.
3.2.5.2.1 Edge failure- For all types of
anchors loaded in shear toward an adjacent, free
edge and exhibiting a concrete failure (Fig. 3.15),
the failure load is influenced by the concrete
tensile strength, the edge distance m and the
stiffness of the anchor. Another influencing factor
is the embedment depth. The failure surface has
a conical shape that may radiate from the embedded end of the anchor for shallow embedments
or from the upper part of the anchorage for deep
embedments.
In the following paragraphs, several formulas
for calculating the failure load for an edge failure
are reviewed.
ACI 349, Appendix B, Commentary gives a
design shear strength of
vu = 24$$n2, lb
(3.23)
RATIO OF ACTUAL TO
F’FQICTED CAPACITY
Fig. 3.18 -Histogram of actual to predicted capacity
ACI 349, Appendix B further recommends a
minimum side cover or edge distance m required
to preclude edge failures: be calculated by Eq.
(3.24).
m=
D = anchor diameter, in.
F t = anchor ultimate tensile load, lb
fr”, = concrete compressive strength, psi
Eligehausen and Fuchs (1988), have suggested,
based on the evaluation of some 80 test results
with headed and expansion anchors (anchorage
depth ld > 4D), the average ultimate failure load
of the concrete of a single fastener in shear be
calculated by:
F,, = 1.4@$n1.s~~, N
where
D
f’,
m
(3.25)
shank diameter (mm) of headed
studs or drill-hole diameter for
anchors, D < 25mm
average concrete compressive
strength (cylinders) at time of testing,
N/mm2
distance from anchor to free edge,
mm
Fig. 3.18, taken from Klingner and Mendonca
(1982b) gives the ratio of actual to predicted shear
capacities for this approach.
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(3.24)
where
where
= 0.85
cb
f’, = compressive strength of concrete
m = distance from anchor to free edge
(see Fig. 3.15)
, in.
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
F8l
ANCHORAGE TO CONCRETE
355.1R-27
h
Xh =-sl
1.4m
where
h = member thickness, mm
Eq. (3.25) is valid for 1,/D = 4 to 6.
Fig. 3.19 shows a comparison between failure
loads according to Eq. (3.25) and test results. The
thickness of the test specimens was h 1 1.4m.
The tests were performed in concretes with
different strengths and anchors ranging in
diameter between 12 and 22 mm. The test results
were normalized to a concrete strength f 'c =
20N/mm2 and D = 18 mm.
If an anchor group is loaded in shear toward an
edge, a common failure cone may occur [see Fig.
3.15(b2)]. T he corresponding failure load may
also be calculated as described in Section 3.2.3.2
for tension loading [Eq. (3.9), (3.11), and (3.12)]
according to the x-method. The x-values for
shear loads, however, depend on the distance from
the free edge measured in load direction.
The critical (minimum) distance between two or
more anchors beyond which no intersection of
failure cone will happen is given by Eligehausen
and Fuchs (1988), as:
a Wit = 3.5m
Similar expressions are proposed for calculating
the failure load of single fastenings or anchor
groups situated in a corner or in narrow members.
The influence of load eccentricity on the failure
load of an anchor group can also be taken into
account by the x-method (Rehm, Eligehausen,
and Mallee 1988). The method has been extended
to anchor groups with an arbitrary number of
anchors.
Klingner, Mendonca, and Malik (1982),
recommend a critical (minimum) edge spacing of:
(3.27)
mkD
For a I a,,i, Eligehausen and Fuchs (1988),
have proposed the calculation of the average
failure load of a group of anchors (see Fig. 3.20)
subjected to shear load by:
Fut in.
-,
(3.29)
%@
where
#C = 0.90 and the other terms are as given
the ACI 349 [Eq. (3.24)].
for
(3.28)
For anchors with small embedment depth
situated away from an edge and loaded in shear,
the failure mode may be a tensile cone failure as
the anchor bends under load and induces a tensile
loading into the concrete. Because of ductility
requirements and reversible load conditions
associated with seismic design, ACI 349 does not
distinguish between embedment requirements for
shear and tension. This is very conservative if only
shear is considered (see Shaikh and Yi, 1985).
where
= 1 + a/a,,i,
&
F, is from Eq. (3.25)
Fig. 3.20 (Eligehausen and Fuchs, 1988) shows
the ratio of the failure load of a group loaded in
shear towards the edge to the failure load of an
individual anchor calculated according Eq. (3.25).
The failure load ratio is plotted against the ratio
of spacing to edge distance.
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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No reproduction or networking permitted without license from IHS
' 3.5
4.0
a/a, [-]
Fig. 3.20-Ratio of actual shear failure load of
anchor group to shear failure load of an individual
anchor as a function of spacing between anchors
where
m = distance to free edge.
FI(, Group = x,F,
3.0
0
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
8
cv
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MANUAL OF CONCRETE PRACTICE
8
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ANCHORAGE TO CONCRETE
3.2.5.2.2 Concrete spall-Anchors away from
an edge will locally spall the concrete in front of
the anchor. The primary factors influencing
concrete spall due to shear are tensile strength of
the concrete, stiffness of the anchorage, anchor
diameter, embedment depth, and deformability of
the concrete. The corresponding shear capacity is
given by Klingner and Mendonca (1982), and
American Institute of Steel Construction (1978),
as:
(3.30)
F, = 0.5 A, fit, lb
where
Ab
= nominal gross cross-sectional area of
anchor shank, in.2
f’,
= specified compressive strength of
concrete, psi
E,
= elastic modulus of concrete, psi
However, according to Eligehausen and Fuchs
(1988), the above described local concrete failure
does not negatively influence the anchor steel
capacity (normal strength steel) and will not cause
subsequent pullout of the anchor, provided the
embedment depth is 1, L 4D.
3.2.6 Combined tension and shear Loading- The
behavior of anchors under combined tension and
shear loading lies in between the behavior under
tension or shear loading, and for a given depth of
embedment, is dependent on the angle of the
loading (Fig. 3.21).
To calculate the failure load under combined
tension and shear loadings three approaches are in
use; a straight-line function, a trilinear function
and an elliptical function.
There are two types of straight-line functions.
The first is a shear friction approach used by ACI
349, Appendix B, and given by Eq. (3.31).
355.1R-29
A second straight-line equation is given by Eq.
(3.32).
T,/T, + VJVu s 1.0
(3.32)
where
applied tensile and shear load,
respectively
V
=
ultimate
tensile and shear load,
T”, u
respectively
These straight-line methods give a conservative
approach to combined loading analyses.
Bode and Roik (1987), propose for headed
studs a trilinear function:
Ta*
=
va
vp,
s 1
TJT,, + VJV,, s 1.2
(3.33c)
where
T,, Va, TU and Vu as defined for Eq. (3.32).
According to Meinheit and Heidbrink (1985),
Eq. (3.33) is valid also for expansion anchors (see
Fig. 3.22).
Load FQ[ kN ]
125
100
75
(3.31)
where
= applied tension load
= 4 F,
r” = 0.85
F, according to Eq. (3.22)
cr = coefficient of friction
= 0.55 to 0.9, depending on the
location of the anchor plate in
relation to the concrete surface
Tall = allowable anchor tensile load
TL?
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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50
25
0
I
I
5
10
I
I
25
15
20
Displacement A,[mml
Fig. 3.21- Shear load-displacement behavior of
headed studs for different tension loads (from Bode
and Hanenkamp 1985)
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MANUAL OF CONCRETE PRACTICE
Many investigators have concluded that shear
and tension combine in an elliptical function as
given by Eq. (3.34).
(3.34)
(T,/T,,Y + CV,lVJ s 1.0
where exponents x and y are determined from
tests and the other terms are as previously defined
for the straight-line equations.
The PCI Design Handbook (1978) uses x = y =
4/3 for precast anchors, while the Teledyne
Engineering Services report (1979) gives x = y =
5/3 as a good fit for expansion anchors.
Fig. 3.22 shows a comparison between test
results with expansion anchors and the different
approaches as described above.
3.3-Behavior of anchors in cracked concrete
3.3.1 Introduction -When anchors are installed
in the tension zone of reinforced concrete members, it must be assumed that cracks will occur in
the concrete because of the rather low concrete
tensile strength. The concrete tensile strength may
be totally or partially consumed by the restraint of
induced deformations due to shrinkage, temperature, or flexure, or from the anchorage itself.
Cracks run either in one direction (single cracks)
or in two directions (intersecting cracks, in the
case of slabs spanning two directions).
If concrete cracks, experience has shown that
there is a high probability that the crack will
propagate through the anchor location (see
Cannon 1981 and Eligehausen, Fuchs, Lotze, and
Reuter 1989). Theoretical considerations also
indicate that cracks should propagate through the
anchor location. When the anchor is loaded, the
anchor creates splitting (tensile) forces at the
anchor embedded end. These tensile stresses in
the concrete would add to other tensile stresses
from locally high bending moments. (i.e., flexural
stresses and restrained shrinkage stresses). For
the case when expansion or undercut anchors are
used, the drilled hole can also act as a notch or
produce a cross section in the concrete member
with reduced concrete area.
The theoretical considerations discussed above,
were confirmed by testing Ml2 (12 mm) torquecontrolled expansion anchors and undercut
anchors in a slab reinforced with welded wire
mesh (AJbd = 0.004) (see Eligehausen, Fuchs,
Lotze, and Reuter 1989). The test anchors were
installed with 1d = 80mm (3.2 in.) and in
uncracked concrete. The anchorage holes were
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drilled either 40 mm (1.6 in.) or 80 mm (3.2 in.)
away from the transverse acting wires, [spacing of
250 mm (10 in.), in the fabric]. Bending of the
slab was in one direction only. All test anchors
were pretensioned or pretensioned and loaded
with their allowable load before the slab was
subjected to flexural loadings.
After preloading the anchors, the concrete slab
was loaded to its service load. Observations
during this part of the testing often showed that
cracking started at the section with transverse
reinforcement but then deviated from that section
to the section that contained the anchor hole.
The cracks propagating through the anchor hole
also were to the depth of the hole (Fig. 3.23 and
3.24). Testing showed that the displacement
characteristics of these anchors remained
essentially unchanged until the slab load was about
40 percent of the slab service load. Beyond that
point, significant increased displacement occurred
(Fig. 3.25). The increased displacement characteristics of the anchor in cracked concrete are
caused by the crack propagating through the load
transfer zone of the anchor (see Cannon 1981).
The crack width can vary over the depth of the
member (bending cracks) or can be of constant
width (parallel cracks, e.g. due to tension loading).
In the worst case the anchor can lie in the intersection of two cracks with constant width over the
member depth. If anchors are situated in or beside
these cracks, their load displacement behavior and
strength may be significantly influenced.
3.3.2 Load-displacement-behavior and failure
modes in tension -Fig. 3.26 presents typical loaddisplacement curves of torque-controlled expansion anchors which were set in uncracked concrete
and in cracks, and loaded statically to failure. The
displacements of anchors located in cracks behave
similarly to anchors in uncracked concrete up to a
critical load. This critical load depends on the
type of crack and the crack width. For higher
loads the displacements of anchors in cracks are
much higher than the values expected in
uncracked concrete and anchor capacity is significantly reduced.
The load-displacement behavior of headed or
undercut anchors may be affected by cracks in
concrete but the displacements at maximum load
are less influenced by cracks than are expansion
anchors (see Fischer 1984).
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
355.1R-30
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ANCHORAGE TO CONCRETE
0
l
l
0
0
I.0
Fig. 3.22- Tension-shear interaction diagram for expansion anchors (from Meinheit and Heidbrink 1985)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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MANUAL OF CONCRETE PRACTICE
I
I______ _;
!
F
I
1.
F
K 884
-(8,84cm2/mI
_,,,:‘,
I
_
_
_
__
_
2
kc
-I
a
I
/
15 ,
l
100
Id
150
1
150
1
,I
100
I
15
L
torque-controlled
undercut
expansion anchors -7 anchors
--
z
--
z
ic
-i
anchor loaded
a n c h o r p r e s t r e s s e d but n o t l o a d e d
o drill hole
l
l
Fig. 3.23 - Torque-controlled expansion anchors and undercut anchors in the cracked tensile zone of a concrete
slab (from Eligehausen, Fuchs, Lotze, and Reuter 1989)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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355.1R-33
ANCHORAGE TO CONCRETE
tension
t
jr
I-
expansion
area
A
A
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Section A - A
Fig. 3.24- Crack pattern in a drilled hole with expansion anchor (from Eligehausen, Fuchs, Lotze, and Reuter
1989)
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355.1R-34
MANUAL OF CONCRETE PRACTICE
-4-l
F .
8
adm
-
1.0
-
0.8
0.6
1
r(I
0.4
,
1
(H
0
,, ,
4
0.2
0.3
0.2
torquee controlled
expansion anchors
1
0.1
0.1
0.2
displacement [mm]
crack width [mm]
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Fig. 3.25-Crack width and anchor displacement as a function of the ratio of applied load to allowable load of
the slab (from Eligehausen, Fuchs, Lotze, and Reuter 1989)
Force
-v
r
Torque Controlled Expansion Anchor
Tension Loading
Uncracked
Cracked Concrete
r---
Displacement
Fig. 3.26-Influence of cracks on the load-displacement relationship of expansion anchors - schematically (from
Rehm and Lehmann 1982)
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Fig. 3.27 shows the typical load-displacement
relationship of torque-controlled expansion
anchors set in intersecting cracks and cycled up to
10’ times between different load levels before
loading to failure. For comparison the loaddisplacement relationship for statically loaded
anchors is also plotted. Provided the upper load
during cycling is smaller than about 50 percent of
the static failure load, cyclic loading results in an
almost linear increase of the anchor displacement
as a function of the logarithm of the number of
cycles. The load-displacement curve for higher
loads than the upper load during cycling is rather
steep up to the static envelope which is followed
thereafter. Anchor capacity and displacement at
failure are not influenced significantly by cyclic
loading with an upper load as given above.
Opening and closing of cracks by cycling the
reinforced concrete while subjecting the anchor to
a constant load has more influence on the anchor
behavior than cycling the anchor with the cracks
kept open (Rehm and Lehmann 1982).
In principle the failure modes described in
Sections 3.2.1 and 3.2.3.1 are also valid for
anchorages in cracked concrete.
However,
expansion anchors which produce a concrete cone
failure in uncracked concrete may slip and pull out
when located in a crack. This possible change of
the failure mode is due to the reduction of the
spreading force as a result of the cracks (see
below).
3.3.3 Relaxation-Expansion and undercut
anchors installed in cracks will show an initial
displacement during widening of the crack. The
amount of this displacement is dependent on the
design of the anchor and on the crack width.
Usually this initial displacement is large enough to
reduce the preload to zero. This is also valid for
bonded anchors.
The relaxation behavior of headed anchors
installed in cracks has not yet been studied.
However, one may assume that the residual
preload is not significantly smaller than for headed
anchors in uncracked concrete.
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[kN]
Torque ConIt rolled Expa c, sion Anchor
FTER CYCLIC LOADING
I
D CYC LES
5
15
Displacement [mm]
Fig. 3.27-Influence of cyclic loading on the loaddisplacement relationship oftorque-controlled expansion anchors (after Rehm and Lehmann 1982)
3.3.4 Ultimate strength in tension-Fig. 3.28
shows the influence of cracks in the concrete on
the strength of headed and undercut anchors
placed in or close to cracks. The ratios of the
failure loads of single anchors measured in
cracked concrete to the value in uncracked
concrete are plotted as a function of the crack
width. The anchors were tested in tension
specimens with almost constant crack width over
the member depth. After installing the anchors in
uncracked concrete or concrete with hairline
cracks, the cracks were opened by loading the
specimen and then the anchors were statically
loaded in tension with the cracks open. Failure
occurred by pulling out a concrete cone.
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m
m
MANUAL OF CONCRETE PRACTICE
355.1R-36
Fu (crack) / Fu (uncracked c o n c r e t e )
I,OA
I
fi- 20-55N/mm2
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
id = 8O mm
The failure load decreases rapidly up to a crack
width of about 0.4 mm (l/64 in.) and is almost
constant for larger cracks. The scatter of the data
is relatively large. On an average, the ultimate
load of anchors installed in or beside cracks with
a width > 0.4 mm (l/64 in.) is about 60 percent of
the ultimate value in uncracked concrete. It
should be noted that, under service load, cracks
with a width no greater than 0.4 mm (l/64 in.) are
tolerated in reinforced concrete structures. The
influence of the type of anchor (headed or undercut) on the failure load reduction is negligible.
An almost similar strength reduction was also
observed with anchors installed deeper in the
tension zone of beams for various anchor-depthto-beam-height ratios (Rehm, Eligehausen, and
Mallee 1988).
The reduction of the anchor strength is due to
the change of the stress distribution in the
concrete caused by cracks (Eligehausen 1984 and
Eligehausen, Fuchs, and Mayer 1987 and 1988).
In the case of uncracked concrete, the stresses in
the concrete are radially symmetric to the anchor
and tensile hoop stresses are caused by the load
transfer into the concrete [Fig. 3.29(a)]. If the
anchor is installed in a crack, tensile stresses
cannot be transferred across the crack. Therefore,
the area which can be used for transmitting the
load into the concrete is smaller than in uncracked
concrete [Fig. 3.29(b)].
0,4
0,8
1,2
1,6
crack width A w [mm]
Fig. 3.28 -Influence of cracks on the ultimate load
of undercut and headed anchors (from Eligehausen
1984)
uncracked concrete
b) cracked concrete
Fig. 3.29 - Load transfer into concrete schematically for a) uncracked concrete and b) cracked concrete (from
Eligehausen, Fuchs, and Mayer 1987, 1988)
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ANCHORAGE TO CONCRETE
Furthermore, a part of the concrete cone may
be cut off by neighboring cracks. These combined
effects cause a strength reduction of approximately
40 percent compared to uncracked concrete.
Some tensile stresses can be transmitted over
small cracks due to aggregate interlock
(Eligehausen and Sawade 1985). This explains the
increasing anchor strength for crack widths less
than 0.4 mm (l/64 in.).
In addition to the above effect, the reduction of
the spreading forces by the crack opening must be
taken into account for expansion anchors (Fig.
3.30). If the anchor lies in an intersecting crack,
the widening of the crack by the width w leads to
a reduction of the effective expansion displacement around the circumference of the anchor by
w/2 [Fig. 3.30(a)]. Assuming elastic behavior of
the concrete, this reduction of the expansion
displacement causes a slight reduction of the
355.1R-37
spreading force from F,, to F, [Fig. 3.30(b)]. If,
on the other hand, it is assumed that the concrete
is subjected to purely plastic deformations during
expansion, then theoretically the expansion sleeve
will free itself around its circumference from the
hole wall and the spreading force will decline to
zero [Fig. 3.30(c)]. In reality the concrete is
deformed elastically and plastically. Therefore,
the actual situation lies between these two
extremes. However, due to the steep gradient of
the unloading curve, it has to be expected that
even a relatively slight increase in crack width will
lead to a substantial reduction of the spreading
force [Fig. 3.30(d)]. For anchors situated in cracks
running in one direction, the spreading force will
also be reduced by the opening of the crack, but
the reduction will be less pronounced than in the
case shown in Fig. 3.30.
anchor unspread
crack opening
spread anchor
a)
Spreading Force
FO
6
I -7 .
-
b) Concrete elastic
c) Concrete plastic
Fig. 3.30-Influence of cracks on spreading force (from Eligehausen and Pusill- Wachtsmuth 1982)
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
1 Spread. Displ.
c
MANUAL OF CONCRETE PRACTICE
355.1R-38
Properly designed torque-controlled anchors
will expand to an upper bound when they are
loaded. This causes an increase of the spreading
force until the holding capacity is reached. If the
crack width is smaller than about 0.4 mm, the
holding capacity of heavy-duty, torque-controlled
sleeve anchors is often large enough to cause
failure by pulling out a concrete cone. Therefore,
the reduction of the failure load is ahnost the
same as for headed anchors (compare Fig. 3.31
with Fig. 3.28). For larger cracks the expansion
cones are often pulled through the expansion
sleeves, because the maximum spreading
displacement reaches the upper bound and the
holding capacity is less than the concrete cone
failure load. This results in an additional decrease
of the failure load in comparison to headed or
undercut anchors.
If torque-controlled expansion anchors do not
properly expand further or when the spreading
displacement is too small, the influence of cracks
on the failure load will be much more pronounced
than shown in Fig. 3.31.
Ku / c r o c k ) / Fu ( u n c r a c k e d
concrete)
Drop-in anchors cannot expand further after
they have been properly installed. Due to the
reduction of the spreading force caused by cracks
(Fig. 3.30), these anchors often fail by pulling out
without significant damage of the concrete while
in uncracked concrete they produce a concrete
cone type failure. Therefore, the reduction of the
failure load caused by cracks is much larger than
for well-designed torque-controlled expansion
anchors (compare Fig. 3.32 with Fig. 3.31).
1,0
bcrack) / F ubncracked concrete)
0,8
0,6
0,4
0,2
0
0,4
0,8
1,2
crack width _w [mm]
^
Fig. 3.32-Influence of cracks on the ultimate load
of drop-in anchors (from Eligehausen, Fuchs, and
Mayer 1987 and 1988)
0,8
1,2
1,6
crack width _ w [mm]
^
For self-drilling anchors the ratio of failure load
in cracked concrete to failure load in uncracked
concrete seems to be independent of the anchor
diameter for constant crack width to maximum
expansion displacement ratio (Fig. 3.33). Because
the maximum expansion displacement increases
with increasing anchor diameter, the reduction of
the failure load for constant crack width is larger
for smaller anchors than for bigger anchors.
Fig. 3.31 -Influence of cracks on the ultimate load
of torque controlled expansion anchors (from
Eligehausen 1984)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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FU (Anchor in Crack)
r
.rU (Anchor in uncracked Concrete)
7
1 Single Cracks ,
,M12
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
*
0
0,1
0,2
0,3
I
I
I
I
0,4
0,5
0,6
0,7
L-7
0,8
0,9
1
1,0
w/a
Fig 3.33 -Relative strength of self-drilling anchors as a function of the ratio of crack width to expansion
displacement (from Eligehausen 1987)
F, (crack) / F, (uncracked concrete)
0,4
0,6
crack width w [mm]
Fig. 3.34 -Ratio of the failure load of chemical
anchors installed in cracks to the failure load in
uncracked concrete as a function of crack width
(from Eligehausen, Mallee, and Rehm 1984)
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In the case of grouted anchors (grouted by
cement-based or chemical-based mortar) cracks
may disturb the bond between the grout-concrete
interface. Therefore, the failure load of grouted
anchors in cracks is significantly smaller than the
value measured in uncracked concrete (Fig. 3.34).
The large scatter of the results is caused by the
random distribution of the crack around the
anchor hole and along the anchor length. If the
crack widths are changing due to fluctuating loads,
the anchor failure load is even more reduced or
the anchor may even be pulled out (Cannon
1981).
Under constant conditions anchors placed in
the intersection of two cracks fail at approximately
20 percent lower loads than anchors set in cracks
running in one direction only (Eligehausen, Fuchs,
and Mayer 1987 and 1988). This can be explained
by the fact that the effects described above will
occur in both directions and not in one direction
as in the case of single cracks.
Anchors are often installed in groups where the
individual anchors a r e c o n n e c t e d b y a n
attachment. In this case some anchors might sit in
uncracked concrete while others are located in
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
355.1R-40
MANUAL OF CONCRETE PRACTICE
cracks. The average strength of groups situated in
cracked concrete was about 30 percent lower than
the value applicable for anchor groups set in
uncracked concrete (Eligehausen, Fuchs, and
Mayer 1987 and 1988). Approximately the same
strength reduction was measured for single
anchors installed in cracks.
Failure of all
fastenings was caused by pulling out a concrete
cone.
The strength of the entire anchor group is
constant for one or more of the anchors in a
concrete crack. The reduction is almost the same
whether one anchor or all are in concrete cracks
(Fig. 3.35). In the test, the anchor plate was
connected flexibly (by hinges) to the hydraulic
cylinder.
Fu [kN]
150 -
125
100
75
50
Number of anchors in cracks
Fig. 3.35-Strength of fastenings with four anchors
as a function of the number of anchors in cracks
(from Eligehausen, Fuchs, and Mayer 1987 and
1988)
Theoretical studies showed that the results
described are also valid for larger groups of
anchors and for applications when the anchor
plate is rigidly attached (Eligehausen, Fuchs, and
Mayer 1987 and 1988).
Based on these results, it can be stated that the
strength of anchor groups placed in cracked
concrete can be taken as n-times (n = number of
individual anchors of the group) the value
expected for one anchor if the influence of cracks
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and anchor spacing is taken into account
simultaneously. This is valid for anchors with a
steadily increasing load-displacement relationship
in both uncracked and cracked concrete.
Fig. 3.36 describes the influence of the loaddisplacement relationship of expansion anchors
placed in cracks on the failure load of anchor
groups. It is assumed that three anchors of a
quadruple fastening (large spacing) are located in
cracks and one anchor is sitting between cracks in
uncracked concrete. If the anchors show a
steadily increasing load displacement relationship
in uncracked and cracked concrete (Lines a1 and
a2 of Fig. 3.36), the failure load of the group is
about four times the failure load of one anchor
placed in a crack. (This theoretical result is in
accordance with Fig. 3.35.) Expansion anchors
located in cracks may slip in the hole before
expanding further and take up more load (Line b
of Fig. 3.36) or may be pulled out at rather low
loads (Line c of Fig. 3.36). If only one of the
anchors shows a load-displacement behavior
according to Lines b or c, the failure load of the
group may be reduced by more than 40 percent.
Anchors which are being used in areas where
cracks may occur, such as the tension zone of a
concrete member, must be suitable for this
application.
3.3.4.1 Influence of tensile stresses generated by
structural action on anchor strength -In tests
summarized to this point, the anchors were placed
in the tension zone with constant stress of the
reinforcement, and therefore, tensile stresses in
the concrete were mainly induced by the anchors.
However, if the anchors are placed in the shear
region of beams and slabs and in the region of
anchorages and lap splices of deformed bars,
locally high tensile stresses are already induced in
the concrete due to the loading of the structure.
If anchors are placed in this region, the tensile
stresses that they induce in the concrete combine
with the tensile stresses due to loading of the
structure. An example is shown in Fig. 3.37. It is
assumed that an anchor is placed in the end
region of lapped splices of large reinforcing bars.
Plotted are stresses in the concrete due to
splicing of the bar and loading of the anchor. The
tensile stresses along the failure surface of the
concrete cone overlap. Therefore, a reduction of
the pullout load compared to anchors placed in
otherwise unloaded concrete must be expected
which, according to tests, is up to 25 percent in
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ANCHORAGE TO CONCRETE
355.1R-41
F
anchor in crack
FUC
load
displacement
relationship
0 a,
0b
C
.o
Fu
4 Fuc
0,94
0,64
0,50
vuc
V
Fig. 3.36- Influence nf load-displacement relationships of expansion anchors on the ultimate load of an anchor
group (from Mayer and Eligehausen 1984)
\
-
stresses caused
by r e i n f o r c e m e n t
~~
expansion anchor
.
\
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
ds = 28mm-,
a
-
stresses caused
by anchor
1
+c
+1
Fig. 3.37-Anchor in the region of an overlap splice (cross section). Overlapping of stresses caused by the bars
and by the anchor (from Eligehausen 1984)
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355.1R-42
MANUAL OF CONCRETE PRACTICE
the assumed case (Eligehausen 1984). Reducing
the size of the reinforcing bars, increasing the
embedment depth of the anchor, or both reduces
the influence of these intersecting stresses. In
summary, the influence of these intersecting
stresses on the failure load is smaller than the
influence of cracks.
In the tests summarized in Fig. 3.28 and 3.31 to
3.35, anchors were used which extended beyond
the tension reinforcement. If short anchors are
used, they are anchored in the concrete cover or
between the bars. In this circumstance, high
tensile stresses are induced in the concrete cover
by the bond action of the reinforcing bars. These
stresses intersect the tensile stresses in the
concrete induced by the anchor. The strength of
the concrete in the cover and in the region of the
bars may be lower than in the core of the
specimen due to poor compaction, especially in
sections with closely spaced reinforcement.
Furthermore, this reinforcement reduces the
concrete area available for transmitting tensile
forces. Because of these conditions a significant
reduction of the failure load of all types of
anchors must be expected. This was confirmed by
tests with expansion and undercut anchors placed
in the cover of a beam with rather heavy
reinforcement (Eligehausen, Fuchs, and Mayer
1987 and 1988) (Fig. 3.38). After loading the
beams to service load (crack width w = 0.3 to 0.4
mm) the anchors were loaded to failure. The
anchor failed when the concrete cover between
two adjacent cracks was pulled off (Fig. 3.39). On
an average the ratio of failure load in cracked
concrete to the value for uncracked concrete was
about 30 percent smaller than shown in Fig. 3.28
and 3.31.
3.3.4.2 Influence of load transfer into the tension
zone on the behavior of the structural element-The
overlapping of concrete tensile stresses caused by
loading the structure, and stresses induced locally
by the loaded anchor affects the strength of the
anchor and may reduce the strength of the
member where the anchor is placed (Rehm and
Eligehausen 1986). Transfer of high tensile forces
into the concrete in the region of overlap splices
and of anchorages of reinforcing bars may be
critical especially if the splice reinforcement is not
enclosed by stirrups (Rehm and Eligehausen
1986). Another critical application is the transfer
of forces into the tension zone in the shear region
of slabs without shear reinforcement.
a
0
135 = 2.15 Id
b
0
180=3ld
t
c
dimensions in mm
Fig. 3.38 - Test specimens (from Eligehausen, Fuchs,
and Mayer 1987 and 1988)
Investigations of this case are described by
Eligehausen and Reuter (1986) and Lieberum,
Reinhardt, and Walvaren (1987).
Slabs 300 mm thick were tested by Eligehausen
and Reuter without shear reinforcement. The
shear-span ratio a/h ranged from 3 to 4.5. A
fraction of the total load was transmitted by
anchors into the tension zone and the rest by
loading plates into the compression zone. Types
of anchors examined were expansion, undercut,
and headed studs. The embedment depth (40 to
130 mm) and the ratio of anchor load to total load
(0 to 100 percent) were varied. In all cases the
slabs failed by an inclined shear crack.
Fig. 3.40 shows the cracking pattern of one
specimen at about 95 percent of the failure load
of the member. The anchor loads must be
transmitted over the tip of the inclined crack to
the supports. This causes high tensile stresses at
the crack tip. Therefore, the failure crack (shown
as a broken line) will occur at a lower total shear
force than loading the slab in the compression
zone only. In the tests a reduction of the shear
carrying capacity of the slabs up to between 15
and 20 percent was found when all the loads were
transmitted into the tension zone and not into the
compression zone. The strength reduction was
smaller when only a fraction of the total load was
transferred into the tension zone. A similar
strength reduction was found by Lieberum,
Reinhardt, and Walvaren (1987), under
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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355.1R-43
ANCHORAGE TO CONCRETE
.b..
_
I
b
Fig. 3.39 - Concrete failure of an anchor group (from Eligehausen, Fuchs, and Mayer 1987 and 1988)
1
7
a =3d
L
I
Fig. 3.40- Crack pattern. of a slab without shear reinforcement (from Eligehausen and Reuter 1986)
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MANUAL OF CONCRETE PRACTICE
355.1R-44
these test conditions. If the anchors are placed
close to the support the strength reduction will be
much more significant.
This reduction of the shear capacity may,
depending on the design of the slab, significantly
change the type of failure from a ductile bending
failure to a brittle shear failure (Eligehausen and
Reuter 1986). To avoid this problem, it is
recommended that the shear forces transmitted
directly into the tension zone should be limited to
about 40 percent of the total shear force, or
alternatively, the shear stress should be limited to
about 80 percent of allowable values.
Composite structures (precast concrete
elements with bonded cast-in-place concrete)
without reinforcement connecting the precast and
cast-in-place concrete, are especially critical.
Failure of this type of structure will often be
caused by a crack in the contact area between the
precast and the cast-in-place concrete. If the load
is transmitted into the precast concrete element,
high tensile stresses are generated in the contact
area. Therefore, the shear stress at failure is
significantly lower than in the case of loading the
specimen in the usual way at the top (Fig. 3.41).
3.3.5 Shear loading-Little investigation of the
influence of cracks on the behavior of anchors
loaded in shear has been conducted. The few
available test results can be summarized as
follows.
Anchors placed in cracked concrete and loaded
in shear will fail the concrete (small edge
distances), or the bolt (large edge distances), or a
combination of both. Under otherwise constant
conditions, the failure load of anchors with a small
edge distance and loaded towards the edge will be
smaller in cracked concrete than in uncracked
concrete due to the disturbance of the distribution
of stresses in the concrete by cracks. It can be
assumed that the strength reduction is almost the
same as for tension loading (reduction by about 40
percent). The strength reduction will be smaller
if edge reinforcement is present. The ultimate
load of anchors with large edge distances (steel
failure) is not significantly influenced by cracks.
The edge distance required to insure a steel
failure of the anchor is about 30 to 40 percent
larger in cracked concrete than in uncracked
concrete.
3.4-Behavior of cast-in-place anchor bolts in
uncracked concrete piers
join f
-7
2
4
a/d
Fig. 3.41 -Shear stress failure of a composite slab
without connecting reinforcement between precast
and cast in place concrete (after Rehm and
Eligehausen 1986)
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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6
3.4.1 Introduction -Anchor bolts are commonly
used in highway and bridge structures to connect
light standards, sign supports, and traffic signal
poles. They are also used to connect steel
columns in industrial structures to structural
concrete members. The anchor bolt installation
discussed in this section is one of the most widely
used cast-in-place anchorage systems. The anchor
bolts used typically have long embedment lengths
and small edge distances. Such installation should
be distinguished from bolts embedded for short
lengths in mass concrete with very large edge
distances. The supporting concrete members
associated with this installation are usually piers,
drilled shafts, or other foundation elements with
limited plan dimensions; however, the concrete is
usually well confined by reinforcement.
The structural behavior of cast-in-place anchor
bolts with long embedment lengths installed in
supporting members with limited dimensions is
distinctly different from that described in the
preceding sections. This section summarizes some
significant results from extensive research conducted for this type of anchor bolt application at
the University of Texas at Austin (see Breen 1964;
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ANCHORAGE TO CONCRETE
Lee and Breen 1966; Lee and Breen 1970;
Hasselwander, Jirsa, and Breen 1974;
Hasselwander, Jirsa, Breen, and Lo 1977; and
Jirsa, Cichy, Calzadilla, Smart, Pavluvcik, and
Breen 1984).
The test results and design
recommendations are valid for anchors in wellconfined concrete.
These studies focused on many significant
factors affecting anchor bolt behavior including
clear cover, embedment length, bolt diameter,
bearing area, type of anchorage device, concrete
strength, steel yield strength, shape of piers, and
bolt group configuration. In addition, a series of
exploratory and supplementary studies were made
to determine the influence of cyclic loading, lateral
loading, transverse reinforcement, and method of
loading on the bolt behavior. Diameters of anchor
bolts ranged from 1 to 3 in. Steel yield strengths
ranged from 33 ksi (A7) to 105 ksi (A139).
Embedment lengths ranged from 10 bolt diameters
to 20 bolt diameters. A typical test specimen
geometry is shown in Fig. 3.42.
355.1R-45
3.4.2 General behavior under loading-A single
anchor bolt transfers tension load to the concrete
member in three successive stages: (1) steel-toconcrete bond, (2) bearing against the washer of
the anchorage device, and (3) a wedging action by
the cone of crushed and compacted concrete in
front of the anchorage device. These three stages
are not entirely distinct, but the exact nature of
the transition from one stage to the next is highly
indeterminate and can only be discussed in a
general manner.
Fig. 3.43 shows tail stress plotted against lead
stress for three 1 3/4 in. anchor bolts with clear
covers of 3 l/2 in. and three different
10, 15, and 20 bolt diameters.
embedments:
Adhesion or bond between the bolt and concrete
is the predominant load carrying mechanism for
early stages of loading; little increase in tail stress
is observed with increasing lead stress. The longer
the bolt, the more load the bolt can carry by the
bond mechanism. Under increasing load, bond
strength decreases along the length of the bolt and
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
8'- o”_
I'' ANCHOR 8OLlI J/4” ANCHOR B O L T -
SECTION A-A
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SECTION B-B
Fig. 3.42 - Typical specimen geometry
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355.1R-46
Bolt failures occurred in several bolts by
necking in the threaded portion of the bolts.
Little damage to the concrete cover over the bolt
was observed at bolt failure. A relatively sudden
spalling of the concrete cover over the anchorage
device at low loads characterized the failure of
bolts with small amounts of clear cover [Fig.
3.44(a)]. For larger amount of clear cover, the
failures were characterized by the splitting and
spalling of the concrete cover into distinct blocks
by the wedging action of a cone of crushed and
compacted concrete which formed in front of the
anchorage device [Fig. 3.44(b)].
The distinguishing feature of a wedge-splitting
failure was the diagonal cracks [marked B in Fig.
3.44(b)] which started just in front of the washer
on the bolt centerline and extended toward the
front and each side of the specimen. These
diagonal cracks were frequently accompanied by a
longitudinal crack along the bolt axis [C in Fig.
3.44(b)], a transverse crack parallel to and near
the washer of the anchorage device [A in Fig.
tail stress begins to increase. The load that was
previously carried by a bond mechanism must be
transferred to a bearing mechanism. In Fig. 3.43
the bond-to-bearing transition is most clearly seen
for the bolt with 200 embedment. For a given
load increment, the tail stress increases more than
the lead stress as the load carried by bond is
unloaded into bearing on the anchorage device.
The bond-to-bearing transition is dependent on
the embedment of the bolt; the shorter the bolt,
the shorter and less well-defined the transition.
After the bond-to-bearing transition, tail stress
increases uniformly with increasing lead stress as
the load is carried by bearing or by wedging
action.
3.4.3 Failure modes-The failures observed
during testing can be described as: (1) bolt failure,
(2) concrete cover failure by spalling, and (3)
concrete cover failure by wedge-splitting. While
these three categories represent distinct failure
modes, combinations of these modes were
observed in several instances.
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
8
10
l
20
I
30
I
40
I
50
s
60
I
70
Tail Stress, ksi
Fig. 3.43 - Tail stress versus lead stress for different embedment lengths
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Tension
Tension
Cover Spalling
Failure
Wedge-Splitting
Failure
Fig. 3.44 - Concrete cover failures
3.4.4 Lead-slip relationships (effect of clear cover
and embedment length)-Bolt tension versus lead
slip curves associated with different clear covers
and embedments are shown in Fig. 3.45 and 3.46.
Slip of the anchor bolts was measured relative to
the front face of the specimen (lead slip). Fig.
3.45 illustrates the effect of clear cover. Since the
effect f concrete strength varied approximately
with P
d lead stress in Fig. 3.45, calculated on the
basis of the anchor bolt stress area, was
d and plotted against
normalized with respect to /-lead slip for four 1 3/4 in. bolts each with an
embedment of 15 bolt diameters (15D) and an
anchorage device consisting of a nut and a 4 in.
diameter, l/2 in. thick washer. As seen in Fig.
3.45, the slopes of the curves are essentially the
same until each bolt approaches ultimate capacity.
A definite trend of increasing ultimate strength
with increasing clear cover is indicated.
Fig. 3.46 illustrates the effect of embedment
length on the stress-slip relationships of three 1
3/4 in. bolts each with a clear cover of 3 l/2 in.
and an anchorage device consisting of a nut and a
4 in. diameter, l/2 in. thick washer. The initial
portions of the curves are essentially the same and
there is no appreciable difference between the
ultimate strengths of the 15D bolt and the 20D
bolt; the ultimate strength of the 1OD bolt,
however, is noticeably reduced.
The failure of the 10D bolt developed initially
as a typical wedge-splitting mode until the
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cracking propagated to the sides and front face of
the specimen. The result was the complete loss of
a rectangular block of concrete cover extending
back to the anchorage device over the full width
of the specimen, as opposed to the usual group of
triangular wedges with a common apex over the
anchorage device. Such a failure indicates that
the wedge-splitting mechanism did not fully
develop and therefore the ultimate strength of the
anchor bolt installation was reduced.
The major effect of embedment length on the
ultimate strength of an anchor bolt installation is
related to the ability of the concrete cover to resist
the wedge-splitting action of the cone of crushed
and compacted concrete in front of the anchorage
device. A certain minimum embedment length is
required to develop this resistance. As illustrated
in Fig. 3.46, increasing the embedment length
beyond this minimum length provides no
significant improvement but decreasing the
embedment length results in a significant
reduction in ultimate strength. A 15D embedment
length can be considered a satisfactory minimum
embedment length.
3.4.5 Ultimate strength-The ultimate strength of
a bolt in a group is clearly not the same as that of
an isolated bolt with similar geometry.
3.4.5.1 Single bolt strength -Hasselwander,
Jirsa, Breen, and Lo (1977), concluded that clear
cover and bearing area are the main variables
governing the strength of single anchor bolts. The
variables were incorporated into an equation for
predicting the strength of isolated anchor bolts,
subjected to simple tension and failing in a wedgesplitting mode:
Tn = 140A, @[O-7 + ln[2C’/(D, -II)]] (3.35)
where
T, =
Ab =
D =
D, =
C' =
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
3.44(b)] or both. Cracking generally started near
the anchorage device and extended toward the
front, toward the sides of the specimen, or both
under increasing load.
ultimate wedge-splitting capacity of
a single bolt, lb, with an
embedment length not less than 12
(D w - D)
net bearing area, in.* , (r/4) $$D”), but not greater than 4D
bolt diameter, in.
diameter of anchorage device
(washer), in. with minimum
thickness of Dd8
clear cover to the bolt, in.
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355.1R-48
:cu
d
.
s
d
s
d
.
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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’
I500
1250
_,--L~l5 0
Jr-:
L = 20 D
1000
A-.._.._& --z-
.
LL=l0D
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
f
A!!L
750
C’ = 3.5 In.
1
0.02
I
0.04
.
0.06
.
0.08
I
0.10
I
0.12
.
0.14
.
0.16
Lead Slip, inches
Fig. 3.46-Effect of embedment length
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.
0.18
.
0.20
.
0.22
.
0.24
355.1R-50
MANUAL OF CONCRETE PRACTICE
The design tensile strength T, was determined
3.5-REFERENCES
as:
(3.36)
where
4
As
fy
= a capacity reduction factor of 0.75
= tensile area of the anchor bolt, as
defined in Eq. (3.1), in.2
= yield stress of the bolt material, psi
The design equation was developed from a
regression analysis on test results of bolts failing in
A minimum
the wedge-splitting mode only.
embedment length of 12(D, - D) was suggested to
allow the wedge-splitting mechanism to occur. A
restriction which accounted for a reduced bearing
efficiency observed for large washers, limited the
net bearing area to 4D2. A minimum washer
thickness, D$?, was suggested to prevent flexibility
of the washer.
Fig. 3.47 shows graphically the suggested
ultimate strength equation and the test data
plotted to illustrate the accuracy of the equation.
The equation provides a reasonable estimate of
strength, yet is simple to use and reflects the
critical parameters observed in the test program.
3.4.5.2 Bolt group strength - Jirsa, et al. (1984),
evaluated the bolt group interaction and strength
reduction by comparing the average test capacity
with the predicted capacity of an isolated bolt with
similar geometry. It was observed that as bolt
spacing decreased, the reduction in strength
significantly increased. From a least squares
analysis of the available data, the following
modification to Eq. (3.35) was produced for the
nominal tensile capacity of an anchor bolt in a
bolt group based on failure of the concrete.
T,, = 140Ab@ {0.7 + ln[2C’/(D,,,-D)]}
(3.37)
(0.02S + 0.4), in.
where
S = bolt spacing, in.
(0.02S+0.4) 5 1.0
and other factors are the same as in Eq. (3.35).
Eq. (3.37) provides an estimate of the strength
of closely spaced anchor bolts with edge cover
typical of highway- related structures. The design
tensile capacity, Tu, can be determined according
to Eq. (3.36).
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ACI Committee 349,1990, “Code Requirements for Nuclear
Safety Related Concrete Structures,” (ACI 349-90) Appendix
B, American Concrete Institute, Detroit.
American Institute of Steel Construction, 1978,
Specifications for the Design, Fabrication and Erection of Structural Steel Buildings, with Commentary, New York, 235 pp.
Best, J. FIoyd and McDonald, James E., 1989,: “Evaluation
of Polyester Resin, Epoxy, and Cement Grouts for Embedding
Reinforcing Steel Bars in Hardened Concrete,” Technical
Report REMR-CS-23, US Army Engineer Waterways Experiment Station, Vicksburg, MS.
Bode, H. and Roik, K., 1987,: “Headed Studs Embedded in
Concrete and Loaded in Tension,” in ACI SP 103 Anchorage to
Concrete, G. Hasselwander ed. , Detroit.
Bode, H. and Hanenkamp, W., 1985, “Zur Tragfshigkeit von
Kopfbolzen bei Zugbeanspruchung,” (For Load Bearing
Capacity of Headed Bolts Under Pullout Loads), Bauingenieu
pp. 361-367.
Braestrup, M.W., Nielson, M.P., Jense, B.C. and Bach, F.,
1976, “Axissymetric Punching of Plain and Reinforced
Concrete, Copenhagen, Technical University of Denmark,
Structural Research Laboratory, Report R 75.
Breen, J.E., 1964, “Development Length for Anchor Bolts,
Research Report 55-1F, Center for Highway Research, the
University of Texas at Austin.
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
T,, si 4 Tn but < A, fy , lb
Burdette, E.G., Perry, T.C. and Funk, R.R., 1987, “Load
Relaxation Tests”, ACI SP-103 Anchorage to Concrete, G.
Hasselwander ed.,Detroit, pp. 297-311.
Cannon, R.W., 1981,: “Expansion Anchor Performance in
Cracked Concrete,” ACI-Journal, November-December, pp.
471-479.
Elfgren, L., Anneling, R., Eriksson, A., and Granlund, S.,
1988, “Adhesive Anchors, Tests with Cyclic and Long-Time
Loads,” Swedish National Testing Institute Report 1987:39,
Bor&.
Eligehausen, R., 1987, “Anchorage to Concrete by Metallic
Expansion Anchors, ACI SP 103 Anchorage to Concrete, G.
Hasselwander ed., Detroit, pp.181-201.
Eligehausen, R., 1984,: “Wechselbeziehungen zwischen
Befestigungstechnik und Stahlbetonbauweise”, (Interactions of
Fastenings and Reinforced Concrete Constructions), in
“Fortschritte im Konstruktiven Ingenieurbau”, Verlag Wilhelm
Ernst & Sohn. Berlin.
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--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Q
4
(I
w
a
I
00000
*.
.*
..
..
l .
a
ma40
44 4
l
0
0
0
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MANUAL OF CONCRETE PRACTICE
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
Eligehausen, R. and Fuchs, W., 1988, “Tragverhalten von
Dfibelbefestigungen bei Querzug-, Schrsgzug- und Biegebeanspruchung,” (bad-bearing Behaviour of Anchor Fastenings
Under Shear, Combined Tension and Shear or Flexural
Loading), Betonwerk + Fertigteil-Technik, No. 2, in German
and English.
EIigehausen, R., Fuchs, W., Lotze, D. and Reuter, M., 1989,
“Befestigungen in der Betonzugzone,” (Fastening in the
Concrete Tensile Zone), Beton-und Stahlbetonbau 84, No. 2
and 3.
Eligehausen, R., Fuchs, W. and Mayer, B., 1987, 1988,
“Tragverhalten v o n D i i b e l b e f e s t i g u n g e n bei Zugbeanspruchung,” (Loadbearing Behavior of Anchor Fastenings in
Tension), Betonwerk + Fertigteil-Technik, No. 12/1987 und
No. l/1988, in German and English.
Eligehausen, R., Mallee, R. and Rehm, G., 1984, “Befestigungen mit Verbundankern,” (Fastenings Formed with
Chemical Anchors), Betonwerk + Fertigteil-Technik, No. 10,
pp. 686-692, No. 11, pp. 781-785, No. 12, pp. 825-829.
Eligehausen, R. and Pusill-Wachtsmuth, P., 1982,“Stand der
Befestigungstechnik im Stahlbetonbau,” (Fastening Technology
in Reinforced Concrete Construction), IVBH Survey S-19/82,
IVBH- Periodica l/1982, February.
Eligehausen, R. and Reuter, M., 1986, “Tragverhalten von
Platten ohne Schubbewehrung bei Einleitung von Lasten in die
Betonzugzone”, (Load Characteristics of Plates without Shear
Reinforcement by Introduction of Loads in the Tensile Zone
of Concrete), Report No. l/17-86/3 of the Institut fiir
Werkstoffe im Bauwesen, Universitgt Stuttgart.
Eligehausen, R. and Sawade, G., 1985, “Verhalten von
Beton auf Zug,” (Behavior of Concrete in Tension), Betonwerk
+ Fertigteil-Technik, No. 5 and 6, May/June.
Fischer, A., 1984, “Befestigen mit Hinterschnittankern,”
(Fastenings with Undercut Anchors), in "Fortschritte im Konstruktiven Ingenieurbau”, Verlag Wilhelm Ernst & Sohn,
Berlin.
Hanks, Abbot A., 1973,: Kwik Bolt Testing Program, Abbot
Hanks Testing Laboratories of San Francisco, File H2189-S1,
Report No. 8783.
Hasselwander, G.B., Jirsa, J.O., Breen, J.E., and L.o, K.,
1977, “Strength and Behavior of Anchor Bolts Embedded Near
Eclges of Concrete Piers, Research Report 29-2F, Center for
Highway Research, The University of Texas at Austin, May.
Hasselwander, G.B., Jirsa, J.O., and Breen, J.E., 1974, “A
Guide to The Selection of High-Strength Anchor Bolt
Materials”, Research Report 29-1, Center for Highway Research,
The University of Texas at Austin, October.
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Jirsa, J.O., Cichy, N.T., CaIzadilla, M.R., Smart, W.H.,
Pavluvcik, M.P., & Breen, J.E., 1984, “Strength and Behavior
of Bolt Installations Anchored in Concrete Piers,” Research
Report 305-IF, Center for Highway Research, The University
of Texas at Austin, November.
Klingner, R.E. and Mendonca, J.A., 1982a, “Tensile
Capacity of Short Anchor Bolts and Welded Studs: A
Literature Review,” ACI-Journal, July/August, pp. 270-279.
Klingner, R.E. and Mendonca, J.A., 1982b, “Shear Capacity
of Short Anchor Bolts and Welded Studs,” A literature review,
ACI Journal, Sept/Oct.
Klingner, R.E., Mendonca, J.A. and Malik, J.B., 1982,
“Effect of Reinforcing Details on the Shear Resistance of
Anchor Bolts Under Reversed Cyclic Loading,," ACI Journal,
Jan/Feb.
Lee, D.W. and Breen, J.E., 1966, “Factors Affecting Anchor
Development, “Research Report 881F,” Center for Highway
Research, The University of Texas at Austin, August.
Lee, D.W., and Breen J.E., 1970, “Model Study of Anchor
Bolt Development Factors, Models for Concrete Structures, SP29, American Concrete Institute.
Lieberum, K.H., Reinhardt, H.W. and Walraven, J.C., 1987,
’ Lasteinleitung fiber Diibel in der Schubzone von BetonPlattenstreifen,” (Fastening of Anchors in the Shear Zone of
Concrete Slabs), Betonwerk + Fertigteil-Technik, No. 10, in
German and English.
Mayer, B., and Eligehausen, R., 1984, “Ankergruppen mit
Dubeln in der Betonzugzone,” (Anchor Groups with Anchors
in the Concrete Tension Zone), Werkstoffe und Konstruktion
Institut ffir Werkstoffe im Bauwesen der Universitit Stuttgart
Badenand
Forschungs-und
Materialpriifungsanstalt,
Wiirttemberg (Eigenverlag) October, pp. 167-180.
Meinheit, D. and Heidbrink, F.D., 1985, “Behavior of
Drilled-In Expansion Anchors,” Concrete International, April,
pp. 62-66.
PCI Design Handbook-Precast and Prestressed Concrete, 1978,
Prestressed Concrete Institute, Chicago, 380 pp.
Pusill-Wachtsmuth, P.,
1982,
“Tragverhalten
von
Metallspreizdiibeln unter zentrischer Zugbelastung bei den
Versagensarten Betonausbruch und Spalten des Betons,”
(Bearing Behavior of Metallic Expansion Anchors, Loaded in
Tension, for the Failure Modes of Concrete Breakage and
Splitting), Doctoral Thesis, University of Stuttgart.
Rehm, G. and Eligehausen, R., 1986, “Auswirkungen der
modernen Befestigungstechnik auf die konstruktive Gestaltung
im Stahlbetonbau,” (Effects of Modern Fixing Technology on
Structural Design in Reinforcing Concrete Construction),
Betonwerk + Fertigteil-Technik, No. 6, in German and
English.
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Rehm, G., Eligehausen, R. and Mallee, R., 1988, “Befestigungstechnik,” (Fastening Technique), in “Betonkalender
1988”, Verlag Wilhelm Ernst & Sohn, Berlin.
Rehm, G. and Lehmann, R., 1982, “Untersuchungen mit
Metallspreizdtibeln in der gerissenen Zugzone von Stahlbetonbauteilen,” (Investigations with Metallic Expansion Anchors in
the Cracked Tension Zone of Reinforced Concrete Members)“,
Research Report of the Otto-Graf- Institut, Stuttgart, July,
unpublished.
Riemann, H., 1985, “Das erweiterte x-Verfahren fiir
Befestigungsmittel: Bemessung an Beispielen von Kopfbolzenverankerungen,” (The Extended X-Method for the Design of
Fastening Devices as Exemplified by Headed Stud Anchorages), Betonwerk + Fertigteil-Technik, No. 12, pp. 806-815, in
German and English.
Seghezzi, H.D. and Vollmer, H., 1982, “Modern Anchoring
Systems for Concrete, ACI SP-103, Anchorage to Concrete,
Atlanta, January.
Sell, R., 1973, “Festigkeit und Verformung von mit
Reaktionsharzmiirtel-Patronen versetzten Ankern,” (Strength
and Displacement of Anchors Installed with Reaction Resin
Mortar Cartridges), Verbindungstechnik 5, Vol. E, August, in
German.
Shaikh, A.F. and Yi, W., 1985, “In-Place Strength of Welded
Headed Studs,” Journal of the Prestressed Concrete Institute,
March/April, pp. 56-81.
Teledyne Engineering Services, 1979, Technical Report
3501-1, Revision 1, August 30.
Wagner-Grey, U., 1976,: “Experimentelle und Theoretische
U n t e r s u c h u n g e n zum Tragverhalten von Spreizdtibeln in
Beton”, (Experimental and Theoretical Investigations on the
Performance of Expansion Anchors in Concrete), Doctoral
Thesis, Technical University of Munich.
Wiewel, Harry, 1989,: ” Results of Long-Term Tension Tests
on ITW Ramset/Red H e a d E P C O N S y s t e m @ A n c h o r s
Installed in Hardrock Concrete,” Techmar Inc, long Beach,
CA. J une.
CHAPTER 4-DESIGN CONSIDERATIONS
4.1- Introduction
The purpose of this section is to discuss the
various factors which affect the ability of concrete
anchorages to perform their intended purpose.
These factors should be considered in the design
of anchorages. The tendency to design anchors
based only on their tensile or shear loading is
discouraged, when actually bending, prying action,
and redistribution of loads are often involved.
4.2 -Functional requirements
4.2.1 Loading Conditions-Major considerations
in determining the requirements for concrete
anchorages include the type of loading which the
anchorage will experience, and the potential for
concrete cracking in the vicinity of the anchors.
There is a high probability of coincidental cracking
when anchors are located in the tensile zone of a
concrete member. As described in Chapter 3, the
capacity of anchors under sustained loading in the
tensile stress zone of uncracked concrete is only 60
to 75 percent of static load capacity of anchors in
unstressed concrete. In cracked concrete, anchor
capacity is significantly influenced by anchor type
and width of the crack in the region of the
anchorage. In regions of tensile stress, since the
width of flexural cracks is maximum at the
concrete surface and decrease with distance away
from the surface, the designer should use deepseated anchors (anchored in the compression zone
of the member), or anchors which are designed to
perform in cracked concrete. Anchors which
perform well, at a given load level in uncracked
concrete, may fail completely in cracked concrete
under loads of the same magnitude. Criteria for
the design and selection of concrete anchorages
should account for these factors.
Economics or related issues may dictate
designing for a selected mode of failure.
Installations such as bridge railings and highway
signs could potentially receive accidental loadings
that are not reasonable design loads. In such
cases it may be prudent to design for the failure of
the most easily replaced segment of the structure,
whether it is the anchor bolt or a separate piece of
the structure. Care must be exercised in designing
for selected failure modes to maintain the integrity
of the primary structural system.
4.2.1.1 Column bases - Simply connected
column bases are normally loaded in compression
of sufficient magnitude that column shear is
transferred through friction and the anchorage
serves only for erection purposes. It has been
common practice for many years to use L- and Jbolts for erection anchors, which do not have
sufficient embedment to develop the strength of
the anchor steel. Headed anchors of the same
size and length as L- and J-bolts have significantly
However, the increase in
higher capacities.
capacity is often not needed for the simple column
base plate connection. Column bases which are
designed as moment connections should require a
--`,``,````,,,`,``,``,,,,,```,`-`-`,,`,,`,`,,`---
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MANUAL OF CONCRETE PRACTICE
rigid base connection and anchors should be
selected which can maintain a sufficient residual
preload to develop applied moments. These
conditions are necessary to achieve fixity of the
column base.
4.2.1.2 Machine Foundations-Anchor bolts
for machinery foundations are generally specified
by the machinery manufacturer and have been
sized by experience. Their general purpose is to
fix the rigid machine housing to concrete in order
to withstand machine vibrations.
They are
generally installed to a relatively low stress level
and may not have sufficient embedment to
develop the anchor steel capacity. Seismic loading
of machine foundation anchorages can be critical
and must be considered.
4.2.1.3 Structural Tension and Shear
Connections-The anchorage of principal
structural connections requires careful
consideration of all possible loading combinations.
Failure of structural connections may be
catastrophic, particularly when there is no
redundancy in the system. It is recommended that
all structural connections be ductile.
Ductility is defined as the ratio of a structure’s
plastic displacement to its maximum elastic (yield)
displacement. The ability of a structure to exhibit
high values of ductility (ten or greater) is an
extremely desirable feature because this can allow
for an overload condition to exist without
producing a catastrophic failure. It can provide
for highly redundant structures (i.e., structures
that provide alternative stress paths) that
redistribute loads internally.
When designing the anchorage of a steel
structure to concrete, ductility of the structure,
including the connection, should be considered.
The desired ductile behavior may occur in any one
or all of the following components: the structural
steel element being connected, the baseplate
attached to the steel member, the steel anchors, or
the concrete. Steel is more ductile than concrete
and it is better to proportion an anchorage so that
the majority of the ductile displacement occurs in
the steel elements of the anchorage or in the
attached structural member. In cases where this
is not possible, extra care should be taken in
selecting anchor types, geometry, and safety
factors.
Temperature changes and the shrinkage of
structural elements should also be carefully
considered in determining connection details
because of the significant effect which tensile
loads have on anchor stress and the manner in
which shear is transferred to the concrete.
Structural connections should also be investigated
for cyclic loadings, vibration loads from wind or
machinery, and seismic loads.
4.2.1.4 Pipe Supports-In most structures, pipe
supports are dead-load hangers or support
brackets. Pipe supports are generally detailed to
provide free expansion and contraction of the
piping system under changing temperatures.
Experience has shown these loosely supported
systems function very well under seismic
conditions without special design considerations.
Vibration problems normally occur under
operating conditions and are corrected by adding
or shifting supports to alter the response
frequency of the system. Design loads for these
supports are generally low and sizing of anchors,
by experience, usually results in large safety
factors.
In contrast to this, the pipe supports for nuclear
applications are often designed to prevent piping
system frequencies from coinciding with predicted
structural frequencies generated by an earthquake
of prescribed magnitude.
As a result,
specifications often limit support displacements to
low values under conservative combinations of
loading. Most anchorages cannot comply with the
imposed displacement limitations without rigid
bases and oversized anchors.
When a pipe has multiple supports and is
loaded along its length, evaluation of the stiffness
of each support with respect to the longitudinal
stiffness of the total support system between
expansion joints or bends should be made to
insure that a particular support is not overloaded
to failure, thus setting up a progressive failure
mechanism.
4.2.2 Anchorage Environment- Consideration of
the service environment is essential for service
longevity, particularly in areas where the
anchorage may come in contact with saltwater
sprays or deicing salts. Unprotected steel is
particularly vulnerable to corrosion when exposed
to the atmosphere.
For expansion anchors,
vulnerability to corrosion exists in the region of
the expansion mechanism where space is available
for moisture collection. Corrosion will reduce the
ability of anchors to function correctly, especially
torque-controlled expansion anchors.
Where steel is under a sustained high stress,
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ANCHORAGE TO CONCRETE
there is a higher potential for stress corrosion
failure. If the yield strength of the anchor steel is
less than 120,000 psi, stress corrosion is less likely
to be a problem. However, precautions must be
taken when chlorides are used in the anchorage
zone either externally or as a part of the concrete
mix. Protective coating systems, or the use of
corrosion resistant materials, should be considered
in corrosive environments. The use of thin zinc
coatings will not provide permanent protection
against corrosion under normal outside exposure
conditions. Proper detailing will insure that runoff
water cannot reach anchors in areas of snow and
ice removal. Alternate periods of wetting and
drying have been known to produce corrosion
even in the absence of chlorides.
Anchor bolts are often set in sleeves to provide
for minor adjustment of the bolt to fit the
foundation base. If the foundation is exposed to
freezing temperatures, the sleeves should be filled
with grout or be otherwise protected against the
intrusion of water. Gaps between a steel base
plate and the concrete surface should be sealed if
the foundation is exposed to an aggressive
environment. In a similar fashion, plain sandcement dry-pack pads which are exposed to
freezing and thawing should be coated with a
sealer to prevent water absorption.
Chemical adhesives, lead caulking, or other
materials which have a high rate of creep at
elevated temperatures should not be used in areas
of high temperature or possible exposure to fire.
Special investigations may also be necessary to
determine the possible effects of process chemicals
on anchors in industrial plants. Intermittent
exposure may be a more severe service condition
than continuous exposure.
4.2.3 Behavior-The behavior of cast-in-place
and post-installed anchors is described in Chapter
3. Well-designed, cast-in-place anchors perform
better than or equally as well as post-installed
anchors, if for no other reason than that they are
normally set deeper into the concrete and at
ultimate load feature failure in the bolt rather
than failure in the concrete. Construction logistics
that admit alternative
and specifications
manufacture of the equipment to be anchored
(and therefore alternative anchorage size and
location) often make the post-installed anchor
more practical. Nonetheless, the designer should
consider use of a cast-in-place anchor whenever
the size and location of that anchor is known prior
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355.1R-55
to casting of the concrete.
Anchor capacity may be limited by the strength
of concrete, by the strength of the anchorage steel,
or by slip of the anchorage mechanism. The mode
of failure is an important design consideration.
Concrete failure may occur before or during
slip of the anchor. In general, the properties of
steel are well defined and steel failure is
predictable and controllable. In contrast to the
controlled ductility of a steel failure mechanism,
concrete is a brittle material with less well-defined
properties. Failure by slip may be either brittle or
ductile depending on the ability of the anchorage
mechanism to maintain load during slip.
4.3 - MATERIALS
4.3.1 Concrete-When the capacity of the
anchorage is controlled by the strength of
concrete, it is generally the tensile properties of
the concrete which control cone failures, and
crushing strength that controls slip failures.
Tensile properties of concrete vary more than
compressive properties. Tensile properties of the
concrete also influence bond and affect those
anchor types which depend on bond to develop
capacity.
The tensile-compressive strength relationship
can be complicated by the influence of grain size,
type, and distribution of aggregate particles. For
this reason, construction practices, which permit
segregation of the aggregate will increase the
variability of tensile strength more than the
compressive strength.
Segregation of the
aggregate is influenced by the slump of the
concrete, the height of the drop of the concrete,
and the amount of vibration during placement.
For this reason, the capacity of anchors may vary
depending on their location in walls and in the top
or bottom of slabs.
4.3.2 Steel-The type of steel used in anchors is
largely dependent on the method of anchorage but
can also be influenced by the method of securing
the base plate or attachment to the anchors. It is
desirable to limit the yield strength of headed
anchors to that of ASTM A 325 or lower strength
material, because of the brittle nature of higher
strength steels. Zinc plating causes additional
brittleness and reduced fatigue resistance for
higher strength steel bolts. Steel with yield
strengths in excess of 120,000 psi have been found
to be highly susceptible to stress corrosion in most
anchorage environments.
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MANUAL OF CONCRETE PRACTICE
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4.4 -Design basis
The safety factor for any element in an
anchorage system should be consistent with the
other elements in the system. Establishing an
allowable stress or load factor must consider
overall behavior of the anchorage. The design of
concrete anchorages is usually controlled by codes
governing both structural steel and concrete.
4.4.1 Types of anchors
4.4.1.1Headed Anchors-Headed anchors may
consist of welded studs or bolting material with
anchor heads manufactured to established
standards. Headed anchors may also be made by
welding a rigid plate to the embedded end of the
anchor or by threading a bar and using a standard
nut. Once the load increases sufficiently to
overcome
n the shank, subsequent loading
anchor head. Headed
efficiently if the shank of the
This will minimize bond and
oad on the anchor by bearing
Anchors-When anchor load
inishes with depth. The
quired to fully develop the
of deformations).
sustained loadi
concrete in the
Bonded anchor
Under
typically been manufactured
deformed reinforcing bars,
s. The basic development
Building Code are based on
d minimum spacing of an
rs. The basic development
ars with a hook or 90” bend
about 50 percent of the
of straight bars. The use of
r reinforcement was excluded
g Code in 1971 (ACI-ASCE
considered as twice that
of deformed ba
insure that the
gths given in ACI 318
crete capacity is higher than the
When evaluating the concrete
e failure modes “splitting of
e concrete between ribs”
The failure mode
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“concrete cone break out” was not considered
because typically this mode does not occur when
developing reinforcing bars. However, the failure
mode “concrete cone break out” is quite typical for
shallow anchors (see Chapter 3).
Excluding edge and spacing conditions, the
yield strength of an individual reinforcing bar can
be developed in 3000 psi uncracked concrete in
about 15 bar diameters (straight bar) or 10 bar
diameters (hooked bar). To preclude a concretecone-break-out failure, the development length
may increase by a factor of up to four to account
for the effects of cover, number, and spacing of
bars. A further increase of the development
length by a factor of one and one-half to two is
necessary if the anchors are located in the cracked
tensile zone of a reinforced concrete member.
Most anchorage situations do not involve
minimum values for spacing and cover. The code
provisions will be very conservative if individual
bars are anchored in uncracked concrete well away
from edges. However, the code provisions may
not be conservative, if a group of bars, with or
without small edge distance, is anchored in
uncracked concrete or in the (cracked) tension
zone of reinforced concrete members.
4.4.1.3 Expansion Anchors-Many patented
expansion devices are used to mechanically fasten
post-installed anchors to the concrete. Most
expansion anchors were originally developed for
short embedment depths to provide an anchor
which failed in the concrete or by slip. Since
ductile steel failure had no opportunity to occur in
this situation, there were no restricting strengths
applied to the steel in these anchors. More
recently developed expansion anchors feature
expansion mechanisms that can fully develop the
strength of the anchor steel, when used as single
anchors. Ductile steels should be specified for this
type of anchor if a ductile failure mode is desired.
4.4.2 Concrete tensile failure -The determination
of concrete pullout strength (cone failure) of
individual anchors and anchor groups is discussed
in Section 3.2.2. Concrete cone failure will occur
when the capacity of the anchor bolt exceeds the
concrete pullout strength. All shell type expansion
anchors are designed to fail the concrete when the
bolt is embedded to shell depth. Concrete failure
can also occur with wedge bolts having shallow
embedment depths.
The concrete may also fail by splitting tension
when there is inadequate lateral confinement of
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(1) Providing for deeper embedment to
preclude the tensile-cone-failure mode.
(2) Using larger number of smaller anchors at
closer spacings to avoid spalling when the edge
distance is too small.
(3) Preloading the anchorage so that shear is
transferred by friction at the interface of the base
plate and the concrete rather than through shear
in the anchor.
4.4.3 Anchor Slip -Anchors which fail by slip,
without causing the concrete to fail in tension,
have load-displacement characteristics similar to
the post-yield behavior of steel. Typically, wedge
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bolts and sleeve anchors with embedment depths
greater than seven bolt diameters will fail by slip.
They cannot be considered ductile, however,
because the relatively wide variation in the slope
of the deflection curves and ultimate loads
distribute loads nonuniformly to the anchors. For
these types of anchors, most manufacturers of
post-installed expansion anchors recommend
limiting normal service loads to 25 percent of the
average published failure loads.
4.4.4 Tensile strength of steel - When the
concrete-failure-cone strength exceeds the tensile
strength of the anchor steel, design is controlled
by the strength of steel.
For structural
attachments, other than simple hangers, load
distribution to the attachments is dependent on
the stiffness of the attachment and its degree of
fixi ty For rigid base connections, anchor stress
may be determined assuming that plane sections
remain plane. However, if the load is transferred
from the attachment to the anchors through a
flexible plate, the determination of anchor stress
is complicated by plate stiffness, prying action, and
the load-displacement characteristics (including
preload) of the anchor steel.
AISC imposes a minimum safety factor of two,
against ultimate, for service loads on high yield
materials. Considering the increased loss of
preload in concrete anchorages (approximately
three times that of steel to steel connections), a
minimum safety factor of three for anchor bolts
would provide residual service load allowables
approximating 85 to 90 percent of the residual
preload for bolts initially preloaded close to yield.
This would appear to be a reasonable limit
considering all the other concrete and anchor
variables. Proof load for concrete anchorages
should be approximately 110 percent of the service
load.
For factored load design, AC I Committee 349
(1990) limits maximum stress to 0.9 of yield for all
types of connections, and with stresses based on
the net tensile area for bolted connections.
Assuming an average load factor of 1.6, service
load stresses would approximate 0.55 yield for
anchors other than bolts. For ASTM A 36 steel,
this also closely corresponds to a factor of safety
of 3 against tensile strength.
The capacity of welded stud anchors appears to
be affected by the thickness of the attachment,
Tennessee Valley Authority (1979). Apparently
prying action, due to the flexibility of the plate,
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the anchor.
This occurs with all types of
expansion anchors that have small edge distances.
Deformation-controlled expansion anchors (dropin, self-drilling, and stud) are especially sensitive
to edge distance because of the high expansion
forces developed during anchor installation.
Splitting may also occur at close edge distances
when the anchorage mechanism expands with load
application.
In the United States, most manufacturers of
expansion anchors recommend limiting normal
service loads to 25 percent of the manufacturer’s
average test failure load. Investigations by the
United States Nuclear Regulatory Commission
(1979) indicated that installation problems
associated with split-shell type expansion anchors
warranted increased safety factors over those
applied to torque-type anchors. For the split-shell
anchor, and others which cause the concrete to
fail, it was recommended that a minimum factor
of safety of five against average test values be
used.
Test results for expansion anchors differ from
job to job and with anchor size, type, and
modifications in anchor design. Assuming a
coefficient of variation of 25 percent, a factor of
safety of five on average tested anchor strength is
appropriate.
The capacities of anchors are affected by
embedment depth, edge distance, and spacing.
Reinforcing steel in the concrete can be used to
enhance the strength of cast-in-place anchors.
When the edge distance is small, closely spaced
spirals of small diameter wire or mesh may be
used to resist the bursting forces. However, more
research is required in this area. Other solutions
may be more effective. They consist of:
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MANUAL OF CONCRETE PRACTICE
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induces very high stress and cracking at the
interior edge of the heat-affected zone of the weld
under relatively low load applications. As a result,
testing clearly indicates loss of capacity with
increasing plate flexibility.
4.4.5 Shear- Shear may be transferred from
base plate to concrete either by friction or by
bearing.
4.4.5.1 Shear transfer by friction - If shear is to
be transferred by friction, no lateral translation
(sliding) of the base plate can occur. The normal
force necessary to develop frictional resistance
may be caused by direct load, by the compressive
reaction of the applied moment, by residual
preload in the anchors, or by any combination of
the three. If the connection is to transfer shear by
friction, the loading combination which controls
should be that which produces the minimum
compressive reaction in conjunction with
maximum shear.
If the connection is fastened to hardened
concrete, the coefficient of friction used to
determine shear resistance should not exceed 0.6.
If the surface of a base plate is in intimate contact
with concrete or grout, shear resistance will be
increased by the cohesion between the two
surfaces and the coefficient may be taken as 0.7.
All forces contributing to frictional resistance
should be conservatively determined in designing
for either total or partial shear resistance by
friction. Note that:
(a) Direct loads normal to the shear plane
should be the minimum associated with the loading condition. For cyclic loading, this would be
the maximum direct pull-off loading including
associated impact factors.
(b) The compression component of the
moment reaction is dependent on the location of
the center of gravity of the compressive reaction.
Conservative assumptions should therefore be
used concerning its location. Without test verification of the analytical procedure, the location
should not be assumed to be farther than pne
plate thickness from the compressive edge of the
attachment.
(c) Residual preload, if any, should be based
on conservative assumptions of preload loss.
Shallow depth anchors having the capability of
failing the concrete in tension may be expected to
experience a total loss of preload. When the
installation procedure requires a positive means of
determining installation preload, residual preload
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should not be assumed greater than 50 percent of
the initial preload without prototype testing.
When the installation load is determined by
calibrated torque wrench or other less positive
means, a higher loss should be assumed. Lost
preload may be regained by retorquing, or
retightening anchors. There appears to be little
advantage in retorquing more than twice.
Sufficient time should be allowed for the majority
of loss to occur before retorquing, but under no
condition should the time period be less than
about 1 week. Effective preload should not be
assumed without verification requirements in the
installation procedure.
4.4.5.2 Shear transfer through bearing- If
frictional resistance is not sufficient to resist
lateral sliding, shear must be transferred by the
plate bearing on anchors, shear lugs, or the
concrete at the end of a fully embedded plate. In
bearing connections, shear is distributed in
proportion to the stiffnesses of the shear-resisting
elements, with each element contributing its share.
Failure of the stiffer elements will increase lateral
translation. The stiffer elements then transfer
their load to the remaining elements.
4.4.6 Preload-Concern for fatigue failure is a
principal consideration in establishing service
stresses. This is particularly true for expansion
anchors. If the element is subject to frequent
fluctuations in stress, the magnitude of the
fluctuating stress range must be restricted to
prevent eventual fatigue failure (see discussion of
behavior under cyclic loads in Chapter 3). This is
best controlled by limiting the maximum level of
design stress. If the bolting system can be
prestressed with sufficient load that the load
remaining after losses exceeds the maximum stress
load, it is generally accepted that fatigue is not
likely to occur. Under these conditions service
load stress should be set at a level that reflects the
residual prestress.
If a sustaining (residual)
prestress cannot be assured, the service load stress,
under fluctuating loads, must be set at a low
enough level to assure that fatigue failure will not
occur.
Assuring a level of prestress in concrete
anchorages is more complicated than steel-to-steel
connections. Preload loss occurs due to creep of
the concrete in the highly-stressed regions of load
transfer from steel to concrete.
For most
embedments the major preload loss occurs within
a few days of preloading. The loss, in percent,
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ANCHORAGE TO CONCRETE
diminishes each time the anchorage is retorqued
such that losses can be minimized by retorquing at
about 1 week intervals. The prestress should not
exceed the yield stress of the steel. Loss of
preload is a function of the strain relaxation
(creep) relative to the total anchor strain. Since
the major portion of load relaxation occurs at the
zone of load transfer into the concrete, the loss of
preload, in percent, can be reduced by increasing
the total anchor elongation which increases the
strain length of the anchor. If the embedment
length of the anchor is the minimum required to
develop its tensile strength, it will lose from 40 to
50 percent of its applied preload unless retorqued
(Burdette, Perry, and Funk 1987). The loss may
be more pronounced if the anchor is situated in
cracked concrete. Loss of preload may approach
100 percent for anchors of lesser embedment
depths which are capable of failing the concrete.
This is especially true for anchors located in
cracked concrete. To achieve an effective residual
preload, care must be taken to exclude any
bonding of the anchor to grout or concrete at the
embedment surface. When bond occurs at the
surface, the confinement of the surface concrete
or grout, by compression of the bearing plate on
the surface, is often sufficient to locally transfer
the entire load for a limited time. When this
occurs, stretch of the bolt may be limited to the
thickness of the bearing plate or attachment. For
effective preload, threads must be excluded from
bonding to either concrete or grout. Grout has
significantly higher bonding qualities than
concrete, therefore the entire length of bolt above
the anchor head should be coated to prevent bond
in grouted systems.
Effective prestress requires intimate contact of
the base plate with concrete or grout at all anchor
locations. When the base plate is bolted directly
to hardened concrete without grout, effective
prestress can be accomplished by placing shims or
washers between the plate and concrete at the
anchor locations. In most moment connections,
shear is transferred to the concrete entirely
through friction and bolts transmit tension only.
If the combined effect of anchor preload and
compressive reaction of the applied moment are
not sufficient for shear transfer through friction,
then shear must be transferred through the
anchors. If this occurs, and shims or washers are
used, the combined stress in the anchor would be
increased by the increased bending stress in the
bolts in transmitting shear through the added
space of the washers. If intimate contact is not
achieved, the danger of high stress accumulations
can be prevented by initially torquing to maximum
values and then loosening the bolts to a minimum
torque value after the concrete has had sufficient
time to consolidate in the region of the anchor
head.
This will eliminate nonlinear anchor
displacement under load and restrict peak stress
accumulation to design stress levels.
4.4.7 Base plate flexibility-The flexibility of the
base plate connecting the attachment to the
anchorage steel is a controlling factor in
determining the magnitude of anchor stress and
the distribution of stress to the anchors. If the
distance between exterior anchors and attachment
is more than two plate thicknesses, the plate may
be considered flexible, otherwise, the plate may be
considered rigid. If the plate is rigid, anchor stress
due to moment is proportional to its distance from
the neutral axis and a conventional summation of
forces and moments can be used to determine
stress. If the plate is flexible, anchor stress is
dependent on plate stiffness as well as distance to
the neutral axis. It can also be influenced by the
effect of other stressed anchors in the group that
cause bending in the plate, and on any prying
forces caused by plate flexure, which may add
directly to the anchor load. Anchor loads,
determined by conventional analysis, may be
significantly in error if the plate is flexible.
4.4.7.1 Prying action-When load is transferred from attachment to anchor through a
flexible plate in full contact with the concrete or
grout, rotation of the plate at the anchor will
induce a prying force beyond the anchor where
the plate bears on the concrete. The prying force
increases the load in the anchor. Prying increases
with plate flexibility which affects the magnitude
of potential downward displacement of the plate
edge beyond the anchor. Prying decreases with
increased anchor displacement. Preload reduces
the displacement characteristics of the anchor
under applied loading and increases the counter
rotation of the plate beyond the anchor. For this
reason anchor stress will increase with applied
load irrespective of preload. The rate of stress
increase, however, decreases with increasing
preload.
If the plate is not in contact with the concrete
beyond the anchor, no prying will occur until the
gap between plate and concrete is closed by the
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355.1R-60
MANUAL OF CONCRETE PRACTICE
downward displacement of the plate edge. If the
anchor is not preloaded, the displacement of the
stressed anchor will add to the gap requiring
closure to develop prying. If the anchor is
preloaded to close the gap, the preload force will
add to the anchor stress resisting applied loads.
4.5-Construction practices
Design of anchor installations must take into
account local construction practice and expected
field conditions. Details should be designed so
that the probability of concrete honeycombing at
anchor locations is minimized.
Placement
tolerances may or may not be critical and should
be determined by the application. See Chapter 5
for more information.
4.6-REFERENCES
Abbot A. Hanks, “Summary Report - Kwik-Bolt Testing
Program”, File No. H2189-S1, Report No. 8783, Abbot A.
Hanks Testing Laboratories, San Francisco, CA
ACI Committee 349,1990, “Code Requirements for Nuclear
Safety Related Concrete Structures (AC1 349-90), “Appendix
B”, American Concrete Institute, Detroit.
ACI-ASCE Committee 326, 1962, “Shear and Diagonal
Tension”, ACI Journal, Proceedings V 59, No. 2, Feb., pp. 277333.
Burdette, E.G., Perry, T., Funk, R.R., 1987, “Load
Relaxation Tests”, ACI SP-103 Anchorage to Concrete, Detroit,
pp. 297-311.
Cannon, Robert W., 1981, “Expansion Anchor Performance
in Cracked Concrete”, ACI Journal Proceedings V. 78,
November-December, pp. 471-479.
Eligehausen, Rolf, 1987, “Anchorage to Concrete by
Metallic Expansion Anchors”, Anchorage to Concrete, American
Concrete Institute Special Publication SP-103, pp. 181-201.
Orangun, C.O., Jirsa, J.O., and Breen, J.E., 1977, “A Reevaluation of Test Data on Development Length and Splices,”
ACI Journal, Vol. 74, No. 3, pp. 114-122.
Raphael, Jerome M., 1984, “Tensile Strength of Concrete”,
ACI Journal No. March - April, pp. 158-165.
Tennessee Valley Authority, 1979, “Welded Stud Anchors,
Effect of Plate Flexibility on Stud Capacity”, CEB Report No.
79-18, TVA, Knoxville, TN.
United States Nuclear Regulatory Commission, 1979, “Pipe
Support Base Plate Designs Using Concrete Expansion Anchor
Bolts”, IE Bulletin No. 79-02, Office of Inspection and
Enforcement, Washington, D.C.
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CHAPTER 5-CONSTRUCTION
SIDERATIONS
5.1 Introduction
CON-
Quality control is the central issue among
construction considerations for anchorage to
In construction, the engineering
concrete.
profession tends to be quite meticulous with
respect to tolerance in the fabrication of structural
steel, but somewhat less so in masonry, timber
Meeting
framing, and reinforced concrete.
tolerances is expensive and, therefore, required
tolerances are limited to what is practical and
what “can be covered by the other trades” and still
yield an acceptable product.
Another concept in establishing tolerances is to
weigh the consequences of constructing less
accurately than specified. Experience has shown
that the secondary costs of compensating for the
structural skeleton being out of square or out of
plumb justify taking great care in the initial
fabrication. This is also true for anchorage to
concrete. There are few details in a structure
where care during installation pays more
dividends, or where carelessness can prove more
costly. Sometimes corrective measures can be so
expensive that they are not taken and the end
product falls far short of what the engineer
intended.
Anchorage details are at the interface and
provide the connecting link between separate
structural systems. The axial load, moment, and
shear required of the connection are typically
quite well defined, and must be accommodated
because there is usually no alternative path for
load transfer. The joint has a minimum of
redundancy to compensate for error in design or
construction. Accordingly, it is important that the
field engineer understands the intent of the
design, to assure that the anchorage be
constructed as specified. This relates to having
the proper device, with the specified size and
material, and having it properly installed.
5.2 Shop drawings/submittals
The first step in quality control is that the plans
and specifications must indicate clearly what is
intended. The next step is the requirement for
submittals and shop drawings for all anchorages.
5.2.1 Cast-in-place systems-For cast-in-place
systems, the submittal is the shop drawing and any
other certifications required by the construction
specifications. With respect to each anchorage
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assembly, the shop drawing should indicate the
material of the anchoring device, its coating,
length, diameter, length of threaded portion,
diameter and thickness of washers, number of nuts
(single, double, single or double plus leveling,
etc.), and torquing requirements, if any.
The shop drawing should also indicate the
location of the anchorage in the structure, the
location of the bolts (or devices) in a group, and
their projection and embedment with respect to
the finished concrete grade. When the completed
anchorage is specified to be either grouted or dry
packed, the dimensional details of the grout or
drypack should be shown.
When the anchorage consists of embedded
dowels of reinforcing steel, the shop drawings for
the anchorage are included in the shop drawings
for the reinforcing steel. They should indicate the
type of steel, details of bending, location (bar or
groups of bars), embedment, and projection.
Often an anchor assembly includes embedded
structural shapes, either as the anchor itself or as
a lower template.
Shop drawings for these
embedded shapes should indicate type of steel;
coating; cross-sectional shape (standard designation); dimensions and details of the member or
group of members in the assembly (location, type,
size, and length of welds); size and location of
holes; and embedment depth.
5.2.2 Post-Installed Systems-For post-installed
systems, the submittal should include the shop
drawings with information similar to that required
for cast-in-place systems, plus manufacturer’s
literature which adequately describes the device
and its capabilities and provides instructions for its
proper installation.
5.3 Tolerances
The acceptable variation from the specified
positioning is the tolerance. The tolerances
should be specified by the engineer and be
appropriate for the application. Table 5.1 gives
suggested tolerances for anchor positioning and
can be used as a guide in determining
acceptability. Other sources such as the American
Institute of Steel Construction (AISC) and
Precast/Prestressed Concrete Institute (PCI) are
available. These requirements are rigorous, but
meeting them is judged to be more economical
than the consequences of not meeting them.
Mounting or anchoring certain special equipment
may require even closer tolerances.
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5.4 lnstatllatlon of anchors
5.4.1 Cast-in-place systems
5.4.1.1 Anchors Embedded, NonAdjustable-Anchorages that fall into this category
(see Table 2.1) can be grouped as follows:
- Bolts installed in plastic concrete - Bolts in
cans or blockouts
- Bolts, with or without sleeves, positioned
without template
- Bolts, embedments, weld plates, or inserts
attached to the formwork
- Bolts or groups of bolts, with or without
sleeves, positioned by top or bottom templates, or
both
- Embedded structural shapes
5.4.1.2 Bolts installed in plastic
concrete-Often in wood frame construction the
bolts connecting the wood sill to the footing or a
wood plate to the top of a wall are installed as
soon as the concrete placement is completed.
This practice is not recommended because a good
bond may not be achieved.
5.4.1.3 Bolts in Cans or Blockouts- T h i s
system can be used in cast-in-place or postinstalled construction.
Often, for machinery
foundations or in situations where it is not
desirable to have anchor bolts protruding from a
slab or penetrating through a wall form, a can or
blockout will be set at the approximate future bolt
location. These blockouts can be made of wood,
metal, or plastic; can be cylindrical or prismatic;
can provide a shear key perpendicular to the floor
or wall; or be battered to provide a dovetail effect.
For flatwork, the cans or blockouts can be
positioned by wood battens or templates which
have a soffit elevation equal to the grade at topof-concrete and are secured to the edge forms; or
they can be wired to the reinforcement or the
edge forms. For vertical surfaces, they can be
fastened to the wall form in their predetermined
positions. In both cases, the blockout should be
wire tied to the reinforcement so that it will not
be vibrated out of position during the placement
of the concrete.
After concreting, wood blockouts are stripped.
Metal or plastic units are typically left in place.
The pocket is blown clean of debris, the anchor
bolt positioned and the pocket grouted.
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Table 5.1 -Suggested tolerances for installation of anchors in concrete
Installed
Location
L and P are Specified
Correct
Location
Plan “A”
/3 Per Plans
Suggested tolerances
Vertical
Alignment,
(r, deg.
Type of anchorage
Positioning
r, in.
Projection
P, in.
A. Cast-in-place
1. Common bolt, J- or Gbolt, continuously threaded rods
k /14
I
1/16
I
3.0
f 1/4
1/8
3.0
4. Weld plates
Flush with concrete
l/8
N/A
5. Troughs for adjustable anchors
Flush with concrete
l/4
N/A
6. Temporary embedded inserts
Flush with concrete
l/2
3.0
1. Drilled and grouted-all types
+ l/4
1/16
3.0
2. Expansion types
k 1/8
1/16
3.0
3. Embedded structural shapes
B. Post-installed
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Per recommendations of Committee 117
2. Reinforcing steel
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5.4.1.4 Anchors with or without sleeve,
positioned without templates-This practice is
generally not recommended, but if proper care is
taken it can be successful. Tolerance criteria
should be met and maintained throughout the
concrete placement. The bolt insert or sleeve
should be rigidly tied with wire to the reinforcement, top and bottom. Sometimes, the
sleeve, the bolt head, bottom washer, or insert is
tack welded, according to approved procedures, to
cross bars which in turn are wire tied or tack
welded to the existing reinforcement.
5.4.1.5 Bolts, embedments, weld plates or inserts
attached to the formwork-This work generally
relates to soffit and wall forms. The important
step is to accurately scribe the inside of the form
for proper location of the anchoring unit. The
anchor unit should then be nailed or bolted to the
form or wire tied to the reinforcing steel, or both
so that neither internal nor external vibration can
disturb or move the anchorage unit out of
position.
5.4.1.6 Bolts or groups of bolts, with or without
sleeve positioned by templates -These installations
are generally used in flatwork, where the bolts are
vertical.
The use of templates is the best
technique for guaranteeing that the anchorage is
correctly positioned.
A top template is often wood, although in
“loose base plate” construction (where the
superstructure is subsequently welded or otherwise
connected to a steel base plate), the base plate
itself can be used as the template. The top
template for a single bolt or a group of bolts
generally has a soffit elevation at or above the top
of the finished concrete. Sometimes top templates
are plywood with the holes either laid out
precisely as the holes in the base plate, or actually
drilled using the base plate holes as a guide for
the drill. Where only a top template is used, there
should be nuts above and below the template to
hold the anchor bolt in a plumb position.
The bottom template is a steel assembly of
angles, channels, or flat bars. Low carbon steel
bolts can be precisely positioned and welded
directly to the steel template, or set in accurately
located holes in the template, and tack welded.
When used in conjunction with a top template, it
is the top template that controls both the bolt
projection and lateral position of the group of
bolts. When there is no top template, the bottom
template must provide those controls and should
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be wire tied or welded, according to approved
procedures, to the reinforcement so that it will be
maintained in correct position while the concrete
is being placed. Engineering approval should be
obtained before welding to high-strength bolts or
reinforcing bar, because material property changes
may compromise expected steel capacities.
Bottom templates are expensive and usually
reserved for larger diameter bolt installations.
They also affect the capacity of an anchorage and
for this reason should only be used where detailed
or approved by the Engineer.
5.4.1.7 Embedded structural shapes -This
system is used mainly for transmission towers,
although it has been used for other applications.
The superstructure can be erected plumb, leveled,
and set to grade in holes augered in the ground.
Then concrete is cast around the structural shape.
Alternatively, the anchoring elements, usually
angles, are cast in the footings and the tower or
superstructure subsequently bolted to them. The
anchor installation is straightforward but care is
required through the use of templates and guides
to maintain proper location in plan, and at the
proper grade, batter, and plane of batter.
5.4.1.8 Adjustable anchors -Anchors of this
type are patented devices used principally in
flatwork. Most often they are used for machinery
installation and are designed to compensate for
normal field tolerances in the positioning of
anchor bolts. They offer an added advantage in
that there are no bolts projecting above the floor
prior to setting the machinery. The machinery can
be moved into place on its base and then the bolts
set. One features a trough set flush with the
surface of the concrete and stud anchored to the
concrete below.
Another features deeply
embedded pockets, housing a tapped bottom
washer plate and having a sleeve extension up to
the surface of the concrete. The devices are
positioned and held in position during concrete
placement in a manner similar to that described
for sleeves. The principal concern is that the
insert be maintained level. The bolt is normally
grouted in place at the same time that the
equipment base plate is grouted.
5.4.1.9 Common bolts pretensioned -Bolt
installation is as described in further detail in
Section 5.5.1. The shank of the bolt should be
coated with bond breaker before placing concrete.
After concreting, the annular space around sleeved
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355.3R-64
MANUAL OF CONCRETE PRACTICE
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bolts is grouted. When concrete and grout (and
dry pack under baseplate) has cured the specified
number of days, screw on the nut and apply the
pretensioning load with a torque wrench. Torque
should initially be about 50 percent of desired
torque, then to 90 percent, working from one bolt
to the one diagonally opposite and thus
progressing through the group. The final 10
percent of torque should be applied to all bolts in
sequence. After 1 week verify that pretension has
held, or retension to specified torque, if necessary.
5.4.2 Post-installed systems
5.4.2.1 General anchor types -Anchors in this
group include:
Common bolts, reinforcing bars, and
continuously threaded rods
- Bonded (grout and chemical) anchors
- Rock bolts
- Expansion anchors
5.4.2.2 Common bolts, reinforcing bars,
threaded rod-Section 5.5.2 applies for positioning
and drilling the hole; Section 5.6 for grouting.
5.4.2.3 Chemical anchors-These are similar
to grouted anchors, with an adhesive, such as
epoxy, polyester, or vinylester taking the place of
the grout.
Section 5.5.2 applies as far as
positioning and drilling the hole for the anchor.
The adhesives are proprietary and installation
should follow manufacturer’s instructions.
Drilled hole diameters may vary from 1.0 to
2.0 mm larger than the nominal steel diameter
without affecting loading capacity for polyester
and vinylester anchoring systems. Storage should
follow manufacturer’s recommendations to prevent
heat, ultraviolet light, or both from shortening the
shelf life of the unused product. Anchoring
systems using epoxies are not sensitive to these
same storage requirements.
5.4.2.4 Rock bolts - Rock bolts occasionally
are used for anchoring to concrete. There are
many types available. Section 5.5.2 applies as far
as positioning and drilling the lead hole. In the
case of the split end variety, bondbreaker is
applied to part of the shank and then the rock
bolt is then inserted in the hole with the wedge
lightly set in the split tail of the bolt. The nut is
in place on the bolt, flush with the end. The bolt
is then rammed down over the wedge until the
bolt is well set in the hole. It is then adjusted for
vertical alignment and grouted per Section 5.6.
5.4.2.5 Expansion anchors-These systems
include a myriad of devices. They are self-drilling,
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or set in predrilled holes. The wedging action
between the device and the sides of the hole is
actuated by placing tension on the bolt, by turning
the bolt, by hammering the bolt onto a spreader
(cone or wedge) in the bottom of the hole, or by
hammering a spreader into the bottom expanding
portion of the anchor.
The manufacturer’s
instructions for installation of expansion anchors
must be followed meticulously. This applies
particularly to the diameter and depth of hole.
Some systems afford the opportunity of using the
base plate or element being connected as a
template in drilling the embedment hole. Others
require a larger hole to accommodate a sleeve
that bears against the bottom of the connected
base plate.
Expansion anchors can lose preload under a
cyclic loading or from concrete creep due to high
local expansion forces unless they are so
pretensioned that the bolt is always in tension
under all loading conditions.
Generally, to
develop the pretension load the wedge or
expansion device must first be “set” against the
side of the hole. With certain types of anchors
there may be an initial slip which should be
anticipated and designed for. In the case of
excessive slip, follow the recommendations in
Section 5.7.2.
5.5 Inspection
5.5.1 Cast-in-place systems -The inspector has
the responsibility to verify that the size and
location of anchors or anchorage assemblies are in
accordance with the construction plans and
specifications, prior to the placement of concrete.
Anchors must be located properly in plan, have
the proper projection, and be rigidly held in place
so as not to be disturbed during the placement
and finishing of the concrete.
Methods of
securing the anchorage in place include:
- Nailing to the forms (conditions applicable)
- Nailing the top template to the forms
- Wire tying individual bolts, or their bottom
template, to the forms or the reinforcement and
- Tack welding to the reinforcement, if
approved. (High strength bolts should not be
welded)
Welding should be to the bottom washer or the
bottom template of the bolt head, rather than the
shank of the bolt.
In the case of bolts that are subsequently to be
tensioned, the inspector should verify that
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unsleeved bolts, or sleeved bolts that are to be
grouted prior to the tensioning, have a bond
breaker (grease or other) on the shank that will
prevent the bolt from bonding to the concrete or
grout.
5.5.2 Post-installed systems -Post-installed
systems involve setting the anchor in blockouts or
drilled holes. The inspector should verify that the
blockouts or holes are properly located. With
drilled holes he should verify that the drill bit is of
the proper diameter, that the hole is plumb to the
surface (bit guides should be used for critical
work), that the finished hole has the proper
diameter and depth, and that the appropriate
drilling equipment is used. This calls for rotary
drills (carbide tip or diamond studded bits) or
hand hammered star drill bits. Jackhammering
should not be permitted because of the damage it
does to the concrete immediately around the hole.
Once the hole is drilled and blown clean, the
anchor should be installed, preloaded, and tested
(as required) in accordance with Section 5.5; or
the hole should be protected by plugging it with a
rag or other suitable stuffing until the time of
anchor installation.
Guidance for inspecting grouted anchors is
given in Section 5.6.
5.6 -Grouting
ACI Committee 351, Foundations for Equipment and Machinery, includes in its work
development of information on grouting. Accordingly, reference is made to publications of that
committee. The statements which follow are intended to be a brief summary of grouting as it
relates to construction considerations for concrete
anchorages.
5.6.1 Materials - Grouting materials fall into two
broad functional categories: nonprecision grouts
and precision, “nonshrinking” grouts.
5.6.1.1 Nonprecision grouts - Nonprecision
grouts include mixtures of cement and water, with
or without the inclusion of sand or admixtures.
The use of the “jobsite mixed” or packaged
products not designed to perform as a precision
The most significant
grout has limitations.
limitation is the lack of a mechanism for
overcoming drying shrinkage which occurs as free
moisture leaves the grout.
Dry packing with cement, sand, and only
enough water to result in a stiff, but cohesive
mixture has been used in grouting for many years
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355.1R-65
and is an excellent method, but it is labor
intensive, and in many installations is impractical.
Epoxy grouts also have been used successfully
for a number of years. These materials offer high,
early strength and provide excellent bond and
protection of steel in corrosive environments.
There are, however, some limitations in the use of
these materials. The concrete and steel surfaces
to be in contact with epoxy must be cleaned and,
for most epoxies, dry. Epoxies also have a
coefficient of thermal expansion several times that
of the concrete or steel, which should be taken
into consideration. Epoxies can creep under
sustained loading of the anchor, and some epoxy
grouts lose strength when exposed to temperatures
over 120 F.
5.6.1.2 Precision, "Nonshrinking" grout-These
portland cement based products are proprietary
and sophisticated in terms of their cement
chemistry and composition. They comply with the
requirements of the U.S. Army Corps of Engineers specifications for nonshrink grouts, CRD-C621.
Precision grouts are proportioned to lessen the
effects of plastic and drying shrinkage in the
plastic and hardened states. Accordingly they are
excellent materials to use in complex grouting
situations, such as the grouting of machinery
bases.
5.6.2 Applications - Grouting of anchorages to
concrete falls into three application categories:
- Grouting of anchor bolt holes and sleeves
prior to base plate installation
- Grouting or dry-packing of base plates and
machinery bases
- Grouting bolt holes after pretensioning of the
anchor bolt
5.6.3 Construction procedures
5.6.3.1 Preparation - Anchor bolt holes and
sleeves should be clean and free of oil, grease,
dirt, or other debris. Bolt holes should preferably
have a textured surface, thoroughly moistened
prior to grouting, but with no free moisture in the
hole.
5.6.3.2 Mixing and placing-Grouts may be
mixed in mortar mixers or in smaller vessels, as is
appropriate to the work. When using proprietary
products, follow the manufacturer’s instructions
for mixing. The “pot” life is a very important
consideration.
Proper placement of grout is important.
Whether dry packed or poured at a fluid
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ANCHORAGE TO CONCRETE
MANUAL OF CONCRETE PRACTICE
consistency, the material should be placed or
poured in a manner which will preclude the
entrapment of air which produces voids in the
hardened grout.
5.6.3.3 Curing-Curing is important in
achieving satisfactory results in any grout
installation. Normally this is accomplished by
placing water-saturated rags over all exposed grout
surfaces as soon as possible after grout placement.
These rags should be maintained wet and in place
for at least 24 hr after which the exposed surface
of the grout is coated with a curing compound if
secondary grouting will not follow. Where
secondary grouting is to follow, continue the water
curing for 7 days, or until placement of the second
grout.
Proprietary grouts should be cured
according to the manufacturer’s recommendations.
5.7 -Field problems
5.7.1 Cast-in-Place Systems-The common
problem encountered in the preconcreting stage is
interference with existing reinforcement. In this
case a decision has to be made whether to move
the anchorage or move the reinforcement. In
weighing the consequences of each, the Field
Engineer, perhaps after consulting the Engineerof-Record, establishes which has priority.
Another common problem is to discover, after
the concrete has hardened, that the anchorage has
shifted during the placement of the concrete, and
that the base plate will not fit in place, or that
there is insufficient thread projecting to fully
engage the nut. These problems can and should
be avoided by proper inspection, or by use of
sleeved or adjustable anchors. The specifications
should cover these possibilities, and state that it is
the contractor’s responsibility to take necessary
precautions and corrective measures. Actions
taken when field errors are discovered should have
the approval of the Engineer-of-Record.
Bending of protruding bolts is discouraged
because the bending stress which results from the
eccentricity of the service load, when added to the
design axial and shear stresses, can often exceed
the yield strength of the bolt. In welding to
compensate for insufficient thread being engaged
by the nut, care should be taken that the weld
acting alone will develop the strength of the bolt,
because the capacity of the welds and the engaged
threads are not additive. When any embedded
anchor is not installed within allowable tolerances,
the structural adequacy of the installation should
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be verified by the Engineer-of-Record and, if
necessary, the design should be modified.
The single most helpful practice for avoiding
the problem of cast-in-place anchor bolts not
fitting the base plates is to make holes in column
and machinery base plates oversize, and then
grout the annular space after the base plate is in
place, or use specially designed washers. The
following schedule of oversize holes is
recommended.
- Bolts less than 1 in. diameter - 5/16 in.
oversize
- Bolts 1 to 2 in. diameter
- l/2 in. oversize
- Bolts over 2 in. diameter
- 1 in. oversize
5.7.2 Post-installed systems-A common field
problem in post-installed systems is interference
with the in-place reinforcement. The location of
that reinforcement can be determined magnetically
or radiographically.
Sometimes, it is simply
discovered when the drill bit, drilling the hole, hits
steel. When an anchorage interferes with any inplace reinforcement, the Engineer-of-Record
should decide on the remedy. Wherever possible,
the anchorage itself should be shifted to a new
location where there is no interference. Moment
reinforcement should never be welded or cut.
With due consideration, temperature
reinforcement can be cut.
A second problem is excessive slip in
pretensioning the bolt. This can be indicative of
an oversized hole or a faulty anchoring device.
When excessive slip occurs, the assembly should
be reinstalled in the hole and the pretensioning
applied such that the slip does not exceed the
allowable limit (i.e., resulting embedment is
adequate). Sometimes the entire anchor will have
to be replaced, or possibly the hole drilled to a
larger size and the next larger sized anchor
installed.
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355.1R-66
CHAPTER 6-REQUIREMENTS IN EXISTING
CODES AND SPECIFICATIONS
6.1 -Introduction
Sources of information relating to codes and
specifications on anchorage to concrete are
presented in this section. Sources are referenced
in alphabetical order. American and international
documents are included in this state-of-the-art
review.
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ANCHORAGE TO CONCRETE
6.2 -Existing codes and specifications
6.2.1 American Association of State Highway
Transportation Officials (AASHTO)
6.2.1.1 Standard Specification for Highway
Bridges -For composite bridge decks, AASHTO
uses the ultimate capacity of stud shear connectors
and a reduction factor t$ of 0.85 for design.
Design checks are required for horizontal shear
under working loads.
Working loads are
compared to allowable loads which include a
reduction for fatigue.
AASHTO Section 1.7.56 bases the number,
required embedment, and size of anchor bolt on
the span of the bridge, and requires that the
anchor bolt be swedged or threaded to insure a
satisfactory grip on material such as the grout.
AASHTO requires that anchor bolts subject to
tension be designed to engage a mass of concrete
which will provide a resistance equal to one and
one-half times the calculated uplift.
6.2.2 American Concrete Institute (ACI)
6.2.2.1 ACI 318, Building Code Requirements
for Reinforced Concrete - ACI 318-63 contained
allowable bond values for plain (smooth) bars.
Many engineers have used these values for
determining embedment requirements for cast-inplace anchor bolts. The current edition of ACI
318 does not give allowable bond values for plain
or deformed bars. Section 12.6.1 states “Any
mechanical device capable of developing the
strength of reinforcement without damage to
concrete may be used as anchorage.” Section
15.8.3.3 of ACI 318 states “Anchor bolts and
mechanical connectors shall be designed to reach
their design strength prior to anchorage failure or
failure of surrounding concrete.”
6.2.2.2 ACI 349, Code Requirements for
Nuclear Safety
Structures-Appendix
Related
Concrete
B of ACI 349 gives
comprehensive procedures for designing
anchorages and steel embedments that are used to
transmit loads from attachments to reinforced
concrete structures governed by ACI 349. The
basic philosophy of anchorage requirements in
ACI 349 is consistent with the ultimate strength
design philosophy of reinforced concrete. The
failure mechanism is controlled by requiring
yielding of the steel anchor prior to brittle failure
of the concrete.
This design method considers not only
traditional design parameters, i.e., steel strength,
concrete strength, and anchor size, but also other
variables such as anchor type or form, spacing,
edge distance, nature of the anchor load, thickness
of the concrete member, and concrete stress in the
anchor zone. Concrete strength is critical to
assure that the reinforced concrete structure
exhibits ductile failure, which is also an ACI 318
requirement. Note, however, that many of the
post-installed systems feature the brittle concretecone failure.
The commentary of ACI 349, Appendix B,
provides an excellent source of information on
types of anchorage devices, design requirements,
modes of failure, and testing.
6.2.3 American Institute of Steel Construction
(AISC)
6.2.3.1 Manual of Steel Construction -The
AISC “Specification for the Design, Fabrication,
and Erection of Structural Steel for Buildings” sets
allowable bolt stresses in Sections 1.5.2 and 1.6.3.
These values apply to certain cast-in-place and
grouted anchor bolts and are valid for allowable
anchor steel stresses, but no values are given
which relate to the transfer of these stresses to the
surrounding concrete.
The AISC specification gives allowable values in
shear for stud shear connectors used for composite
design in Table 1.11-4. The listed values cannot
be used for anchor bolts of the same size. The
values used in Table 1.11-4 are based on equations
derived from a testing program and the ultimate
strength of the composite member, using a factor
of safety of 2.0.
The AISC code commentary contains the
following warning:
“The values of q in Table 1.11-4 must not be
confused with shear connection values suitable for
use when the required number is measured by the
parameter VQ/I, where V is the total shear at any
given cross-section. Such a misuse could result in
providing less than half the number required by
Formulas 1.11-3, 1.11-4, or 1.11-5.”
The AISC specification also gives setting
tolerances for bolts used to anchor structural
members; however, these tolerances are unsuitable
for anchoring machinery.
6.2.4 American Society for Testing and Materials
(ASTM)
6.2.4.1 Annual Book of Standards - Volume
04.07 contains test standard ASTM E 488,
“Standard Test Methods for Strength of Anchors
in Concrete and Masonry Elements.” This test
standard describes procedures for determining the
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MANUAL OF CONCRETE PRACTICE
static, dynamic, and fatigue tensile and shear
strengths of cast-in-place, chemical, grouted, and
expansion anchors.
Volume 15.08, Fasteners, contains various
ASTM specifications for the steel used for bolts,
including A 193, A 307, A 325, A 449, and A 490.
6.2.5 Construction Industry Research and
Information Association (CIRA) (Great Britain).
6.2.5.1 Section and Use of Fixings in Concrete
and Masonry (Guide 4) - CIRA Guide 4, is a
comprehensive guide on the selection and use of
anchors installed in concrete.
Three main
categories of anchor types are covered. These
include cast-in-place, expansion, and bonded
anchors. The guide also covers behavior of
fastener assemblies under load, design
considerations, limitations, durability, testing, and
practical considerations.
6.2.6 Institut fir Bautechnik (IfBT)(West
Germany)
6.2.6.1 Tests to Evaluate the Strength of
Metallic Expansion Bolts for Anchorage in Concrete
with an SC of 20 MPa (2500 psi) or
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Greater-Approvals are based on results of tests
carried out by licensed universities.
In the tests the proper functioning of the
anchors under extreme conditions are checked,
and tests to evaluate allowable loads for design
are performed.
For evaluating allowable conditions of use (e.g.,
allowable loads, required edge distance, and
spacing), a sufficient number of tests have to be
performed to calculate a statistically reliable
confidence level for the failure loads [5 percent
fractile (or 95 percentile) of failure loads]. A
safety factor of 3 is applied to the determined 5
percent fractile of the failure loads to account for
the variations of the concrete tensile strength and
of jobsite installation quality. For reasons of
simplicity, one value for the allowable load is
given per anchor size which is valid for all loading
directions (tension, shear, combined tension, and
shear). Expected displacements of anchors under
allowable loads are given which should be taken
into account in the design of the fastened element
(when appropriate).
6.2.7 International Conference of Building
Officials (ICBO)
6.2.7.1 U n i f o r m B u i l d i n g C o d e ( 1 9 8 5
Edition) -The Uniform Building Code (UBC),
Table 26-G sets forth allowable shear and tension
loads for cast-in-place bolts of at least ASTM A
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307 quality or better.
The table assumes an anchor spacing of 12
anchor diameters. The spacing may be reduced
down to 6 anchor diameters with a 50 percent
reduction in allowable load values. A minimum
edge distance of 6 anchor diameters is required.
Edge distance may also be reduced up to 50
percent, provided that the listed values are
reduced in equal proportion. Tension values listed
in the table may be increased 100 percent when
“special inspection” is provided. UBC Section
2719, on anchor bolts for steel column bases, does
not provide design values for anchor bolts, but
simply states that “Anchor bolts shall be designed
to provide resistance to all conditions of tension
and shear at the bases of columns.” The section
on steel column anchorage does not refer to Table
No. 26-G. Application of this table to steel
column anchorage would greatly affect current
design practice because of the requirement in
Table No. 26-G of a minimum spacing of 6 anchor
diameters.
6.2.8 Precast/Prestressed Concrete Institute (PCI)
6.2.8.1 PCI Design Handbook-The handbook
gives equations for shear and tension load
allowables for headed shear stud anchors.
Combined loading, as well as required edge
distances and anchor spacing for groups of
anchors, are covered.
Based on a review of past design methods and
actual testing and modeling, the PCI Connection
Details Committee recommends the use of a
projected cone model to define the actual bolt
tension at which concrete failure will occur. The
PCI cone surface equation is:
Pm = 2.8 hL@ [fi 7~ ld (li + da]
(6.1)
where
iz =
1 =
=
;=
d,, =
f’, =
P =
IlC
1.0 for normal weight concrete
0.85 for sand lightweight concrete
0.75 for all lightweight concrete
embedment, in.
diameter of anchor or stud head,
in.
specified 28-day compressive
strength of concrete, psi
nominal tensile capacity of anchor
as governed by concrete failure
In anchor bolt design where the concrete does
not fail, the anchor bolt fails via a combination of
The PCI equation for
tension and shear.
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ANCHORAGE TO CONCRETE
combined tension and shear strength is:
where
4 = strength reduction factor
Pu = applied factored tension load
P = nominal tension strength of
anchor
vu = applied factored shear load
Kc = nominal shear strength of anchor
as governed by steel failure
In-depth discussions of these equations may be
found in Klingner and Mendonca (1982) and
Shaikh and Yi (1985).
6.2.9 The Agrbnent Board (Great Britain)
YlC
6.2.9.1 The Assessment of Torque-Expanded
Anchor Bolts When Used in Dense Aggregate
Concrete (M.O.A. T. No. 19:1981) -This document
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presents the procedures for deriving design
information and classifies ten different types of
expansion anchors according to the mechanism for
achieving expansion. It considers the effects of
different types of loading conditions and typically
requires a minimum of 277 tests (for six different
anchor diameters) to calculate safe working loads
as the lower of:
a. The 5 percent exclusion value (or 95th
percentile, calculated by regression analysis or
other statistical techniques), then divided by three
or,
b. The mean of the loads determined at a
displacement of 0.1 mm (0.004 in.) under direct
tension or,
c. The mean of the loads determined at a
displacement of 1.0 mm (0.039 in.) under direct
shear.
6.2.10 UEAtc (Union European of Agrbment)
The UEAtc Directives for the Assessment of
Anchor Bolts (December, 1986) is a European
code for the assessment and approval of anchor
bolts. The document has been adopted by the
Common Market Countries of Germany, U.K.,
France, Austria, Italy, Spain, Ireland, Netherlands,
Portugal, Denmark, and Belgium.
6.2.11 Nuclear Regulatory Commission (NRC)
Bulletin 79-02 and 79-14).
Anchor bolt design methods have been revised
based on the United States NRC Office of
Inspection and Enforcement Bulletins No. 79-02
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355.1R-99
and 79-14. Only Class I piping (piping used to
safely shut down a nuclear power plant) was
impacted by Bulletins 79-02 and 79-14. The NRC
requires that during anchor bolt design, the
following must be considered: baseplate flexibility,
(i.e., baseplate prying action that increases anchor
bolt loading), performance of anchors due to
cyclic loading, anchor performance in masonry
walls, the effect of pipe support loads on masonry
walls, and the maximum support load considered
for anchor bolt design.
Concrete expansion
anchors must have the following minimum factor
of safety between the bolt design load and the bolt
ultimate capacity determined from static load
tests, (e.g., published data from the anchor bolt
manufacturer) which simulate the installation
conditions, (i.e., type of concrete and its strength
properties): (1) a safety factor of 4:1 - for wedgeand sleeve-type anchor bolts, (2) a safety factor of
5:l - for shell-type anchor bolts.
The bolt ultimate capacity should account for
the effects of shear and tension interaction,
minimum edge distance, and proper bolt spacing.
A summary of the USNRC criteria is found in
USNRC “Anchor Bolt Study Data Survey and
Dynamic Testing” by the Hanford Engineering
Development Laboratory.
6.2.12 Draft 1 Regulatory Guide MS 129-4
“Anchoring Component and Structural Supports in
Concrete”
This draft guide from the U.S. Nuclear
Regulatory Commission provides the criteria for
acceptance, qualification, design, installation, and
inspection for steel embedments anchored in
concrete. It also provides information on the
acceptability for NRC licensing actions in
accordance with Appendix B, of ACI 349-80.
6.3 -Application and development of codes
ASTM E 488 is the only existing American
standard exclusively and specifically concerned
with testing to determine the performance of all
types of concrete anchors. It is not intended to
describe design procedures for anchorage
connections, nor to identify characteristics which
affect performance in conditions other than astested. ICBO has also published a limited test
standard for expansion anchors only.
ACI 349, Appendix B, specifies anchorage
design and applies ultimate strength design
philosophy to all types of anchorages. Other
American codes limit their consideration to cast-
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MANUAL OF CONCRETE PRACTICE
in-place or grouted anchorages. The Uniform
Building Code (UBC) allows for alternative
devices as specified in the code, generally applying
the same conditions as specified for cast-in-place
anchors.
American codes generally base recommended
design procedures on ultimate strength data.
European codes recommend the criterion of
displacement (slip) for post-concreting anchors,
supported by ultimate strength data derived by
regression analysis of other statistically reliable
techniques.
Codes cannot address all the conditions
applicable to a particular design or absolve the
designer of the responsibility to check the
relevance of code data for a given design. New
and technically reliable information will inevitably
be developed between publication dates of
amendments to existing codes. Designers are
encouraged to maintain familiarity with ongoing
research and other developments and to
supplement the provisions of governing codes with
such information as it becomes available.
“Prtifungen zur Beurteilung d e r Tragfghigkeit v o n
zwangsweise s p r e i z e n d e n Diibeln aus MetaIl nach d e r
Verankerung in Normalbeton 1 Bn 250” (Tests to Evaluate the
Load Capacity of Metal Expansion Anchors Fastened into
Normal Concrete, r Bn250), Institute for Construction (IfBT),
Berlin, West Germany, January 1974.
Shaikh, A.P., Yi, W., “In-Place Strength of Welded Headed
Studs,” PCI Journal, V.30, No. 2, March-April, 1985.
“Standard Specification for Highway Bridges”, Twelfth
Edition, American Association of State Highway
Transportation Officials, 1977.
“Standard Test Methods for Strength of Anchors in
Concrete and Masonry Elements”, (ASTM E488-88), 1988
Annual Book of ASTM Standards, Volume 04.07, American
Society for Testing and Materials, Philadelphia, PA, October,
1988.
“The Assessment of Torque-Expanded Anchor Bolts when
used in Dense Aggregate Concrete”, M.O.A.T. No. 19:1981,
Agrkment Board, Watford, Herts., England, January, 1981.
“UEAtc directives for the Assessment of Anchor Bolts”,
M.O.A.T. No. 42:1986, European Union of AgrCment;
December, 1986.
Uniform Building Code, International Conference of
Building Officials, Whittier, CA. 1985.
6.4 - References
ACI Committee 318,1989, “Building Code Requirements for
Reinforced Concrete (ACI 318-89) and Commentary - ACI 318R89, American Concrete Institute, Detroit, MI, November.
USNRC “Anchor Bolt Study Data Survey and Dynamic
Testing”, Hanford Engineering Development Laboratory,
NUREG/CR-2999, December, 1982.
ACI Committee 349, 1990, “Code Requirements for Nuclear
Safety Related Concrete Structures (ACI 349-90) and
Commentary - ACI 349R-90, American Concrete Institute,
Detroit, MI, March.
Fasteners. 1988 Annual Book of Standards, Volume 15.08,
American Society for Testing and Materials, Philadelphia, PA,
January, 1988.
Klingner, R.E. and Mendonca, J.A., (1982a) “Tensile
Capacity of Short anchor Bolts and Welded Studs: A Literature
Review,” ACI Journal, Proceedings, V. 79, No. 1, July-August.
Manual of Steel Construction. Eight Edition, American
Institute of Steel Construction, Inc., New York, NY, 1980.
Paterson, W.S., “Selection and Use of Fixings in Concrete
and Masonry”, CIRA Guide 4, Construction Industry Research
and Information Association, London, England, October, 1977.
PCI Design Handbook, Third Edition, Prestressed Concrete
Institute, Chicago, IL, 1980.
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ANCHORAGE TO CONCRETE
APPENDIX A-CONVERSION FACTORS:
INCH-POUND TO SI
By
Multiply
To obtain
Length
ft
3.048 x 10-l
Area
ft2
9.290 x 10-2
m2
Volume
ft3
2.832 x 1O-2
m3
Velocity
ft/s
3.048 x 10-l
m/s
Acceleration
ft/s2
3.048 x 10-l
m/s2
Mass
“An
4.536 x 10-l
kg
Force and Weight
lb f
4.448
N
Pressure and Stress
lb$ft2
psi
psi
4.788 x 101
6.895 x lo3
6.895 x 1O-3
Pa or N/m2
Pa or N/m2
N/mm2
Work and Energy
ft-lbf
1.356
J
Mass Density
lb,/ft3
1,602 x 10
kg/m3
Weight Density
lbf/ft3
1.571 x lo2
N/m3
n = number of anchors
N = factor which takes into account steel shear strength, usually 0.6 to 0.7
pnc = bolt tension load at which concrete failure will occur
P, = applied factored tension load
S = spreading force, as from expansion sleeves of an expansion anchor, also anchor spacing
T, = applied tension load
T,,, = allowable anchor tensile load
T,, = ultimate wedge-splitting capacity of a singlt bolt
r, = ultimate tensile load, also design tensile load
V, = applied shear load
V, = nominal shear strength of anchor as governed by steel
failure
=
shear strength, ultimate shear load, or applied factored
Yl
shear load
W
= crack width usually measured at the concrete surface
(Y = included angle of concrete spa11 cone measured from the
axis of the anchor to the failure cone surface
p = coefficient of friction
4 = strength reduction factor
x = chi factor which represents a partial influencing factor
such as a load capacity reduction based on anchor
spacing interaction (x,), edge distance influence (x,),
etc.
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This report was submitted to letter ballot of the committee
was approved according to Institute procedures.
APPENDIX B-NOTATION
= distance between center of anchors
= summation of projected areas of individual stress
cones, in.2
=
net
bearing area of head of embedded anchorage, in.’
Ab
A, = tensile stress area, psi
C’ = clear cover to bolt, in.
d/I = head diameter of headed stud or bolt
D = anchor diameter
DUJ = diameter of anchorage device such as embedded washer,
in.
E, = elastic modulus of concrete, psi
f, = compressive strength of concrete measured by cylinders
psi or N/mm2
fee = compressive slrength of concrete measured by cubes, psi
or N/mm2
= yield stress of anchor or bolt, psi
fY
F,, = ultimate strength or capacity, lb or N
F,, = ultimate tensile stress of steel, psi
h = member thickness
1, = embedment depth of anchor
= distance from anchor centerline to free unsupported edge
1?1
0
A
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