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PUBLICATIONS

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NBSIR 88-3797

Literature Review of Post-Installed

Anchorage in Concrete

Mark K. Johnson

H. S. Lew

Long T. Phan

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Structures Division

Gaithersburg, MD 20899

June 1988

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

75 Yssrs Stimulating America's Progress

1913-1988

Research Information Center

National Bureau jt>urcuu ofi Standard; utuiiu&rds

Gaithersburg, MaxyLaad 20899

NBSIR 88-3797

LITERATURE REVIEW OF POST-INSTALLED

ANCHORAGE IN CONCRETE

Mark K. Johnson

H. S. Lew

Long T. Phan

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Structures Division

Gaithersburg, MD 20899

June 1988

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
.
ABSTRACT

This report summarizes current knowledge of post- installed anchor

behavior in concrete. Load- displacement behavior and ultimate strength of

the various types of post- installed anchors are discussed for different

loading conditions in both uncracked and cracked concrete. Most knowledge

of anchor behavior concerns the response to static tensile loads in uncracked

concrete. Many aspects of anchor behavior require further study, especially

the behavior of anchors in cracked concrete subjected to combined loadings.

Keywords : anchors

;

anchor ; expans ion

combined loading; concrete; drilled- in anchor; epoxy

anchor; grouted anchor; post- installed anchor; shear;

tension.
TABLE OF CONTENTS

Page

ABSTRACT i

1 . 0 INTRODUCTION 1

1 . 1 General 1

1 . 2 Obj ective and Scope 2

2 . 0 TYPES OF POST -INSTALLED ANCHORS 3

2 . 1 Introduction 3

2 . 2 Expansion Anchors 4

2.2.1 General 4

2.2.2 Torque - Controlled Anchors 4

2.2.3 Deformation- Controlled Anchors 6

2 . 3 Grouted Anchors 9

2 . 4 Chemical Anchors 10

3.0 BEHAVIOR OF POST- INSTALLED ANCHORS 12

3 . 1 Introduction. 12

3.2 Behavior in Uncracked Concrete 13

3.2.1 Tension Loading...... 13

3. 2. 1.1 Load-Displacement Behavior 13

3. 2. 1.2 Ultimate Strength 15

3. 2.

1.2.1

General. 15

ii
3. 2. 1.2. 2 Steel Failure 16

3 . 2 . 1 . 2 . 3 Pullout Failure 16

3. 2. 1.2. 4 Concrete Cone Failure ..20

3. 2. 1.2.

5

Splitting Failure 24

3.2.2 Shear Loading 25

3 . 2 . 2 .

1

Load-Displacement Behavior 25

3. 2. 2.

2

Ultimate Strength 26

3. 2. 2. 2.1 General... 26

3 . 2 . 2 . 2 .

2

Steel Failure .27

3. 2. 2. 2.

3

Concrete Failure 27

3.2.3 Combined Tension and Shear Loading 29

3.2.4 Combined Loading With Bending 31

3.2.5 Survivability 31

3 . 3 Behavior in Cracked Concrete 32

3.3.1 General 32

3.3.2 Tension Loading 32

3. 3. 2.1 Load-Displacement Behavior.. 32

3. 3.2.2 Ultimate Strength 34

3.3.3 Shear Loading 36

3.3.4 Combined Loading .......................................... 37

3 .

4

Research Needs 37

4 . 0 SUMMARY AND CONCLUSIONS .......................... 40

4 .

1

Summary 40

4.2 Conclusions 41

REFERENCES 43

iii
1.0 INTRODUCTION

1 . 1 General

The basic purpose of anchorage is to provide a means of attachment

between two or more separate elements. In the construction industry, anchors

are used in many applications, including the attachment of structural

elements to one another and the attachment of equipment to floors, ceilings,

and walls. They are installed primarily in concrete and masonry elements.

There are two fundamental types of anchors, cast = in-place and postinstalled. Cast- in-place anchors are installed prior to concrete or masonry

placement and thus their use must be anticipated before construction. Postinstalled anchors, on the other hand, are installed after the concrete or

masonry has cured. They are advantageous in that they may be used after

construction and knowledge of intended use and location is not required

during design.

One important application of post- installed anchors is in strengthening

existing buildings. Strengthening is often required to satisfy new building

code requirements or to improve the capacity of the building for additional

anticipated loads. When using post- installed anchors to strengthen an

existing structure, the improved capacity of the structure is often dependent

on the capacity of the anchors [27]. Understanding the behavior of anchors

1
in these structures, therefore, is important to ensure adequate

serviceability and ultimate capacity of the structure.

1.2 Objective and Scope

The objective of this report is to summarize current knowledge of the

behavior of post- installed anchors embedded in concrete. The extent of

understanding of anchor behavior in the realm of strengthening is also

assessed.

Chapter 2 describes the various types of post- installed anchors.

Mechanisms of load transfer to surrounding concrete and methods of

installation for typical anchors are presented.

Chapter 3 discusses the behavior of post- installed anchors in concrete.

Load- displacement behavior and ultimate capacity are discussed for different

loading conditions in both cracked and uncracked concrete.

Chapter 4 presents a summary and conclusions drawn from the literature

survey on the current state of knowledge of anchor behavior in the realm of

strengthening

.

2
2 .

0

TYPES OF POST- INSTALLED ANCHORS

2 , 1 Introduction

Post- installed anchorage is attached to existing concrete structural

members. This type of anchorage differs from the cast- in-place type, which

is installed prior to concrete placement. For post- installed anchorage, the

anchor is inserted into a hole drilled in the surface of the cured concrete

member. The different means employed to attach the anchor to the concrete

have given rise to three main groups of post- installed anchors: 1) expansion

anchors, 2) grouted anchors, and 3) chemical anchors.

Post- installed anchors are usually preloaded in tension. They may

either be preloaded during the installation process or after installation.

Preloading is beneficial in that it reduces or eliminates anchor

displacements under service loads. It also produces a clamping force between

the attachments which serves to reduce the effect of cyclical loads on

anchors and provides shear transfer resistance. Preloading is accomplished

by torquing or jacking a nut on the top of the embedded anchor. High

stresses induced around the anchor after preloading cause the concrete to

creep and the force in the anchor to relax. Consequently, the preload force

decreases with time from its initial value.

3
2.2 Expansion Anchors

2.2.1 General

Expansion anchors attach inside the drilled hole by mechanical means.

For most expansion anchors, load is transferred from the anchor to the

concrete by friction between the bottom end of the anchor and the wall of the

hole. Two distinct methods are used to expand the anchor to bear against the

wall of the hole, as shown in Figure 2.1. The first method is to apply

torque to the anchor. Anchors installed in this manner are known as torquecontrolled anchors (Type A) . The second method is to expand the anchor

either by hammering it over an end cone or by hammering a cone into the

anchor. Anchors installed by this method have two forms (Type B and C) and

are known as deformation-controlled anchors.

2.2.2 Torque-Controlled Anchors

Torque -controlled expansion anchors have some type of sleeve surrounding

them and are tapered outward at the bottom end. Torquing forces the tapered

end upward into the sleeve, pushing the sleeve against the side of the hole.

The amount of expansion is dependent on the magnitude of applied torque and

on the deformability of the concrete. As the anchor is torqued during

installation, the anchor bolt is preloaded. Subsequent applied loads in

excess of the preload cause the cone to be drawn further into the anchor

sleeve, resulting in increased expansion forces. Types of torque-controlled

4
expansion anchors, shown in Figure 2.2, include wedge, shell, sleeve, and

undercut anchors

.

Wedge anchors consist of a steel bolt which is tapered at the bottom

end. An expandable pair of wedges lies on the anchor above the taper and a

nut is located on the threaded top. When the anchor is placed in the drilled

hole and the nut is torqued, the wedges are forced outward against the hole

wall by the tapered end.

Shell anchors come in two forms. The first form consists of a two-piece

shell which is held together by steel tabs and has a tapered internallythreaded end cone at the bottom. The second form consists of a two-piece

shell with tapered cones at the top and bottom held together by a spring at

the center. The bottom cone is internally threaded. When a fastener is

threaded onto the cone and torqued, the cone is forced upward to expand the

shell against the hole wall.

Sleeve anchors consist of a steel bolt which is tapered at the bottom

and surrounded by a sleeve. The sleeve is slit at the bottom to allow for

expansion. When the nut on the top of the anchor is torqued, the tapered end

moves upward, expanding the sleeve against the hole wall.

Undercut anchors have a threaded steel bolt with a tapered expander plug

at the bottom end and are surrounded by a sleeve which is slit at the bottom.

When the nut is torqued, the plug is forced upward and either expands the

sleeve into a predrilled undercut hole or expands the sleeve to create an

5
undercut hole. This type of anchor differs from other torque -controlled

anchors in that load transfer from anchor to concrete is accomplished by

bearing on the underside of the hole rather than by friction against the hole

wall (see Figure 2.2). It is thus possible to develop the tensile strength

of the steel in undercut anchors.

Installation of torque -controlled anchors requires preloading. The

magnitude of preload, however, is not constant but reduces with time. In

Figure 2.3, the results of a relaxation test show how preload diminishes with

time for wedge and undercut anchors [5]. Immediately after preloading there

is an exponential loss of preload. In time, the preload force approaches a

limiting value, which is about 60% and 53% of the initial value for undercut

and wedge anchors, respectively [ 5 ] . In general, the final preload value of

torque-controlled anchors is about 40-60% of the initial value[14]. If

anchors are retorqued, the process of relaxation is repeated; however, the

final preload value after retorquing has been found to increase [ 14 ] . There

is a lack of published data on the amount of time required to reach the final

preload value, although undercut anchors have been found to reach the final

value in about 70 days [5]. There is also a lack of available information on

the effect of such variables as concrete strength and preload force on

relaxation.

2.2.3 Deformation-Controlled Anchors

There are two types of deformation-controlled expansion anchors. In the

first type (Type B) , the anchor is expanded by hammering a cone into the

6
outer sleeve of the anchor. In contrast to torque-controlled anchors, all

expansion is achieved during installation and subsequent applied loads do not

affect expansion of the anchor. The expansion force depends on the lateral

expansion displacement, the gap between the anchor and the hole wall, and the

deformability of the concrete [ 14] . This force is usually larger than the

expansion force of torque-controlled anchors.

Drop-in anchors, shown in Figure 2.4, are an example of a deformationcontrolled, Type B anchor. They consist of a steel shell and a steel

expander plug. The lower end of the shell is internally tapered to accept

the steel plug and the bottom of the shell is longitudinally slit to allow

for expansion. By hammering the plug into the internal taper of the shell,

the sides of the shell are forced outward to bear against the hole wall. The

top portion of the shell is internally threaded so that a bolt or threaded

rod can be attached.

In the second type of deformation-controlled anchor (Type C) , the anchor

is expanded by hammering the outer shell or sleeve of the anchor over a cone.

The outer shell is forced against and into the hole wall, crushing the

concrete at the tip of the shell. Like Type B anchors, all expansion is

achieved during installation. The expansion force is smaller than that of

Type B anchors and load is transferred from anchor to surrounding concrete

mainly by mechanical interlock. As shown in Figure 2.5, there are several

types of these anchors, including self -drilling , stud, and lead caulking

anchors

.

7
Self -drilling anchors consist of a steel shell and a tapered steel plug.

The shell has teeth at its tip so that the anchor can drill its own hole.

This manner of installation results in a hole which is the exact diameter of

the anchor. The anchor is then hammered over the tapered plug, expanding the

bottom of the slit shell against and into the wall of the hole. The top of

the anchor is internally threaded so that a bolt or threaded rod can be

attached.

Stud anchors consist of a steel bolt which has a hole and longitudinal

slits at the bottom to accept a tapered steel plug. The upper end of the

bolt is threaded. When the anchor is hammered over the tapered plug, the

bottom of the anchor expands over the plug against the hole wall.

Lead caulking anchors are of two types. The first type is a single unit

anchor consisting of a lead cylinder and a tapered steel cone. The second

type, a multiple unit anchor, is used for deeper embedments and consists of

a series of lead cylinders and tapered steel cones that are placed on top of

each other. Hammering expands the lead over the cone (or cones) and against

the hole wall. The bottom cone is internally threaded to accept a bolt or

threaded rod.

Installation of deformation- controlled anchors does not involve

preloading; however, preloading is often applied after installation. There

is a scarcity of published information on the relaxation of deformationcontrolled anchors and so it is uncertain how relaxation differs from that

8
of torque-controlled anchors. Stud anchors, however, have been found to

relax half as quickly as shell anchors [20].

2 o 3 Grouted Anchors

Grouted anchors are attached inside the drilled hole by a cement grout.

The anchors are inserted into the hole and then the grout, which usually

consists of a mixture of cement, sand, and water, is injected into the hole.

The manner in which load is transferred from anchor to grout depends on the

type of anchor. Headed anchors are the most common type and transfer load

primarily by bearing at the end of the anchor. Typical headed anchors are

shown in Figure 2.6. Unheaded anchors transfer load near the surface by bond

development. Load transfer from grout to surrounding concrete is usually

accomplished by bond development between the grout -concrete interface. The

hole wall is often roughened to increase the bond strength of the interface

and to provide mechanical interlock.

Like deformation-controlled expansion anchors, grouted anchors are not

preloaded during installation. However, if they are preloaded after

installation, the preload force relaxes with time. Figure 2.7 shows a

typical relaxation test of a grouted bolt. The shape of the relaxation curve

is similar to that of expansion anchors, although the limiting preload value

has been found to be only about 34% of the initial value [5]. The large

magnitude of preload loss is attributed to creep of the grout plug at the

interface between the grout and concrete [5]. Effects of such variables as

9
grout strength, grout shrinkage, roughness of concrete surface, and anchor

type on relaxation have not been reported.

2.4 Chemical Anchors

Chemical anchors are attached inside the drilled hole by chemical

adhesives. There are several types of chemical adhesives, including epoxies,

polyesters, and vinylesters. In this study, however, different types of

adhesives are not distinguished and all types of anchors are collectively

referred to as chemical anchors. The manner in which load is transferred

from anchor to adhesive depends on the type of anchor. Unheaded anchors, the

most common type, transfer load near the surface by bond development.

Typical unheaded anchors are shown in Figure 2.8. Headed anchors, on the

other hand, transfer load primarily by bearing at the end of the anchor. As

in grouted anchors, load transfer to the surrounding concrete interface is

by bond development and, if the hole wall is sufficiently rough, by

mechanical interlock.

Chemical adhesives are available in four primary forms: glass

cartridges, plastic cartridges, tubes, and bulk. Although each form requires

a different method of installation, all forms have two-component systems, an

active component and a reactant, which are mixed together to cause bonding.

Installation of chemical anchors begins with cleaning the drilling dust

from the hole. The adhesive and anchor are then inserted in the hole. When

the adhesive is in the form of a glass cartridge, the cartridge is inserted

10
into the hole and crushed when the anchor is driven in behind it. The

adhesive and crushed glass are mixed together and bond the anchor to the hole

wall. For plastic cartridges, the two-part adhesive is mixed together by a

nozzle while being injected into the hole. The anchor is then inserted. In

the tube type , the two components are mixed by kneading the tube and then are

inserted into the hole. The anchor is then inserted. In the bulk form, the

adhesive (usually epoxy) is first mixed, followed by insertion of the

adhesive and anchor.

Like grouted anchors , chemical anchors do not require preloading for

installation. They are often preloaded after the adhesive has set prior to

being subjected to applied loads. Preloaded chemical anchors, because of

high stresses in the adhesive bond, relax faster and reach slightly lower

final preload values than torque -controlled expansion anchors[2]. However,

there is a lack of information on the relaxation of chemical anchors and the

effect of such variables as type of adhesive and temperature on relaxation.

11
3.0 BEHAVIOR OF POST- INSTALLED ANCHORS

3.1 Introduction

The behavior of post- installed anchors in concrete is largely influenced

by the type of loading applied to the anchor. There are five primary types

of loadings on anchors, as shown in Figure 3.1: 1) tension, 2) shear,

3) combined tension and shear, 4) combined bending and shear, and 5) combined

bending, shear, and tension. In addition, the applied load may either be

static or dynamic. Since most research to date has been conducted on anchors

under static tension or shear, knowledge of anchor behavior is focussed on

the response to these two types of loadings.

The behavior of anchors is also strongly influenced by the presence of

cracks in concrete. Anchors located in or near cracks have markedly

different load- displacement behavior and ultimate strengths than do similar

anchors in uncracked concrete. The behavior of anchors in uncracked concrete

is discussed first, followed by a discussion of anchor behavior in cracked

concrete

.

12
3.2 Behavior in Uncracked Concrete

3.2.1 Tension Loading

3. 2. 1.1 Load-Displacement Behavior

Load- displacement behavior of anchors loaded in tension depends on the

failure mode. Failures in which either the concrete or steel tensile

strength is developed have similar displacements at failure [25]. When the

anchor pulls out of the hole, displacements are much larger. Loaddisplacement behavior also depends on whether or not the anchors are

preloaded in tension. Anchors that are not preloaded begin to displace

immediately with the application of external load.

Figure 3.2 presents typical load-displacement relationships for the

three main types of expansion anchors described in Chapter 2. The anchors

have no preload and fail by developing the concrete tensile strength. The

displacements shown represent the combination of axial deformation of the

expansion bolt, deformation of the concrete, and slip of the anchor.

Type B anchors exhibit a relatively small displacement due to the low

amount of slip resulting from high expansion forces. The expansion force of

Type A anchors is smaller than that of Type B anchors and, as a result, the

displacement is larger in Type A anchors. Because Type C anchors transfer

load by mechanical interlock, which causes large concrete deformation, they

have the largest displacement prior to ultimate load. Undercut anchors,

13
which also transfer load by mechanical interlock, have large displacements

as well. Increasing the concrete strength results in an increase in anchor

stiffness (slope of the load- displacement curve) and a reduction in anchor

displacements [ 30 ]

.

For chemical anchors without preload, the load- displacement behavior is

approximately linear to the ultimate load. A typical load- displacement curve

for such an anchor is shown in Figure 3.3. Anchor stiffness for both

chemical and grouted anchors increases with increasing concrete strength and,

for grouted headed anchor bolts, with increasing washer size [13].

The load-displacement behavior of anchors preloaded in tension differs

from that of nonpreloaded anchors. Preloaded anchors produce a clamping

force which must be overcome before significant anchor displacement can

occur. Consequently, there is little displacement until the applied load

exceeds the preload force [25] . Since preloading does not affect the ultimate

static tensile anchor capacity [ 22 ] , the ultimate anchor displacement

decreases with increasing magnitude of preload force. Preloading has not

been found to have any effect on anchor stiffness

.

Load- displacement behavior also depends on the manner of loading.

Sustained tensile loads influence load- displacement behavior by causing the

stressed concrete to creep, resulting in anchor displacement. Torque

controlled expansion anchors subjected to sustained loads of more than 70-

80% of ultimate capacity experience time -dependent displacement [2] . Figure

3.4 shows the time -dependent displacement of a torque -controlled anchor for

14
a sustained load of 70% of ultimate. The rate of displacement decreases with

time from its initial value and the displacement eventually approaches a

limiting value. As the magnitude of sustained load relative to ultimate load

capacity increases, the limiting displacement increases. Sustained loads

smaller than 70-80% of ultimate capacity do not influence the displacement

of torque -controlled expansion anchors at ultimate capacity [2]

.

Like expansion anchors, chemical anchors experience time -dependent

displacement under sustained loads. The rate of displacement decreases with

time and eventually approaches zero. However, as shown in Figure 3.5, this

rate is temperature -dependent and increases with increasing

temperature [ 18 , 26 ] . The magnitude of the limiting displacement depends on

the type of anchor. Unheaded anchors have been found to have less long-term

displacement and unrecoverable anchor movement than headed anchors [21].

The effect of cyclic loading on anchor displacement can also be

significant. However, the displacement at failure has been found to be

unaffected by cycling even up to one million load repetitions if the maximum

load is less than 50% of the static load capacity [2].

3. 2. 1.2 Ultimate Strength

3 . 2 . 1 . 2 .

1

General

The ultimate strength of anchors loaded in tension depends on the

controlling failure mode which in turn is dependent on such factors as edge

15
distance, embedment depth, concrete and/or anchor steel strength, type of

anchor, and loading condition. As indicated in Figure 3.6, there are four

primary failure modes for anchors in tension: 1) steel failure, 2) slip

or pullout failure, 3) concrete cone failure, and 4) splitting failure.

3. 2. 1.2. 2 Steel Failure

Steel failure is characterized by anchor fracture and so the ultimate

capacity depends on the strength and cross sectional area of steel. The

failure load is calculated by the equation:

Fu

- As x fut (D

where

As - steel cross sectional area

fut - steel tensile strength

Due to the relatively ductile and predictable nature of such a failure,

it is a desirable mode of failure. Because undercut expansion anchors

transfer load by bearing, they are able to develop the tensile capacity of

the steel and are ductile in failure [ 6 , 32 ]

.

3. 2. 1.2. 3 Pullout Failure

In pullout or slip failure, the anchor is pulled out of the concrete in

which it is embedded without significant damage to the concrete. For

expansion anchors, the applied tensile load is resisted by friction of the

expansion device against the wall of the drilled hole. The expansion device

16
enlarges the hole and produces a radial spreading pressure, the summation of

which over the contact area yields the spreading force. The failure load is

given by the equation:

Fu - p x S (2)

where

/x - coefficient of friction

S - spreading force

The pullout capacity of most expansion anchors is governed by friction.

The coefficient of friction depends on the roughness of the surfaces in

contact and on the spreading force. The spreading force is a function of the

amount of radial expansion, the modulus of elasticity of the surrounding

concrete, and the magnitude of gap between the anchor and the hole wall [31].

Values of the coefficient of friction have been found to be about 0.2 - 0.3

for Type A anchors and about 0.35 for Type B anchors [31]. Equations for

estimating the spreading force are also presented in Ref. 31, based on

theoretical considerations. However, it is reported in Ref. 14 that an

extensive testing of pullout of expansion anchors found the equations to be

unreliable estimates of pullout capacity.

Wedge and sleeve torque -controlled expansion anchors with embedment

depths greater than about four bolt diameters typically fail by pullout [25].

The pullout capacity of wedge anchors is affected by the presence of dust

which can act as a lubricant to reduce friction, resulting in a lower

ultimate capacity [30] . The pullout capacity of wedge anchors is also

affected by the presence of nearby empty drilled holes, which most likely

17
reduce the spreading pressure. Holes located nearer than 3 bolt diameters

from the anchor reduce the strength unless the holes are filled with

mortar [7]. The pullout capacity of expansion anchors has not been found to

be affected by edge distance and anchor spacing.

Pullout of grouted anchors is a bond failure that occurs along either

the grout -concrete interface, the grout-anchor interface, or both interfaces

simultaneously. The particular interface along which failure takes place

depends in part on the manner of load transfer from anchor to grout and on

the relative bond strength of each interface. For headed anchors, in which

load is primarily transferred from anchor to grout by bearing, bond failure

is limited to the grout-concrete interface [ 10 ] . For unheaded anchors, in

which load is transferred from anchor to grout by bond development, failure

usually occurs along both interfaces simultaneously. Failures have been

reported, however, along only the grout -anchor interface for poorlyconsolidated grouts [26].

The pullout capacity of grouted anchors is strongly influenced by

shrinkage of grout, which weakens the bond strength at the grout -concrete and

grout-anchor interfaces. The pullout strength of unheaded anchors failing

along both interfaces simultaneously has been found to be less than that of

cast- in-place anchors because of grout shrinkage [ 26 ] . In addition, grout

shrinkage has been found to alter the mode of failure of headed anchors from

steel fracture to bond failure along the grout -concrete interface [ 10 ]

.

Pullout capacity is also dependent on embedment depth. For unheaded anchors

that experience bond failure along both interfaces simultaneously, the

18
ultimate strength increases with increasing embedment depth, although for

large depths the mode of failure changes to steel fracture [ 26 ] . The effect

of embedment depth on pullout capacity of headed anchors has not been

reported. Edge distance and anchor spacing have not been found to have any

influence on pullout capacity of headed or unheaded anchors.

Pullout of chemical anchors is similar to that of grouted anchors in

that it involves a bond failure along one or more interfaces . Bond failure

along the adhesive -anchor interface is possible for plain unheaded bars. For

this type of failure, slight rusting of the steel improves the bond between

the adhesive and anchor and increases the pullout capacity [12] . For unheaded

chemical anchors, however, bond failure is almost always along the adhesiveconcrete interface. Bond strength thus depends on the cleanliness of the

drilled hole prior to installation of the anchor [21]. Bond strength also

depends on temperature. Bond strengths at 80° C and 50° C are only about

70 - 75% and 85 - 90%, respectively, of the value at 20° C[3,18],

Because load is transferred from anchor to adhesive by bond development,

the pullout capacity of chemical anchors increases in proportion to

embedment depth. For embedment depths larger than nine anchor diameters,

however, the pullout capacity does not increase in proportion to depth

because most of the load is transferred near the concrete surface [2] . If the

embedment depth becomes large enough, the mode of failure changes from

pullout to steel fracture. Pullout failure has been found to control for

embedment depths up to 15 anchor diameters [ 23 ] . Edge distance or spacing of

anchors have not been reported to have any effect on pullout capacity.

19
3. 2. 1.2.

4

Concrete Cone Failure

Concrete cone failure is a failure of concrete in tension along a

conical surface. For expansion anchors with embedment depths less than

10 - 15 cm (4 - 6 in.), the cone angle measured from the axis of the anchor

to the failure surface is about 60 - 75° [2, 14] and the depth of the cone

ranges from 80 - 100% of the depth of the anchor [14]. Figure 3.7 shows a

typical failure cone of an expansion anchor with an embedment depth of 13 cm

(5 in.). For larger embedment depths, the failure surface becomes a double

cone. The cone angle is about 45° at the end of the anchor, but changes

to about 60 - 75° at 10 - 15 cm (4 - 6 in.) from the concrete surface[2].

When there is sufficient side cover and anchor spacing, the strength of

expansion anchors in concrete cone failure depends mainly on the concrete

tensile strength and the depth of embedment [ 18 ] . ACI 349, Appendix B [ 1 ]

assumes that the strength increases in proportion to the surface area of a

45° cone and that the average tensile stress at failure is 4./f' c

. The

ultimate strength of expansion anchors is given by the equation:

Fu - 1.043 <f> 1 Jf e(in Newtons) (3)

where

- capacity reduction factor

1^ - depth of anchor, mm

f

l c - concrete compressive strength, N/mm^

From an evaluation in Ref. 14 of about 2000 tests on expansion anchors

with embedment depths of up to 15 cm (6 in.), it has been found that the

20
strength of such anchors does not increase in proportion to the area of the

cone, indicating that the tension force is not resisted by the entire area

of the cone for increased embedment depths. Equation (3) of ACI 349,

Appendix B[X] was found to be unconservative for embedment depths greater

than 20 cm (8 in.). Based on the test results, an equation for the ultimate

capacity is presented in Ref. 14 as:

Fu - 7.4 1^1*^ f' c 2/3 (in Newtons) (4)

This equation closely agrees with an equation proposed in Ref. 4 which

predicts the strength of cast- in-place anchors. The ultimate capacity, then,

may be assumed to be nearly independent of the mechanism of load transfer,

whether it is by friction (expansion anchors) or by bearing (headed cast- inplace anchors) [ 14]

.

These predictive equations are based on the assumption that a sufficient

volume of concrete is available to develop an entire conical surface. If the

anchor is located near an edge, the failure surface consists of only part of

a cone. It has been proposed that when the edge distance is smaller than a

critical value, the strength decreases in proportion to e/e c , where e is the

actual edge distance and e c , given as 1.75 1^, is the critical edge distance

for full anchor strength [14] . The strength predicted by the model has been

found to be conservative.

In addition, if anchors in a group are spaced too closely, the failure

surfaces overlap and a single combined cone may develop. The strength is

reduced when the spacing between anchors decreases below a critical value.

21
In Ref. 14 it has been proposed that the critical spacing is 3.5 1^ and that

the strength of the group decreases linearly as -he spacing decreases to

zero, at which point the strength of the group is equal to that of a single

anchor

.

Concrete cone failure of unheaded chemical anchors differs somewhat from

that of expansion anchors. The depth of the cone typically ranges from

25 - 40% of the bond depth of the anchor [18]. Along the remaining length of

the anchor the bond between the adhesive and concrete is overcome, as shown

in Figure 3.8. The cone angle measured from the axis of the anchor to the

failure surface is about 50 - 70° [21, 26]. The failure cone associated with

chemical anchors is closer to the concrete surface than for expansion anchors

because chemical anchors transmit most of the applied load near the concrete

surface by bond development, whereas expansion anchors transmit all load at

the end of the anchor. Because of a smaller concrete cone, the strength of

chemical anchors is less than that of expansion anchors for similar embedment

depths [18]. Based on test results, an equation has been presented in Ref.

18 to predict the strength of unheaded chemical anchors for large edge

distances and anchor spacing:

Fu - 0.95 1^ Jf c (in Newtons) (5)

For embedment depths greater than nine anchor diameters, the capacity

increases more gradually than that predicted by the Equation (5) because most

of the applied load is transferred near the surface [18]. For unheaded

chemical anchors with edge distances less than a critical value, the strength

depends on edge proximity. In Ref. 18 it is presumed that the critical edge

22
distance is equal to the embedment depth and that the strength decreases

linearly with edge distance, similar to that for expansion anchors. For a

group of anchors, the strength also depends on anchor spacing. When the

spacing is less than a critical value, found to be 2 1^, the strength of the

group decreases with decreasing spacing in a manner similar to that of

expansion anchors[18].

Concrete cone failure of debonded headed chemical anchors is different

from that of unheaded chemical anchors in that the failure surface is a

double cone which extends from the concrete surface to the top of the anchor

head. Because the cone is deeper than that in unheaded anchors, the ultimate

strength of headed anchors is much larger than that of unheaded anchors [21].

The depth of the lower cone is about 50 - 60% of the depth of the debonded

anchor [ 21 , 24 ]

. The cone angle measured from the axis of the anchor to the

surface of the lower cone ranges from about 55 - 70°[21,24]. Based on test

results and assuming an average concrete tensile strength of 2.28 N/mm^ (331

psi)

,

an equation is presented in Ref. 21 to predict the ultimate capacity

of debonded headed chemical anchors:

Fu - 7H (H + D) (in Newtons) (6)

where

D - hole diameter, mm

H - distance from concrete surface to top of anchor head, mm

If headed chemical anchors are placed in groups, interaction between

individual anchors is possible if the spacing is sufficiently small. When

the spacing is less than about 2H for headed anchors placed in pairs, the

23
strength of the pair decreases as the spacing decreases [ 21 ]

. The failure

surface is a double cone at the ends and is almost uniform in depth between

the anchors. When the spacing is larger than 2H, the capacity is unaffected

by spacing and failure is controlled by the pullout of a concrete cone on

only one of the anchors [21].

Concrete cone failure of grouted anchors has only been reported for

headed anchors, in which the applied force is transferred to the concrete

primarily by bearing. For such anchors, the capacity depends mainly on the

depth of embedment and the concrete tensile strength. For headed anchors

with washers, the washer size has been found to have a slight influence on

capacity [ 26 ]

,

probably because it increases the area of the conical failure

surface. Cone depth and angle of inclination of the failure surface have not

been reported. In addition, there is a lack of available information on the

effect of type, shrinkage, and strength of grout on the concrete cone

capacity

.

3. 2. 1.2.

5

Splitting Failure

Splitting failure occurs when splitting cracks form in the concrete at

anchor locations . Splitting is usually due to edge proximity of one or more

anchors or close spacing of a group of anchors. The strength of expansion

anchors that fail by splitting the concrete has been investigated in Ref. 28

by assuming that splitting occurs when tensile stresses averaged over a

critical area reach the tensile strength of the concrete. Minimum values of

edge distance, anchor spacing, and concrete dimensions to prevent splitting

24
failure have been proposed in Ref. 28. However, they are based on limited

test results. Splitting failure associated with grouted or chemical anchors

has not been reported.

Splitting failure of concrete may occur for expansion anchors during

installation and is more likely for anchors with larger spreading forces.

Splitting has been found to occur for wedge anchors with edge distances of

less than 6 bolt diameters [ 2 ]

.

3.2.2 Shear Loading

3. 2. 2.1 Load-Displacement Behavior

Load- displacement behavior of anchors loaded in shear is dependent on

whether or not the anchor is pretensioned. Anchors that are not pretensioned

displace immediately at the application of load. Figure 3.9 shows a typical

load- displacement curve of an expansion anchor without preload. The initial

portion of the curve represents movement of the anchor to the wall of the

drilled hole. As further load is applied, the anchor bears against the

concrete and additional displacement is due to both bending of the anchor and

concrete deformation under bearing pressure. Anchor displacement thus

depends on the gap between the anchor and the hole wall, the stiffness of the

surrounding concrete, and the bending stiffness of the anchor. Decreasing

the strength (and stiffness) of the concrete and increasing the size of the

hole have been found to increase anchor displacements for undercut

anchors [ 6 ]

.

25
The load- displacement behavior of nonpreloaded chemical and grouted

anchors is similar to that of expansion anchors. Displacement of the anchor

is due to bending of the anchor and deformation of the concrete. Since the

hole is usually completely filled with adhesive or grout, there is no initial

movement of the anchor to the side of the hole. A typical load-displacement

curve for a chemical anchor is presented in Figure 3.10.

For pretensioned anchors, the friction force between the baseplate and

concrete surface must be overcome before significant anchor displacements can

occur. Values for the coefficient of friction have been found to be in the

range of 0.57 - 0.70 for steel-concrete and steel-grout interfaces [ 29 ]

.

Preloading in tension limits the ultimate deflection and has also been found

to affect the dynamic stiffness of wedge and shell expansion anchors[22].

3. 2. 2.

2

Ultimate Strength

3 . 2 . 2 . 2 .

1

General

The ultimate strength of anchors loaded in shear depends on the mode of

failure. There are two main failure modes: 1) steel failure and 2) concrete

failure. The controlling mode depends primarily on the edge distance and

depth of embedment.

26
3. 2. 2. 2.

2

Steel Failure

Steel failure is marked by anchor rupture and is relatively ductile,

usually occurring after large displacements. It is a typical mode of failure

for expansion anchors with large edge distances and deep embedments [ 14 ] . The

ultimate strength depends on the strength and cross sectional area of steel

and is given by the equation:

Fu - As x fus (7)

where

As — steel cross sectional area

fus — steel shear strength

The ultimate strength is also influenced by the magnitude of anchor

displacement. For undercut anchors, increasing the anchor displacement by

decreasing the concrete stiffness and increasing the hole diameter allows the

anchor to develop a greater tensile component of force and hence a larger

capacity [ 6 ]

.

3. 2. 2. 2.

3

Concrete Failure

As shown in Figure 3.11, concrete failure can take one of two forms,

depending on the edge distance. For small edge distance (Figure 3.11a),

breakout of the concrete occurs , usually in the form of a cone . When the

edge distance is large (Figure 3.11b), the concrete spalls or crushes

accompanied by anchor pullout.

27
For conical concrete breakout failures, the failure surface is inclined

at an angle of about 30° with respect to the concrete surface and has a depth

of 1.3 - 1.5 times the edge distance of the anchor [16]. The ultimate

strength depends primarily on the edge distance e, although the concrete

tensile strength and anchor diameter also affect the capacity [ 16 ]

.

Theoretically, the strength should increase in proportion to the area of the

failure surface, which is a function of e^ . However, for expansion anchors,

the strength increases approximately in proportion to e^-^ as indicated in

the equation proposed in Ref. 16:

Fu - 1.3 e^-5 db®--* JV C (in Newtons) (8)

where

e - edge distance , mm

d^ - anchor diameter, mm

f' c - concrete compressive strength, N/mm^

For chemical anchors, the strength increases only in proportion to e [ 2 ]

.

Furthermore, the shear strength of chemical anchors is lower than the tensile

strength for equal edge distance to embedment depth ratios when conical

breakout failure controls [ 18 ] . No information has been found concerning the

influence of edge distance on the strength of grouted anchors in conical

breakout failures.

Failure by concrete crushing or spalling followed by anchor pullout has

only been reported for grouted anchors. For such anchors, the capacity

depends mainly on the resistance of the grout to crushing, in contrast to

tensile loading, in which the capacity often depends on bond strength.

28
Consequently, the shear capacity is not as reliant on the type and shrinkage

of grout as is tensile capacity and is larger than the tensile pullout

capacity [ 10]

.

3.2.3 Combined Tension and Shear Loading

The behavior of anchors under combined tension and shear loading has not

been extensively reported. When anchors are subjected to combined loading,

the tensile and shear forces interact. For preloaded anchors, the tensile

force reduces the shear transfer resistance provided by the clamping force

and can reduce the preload in the anchor; however, preload has not been

reported to have any effect on the ultimate strength under combined tension

and shear. The strength of wedge and shell torque -controlled expansion

anchors under combined tension and shear, in fact, has been found to be

independent of preload [22],

The load-displacement behavior of anchors is affected by interaction

between tensile and shear forces. The stiffness of expansion anchors under

combined loading has been found to be smaller than that under either tension

or shear loading[9]. The effect of combined loading on the load- displacement

behavior of chemical and grouted anchors has not been reported.

The strength of anchors in combined tension and shear depends on the

relative magnitude of the two forces. It has been found, for example, that

the strength of self- drilling anchors is a minimum when the resultant of the

tension and shear forces is oriented at an angle of about 40° with respect

29
to the concrete surface [9]. In Figure 3.12 an interaction diagram is

presented from test results of expansion anchors in combined tension and

shear in which concrete cone failure controls . Two lines representing

predictions of anchor capacity are also plotted. The dashed straight line

between pure tension and pure shear, which is recommended by ACI 349,

Appendix B [ 1 ]

,

is a conservative prediction of strength. The trilinear curve

(solid line) proposed in Ref. 25 is less conservative than the straight line

and is a reasonable lower bound of the ultimate capacity. It assumes that

no reduction in strength occurs when the applied load is either predominantly

tension or shear.

An identical trilinear curve has been proposed in Ref. 4 to predict the

strength of cast- in-place anchors in combined tension and shear. Based on

limited test results, the curve is a reasonable approximation of the lower

bound of strength. The strength of anchors in concrete cone failure

subjected to combined tension and shear, then, may be assumed to be

independent of the type of anchor.

The effect of interaction between tensile and shear forces on the

strength of expansion anchors when failure is controlled by steel fracture,

anchor pullout, or splitting of concrete has not been reported. In addition,

the strength of grouted and chemical anchors in combined tension and shear

is not documented. The effect of anchor spacing and edge distance on anchor

strength is not established.

30
3.2.4 Combined Loading With Bending

For other combined loading conditions in which bending is present,

little information is available. The cause of failure under such loading

conditions is usually anchor fracture. Factors that influence the ultimate

strength are the bending resistance of the anchor and its embedment in the

concrete [ 2 ]

.

3.2.5 Survivability

Anchors are often subjected to cyclic or vibratory loads instead of

static loads. The ability of anchors to sustain such loads depends on

several factors, such as the stress range, flexibility of support, and

quality of installation.

Anchor survivability under dynamic loads is largely governed by the

stress range, since bolts have a low fatigue capacity. Preloading in tension

can reduce the stress range by as much as 50 » 75% and can thus improve the

fatigue life [13]. Support flexibility also affects the survivability by

allowing the base plate underneath the anchor to rotate , which makes the

support more passive in resisting transient loads [19]. Proper installation

is another important factor in increasing the fatigue life of an anchor [19].

31
3.3 Behavior in Cracked Concrete

3.3.1 General

The load- displacement behavior and ultimate strength of anchors

installed in or near cracks is markedly different from that in uncracked

concrete. Anchor behavior in cracked concrete depends on the location,

width, and number of cracks. The majority of reported data on anchor

behavior in cracked concrete pertains to cracking in one direction only.

3.3.2 Tension Loading

3. 3. 2.1 Load-Displacement Behavior

The load-displacement behavior in tension of anchors installed in

cracked concrete differs from that in uncracked concrete. Figure 3.13

illustrates the effect of the presence of a crack passing through a torque

controlled expansion anchor. The crack reduces the spreading force of the

expansion device, resulting in a decrease in strength and an increase in

ultimate deflection due to anchor slip. As the figure indicates, anchors set

in intersecting cracks are affected more than anchors set in a single crack.

It is intuitively assumed that the load- displacement behavior of grouted and

chemical anchors would also be influenced by the presence of cracks, although

there is no such documented information. The effect of preload on the loaddisplacement behavior of anchors in cracked concrete is not as significant

32
as in uncracked concrete. In fact, the intersection of flexural cracks with

expansion anchors has been found to completely eliminate preload[8].

Load-displacement behavior of anchors in cracked concrete is also

affected by the state of stress in the surrounding concrete. When anchors

are placed in tensile stress regions of cracked reinforced concrete members,

the tensile stresses in the member generated by structural action interact

with the tensile stresses induced by the anchor. The displacement of

expansion and grouted anchors located in tensile stress regions of reinforced

concrete slabs has been found to be dependent on the magnitude of applied

moment in the slab [11].

The presence of cracks also affects the displacement of anchors

subjected to cyclic tension loading. Under cyclic loading, expansion anchor

displacements increase with increasing crack width and load intensity [ 15 ]

.

However, anchor capacity and displacement at failure are not significantly

influenced by cyclic loading provided the maximum load is smaller than 50%

of the static failure load for expansion anchors set in intersecting

cracks [2]. The flexibility of the attachment strongly influences the

response of anchors to cyclic loading. Flexible attachments tend to

stabilize and decrease the rate of displacement, whereas the rate of

displacement of rigid attachments either increases or maintains a steady rate

to failure under cyclic loading[8].

33
3. 3. 2.

2

Ultimate Strength

Cracking in concrete affects the ultimate strength of anchors in tension

that fail by pullout of a cone-shaped section of concrete. In uncracked

concrete, the stresses in the concrete are radially symmetric about the

anchor. The presence of cracks in or near the anchor creates a boundary

across which tensile stresses cannot transfer unless the cracks are small

enough for aggregate interlock to be effective (less than about 0.4 mm or

0.016 in.). When a crack passes through an anchor, the area onto which load

can be transferred to the concrete is potentially smaller than in uncracked

concrete. Alternatively, when a crack passes near an anchor, part of the

surface of the concrete failure cone may become ineffective. The strength

of anchors in concrete cone failure will thus be smaller in cracked concrete

than in uncracked concrete.

Expansion anchors are further affected when they are located in cracked

concrete because of the reduction in the spreading force of the expansion

device. If the spreading force is sufficiently reduced, the failure mode may

change from concrete cone to pullout. For torque -controlled expansion

anchors (Type A) whose expansion devices expand with the application of load,

the spreading force usually remains large enough for relatively small crack

widths so that concrete cone failure controls. The effect of crack width on

the strength of such expansion anchors located in cracks is shown in Figure

3.14. The strength of the anchors decreases to about 50 - 80% of the

strength of similar anchors in uncracked concrete as the crack width

increases to about 0.3 - 0.5 mm (0.012 - 0.020 in.) [14]. For cracks much

34
wider than 0.3 - 0.5 mm (0.012 - 0.020 in.), the spreading force can become

small enough to change the mode of failure to pullout and furtner reduce the

failure load.

Also shown in Figure 3.14 is the effect of crack width on the strength

of deformation-controlled expansion anchors (Types B and C) . The strength

of the anchors decreases to about 40 - 70% of the strength of similar anchors

in uncracked concrete as the crack width increases to about 0.3 - 0.5 mm

(0.012 - 0.020 in.) [14]. Since the expansion devices of such anchors do not

expand after installation, the intersection of a crack with the anchor is

likely to result in a change in failure mode to pullout even for relatively

small crack widths [17].

The effect of cracking on the ultimate strength of chemical anchors in

concrete cone failure is similar to the effect on the strength of expansion

anchors. In Figure 3.15 test results of three different sizes of anchor

bolts located in cracks show that the strength of chemical anchors decreases

to about 20 - 60% of the strength in uncracked concrete as the crack width

increases to 0.3 - 0.4 mm (0.012 - 0.016 in.) [18]. The strength reduction

is larger for anchors of smaller diameter [18]

.

The presence of cracks also influences the ultimate strength of anchors

that fail in pullout, which are typically unheaded grouted or chemical

anchors . Cracks that intersect anchor locations reduce the bond strength

between the grout or adhesive and concrete. However, there are no reported

tests of anchors in cracked concrete failing by pullout.

35
The strength of anchors in which steel failure controls is assumed to

be independent of cracks in the concrete since the failure load depends only

on the steel area and steel strength. The effect of cracks on splitting

failures has not been reported.

The ultimate strength of anchor groups is also affected by cracking.

In cracked concrete, some anchors may be located in cracks while others are

not. It is reported in Ref. 2 that, based on theoretical and experimental

investigations of expansion anchors failing in concrete cone failure, the

strength of an anchor group in cracked concrete is about 70% of the strength

of a comparable group of anchors in uncracked concrete and is independent of

the number of anchors located in cracks. Theoretical studies have also shown

such behavior to be valid for different types of anchor groups and for rigid

attachments. When cracking causes any of the expansion anchors in a group

to slip and pull out of the hole, the failure load of the group is reduced

even further [17],

3.3.3 Shear Loading

The behavior of anchors in cracked concrete under shear loading has not

been extensively investigated. The effect of cracking on load- displacement

behavior is not documented. The effect of cracking on the ultimate capacity

depends on edge distance. For anchors with a sufficiently large edge

distance and embedment depth, failure is controlled by rupture of the anchor

steel. In this circumstance, the strength is not appreciably affected by

cracks [16]. Anchors with a small edge distance which fail by breakout of a

36
concrete cone experience a reduction in strength when cracking is present,

presumably to about 60% of the strength in uncracked concrete for expansion

anchors as in the case of tension loading[X6]. For chemical anchors, it is

assumed that cracking has less influence on strength reduction in shear than

in tens ion [18] . The effect of cracking on the strength of anchors with large

edge distances in which failure is controlled by concrete crushing or

spalling has not been reported.

3.3.4 Combined Loading

The behavior of anchors in cracked concrete under any type of combined

loading has not been reported. Specifically, no research has been conducted

on anchors under combined tension and shear, although it may be presumed that

the trilinear interaction curve of Figure 3.12 which predicts the strength

of anchors in uncracked concrete would also be valid for similar anchors

installed in cracked concrete [ 16 ] . No studies on the effect of cracking on

anchor behavior for any combined loading involving bending are available.

3.4 Research Needs

There is a substantial amount of reported information on the behavior

of post- installed anchors embedded in concrete. However, most of this

information concerns the response to static tensile loads in uncracked

concrete. There is a lack of detailed knowledge in many areas of anchor

behavior, especially for anchors under combined loadings and in cracked

37
concrete. The following list summarizes the particular areas in which

additional knowledge is required.

1 . Anchors in Uncracked Concrete

a) Tension Loading

- effect of cyclic loading on anchor displacement and strength

- effect of sustained loading on anchor strength

- predictive equations for anchor capacity in pullout and splitting

failures

b) Shear Loading

- anchor strength when failure is controlled by concrete spalling or

crushing followed by anchor pullout

- effect of cyclic and sustained loading on anchor displacement and

strength

c) Combined Tension and Shear Loading

- effect of edge distance and anchor spacing on anchor behavior

- effect of cyclic and sustained loading on anchor behavior

G

d) Combined Loading With Bending

- effect of interaction on anchor behavior

2 . Anchors in Cracked Concrete

a) Tension Loading

- effect of cracking on displacement of grouted and chemical anchors

38
- effect of cracking on grouted anchor capacity in concrete cone

failure

- effect of cracking on anchor capacity in pullout and splitting

failures

b) Shear Loading

- effect of cracking on anchor displacement and strength

c) Combined Loading

- effect of cracking on anchor behavior under any type of combined

loading

39
4.0 SUMMARY AND CONCLUSIONS

4 . 1 Summary

This report summarized published and available information concerning

the behavior of post- installed anchors embedded in concrete. From this

literature survey, the extent of understanding of anchor behavior for

various loading conditions , types of anchors , and states of concrete was

assessed.

Chapter 2 described the different types of post- installed anchors.

Mechanisms of load transfer from anchor to concrete and methods of

installation for typical anchors were presented.

Chapter 3 investigated the behavior of post- installed anchors in

concrete. Load- displacement behavior and ultimate capacity were discussed

for anchors subjected to various loading conditions in both uncracked and

cracked concrete. In addition, particular areas in which further

understanding of anchor behavior is required were identified.

40
4.2 Conclusions

A significant amount of published information exists concerning the

behavior of post- installed anchors in concrete. However, most studies have

dealt with the behavior of anchors subjected to tensile loads in uncracked

concrete. While there is a thorough understanding of the load-displacement

behavior and ultimate capacity of anchors in tension embedded in uncracked

concrete, there are other conditions in which anchor behavior is not well

known. In particular, knowledge of the behavior of anchors subjected to any

type of combined loading involving tension, shear, or bending is incomplete.

One aspect of anchor behavior under combined loading in which further

understanding is needed is the response of anchors to combined tension and

shear. Although a limited amount of research has been conducted by several

researchers on anchors in uncracked concrete subjected to combined tension

and shear [ 9 , 22 , 25 ] , full knowledge of the effects of interaction on loaddisplacement behavior and ultimate capacity is lacking. In addition, there

is no information on the behavior of anchors subjected to combined tension

and shear in cracked concrete.

The understanding of anchor behavior in combined tension and shear is

important in strengthening existing buildings . Many methods currently used

to strengthen existing structures involve the attachment of additional

elements to structural members by means of post- installed anchors. A

thorough literature review of strengthening methodologies has reported that

such anchors are often subjected to combined tension and shear loadings [ 27 ]

.

41
Furthermore, the structures which require strengthening are often cracked or

damaged. In order to describe the behavior of anchors in strengthened

structures, it is necessary to have a thorough understanding of the behavior

of anchors in combined tension and shear in both uncracked and cracked

concrete

.

42
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,

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,

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,

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,

and Funk, R.R.

,

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43
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,

"Load Relaxation of Concrete Expansion Anchors," ACI

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,

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,

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,

and Snell, C. , "Resin Anchorages," Civil

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,

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,

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,

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44
27. Phan, L.T. , Lew, H.S., and Johnson, M.K. , "Literature Review of

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30. Schwarz, F. , "Wedge-Type Expansion Anchor Performance in Tension,"

Anchorage to Concrete, SP 103-5, American Concrete Institute, Detroit, 1987,

pp. 89-106.

31. Wagner-Grey, U. , "Theoretical Considerations on Loadbearing Behavior of

Expansion Anchors," Anchorage to Concrete, SP 103-13, American Concrete

Institute, Detroit, 1987, pp . 257-282.

32. Wiewel, H. , "Performance Characteristics of Undercut Anchors," ACI

Symposium on Anchorage to Concrete, Phoenix, March 1984.

45
-err

jQ • v. %' °-

. <5 °

o o ' .•<?>• * 9 o

torque controlled deformation controlled

expansion anchors

TYPE A TYPE B TYPE C

Figure 2.1 Classifications of Expansion Anchors (From [14])

46
I

Single-acting Double acting

(shell expanded (shell-expanded

by single wedge nut) by apposing wedge)

Wedge Anchor Shell Anchor

Sleeve Anchor Undercut Anchor

Figure 2.2 Torque -Controlled Expansion Anchors (Type A)
Preload

(%

of

Initial

Value)

Figure 2.3 Relaxation of Preload in Torque-Controlled

Expansion Anchors (From [5])

Drop-In Anchor

Figure 2.4 Deformation-Controlled Expansion Anchor (Type B)

48
Self-Drilling Anchor Stud Anchor

« i

1 i “*ir»

• !' ii j f M

• !'

:

8

1

• ;;

:

i

»

n

' %

. •« 11 «

Single Unit

Lead Caulking Anchor

Figure 2.5 Deformation-Controlled Expansion Anchors (Type C)
Croat

Bolt Threaded Rod Threaded Rod With

With Nut Nut and Washer

Figure 2.6 Typical Grouted Anchors

Figure 2.7 Relaxation of Preload in Grouted Anchors

(From [5])

50
Threaded Rod

Figure 2.8

tr

Reinforcing Bar

Typical Chemical Anchors

51
a) Tension c) Combined Tension

and Shear

d) Combined Bending

and Shear

e) Combined Bending,

Shear, and Tension

Figure 3.1 Types of Loadings on Anchors

toad F ( k N

1

r® /

/ Ad /vD

#c HImm2

0 2 4 6 8 displacement s(mml

tine anchor type bolt diameter mmanchorage depth mm © A to 65

© 6 16 65

© C 16 63

Figure 3.2 Typical Load-Displacement Relationship of

Expansion Anchors in Tension (From [14])

52
Figure 3.3 Typical Load-Displacement Relationship of Chemical

Anchors in Tension (From [18])

Figure 3.4 Effect of Sustained Tension Loads on Displacement

of Torque -Controlled Expansion Anchors (From [2])

53
Displacement (mm)

Figure 3.5 Effect of Sustained Tension Loads on Displacement

of Chemical Anchors (From [18])

a) Steel Failure b) Slip or Pullout Failure

I

c) Concrete Cone Failure

Figure 3.6 Types of Failures of Anchors in Tension

54
Figure 3.7 Typical Failure Cone of Expansion Anchors (From [14])

Figure 3.8 Typical Failure Cone of Chemical Anchors (From [18])

55
Load

Figure 3.9 Typical Load-Displacement Relationship of

Expansion Anchors in Shear (From [16])

Figure 3.10 Typical Load-Displacement Relationship of

Chemical Anchors in Shear (From [18])

56
F

a) Conical Breakout b) Spall or Crush

of Concrete

Figure 3 . 11 Types of Concrete Failures of Anchors in Shear

Figure 3.12 Tension-Shear Interaction Diagram for

Expansion Anchors (From [25])

57
Force

Figure 3.13 Influence of Cracking on Load-Displacement

Relationship of Torque-Controlled Expansion

Anchors in Tension (From [14])

0 0,5 1,0 1,5 2.0 2.5 Crack Width (mm)

Figure 3.14 Influence of Crack Width on Strength of Expansion

Anchors in Tension (From [14])

58
02 0> 06 0.1 Crack Width (mm)

Figure 3 . 15 Influence of Crack Width on Strength of Chemical

Anchors in Tension (From [18])
NBS-T14A irev. 2 -ec) 1

4. TITLE AND SUBTITLE

Literature Review of Post-Installed Anchorage in Concrete

5. AUTHOR(S)

Mark K. Johnson, H.S. Lew, Long T. Phan

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

7. Contract/Grant No.

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP

)

•

| 10. SUPPLEMENTARY NOTES

| Document describes a computer program; SF-185, FIPS Software Summary, is attached.

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

NBSIR 88-3797

2. Performing Organ. Report No. 3. Publication Date

JUNE 1988

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report summarizes current knowledge of post-installed anchor behavior

in concrete. Load-displacement behavior and ultimate strength of each type

of post-installed anchor are discussed for different loading conditions in

both uncracked and cracked concrete. Most knowledge of anchor behavior

concerns the response to static tensile loads in uncracked concrete. Many

aspects of anchor behavior require further study, especially the behavior

of anchors in cracked concrete subjected to combined loadings.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) anchors; combined loading; concrete; drilled-in anchor; epoxy anchor;

expansion anchor; grouted anchor; post-installed anchor; shear; tension.

13. AVAILABILITY

; X 1 Unlimited

| | For Official Distribution. Do Not Release to NTIS

| Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

I X 1 Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

65

15. Price

$13.95

U SCOMM-DC 6043-P80