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test
2www.ca.hilti.com Adhesive Anchor Systems / Fall 2007
John Sandmoen, P. Eng. November 7, 2007
Edmonton, AlbertaEdmonton, Alberta
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Adhesive Anchoring Systems
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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
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Boston - Big Dig Tunnel Failure
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Boston - Big Dig Tunnel Failure
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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
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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
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What is Creep?
Everything flows (Heraclitus ~500 BC)
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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
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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
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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
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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
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Effects of Temperature
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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
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During Installation:
Elevated installation temperature: Faster curing Shorter working time Lower dispensing forces
Low installation temperatures: Slower curing Longer working time Higher dispensing forces
Effects of temperature on Adhesive Anchoring Systems
Observe Manufacturers installation instructions (IFU)
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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
Effects of temperature on Adhesive Anchoring Systems
Temperature must be considered for design
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How was the creep behavior tested?
(Spring pots for sustained loading)
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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.
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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
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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
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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
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Test requirements and technical data (AC58)
0 50 100 200
100%AC58 range
110(0F)
50%
%
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Creep test at 110 0F
250
AC58 - regardless of maximum temperature, creep test performed @ 110 0F
Product BProduct A
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Test requirements and technical data (AC58)
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
0
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60
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0 50 100 150 200Temperature, F
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Installed @ 70 F Installed @ 14 F
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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.
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AC58 AC308
Temperature evaluation principles evolved
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Test requirements and technical data (AC308)
T
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Time
Maximum Long Term temperature
Maximum Short Term temperature
60%
100%
Service temperature range is more specific in AC308 than AC58:
night
day
AC308 links short term temperatures to long term temperatures
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Test requirements and technical data (AC308)
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
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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
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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:
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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
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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)
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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
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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
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Creep Testing
Hiltis Expertise: Some creep tests with an Adhesive Anchoring Systems have been already running for the last 27 years and continue
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Effects of Installation
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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
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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
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Resulting borehole conditions vary greatly depending on cleaning method
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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
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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
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Hilti Profi Kit Boxes
Developed to increase the reliability of the fastening to enablemaximum performance.
Made for anchor and rebar installations
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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
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..\..\Movies\Anchors\Adhesive Anchors\Cleaning and overhead produced in Canada\InjectionEng.wmv
Overhead Installation Video
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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
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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
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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
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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
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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