Adhesive Anchor Systems

1www.ca.hilti.com Adhesive Anchor Systems / Fall 2007

test


John Sandmoen, P. Eng. November 7, 2007

Edmonton, AlbertaEdmonton, Alberta


Adhesive Anchoring Systems


Situation and Objectives

What is Creep

Effects of Temperature

How is Creep Tested AC58 vs AC308

Product Performance

Effects of Installation Conditions

What Does or equal Really Mean

Summary

Content


Boston - Big Dig Tunnel Failure


Situation

Key message of the synopsis of NTSB report HAR-07-02 regarding the fatal accident in the Big Dig tunnel:

Insufficient understanding among designers and builders of the nature of adhesive

anchoring systems


The NTSB report concluded that poor creep resistance of the adhesive anchor was the primary contributor to the anchor failure

The report also states that the anchors were not installed correctly and that this influenced their capacity significantly

Situation

The Adhesive Anchoring System that failed in the Big Dig tunnelwas not a Hilti product


What is Creep?

Everything flows (Heraclitus ~500 BC)


What is creep?

Creep is the slow and continuous deformation of a material under a sustained stress and is mainly influenced by:

material / product load level & duration of loading temperature installation

Creep is a typical behavior of construction materials that needs to be considered for design


Key pillars of Creep behavior

Load (ASD) / Design Resistance (LSD)

Installation temperature and in-service temperature

Hole condition, hole cleaning, adhesive injection

Creep behavior

Properly installed adhesive anchors in properly designed applications are extremely reliable


Creep behavior of Adhesive Anchoring Systems

Adhesive anchors exposed to sustained tension loads must have sufficient creep resistance for long term loading

Rule of thumb: A higher temperature, a higher sustained load or a longer duration of loading increased creep displacement

The creep displacement rate significantly decreases over time for a properly selected, designed and installed anchor viscoelastic behavior

Creep of Adhesive Anchoring Systems under sustained tension loads can be described as viscoelastic behavior


The creep displacement rate significantly decreases over time the displacement stabilizes

Creep Basics

Time t

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Initial elastic displacement: s0

Creep displacement: screeptime dependent

Total: s(t) = s0 + screep (t)Load N is applied

Load N is maintained

Load N = 0


Effects of Temperature


Effects of temperature on Adhesive Anchoring Systems

Temperature influences have to be considered throughout the lifecycle of an Adhesive Anchoring System:

Installation Lifetime (in-service)Storage

StorageObserve Manufacturersrecommended storagetemperature

InstallationDispensing forcesWorking timesCure timeLoad values

In-ServiceShort TermLong Term (creep)Fire

Temperature must be considered for Adhesive Anchoring Systemsfor the various stages of the fastenings lifecycle

AdhesiveAdhesive &

base material Base material


During Installation:

Elevated installation temperature: Faster curing Shorter working time Lower dispensing forces

Low installation temperatures: Slower curing Longer working time Higher dispensing forces


Observe Manufacturers installation instructions (IFU)


During the Lifetime (In-Service temperatures):

Elevated in-service temperature: May cause decreased short and long term resistance (lt = creep) May lead to higher displacements Consider fire resistance of the fastening

Low in-service temperature: Freeze-Thaw conditions need to be considered Limited effect on properly installed and cured adhesive


Temperature must be considered for design


How was the creep behavior tested?

(Spring pots for sustained loading)


Test Methods / Acceptance Criteria

Adhesive anchor performance is objectively evaluated through:

ASTM E 1512 Standard Test Methods for Testing Bond Performance of Bonded Anchors

ASTM E 488 - Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements

AC 58 (USA) Acceptance Criteria for Adhesive Anchors in Concrete and Masonry Elements (January 1995 to Present)

AC 308 (USA) Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements (July 1, 2005 to Present)

AC 308 developed prior to the Big Dig accident it was

NOT a response to that specific event.


Creep Test in AC 58

A standard method to test and evaluate the creep behavior of Adhesive Anchoring Systems can be found in ICC-ES AC58

AC58 was introduced in January 1995

More than 25 different products from various manufacturers have been tested and evaluated

The NTSB expressed no concern or criticism in AC58 qualifying suitable creep-resistant adhesives, instead stating that failing AC58 testing indicated an adhesive's inappropriateness for sustained-loading applications

The creep test was optional

The test method under AC58 is appropriate for identifying the general suitability of Adhesive Anchoring Systems for sustained tension loads


Examples for possible creep test curvesD

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Passed

Not acceptedFailed

600 days

Limit acc. to AC58: su or 0.12 in.

42 d (test period)

Test data Extrapolation


Test requirements and technical data (AC58)

Temperature influences on Adhesive Anchoring Systems were evaluated according to AC58, ASTM E 1512 and ASTM E 488:

Short term tension tests

Installation temperature In-service temperature

Required

Long term tension tests

Creep test Freeze thaw test Pass / fail criteria only

Optional

AC58 evaluated temperature effects for installation and in-service conditions



0 50 100 200

100%AC58 range

110(0F)

50%

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Creep test at 110 0F

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AC58 - regardless of maximum temperature, creep test performed @ 110 0F

Product BProduct A



Note: Test procedures involves the concrete being held at the elevated temperature for 24 hours, then removed from the controlled environment and tested to failure.Applies to both tension and shear loads (AC58)

HIT HY 150 MAX IN-SERVICE TEMPERATURE

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0 50 100 150 200Temperature, F

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Installed @ 70 F Installed @ 14 F


How was the creep behavior tested AC58

Determine sustained tension load:=> Ultimate load at 70F Nu x 0.4

Apply load / measure displacement:

For 42 days at 110F

Determine displacement criteria:

=> su at ultimate load at 110F

Extrapolate displacement (600 days):=> stotal = c ln t + b

Conditions of acceptance stotal < su

passed:

Safety factor 4

Allowable load

= Nu / 4

not passed

Safety factor

5.33 (UBC)6.67 (IBC)

Product not permitted for sustained loads

ESR-TextExample:The allowable load values for the Adhesive installed with threaded rod or fully threaded bolts is permitted for short-term loads, such as those resulting from wind or earthquake forces only.

Product permitted for sustained loads

A product could get an AC58 ICC-ESR without passing a creep test (optional!).The product was consequently limited to short term load.


AC58 AC308

Temperature evaluation principles evolved



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Time

Maximum Long Term temperature

Maximum Short Term temperature

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100%

Service temperature range is more specific in AC308 than AC58:

night

day

AC308 links short term temperatures to long term temperatures



60%

1630 50 100 200

100%AC308 range

115

50%

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150 250

AD308 - creep test temperatures linked to maximum published temperatures

Product BProduct A


Define maximum Short Termservice temperature

Max. Long Term temperature 0.6 x max. ST temp. [C]

Reduction factorShort term st

Static short termtension tests

Creep test (max. Long Term temp.)s(t) < su,adh & Nresidual > 0.9 x Nreference

Reduction factorLong term lt

passed Not passed

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Creep Test done (any additional reduction factor applies to the characteristic bond strength)

Applied load:~ 0.55 / (0.65x0.75/1.4) ~ 160% of design load converted to ASD load

Note:AC308 permits options to attain sustained load status at some reduced load capacity or temp. range!

How is creep tested now AC308


Current Acceptance Criteria Why Change?

Creep test mandatory

Product can pass with reduced published load and or published temperature range

Test temperature determined through published service temperature range

Extrapolation to 10 years (elevated temp.)

50 years (normal ambient temp)

AC308

Application oriented evaluation

Pass / Fail

better coverage of relevant time periods

Extrapolation to 600 days only

No backdoor or misunderstanding

Creep test optional

Wider temperature ranges possible

Test temperature fixed (110F)

BenefitAC58

AC308 creep test is mandatory and published technical data directly depend on the result of creep tests

AC58 has evolved into AC308. The main developments:


Main reasons for the need of a new creep test criteria:

More experience with Adhesive Anchoring Systems

Extrapolation of displacement for longer periods necessary

New design concept (Limit States Design) requires new test concept

More specific consideration of temperature effects & installation conditions

AC308 creep test criteria matches the Limit States Design conceptand represents the current experience with Adhesive Anchoring Systems

State of the Art Acceptance Criteria AC308


Fast Cure vs. Slow Cure:

There are two different basic resin types / reaction mechanisms that are currently used for chemical anchoring systems:

Polymerization Acrylate: shorter curing time (Fast Cure)

Polyaddition Epoxy: longer curing time (Slow Cure)

There are some Epoxy based products that are chemically accelerated in order to achieve faster curing (Fast Cure Epoxies)

Creep performance cannot be generalized for a basic resin type

How do products perform in creep tests?

Creep performance can only be determined by testing and evaluation in accordance with the available state of the art (AC58, AC308)


HFX (A, internal)

HIT-ICE (A, internal)

HIT-RE 500(EP, ESR-1682)

HIT-HY 20 (A, ER - 4815)

HIT-HY 150 (A, ER-5193)

HIT-HY 150 MAX (A, ESR-1967)

HVU (A, ER-5369)

HIT-HY 10 (A, internal)

How do Hilti products perform in

creep tests?

Hiltis current product portfolio passed an AC58 creep test:

(A=Acrylate, EP=Epoxy)

Hiltis current product portfolio passed an AC58 creep test

HIT-C100, HVA [glass capsule], HSE2421, HIT-C20, HIT-C10 have pass creep testing as well


HIT RE 500 SD(EP, Internal)

How do Hilti products perform in creep tests?

Hiltis RE 500 SD passed an AC308 creep test:

(EP=Epoxy)

Hiltis current portfolio continues to undergo testing to AC308 test standards


Creep Testing

Hiltis Expertise: Some creep tests with an Adhesive Anchoring Systems have been already running for the last 27 years and continue


Effects of Installation


Performance of adhesive anchors are related to

installation procedures and accessories

Blow-out pump

Compressed-air gun

Compressed-air gun+ air nozzle

Bristle Brush

Steel Brush

Injection nozzle

Injection extension

Piston plugs

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Blowing out Brushing Injecting


Cleaning is required by bonding mechanisms between concrete and adhesive

Choice of cleaning procedure is determined by:Base material conditionsDrilling methodsMortar characteristics

Application geometry (e.g. drilling depth, borehole, )

Dust, water and other external participles present at the bond interface hinder the bonding mechanisms

=bb

=beBond stress, adhesive & base matl

Bond stress, adhesive & element


Resulting borehole conditions vary greatly depending on cleaning method


Adhesive Injection

Improper injection can result in air voids within the borehole

Air voids may cause inconsistent behavior : Reduced bond surface may affect performance Distribution of stresses in base material is uneven Air voids may not protect rod/rebar from corrosion


Anchor Installation Accessories

Air diffusers / nozzles to be used in conjunction with compressed

air to maximize dust removal from bore hole

Wire brushes Chucks into hammer drill for cleaning large

diameter holes

Hose extensions and piston plugs Reduces risk of air voids Confidence when injecting into deep holes


Hilti Profi Kit Boxes

Developed to increase the reliability of the fastening to enablemaximum performance.

Made for anchor and rebar installations


MD 2500

Injection and blowing elongations

Air nozzles

Piston plugs

Steel Brushes and extensions

HIT Setting Instructions

Box for small elements

Safety goggles

Installation Rebar Protocol

HIT Profi case

Air gun

PROFI Kits Help Ensure Proper Installation


..\..\Movies\Anchors\Adhesive Anchors\Cleaning and overhead produced in Canada\InjectionEng.wmv

Overhead Installation Video


What is or equal?

There is no such thing as or equal based on just loads. When specifying, consider:

Whether the products have or have not been qualified for sustained tensile loads

Limitations in regards to in-service and installation temperature

Freeze / Thaw Resistance

Chemical Resistance

Include requirement for manufacturer installation training


What is or equal?

Suggested specification

We recommend the following or equal clause:

Use Hilti [adhesive anchor] or equal considering load resistance, in-service and installation temperature, availability of comprehensive installation instructions, and creep


Hilti production

Expertise in R & D

With you during and

after the spec

On the job. Everyday.

Our anchors are just that, our anchors and are manufactured to the tightest standards at Hilti production facilities around the world

Over the last 40 years, Hilti has invested hundreds of millions of dollars into the research and development of adhesive and mechanical anchoring solutions

More than 2,000 Hilti reps on the job everyday

More than 100 strong, our technical services team is in the office and also on the job consulting, testing and teaching

Equal to isnt the Hilti Difference

People, products and our development process has made Hilti the industry leader

Testing and technical approvals

Five testing and development centers held to stringent standards


Summary

An adhesive anchorage that is properly qualified, designed and installed is appropriate for resisting sustained long-term loading

Hilti's current adhesive products pass AC58 creep testing. RE 500-SD passes creep testing under AC308.

AC308 was developed prior to the Big Dig accident. AC308 have been harmonized with the latest state of the art to reflect the changed design environment associated with Limit States Design methods

Consider adhesive anchoring a SYSTEM its NOT just load so consider freeze thaw and chemical resistance, creep, temperatureand installation conditions when designing and reviewing for or equal


For additional information please contact:

John Sandmoen1-800-363-4458 or 780-458-1808

Or visit www.ca.hilti.com

People, products and our development process has made Hilti the industry leader

Documents

Adhesive Anchor Systems