5-81 A to oncrete - California Department of Transportation

5-81AnchorAge to concrete 1

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Bridge design Aids 5-81 • JAnuAry 2012

5-81 AnchorAge to concrete

1.IntroductionSteel-to-concrete or concrete-to-concrete connections can be accomplished through theuseofseveraltypesofanchoragesystems.ThisdesignaiddescribestheconcreteanchorsystemsthataremostwidelyusedonCaltrans’jobsandassiststhedesignerinselectingthesystemthatisbestsuitedforaparticularapplication.

2.AnchorSystemsandDesignCriteriaThereare twobroad typesofanchorsystems–post-installedanchorsandcast-in-place(CIP)anchors.

The design recommendations for post-installed anchors in this aid conform tothe requirements in the California Amendments to AASHTO LRFD Bridge Design Specifications.

For CIP anchors, the design recommendations are based on ACI 318-08 as well asCalifornia AmendmentstoAASHTO LRFD Bridge Design Specifications.

Thedesignershoulddeterminetheloadingcombinationsandthecorrespondingloadfactorsforeachapplication.

3.Post-InstalledAnchorsThistypeofananchorisinstalledinaholethatisdrilledinhardenedconcrete.Therearetwomain typesofpost-installedanchors–MechanicalExpansionAnchors (MEA)andBondedAnchors.

3.1MechanicalExpansionAnchorsMEAsare inserted inpre-drilledholes.These anchors expandandbear against theconcretesurfaceandareplacedusinganyofthefollowingtechniques:

a) Hammeringtheanchor(deformationcontrolled)b) Tighteninganut(torquecontrolled)c) Expandingintoanundercut(expandingintoanotchedopeningatthebottomof ahole).


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MEAsarefrequentlyusedtoanchorminorortemporaryattachmentssuchassigns,brackets, inspection ladders, safety railing, utility pipes and light fixtures to hardened concrete.MEAshavethefollowingadvantages:

● Areinexpensive● Arequickandeasytoinstall● Canbeinstalledinanyorientation● Loadingcanbeappliedimmediatelyafterinstallation

MEAshavethefollowingdisadvantages:

● Haverelativelysmalltensilestrength● Arenotrecommendedforuseintensionzonewhereconcreteislikely tocrack● Arenotsuitableforresistingdynamic(vehicleloading,seismicetc.)or vibratoryloads

Materialsand installationmethodsofMEAsmustcomplywith the requirementsofSection 75 of the Standard Specifications. Designers should refer to the Caltrans’“Authorized Materials List”foralistofapprovedMEAs.

BasedontestsperformedattheTransportationLaboratory(Translab) by the Office of StructureMaterials,METS,thefollowingtwotypesofMEAsarecurrentlyapprovedforuseonCaltrans’projects[JohnP.DuselandCraigN.Harrington,1986]:

a) Shellexpansionanchorwithinternalthreads– Thisanchorrequiresanindependentstud,nutandwasher,andisstrongerin tensionthanothertypesofshellanchors.

b) Integralstudanchor(wedgetypeandexternalplug)– Thisanchor,whichisfurnishedwithnutsandwashers,iseasiertoinstallina multi-holebaseplateandisstrongerinshear.

Figure3.1-1showssomecommontypesofMEAs.

Withpriortesting,othertypesofMEAs(example:undercutanchors)maybeapprovedforuseonCaltrans’jobs.Whileundercutanchorsarerelativelymoreexpensivethanshellandstudtypeanchorssinceadditionaldrillingisrequired,theyarebettersuitedfordynamicloads.


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Self-drillingMEAs,becauseofapotentialforfatigue-relatedcrackinginthehardenedskirt,arenotapproved.StudsleeveanchorsarealsonotapprovedbecausetheyhaveexhibitedlargedisplacementsintheTranslabtests.

Undercertainconditions,ResinCapsuleAnchors(asdiscussedinalatersection)mayalsobeusedasanalternativetoMEAs.

Independent stud

Expander plug

Shell body

Face of Concrete

Member

Nut and washer

Depth of recessto top of shell

1/2”

min

1” m

ax

Integral stud

Sliding collar

Typical Shell - Type MEA Typical Stud - Type MEA

Cone

Figure 3.1-1 Common Types of MEAs

3.1.1 Resistance (Design Strength)Generally,expansionanchorsthatareloadedintensionfailbyinitialslippingfollowedbyconcretecone failure.The tensile resistance (design tensionstrength)ofaMEAisbasedonitscreepperformanceratherthantheyieldstrengthofthematerial.Thisdesignstrengthcorrespondstoasustainedtensionload,thatwillcausetheanchortoslipatahigherrateastheloadincreases,multipliedbyaresistance(strengthreduction)factorof0.5.

Table3.1-1liststheshearandtensiledesignstrengthsofshellandstud-typeMEAs.

ThedesignstrengthslistedinTable3.1-1arevalidforthefollowingconditions:

a) Forstaticloadconditionsonly. Whendynamic loadinggovernsor forcritical applications suchas installations


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over traffic, CIP anchors should be the preferred option. If CIP anchors cannot be provided,thenResinCapsuleAnchorsorbondedanchorsmaybeconsidered.

b) Fornormalweightconcretehaving cf ′ =�000psi. Forotherconcretestrengths,multiplythevaluesinthetableby:

4000

)( actualf 'c

c) Foranedgedistanceof6dhorgreater(wheredhistheholediameterandis consideredequaltothenominaldiameteroftheanchorplus1/8").

Edgedistancecanbereduceddownto3dhifthedesignstrengthisalsolinearly reducedto50%.Anedgedistanceoflessthan3dhisnotrecommended.

d) Foracenter-to-centerspacingbetweenanchorsof12dhorgreater(i.e.,100%effective).Thisspacingcanbereduceddownto6dhifthedesignstrengthislinearlyreducedto50%ofthatshowninTable3.1-1.

e) Whenmultipleanchorsareusedtoholdanattachment.

IfasingleMEAisusedtoholdanattachment,thenthedesignstrengthsshownin3.1-1shouldbereducedby50%.

f) Whenananchorissubjectedtocombinedtensionandshearloading,thefollowingequation should be satisfied:

1≤+resistancetensileFactored

loadtensileFactored

resistanceshearactoredF

loadshearFactored

Table 3.1-1 Factored Resistance (Design Strength) for Shell and Stud-Type MEAs

Stud Diameter (inches) Shear Strength (kips) Tensile Strength (kips)

1/� 0.� 0.�

3/8 0.8 1.0

1/2 1.5 1.1

5/8 2.1 2.1

3/� 2.� 2.�


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3.1.2 Design and Detail GuidelinesTheDesignersshouldconsiderthefollowingissueswhenMEAsareselected:

a) ThePlansshouldshowthesizeofMEArequired,butnotshowthedepthorthediameterofthehole–thesizeoftheholeisaddressedintheStandard Specifications.Figure3.1.2-1showsatypicaldetailforMEAstobeusedinthePlans.

b) The thicknessofconcrete,whereananchor isembeddedshouldbeadequate toresist driving forces during anchor seating – typically, the minimum concretethicknessshouldbe1.5timesthedepthofembedment.

c) ToensureproperseatingofshelltypeMEAs,thetopoftheshellbodyistypicallyrecessedbetween1/2" and1" belowtheconcretesurface,andan independentthreadedstudratherthanaheadedboltisrequired.

d) As the design strength of shell and stud type MEAs is governed by creepconsiderations,themaximumanchorsizeislimitedto3/�inch.

e) Incorrosiveenvironments,useotheranchoragesystems.Whiletherearenopre-approvedMEAsforthisenvironment,stainlesssteelMEAsshouldbeconsideredonajob-by-jobbasis.

5/8” MechanicalExpansion Anchor

φ

Figure 3.1.2-1 Typical Detail for MEAs



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3.2BondedAnchorsBondedanchorsystemsincludethefollowing:

a) DrillandBondDowel:Magnesiumphosphate(mag-phos)isusedasabondingagent(seeSection51oftheStandard Specifications).

Mag-phosconcretehardensorcuresinaboutthreehoursanddoesnotrequireanyspecialtreatmentduringcuring.Italsodevelopsfullstrengthinthreedays.Mag-phoshasthefollowingadvantages:

● Hasrelativelyhightensilestrength● Hasquicksettingtime● Exhibitsminimalshrinkage.

Mag-phoshasthefollowingdisadvantages:

● Can not come into contact with zinc, aluminum, copper or cadmium (e.g.,Mag-phoscannotbeusedforgalvanizedanchors)

● Isnotlikelytobefullyeffectiveincrackedconcrete

b)DrillandGroutDowel:Neatportlandcementpaste(grout)isusedasabondingagent(seeSection51oftheStandard Specifications).

Generally,cementgroutislessexpensivethanmag-phosconcrete,butcuresmoreslowly.Grouthastobecuredforatleastthreedaysduringwhichtimethedowelsshouldnotbedisturbed.Thegroutnormallydevelops50%ofitsstrengthinthreedays,andreachesfullstrengthinabout28days.Inaddition,grouthasatendencytoshrink–leadingtocracks.

c) DrillandEpoxyBondDowel:Bulkepoxyisusedasthebondingagent.

This method of bonding anchors to concrete is no longer used in structuralapplications as several bulk epoxies exhibit high creep characteristics undersustainedtensileloads.Inadditiontheseepoxiesmayrequireexactmixratiosandaresensitivetofreeze/thawconditions.

d) DrillandBondDowel(chemicaladhesive):Achemicaladhesiveoracartridgeepoxyisusedasabondingagent(seeSection51oftheStandard Specifications).


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Theadvantagesofchemicaladhesivesinclude:

● Higherviscosity(thanmag-phosorgrout)thathelpstheadhesivetoberetainedinadrilledhole

● Relativelyquicksettingtime● Lowshrinkage

Oneofthedisadvantagesofthissystemistheneedforstringentqualitycontrolandqualityassurancetesting,particularlysincecreepdeformationscanbeaconcern.

Thechemicaladhesivesindrillandbondapplicationsmustbepre-approvedandlistedunderthe“Authorized Material List”priortouseonCaltrans’projects.

Bonded anchors provide a simple, effective, economical and preferred system forattaching metal fixtures or new concrete to existing/hardened concrete. In this system, bar reinforcement dowels or threaded rods are placed in drilled holes filled with either grout or a bondingmaterial.Typically, bonded anchors are used for attaching newbridgebarriers,signframesorelectroliersontoexistingbridgedecks,wideningbridgeabutments and bridge decks, and in seismic retrofits.

3.2.1 Applications Typical applications of different types of bonded anchors are discussed in thefollowing:

a) Ingeneral,drillandgrout,drillandbondordrillandepoxybonddowelsshouldbeusedonly inholesdrilledatadownwardangleofat least20degrees to thehorizontal–generallydetailedasa3:1slopeonPlans.

b) Drill and Bond (Chemical Adhesives) dowels should be used when a drilledholeata3:1slopecannotbeachieved.Inhorizontalholes,chemicaladhesivesshould always be used since the adhesives have a higher viscosity (example:indeckoverhangswherehorizontalholesmaybe theonlyoptiondue to smalldeckthickness).Thisanchoragesystemisnotrecommendedforuseinoverheadapplications.

c) Ingeneral,drillandbonddowelsshouldbeusedonlyinapplicationswheretensionistheprimaryforceintheanchor;grouting,withbondingasanoption,shouldbeusedwhenshearistheprimaryanchorforce.



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d) Theuseofbondedanchorsystemisnotrecommendedwhereseismicductilityiscritical(suchasinseismiccriticalelements).

e) Proportioning,mixing,andholepreparationforgroutingaremorecriticalthanthoseforothertypesofbonding.Therefore,theresistance(strengthreduction)factor(φ)foragroutedanchorislargerthanthatforothertypesofbondedanchors.

3.2.2 Resistance (Design Strength)TherecommendationsfortheuseofdifferenttypesofbondeddowelsandtheirdesignstrengthsarebasedonvariouspullouttestsperformedattheTranslab(AbidA.MirandJohnP.Dusel,1993).Tables3.2.2-1and3.2.2-2listthefactoredresistance(designstrengths)ofDrillandGroutdowelsaswellasDrillandBonddowels(bothmag-phosandchemicaladhesive)basedontheTranslabtests.

Theresistanceofbondedanchorsunderall limitstatesaredeterminedasdescribedbelow:

a) Resistance(designstrength)intensionissmallestofthefollowing:

● Ashort-termstaticloadthatcausesananchorsliporamovementof0.01 inch. ● Ashort-termdynamicloadthatcausesananchorsliporamovementof0.02 inch. ● φ*(theoreticalyieldstrengthoftheanchor),whereφ=0.5forgrouted anchorsand0.75forbondedanchors.

Note: For the design parameters shown in Tables 3.2.2-1 and 3.2.2-2, the tensilestrengthsofrebar(bothgroutedandbonded)aswellasthoseforgroutedanchorrodsare controlledby anchor slipwhile the tensile strengthsofbondedanchor rods arecontrolledbyyieldingofanchor.

b) ShearResistance(V)isdeterminedasfollows:

● Whentheminimumedgedistancetotheanchorisatleast10db(dbisthe nominalanchordiameter),then,

V=φ*(0.55*yieldstrengthofanchor);φ=0.8

Thisvalueofshearstrengthistheupperboundvalueforalltypesofbonded anchors.


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● Fordrillandbonddowels,whentheedgedistanceislessthan10db:

241 e'c df.V π= ≤ [ φ*(0.55*yieldstrengthofanchor)]

φ=0.8

Fordrillandgroutdowels,V iscalculatedusing thesameequationabove,but thevalueofde cannotexceed8db .Tables3.2.2-1and3.2.2-2havebeendeveloped for

cf ′ =�000psi.

Intheshearstrengthequationbasedonedgedistanceshownabove,Visinpounds(lb),theedgedistancedeisininches(in.)andtheconcretestrength cf ′ isinpsi.Afactorof0.7isincorporatedintothisequation.

c) EdgedistancethatissmallerthantheminimumedgedistanceshowninTables 3.2.2-1and3.2.2-2isnotpermitted.

d) Whenananchorissubjectedtocombinedtensionandshearloading,thefollowingequation should be satisfied:

1≤+

resistancetensileFactored

loadtensileFactored


loadshearFactored

Table 3.2.2-1 Factored Resistance (Design Strength) for ASTM A 706 Rebars (Grade 60)

Rebar Size

Minimum Edge

Distance-de(inches)

Minimum Embedment

Depth-le(inches)

Hole Diameter (inches)

Design Strength for Minimum de and le

(kips)

Design Shear Strength

(kips) (de ≥10 db)Tension Shear

Grout Bond Grout BondGroutand

Bond

Grout and

Bond

#5 3 5 7/8 11/8 3.1 10.5 2.5 8.2

#6 � 6 1 11/� �.� 1�.8 �.5 11.6

#7 � 7 11/8 13/8 6.0 20.3 �.5 15.8

#8 5 8 11/� 11/2 7.9 26.7 7.0 20.9



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Table 3.2.2-2 Factored Resistance (Design Strength) for ASTM A 307 Threaded Rods

Anchor Size

(inches)

Minimum Edge

Distance-de(inches)

Minimum Embedment

Depth-le(inches)

Hole Diameter (inches)

Design Strength for Minimum de and le

(kips)

Design Shear

Strength (kips)

(de ≥10 db)Tension Shear

Grout Bond Grout BondGrout and

Bond

Grout and

Bond

5/8 3 5 7/8 11/8 2.3 6.1 2.5 3.6

3/� � 6 1 11/� 3.3 9.0 �.5 5.3

7/8 � 7 11/8 13/8 �.6 12.5 �.5 7.3

1 5 8 11/� 11/2 6.1 16.3 7.0 9.6

3.2.3 Design and Detail GuidelinesTheDesignersshouldconsiderthefollowingissueswhendrillandbonddowelsareselected:

a) ThePlansshouldshowthetypeoftheanchor[e.g.,DrillandBondDowel(ChemicalAdhesive)],theanchorsizeandtheembedmentdepthrequired.ThePlansshouldnotshowthediameterofthehole–thisinformationisaddressedintheStandard Specifications.Figure3.2.3-1showstypicaldetailsforadrillandgroutdowelthatcanbeusedinthePlans.

Drill and grout#6 x 1’-6”@24

6”

8”

Figure 3.2.3-1 Typical Detail for Grouted Anchor


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b) The embedment depths listed inTables 3.2.2-1 and 3.2.2-2 are not necessarilysufficient to develop the yield strength of the anchor. Deeper embedments may provide the required ductility under certain conditions.Generally, holes havingtwotimestheminimumembedmentdepthforreinforcementbarsoroneandone-halftimestheminimumembedmentdepthforthreadedrodswilllikelydeveloptheyieldstrengthofananchor.Otherpotentialfailuremodessuchasconcreteconefailureorconcreteshearfailurehavetobeconsideredwhenadeeperembedmentisprovided.

c) For anchors spaced closer than two times the embedment length, the concretestrengthmaycontrolthedesignduetooverlappingofthefailurecones(seeFigure3.2.3-2).Thedesignstrength,basedontheconcretestrengthandthesurfaceareaofthefailureconeiscalculatedasfollows:

● Tensiledesignstrength(lb):

φ[2 'cf *(surface area of the failure plane)],

where, '

cf istheconcretestrength(inpsi)andφ=0.9. ● Sheardesignstrength(lb):0.5*[Tensiledesignstrength]

Formultipleanchors,thedesignstrengthcorrespondstothelowerofthetwovalues–thosebasedonconefailureorthoseobtainedfromTables3.2.2-1and3.2.2-2.Anyacceptablemethod(suchasthatbasedonACI318-08)mayalsobeusedtocalculateeffectivesurfaceareaofafailureplane.

d) Incorrosiveenvironment,stainlesssteelanchorsshouldbeconsidered.Galvanizedanchorsshouldnotbeusedwithmag-phosconcrete.

SeeMemotoDesigners9-3foradditionalexamplesontheuseofAnchors.



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Failure plane whenanchors are closer thanthe minimum spacing

Failure cone

ElevationFailure cone overlap

Potential failure plane

Plan

Figure 3.2.3-2 Effect of Anchor Group

3.3ResinCapsuleAnchorsAResinCapsuleAnchor (RCA) isa special typeofabondedanchorused tobondathreadedrodorarebarintohardenedconcrete.RCAsaretypicallyusedin-lieuofMEAs. They can also be used in-lieu of “Drill and Bond (ChemicalAdhesives)”anchors only if they conform to all the test requirements specified for a chemical adhesiveasdiscussedinSection3.2.1.

The RCA system is composed of a two-chambered glass/foil capsule that containstheresinandthecatalyst(hardener).Thesizeofacapsuledependsonthesizeoftheanchor.Thecapsuleisinsertedinaclean,pre-drilledholeofpropersize.Next,achisel-pointedthreadedsteelrodorrebarisattachedtoaroto-hammerandpowerdriventothebottomofthehole.Thisprocesswillbreakthecapsuleandmixitscontents.Themixedresincompoundformsastrongwaterproofbondwithboththeembeddedanchorandconcrete.

RCAscanbeloadedsoonercomparedtootherbondedanchorsbecauseoftheirshortcuretimes.IngeneralRCAscanbeusedinawidevarietyofapplicationsincludingin corrosive environments, or where dynamic loading is present. They are notrecommended for use under water or where fires are likely to occur.

Unless approved by the State Bridge Engineer, the use of RCA in an overheadapplicationisnotpermitted.


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3.3.1 Resistance (Design Strength)The design strengths of RCAs are based on limited pullout tests performed at theTranslab (AbidA. Mir and John P. Dusel, 1993) as well as data furnished by themanufacturersinthetestingprogram.

Thefactoredresistance(designstrengths),summarizedinTable3.3-1,arebasedonthefollowingcriteria:

a) They are controlled by creep deformations (for creep limits, see Section 75,Standard Specifications),andincludearesistancefactor(strengthreductionfactor)of0.33,bothfortensionandforshear.

b) TheyarebasedontestsusingASTMA307threadedrodsasanchors;thesestrengthsmayalsobeusedforothertypesofanchorsthathaveahigherstrength.

c) The anchors are assumed to be subjected to static load conditions only.Whendynamicloading(movingloads,vibratoryloadsetc)governs,theresistanceslistedinthetableshouldbemultipliedby0.5.

d) Theyarevalidforaconcretestrength( 'cf )of5000psi.For '

cf otherthan5000psi,theanchorstrengthisobtainedbymultiplyingthevalueslistedinTable3.3.1-1bythefollowingfactor:

5000

)( actualf 'c

e) Theyarevalidforconcretetemperaturesupto70°F.Atatemperatureof120°F,thedesign strengths reduce to approximately75%of those shown in the table.Forintermediatetemperatures,thedesignstrengthsshouldbecomputedthroughlinear interpolation. However, RCAs are not recommended where the ambienttemperatureislikelytoexceed120°F.

f) They are applicable when the center-to-center distance (spacing) between theanchorsisatleastequaltoitsstandardembedmentlength.SpacingcanbereducedtohalfthestandardembedmentdepthonlyifthedesignstrengthintheTableismultipliedby0.5.Forintermediatespacing,linearinterpolationmaybeused.

g) Theyareapplicablewhentheedgedistancetotheanchorisatleastequaltoitsstandardembedmentlength.TheedgedistancecanbereducedtohalfthestandardembedmentdepthonlyifthedesignstrengthintheTableismultipliedby0.7.Forintermediateedgedistance,linearinterpolationmaybeused.


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h) Whencombinedshearandtensileloadingispresent,thefollowingequationshouldbe satisfied:

1≤+resistancetensileFactored

loadtensileFactored


loadshearFactored

Ifnecessary,thedesignermayrefertotheCaltrans’“Authorized Materials List”andreviewmanufacturer’sbrochurestogetanupdatedestimateofdesignstrengths.Thecapacities should not exceed the strength shown on the manufacturer’s data sheetmultipliedbyareductionfactorof0.33.

Table 3.3.1-1 Factored Resistance (Design Strength) for Resin Capsule Anchors

AnchorSize

(inches)

Minimum Embedment

Depth(inches)

HoleDiameter(inches)

Design Strength for ASTM A 307 Threaded Rods (kips)

Tension Shear

3/8 31/2 7/16,15/32 2.1 1.7

1/2 �1/� 9/16 3.9 2.1

5/8 5 11/16,3/� 5.8 2.7

3/� 65/8 7/8 8.6 3.1

7/8 65/8 1 10.8 8.2

1 81/� 11/8 13.0 9.6

11/� 101/� 11/2 22.8 15.8

3.3.2 Design and Detail GuidelinesTheDesignersshouldconsiderthefollowingissueswhenRCAsareselected:

a) ThePlans should call out the anchor asResinCapsuleAnchor and specify theanchordiameter.ThesizeoftheholeandanchorembedmentareaddressedintheStandard Specifications.


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b) RCAsshouldbeinstalledinhardenedconcretethatisatleast28daysold.

c) RCAsshouldbeinstalledindryholesonly.Theinstallationtemperatureshouldnotexceedthemaximuminstallationtemperaturerecommendedbythemanufacturer.

d) Typically, the anchor embedment as specified by the manufacturer will develop thestrengthsshowninTable3.3.1-1.However,todeveloptheyieldstrengthoftherodandensureamoreductileperformance,thedepthofembedmentshouldbeincreasedtoabouttwicethatshowninthemanufacturer’sdata(andthisincreaseddepthshouldbeshownonPlans).Tworesincapsulesforbondinglongeranchorsindeeperholesmayberequired.Insuchcases,thestrengthofananchorbasedonconcrete failure should be verified. Deep holes that require more than two standard capsules to fill should not be used.

e) Incorrosiveenvironments,galvanizedorstainlesssteelthreadedrodsshouldbeused.

3.�Summary

Table3.�-1summarizesthetypicalapplicationsfordifferenttypesofbondedanchorsinconcrete.

Table 3.4-1 Summary of bonded anchor applications

Hole Orientation Preferred Anchor Type Comments

Holeanglegreaterthan20degrees(tohorizontal)generallydetailedasaholeata3to1(minimum)slope

DrillandBondDoweloraDrillandGroutDowel

BothRCAandDrillandBond(chemicaladhesive)mayalsobeusedbutmaynotbecost-effective

Horizontalhole DrillandBondDowel(chemicaladhesive)

ResinCapsuleAnchormayalsobeused

Verticallyoverheadhole ResinCapsuleAnchor PriorApprovalfromtheStateBridgeEngineerisrequired



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�.RockBoltAnchorsRockboltsarecommonlyusedtoanchorortieattachmentstorockfoundations.Shortrockboltscanalsobeusedtoanchorintoconcretewherelargetensileloadingisexpected.

Rockboltanchoragesystemsexhibitductilefailureandlowcreeprate,butthecostsarerelativelyhigh.

Figure�-1showstheengineeringdetailsofarockboltanchor.Thesedetailsarebasedontests performed by the Office of Structural Materials, METS at the Translab(J.P.Duseletal, 1979). This figure shows an expansion shell type anchored rock bolt where the bolt is placedinsideacoredholeandthenrotated.Therotationpullsawedgeintoanexpansionshell,whichexpandsagainstandintothewallofthecoredhole.Thevoidbetweentheboltandthecoredholeisthengrouted.

Yield TensileStrength = 37 kips

Ultimate TensileStrength = 53 kips

Stressed Area ofBolt = 0.544 sq. in.

6" min

12" m

in

Edge ofconcrete

12" m

in

1" hollow core galvanizedrock bolt. Torque to 250 ft lbs.before grouting.

Mechanical expansion headassembly (long or short coneand shell).

1 / " cored hole. Pump fullwith expansive cement grout.

3 4

Plan Elevation

φ

φ

Figure 4-1 Rock Bolt Anchor

5.Cast-In-PlaceAnchors

5.1Cast-In-PlaceBoltsorHeadedStudsCast-in-place(CIP)boltsincludecommonbolts,hookedbolts,headedboltsandstudsweldedtoplates.Suchanchorsarebestsuitedforattachingmetalorprecastelementstostructuralconcretesuchasforattachingbaseofmessagesignstoconcretefoundationsandcolumnstosubstructures/foundations.


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Thedesignstrengthofananchorsystemisaffectedbyparameterssuchasboltdiameter,embedmentdepth,edgedistanceandthespacingbetweentheanchors(Figure5.1-1).

d

L

Em

bedm

ent

dept

he

h Normal diameterof anchor head

Anchor bolt orwelded stud

de Edge distance

Figure 5.1-1 Typical Anchor Bolt

Ingeneral,commonboltsaredesignedtohavefullembedmentinordertodeveloptheyieldstrengthoftheanchorsteelandensureaductilefailure.However,thedesignermaychoosetouseashorter(partial)embedment(duetolimitedconcretethickness).Inthecaseofpartialembedment,thecapacityoftheconcrete“failurecone”maylimittheanchoragedesignstrength(Figure5.1-2).Concretefailuresaregenerallybrittleinnature.

Stud-weldedplateanchorsarecomprisedofsteelplatesthathaveeitherheadedstudanchorsorhookedbars.Theseanchorsdevelopstrengththroughbondand/orbearing.

Potentialfailure plane

Tie backreinforcement

Hairpinreinforcement

Shearforce

Tension force

Potentialfailure plane

Figure 5.1-2 Typical Partial Embedment Failure Planes and Reinforcement



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5.1.1 Resistance (Design Strength) ThedesignstrengthsofCIPanchorsaresummarizedinTable5.1.1-1andarederivedusingACI318-08,AppendixD.Table5.1.1-1alsoliststhedesignparameters,includingtheminimumrecommendededgedistance,theminimumembedmentdepthtodevelopthe ultimate strength of a single anchor, and the tensile and shear design strengthsbasedonthefullembedmentcondition.

Thefactoredresistances(designstrengths)showninTable5.1.1-1arebasedon thefollowingcriteria:

a) Thedesignstrengthofconcreteisassumedas3600psi.ThedesignstrengthsofboltsshowninTable5.1.1-1mayalsobeusedforhigherconcretestrengths,unlessmoreupdatedstrengthsarerequired.

b) The tensileandshearstrengthsareshownforsingleanchors. Foranchors inagroup,groupeffectsshouldbeconsideredperACI318-08.

c) Case1andCase2valuesforthetensilestrengthofboltsapplytobolttypesotherthan“J”bolts.Case3 applies to “J”bolts.For shear strength, there isno suchdistinctionbetween“J”boltsandothertypesofbolts.

d) Case1valuesforthedesignstrengthofboltsarecontrolledbytheminimumedgedistanceandCase2valuesassumethattheedgedistancesaregreaterthanorequalto1.5timestheminimumembedmentdepth.Whentheedgedistanceisbetweenthesetwoextremevalues,thenanchorstrengthshouldbecalculatedperACI318-08.

e) TheanchorstrengthsinTable5.1.1-1arebasedoncrackedconcrete.Ifthedesignengineer determines that the concrete in which the anchors are installed willremain uncracked during service conditions, then the design strength shown inTable5.1.1-1maybemultipliedby1.�0.

f) Whencombinedshearandtensileloadingispresent,thefollowingequationshouldbe satisfied:

1≤+

resistancetensileFactored

loadtensileFactored


loadshearFactored


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Table 5.1.1-1 Factored Resistance (Design Strength) for Cast-In-Place ASTM A 307 Anchor Bolts

BoltDiameter(inches)

Minimum Edge

Distance(inches)

MinimumEmbedment

Depth(inches)

Tensile Strength(kips)

Shear Strength (kips)

Case 1 Case 2 Case 3 Case 1 Case 2

1/2 21/2 � 3.3 7.3 2.3 0.8 1.1

5/8 3 5 �.5 11.3 2.8 1.1 1.7

3/� 3 6 5.3 1�.8 5.1 1.2 1.8

7/8 � 7 7.3 18.7 5.9 2.0 3.0

1 � 8 8.1 22.8 9.1 2.1 3.2

5.1.2 Design and Detailing Guidelinesa) ThePlansshouldshowthediameteroftheanchorbolt,itsembedmentdepthand

thedesirednut/washercombinationifrequired.

b) Where possible, supplementary “hairpin” or tie back reinforcement should bedetailedonPlans(Figure5.1-2).Thisreinforcementwillhelptopreventsuddenconcreteconeorsideblow-outfailures.

Wherelargersizeboltsunderlateralloadingareused,suchassteelsuperstructuretoconcretesubstructureconnections,refertothepublication“Lateral Resistance of Anchor Bolts Installed in Concrete”(R.A.Swirskyetal,1977).

5.2Cast-In-PlaceInsertsCIP Inserts are prefabricated metal devices with female threads which are specifically made for attachment of bolted connections (Figure 5.2-1). Such inserts, which arecommerciallyavailable,aresimpleandeasytouseinconstruction.Otheradvantagesincludethefollowing:

● Theyarerelativelyinexpensive ● Theycanbeattachedtotheformspriortoconcreteplacementwithoutthe needtodrillholesintheforms ● Theseinsertswillnotextendoutsidetheforms



LRFD

Figure 5.2-1 Ferrule Loop Insert

Theprimarydisadvantageofsuchinsertsisthelocationoftheinsertsandtheattachmentsneedtobepreciselyestablishedbeforeconcreteisplaced.

CIP inserts may be used for either temporary or permanent applications. Suchapplications include overhead signs and fixtures, safety railings, inspection ladders andfalseworktoconcreteconnections.CIPinsertsshouldmeettherequirementsofSection75oftheStandard Specifications.TensiledesignstrengthsforvarioussizesofinsertsarelistedinTable5.2-1andincludearesistancefactorof0.7.

ThePlansshouldidentifythelocationoftheCIPinsertandindicatethediameteroftheboltorthreadedrodbeassociatedwiththeinsert.

Table 5.2-1 Tensile Factored Resistance (Design Strength) for Cast-In-Place Inserts

Bolt Size (inches) Design Strength (kips)

1/2 3

5/8 �

3/� �.6

7/8 6.3

1 6.3


LRFD


6.References1. R.A.Swirsky,J.P.Dusel,W.F.Crozier,J.R.StokerandE.F.Nordlin,1977,“Lateral

Resistance of Anchor Bolts Installed in Concrete”,ReportNo.FHWA-CA-ST-�167-77-12.

2. J. P Dusel, J. H.Andersen and J. R. Stoker, 1979, “Evaluation of Rock Bolts for Installation in Existing Concrete”,ReportNo.FHWA-CA-TL-79-03.

3. JohnP.DuselandCraigN.Harrington,1986,“Evaluation of Mechanical Expansion

Anchors – Vol. 1 & 2”,ReportNo.FHWA/CA/TL-86/09.

�. AbidA. Mir and John P. Dusel, 1993, “Evaluation of New Bonding Materials for Anchoring Dowels in Existing Concrete”,ReportNo.FHWA/CA/TL-93/11.

5. ACI318-08,BuildingCodeRequirementsforStructuralConcrete.

6. Caltrans,(2008&2011).California AmendmentstoAASHTO LRFD Bridge Design Specifications, 4th Edition, California Department of Transportation, Sacramento,CA.

5-81 A to oncrete - California Department of Transportation

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