Adhesive Anchors Part 2A

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What About Adhesive Anchors?

Part 2(A)

ACI Spring 2010 Xtreme Concrete Convention

March 21 - 25, Chicago, IL

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Please enjoy the presentations.

What About Adhesive Anchors?

Part 2(A)

ACI Spring 2010 Xtreme Concrete Convention

March 21 - 25, Chicago, IL

Todd Davis is a Research Assistant and Ph.D.

student in the Department of Civil Engineering

at the University of Florida. His research

focuses on the long-term performance of

adhesive anchors in concrete. Todd graduated

summa cum laude in 1995 with a Bachelor of

Science in Civil Engineering from Auburn

University, and then served four years as an officer in the U.S.

Navy Civil Engineer Corps. He then moved to Guatemala to

work with an engineering organization involved in the design

and construction of community development projects. In 2001,

he and his wife founded the organizations Latin American

regional office. In 2007, Todd returned to the United States to

earn his Masters of Engineering with a focus on Structural

Engineering from the University of Florida.

StressversusTimetoFailureTest

MethodforEvaluatingtheSustained

LoadPerformanceofAdhesive

AnchorSystemsinConcrete

ToddM.Davis

RonaldA.Cook,Ph.D.,PE

UniversityofFlorida

DepartmentofCivilEngineering

Outline

Introduction

BackgroundonTesting

ASTME48896

ASTME151201

ICCESAC58,AC308,andACI355.Y

StressversusTimetoFailureTestMethod

CurrentResearchEfforts

IntroductiontoAdhesive

Anchors

BostonTunnelCollapse


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CeilingCollapse

Source:NTSB(2007)

DisplacedAnchors

Source:NTSB(2007)

Time (Days)

0 10 20 30 40 50 60 70 80

Displacement(inch)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

#9-409

2lb

s

#10

-401

4lbs

#8 - 4081 lbs

#7 - 4080 lbs

LaboratoryAnchorTesting

Source:FHWATFHRC

Anchorsloadedat4000pounds

BackgroundonSustainedLoad

TestingforAdhesiveAnchors

ASTME48896

StandardTestMethodsforStrengthofAnchorsinConcreteandMasonryElements

StaticLoadTesting

CONFINED UNCONFINED

Source:ACI355.Y


TestingforAdhesiveAnchorsASTME151201(reapproved2007)

StandardTestMethodsforTesting

BondPerformanceofBondedAnchors


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ASTME151201CreepTest

TestSeries

Static

load

test: 75Fand110F

Sustainedloadtest:

110F

40%meanstaticload

42days(1000hours)

DataAnalysis

Logarithmictrendlineto600days

(last20datapoints)

ASTME151201CreepTest

Duration ofload t [hours]

Displacement[mm]

2000

600

days

1000 4000

1000 Duration of load t

[hours]

2

1

2

Displacement[mm]

Detail A

Detail A

data points used for extrapolation

log function extrapolation

600

Duration ofload t [hours]

Displacement[mm]

2000

600

days

1000 4000

1000 Duration of load t

[hours]

2

1

2

Displacement[mm]

Detail A

Detail A

data points used for extrapolation

log function extrapolation

600

Source:EligehausenandSilva(2008)


TestingforAdhesiveAnchors

ICCESAC58&AC308

ACI355.Y

ICCESAC58

Displacement

Load

Nu75

u75 Displacement

Load

Nu110

u110

Static Tension Test @ 75F (24C) Static Tension Test @ 110F (43C)

Time

Displacement

600 days

Creep Test Series @ 40% Nu75

and 110F (43C)

u110& 0.12 (3.0mm)

0

creep

0+ creep u110& 0.12 (3.0mm)

Displacement

Load

Nu75

u75 Displacement

Load

Displacement

Load

Nu75

u75 Displacement

Load

Nu110

u110

Static Tension Test @ 75F (24C) Static Tension Test @ 110F (43C)

Time

Displacement

600 days

Creep Test Series @ 40% Nu75

and 110F (43C)

u110& 0.12 (3.0mm)

0

creep

0+ creep u110& 0.12 (3.0mm)

* The mean ultimate loads associated with standard temperature and elevated temperature conditions are used for the

sustained load tests at room temperature and elevated temperature, respectively.** The calculated estimated displacement service for any one test may not exceed 1.2lim

TestCondition AC58 AC308

Statictensionload *

Temperature(s) duringtest 110F(43.3C) standard(room)temp.

max.shorttermelevatedtemp.

Durationoftest min.42days min.42days

Extrapolationperiod 600days(elevatedtemp.) 50years(roomtemp.)

10years(elevatedtemp.)

Extrapolationmethod Logarithmic Findley

power

law

Residualcapacity Notestrequired Testanchorsintensiontofailure

followingapplicationofsustainedload

Acceptancecriteria

**

Residualload:

u,stdtemp

0.40 N u,stdtemp

0.55 N

( t ) a ln t b0 b

( t ) a t 0

u,elevated temp(600days) min

3mm

lim,roomtemp

lim,elevatedtemp

(50 yrs)

(10 yrs)

req=0.90

ICCESAC58&AC308Comparison


DataProjectionComparisons

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 20000 40000 60000 80000 100000 120000

Displacement[mm]

Duration of load [hrs]

AC308 (Findley) projection

AC58 logarithmic projection

Measured displacements

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 20000 40000 60000 80000 100000 120000

Displacement[mm]

Duration of load [hrs]





~12.5yrs


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DataProjectionComparisons

y = 0.1629Ln(x) - 0.7079

y= 0.018x0.4565

0

1

2

3

4

5

6

0 50000 100000 150000 200000 250000

D

isplacement[mm]

Dur




y = 0.1629Ln(x) - 0.7079

y= 0.018x0.4565

0

1

2

3

4

5

6

0 50000 100000 150000 200000 250000

D

isplacement[mm]

Dur




Source:Eligehausen andSilva(2008)

~27yrs

Duration of load [hrs]Duration of load [hrs]

ProjectionMethod

SECONDARYPRIMARY TERTIARY

INTIAL PLASTIC DISPLACEMENT

INTIAL ELASTIC DISPLACEMENT

TIME

DISPLACEMENT

X

RUPTURE




TIME

DISPLACEMENT

X

RUPTURE

ActualResponse




TIME

DISPLACEMENT

X

RUPTURE




TIME

DISPLACEMENT

X

RUPTURE

Time (Days)

0 10 20 30 40 50 60 70 80

Displacement(inch)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

#9-40

92lbs

#10

-401

4lbs

#8 - 4081 lbs

#7 - 4080 lbs

LaboratoryAnchorTesting

Source:FHWATFHRC

Anchorsloadedat4000pounds

StressversusTimetoFailure

TestMethod

AASHTOTP84

SampleStressversusTimetoFailure


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StressversusTimetoFailure

Precedent

ASTMD468098WoodtowoodadhesivesASTMD178005Metaltometaladhesives

ASTMD229496Metaltometaladhesives

ASTMD299001Plastics

AASHTOTP84TestProcedure

110Felevatedtemperature

5staticloadtests Determinemeanstaticload(100%)

6sustainedloadteststofailure

3at75%meanstaticload

3at65%meanstaticload

Definefailureasinitiationoftertiarycreep

Plotonstressversuslogtimetofailuregraph

Extrapolatelinearlinethroughpoints

StressversusTimetoFailureGraph

Source:Eligehausen etal.(2010)

Advantages

Resultsusefultothepracticingengineer

Reductionfactorforsustainedload

IncorporationofexistingICCESAC308data

Manufacturerscanqualifyabovecurrentpass/failcriteria

Removesuncertaintywithprojectionmethods

Platformforevaluatinglongtermeffects

CurrentResearchEfforts

NCHRPProject0437

LongTermPerformanceofEpoxy

AdhesiveAnchorSystems

ParametersIncluded

Increasedservicetemperature

Horizontalinstallationdirection

Verticalinstallationdirection

Moistureduringinstallation

Moistureduringservice

Reducedholecleaning

Reducedinstallationtemperature

Reducedservice

temperature

Anchordiameter

Typeofholedrilling

Concretecomposition:

Withblastfurnaceslag

Withflyash

Unconfinedsupport

condition


7/12

10/21/20

CalculationofReductionFactor

DISPLACEMENT

LOAD

NBL

NVARIABLE

NBL

NVARIABLE=

EvaluationofLongTermSensitivity

0.01 0.1 1 10 100 1000 10000 100000 1 000000

Log Time (hr)

PercentofBaselineShort-termLoad

100

-BASELINE

VARIABLE HAS NO EFFECT ON

SUSTAINEDLOADOVER TIME(COLINEAR TO -BASELINE)

VARIABLE HAS IMPACT ON

SUSTAINED LOADOVER TIME

(STEEPERTHAN -BASELINE)

BASELINECURVE

Acknowledgements

Todd M. Davis

[email protected]

QuestionsorComments?

Rolf Eligehausen is Professor, University of

Stuttgart Institute of Construction Materials, in

Stuttgart, Germany. He is an active member of

ACI Committees 349 (Concrete Nuclear

Structures), 355 (Anchorage to Concrete), and

408 (Development and Splicing of Deformed

Bars).

UniversityofStuttgart

InstituteofConstructionMaterials

Bonded anchors under sustained tension loadsBonded anchors under sustained tension loads

Behavior, testing and design of

bonded anchors under sustained

tension loads

ACI Spring 2010 Convention

March 21-25, 2010Chicago, IL, USA

by

Rolf Eligehausen, Ronald Blochwitz, Werner Fuchs

Institute of Construction Materials

University of StuttgartUniversityofStuttgart





Content

Introduction

Assessment of the behavior of bonded

anchors under sustained loads according to

ICC-ES AC308 and ACI 355.Y

Test resul ts

Evaluation of sustained bond strength

measured with the procedure according to

ICC-ES AC308 and ACI 355.Y

Design of bonded anchors according to the

provisions proposed for ACI 318, App. D

Conclusions

Content


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10/21/20




On July 10, 2006, partial collapse of the ceiling

system in the I-90 Seaport Tunnel in Boston occurred

On July 10, 2007, the NTSB issued its final report1)

.

Main conclusions and recommendations:- The collapse was caused by creep failure of

the adhesive anchors installed overhead and

subjected to sustained tension loading

- Insufficient understanding on the part of

designers and builders regarding the nature of

adhesive anchoring systems

- Lack of standards for testing of adhesive

anchors in sustained tensile load applications

-

1) National Transportation Safety Board, Accident Report No. NTSB/HAR_07/02 Ceiling Collapsein the Interstate 90 Connector Tunnel, Boston, Massachusetts, July 10, 2006, July 10, 2007 U

niversityofStuttgart



On July 10, 2007, the NTSB issued its final report.

Main conclusions and recommendations:

- Prohibit the use of adhesive anchors in

sustained tensile-load overhead highway

applications where failure of the adhesive

would result in a risk to the public until testing

standards and protocols have been

developed and implemented that ensure the

safety of these applications.

Un

iversityofStuttgart



Test procedures and assessment criteria

for bonded anchors

ICBO-ES AC58 Acceptance Criteria for Adhesive

Anchors in Concrete and Masonry Elements was

published in 1995. AC58 contains creep tests.

However, they are optional. AC58 for bonded

anchors in concrete has been replaced by AC308

ICC-ES AC308 Acceptance Criteria for Post-

Installed Adhesive Anchors in Concrete Elements

was first published in 2005. Creep tests are

mandatory.

ACI 355.Y Acceptance criteria for Qualification of

Post-Installed Adhesive Anchors in Concrete is

based on ICC-ES AC308. It is expected that the

standard will be published in 2011

Un

iversityofStuttgart



ICC-ES AC308 and ACI 355.Y creep

test procedure

Test one anchor size (d = 12 mm (1/2 in.)) at

standard and maximum long-term elevated

temperature (43C (110F)).

Nsust = 0.55 Nu,mNu,m = mean failure load for pullout failure

measured in unconfined tests at the test

temperature.

Type of support for creep tests not defined.

Usually they are performed confined.

Measure creep displacements over at least 6

weeks (1008 hrs).

After creep test, measure the residual capacity

using a confined test setup




a) b)

Test set-up for

unconfined testsTest set-up for

confined testsUniversityofStuttgart



Test set-up for creep tests (schematic)

LVDT ea. side

temperature-

controlled

chamber

spring dashpot

a) Unconfined test configuration

spring dashpot

LVDT ea. side

temperature-

controlledchamber

spring dashpot

LVDT ea. side

temperature-

controlledchamber

b) Semi-confined test configuration

spring dashpot

LVDT ea. side

temperature-controlled

chamber

1.5 do

do

spring dashpot

LVDT ea. side

temperature-controlled

chamber

1.5 do

do

c) Confined test configuration

Unconfined Semi-confined Confined


9/12

10/21/20




ICC-ES AC308 and ACI 355.Y:

Assessment criteria for creep tests

Extrapolate the measured creep displacements

using the Findley Power Law to 50 years(standard temperature) or 10 years (elevated

temperature), respectively

m (50 years) m,adh (room temperature)

m (10 years) m,adh (elevated temperature)

(extrapolated) for any test 1.2 m,adh

m,adh = mean displacement at loss of adhesion

measured in confined short-term reference tests

u (residual) 0.9 u (reference)UniversityofStuttgart



Findley Power Law (1976)

The Findley Power Law was developed for plastics

(e.g. polyamide) under tension load and modified

for bonded anchors(t) = t=0 + a t

b

(t) = displacement at time t

t=0 = displacement at t = 0

a,b = constants

t = time

The constants a and b are evaluated from the

measured creep displacements by regression

analysis. The Findley Power Law is a straigh t line

when plotted in double-logarithmic scale.

Un

iversityofStuttgart



Evaluation of displacement at loss of adhesion

adh adh

Nu

NuNadhNadh

displacementdisplacement

load N load N

0.3Nuk

k/1.5

Un

iversityofStuttgart



ICC-ES AC308 and ACI 355.Y:

Assessment criteria for creep tests

If the requirements on displacement behavior are not

met, the creep tests must be repeated with a reduced

sustained load until the requirements are met

The characteristic bond strength given in the

Evaluation Report will be reduced

k = k,0

where

k = bond strength given in Evaluation Report

k,0 = characteristic bond strength evaluated

from results of short-term tests

= Nsust,red / Nsust,req




0.1

1

1 10 100 1000 10000 100000 1000000 10000000

Time [hrs]

Displacem

ent

[mm]

measured values

extrapolation

acc. to FINDLEY

m,lim

m,lim= mean displacement at loss of

adhesion from confined tension tests

period:

50 years

(= 20C / 68F)

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

100

101

102

103

104

105

106

107

Assessment of creep behavior according to ICC-ES AC308 and ACI 355.Y UniversityofStuttgart



Validity of current method to predict

creep behavior

Assumptions

Long-term behavior can be predicted by creep

measurements over a short time (~1000 hrs) All factors influencing the short-term bond

strength will influence the long-term bond

strength to the same degree

Creep behavior is not influenced by type of

support (confined, unconfined)

Assessment criteria (extrapolation by Findley

Power Law, limiting displacement) are correct


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10/21/20




a) b)

u (unconfined) ~ 0.75 u (confined)

Confined creep tests:

Nsust ~ 0.75 0.55 Nu,m (confined)

~ 0.41 Nu,m (confined) UniversityofStuttgart



Comparison of measured and extrapolated creep

displacements (Eligehausen, Silva (2008))

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 20000 40000 60000 80000 100000 120000



0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 20000 40000 60000 80000 100000 120000

Findley projection


Injection anchor M12,

fc 29 N/mm,

Nsust~ 0,41 Nu,m

20000 40000 60000 80000 100000 20000

Duration of load [ hrs ]

00

0.2

0.4

0.6

Displacement[mm]

0.8

1.0

1.2

1.4

Un

iversityofStuttgart



Comparison of measured and extrapolated creep displacements.

Bonded capsule anchor M12. Test results provided by Hilti.

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0 50000 100000 150000 200000 250000

Measured displacement, test 1

Measured displacement, test 2

Approximation, test 1, 2000 h




sustained load tests with bonded capsule anchor

Duration of load [ hrs ]

Displacement

[mm]

25years

Un

iversityofStuttgart



Comparison of measured and extrapolated creep displacements.

Bonded expansion anchor M12. Test results provided by fischerwerke.

0.00

0.50

1.00

1.50

2.00

2.50

0 10000 20000 30000 40000 50000 60000 70000 80000 90000 100000

Duration of load [hrs ]

Displacement

[mm]

Sustained load tests with bonded expansion anchorM12x100

cracked concretew = 0,3 mmfcc,150= 21,9 N/mm

Nsust= 20,3 kN ~ 0,5 Nu,m

Test 1

Test 2

Findley projection

Findley projection

measured

measured




Load-displacement relationships of bonded injection anchors M12 measured

in confined reference tests. Anchors were also tested in creep tests.

0

20

40

60

80

100

120

0.00 0.50 1.00 1.50 2.00

Verschiebung [mm]

Kraft[kN]

1 2

3

V8.56

Displacement [mm]

L

oad[kN]

Displacement atloss of adhesion:

adh,m1,0 mm

Confined referencetension tests

Confined reference

tension tests

Epoxy resin

= 43C (110F)d = 12 mm

hef= 80 mm




0,1

1,0

1,E-03 1,E+00 1,E+03 1,E+06 1,E+09 1,E+12

Time to Failure [h]

Tau/

Tau,u

(ref)[-]

tests to failure

no failure during test

time to failure extrapolated

tests notused for regressionanalysis

regression

10 years

Tests extrapolated acc. to

FINDLEY.

Failure displacement = mean

failure displacement during

creep tests (2,7 mm).

0,1

1

10

1 ,E -01 1 ,E+0 0 1 ,E+0 1 1 ,E +02 1 ,E +03 1 ,E+0 4 1 ,E+0 5

Versuchsdauer [h]

Dbelverschiebung[mm]

10-1

100

101

102

103

104

0.1

0.5

1

5

10

Anchordisp

lacement[mm]

Time to failure [hrs]

Failure displacement: ~2.1 mm

105

2.1

measured

displacemen

t

Measured creep displacements (confined support) and

evaluation of the failure displacement

Epoxy resin

= 43C

(110F)d = 12 mm

hef= 80 mm


11/12


12/12

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Adhesive Anchors Part 2A