ultrasonic detection of simulated corrosion in 1 inch diameter steel tieback rods

7/31/2019 ULTRASONIC DETECTION OF SIMULATED CORROSION IN 1 INCH DIAMETER STEEL TIEBACK RODS

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ULTRASONICDETECTIONOFSIMULATEDCORROSIONIN1INCH

DIAMETERSTEELTIEBACKRODS

By

KARLR.OLSEN

Adissertationsubmittedinpartialfulfillmentof

therequirementsforthedegreeof

DOCTOROFPHILOSOPHY

WASHINGTONSTATEUNIVERSITY

DepartmentofCivilandEnvironmentalEngineering

August2009


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TotheFacultyofWashingtonStateUniversity:

ThemembersoftheCommitteeappointedtoexaminethedissertationofKARLR.OLSENfindit

satisfactoryandrecommendthatitbeaccepted.

DavidPollock, Ph.D.(Chair)

DavidMcLean, Ph.D.

DonaldBender, Ph.D.

William Cofer, Ph.D.


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Acknowledgements

"Forbyhimallthingswerecreated:thingsinheavenandonearth,visibleandinvisible,

whetherthronesorpowersorrulersorauthorities;allthingswerecreatedbyhimandforhim."

Colossians1:16

FirstandforemostIwouldliketothankmyparents. Dad,withoutyourencouragementtosee

beyondmytrialsIwouldhavegivenuplongago. Iconsideritanhonortohaveyouasafather,

amentorandafriend. Mom,thankyouyourunwaveringlove,regardlessofmy

accomplishmentsorfailures. Iamproudtobeyoursonandthankfulforeverysmileandhug

thatawaitsmeeverytimeIseeyou.

Dr.Pollock,IhavelearnedasmuchfromwatchingyouasIhavefromlisteningtoyour

feedback. Yourcareforyourstudentsaboveyourselfisevident,andaninspiration. Toall

thosethathelpedkeepmesanethroughoutthisprocessandremindmethatthereismoreto

lifethanadissertation: Alan,Neil,Mike,Chuck,Jacob,Rebekah,Jessie,Laura,andKristinayour

friendshipmeansmorethanyouknow.

Also,thisdissertationwouldnothavebeenpossiblewithoutfundingforthisproject,whichwas

providedbytheU.S.DepartmentofTransportation(USDOT),TransportationNorthwest

(TransNow)RegionalResearchCenterthroughcontractnumber430820. Thecommercialall

threadtiebackrodswereprovidedbyWilliamsFormEngineeringCorporation.


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Contents

1 IntroductionandObjectives.................................................................................................... 1

1.1 TiebackRods..................................................................................................................... 1

1.2 ProblemStatement.......................................................................................................... 2

1.3 ResearchObjectives......................................................................................................... 3

1.3.1 DetectPhysicalGeometryofSimulatedCorrosioninSteelRods.............................3

1.3.2 EvaluateThreadedWilliamsTiebackRods............................................................... 4

1.4 OutlineofDissertationContents..................................................................................... 4

2 BackgroundandLiteratureReview......................................................................................... 6

2.1 PressureWaveProperties................................................................................................ 6

2.2 TwomethodsforSolvingtheWaveEquation.................................................................. 8

2.3 BackgroundinUltrasonicWavesinRods....................................................................... 13

2.3.1 UltrasonicWave...................................................................................................... 14

2.4 UltrasonicApplications.................................................................................................. 17

2.4.1 PreviousUltrasonicResearch................................................................................. 17

3 ExperimentalSetupandTesting............................................................................................ 22

3.1 ExperimentalSetup........................................................................................................ 22

3.2 LabviewProgram............................................................................................................ 23

3.3 TransducerCharacterizationandSelection................................................................... 23

3.4 WavelengthinSteelRod................................................................................................ 26

3.5 EndPreparationandTransducerCoupling.................................................................... 27

3.6 SteelRodsUsedinTesting............................................................................................. 28

3.7 VelocityCalculationforSteelRods................................................................................ 29

4 DetectingPhysicalGeometryofSimulatedCorrosion..........................................................33

4.1 LocationofLeadingEdgeofSimulatedCorrosion.........................................................33

4.2 DiameterCharacterization............................................................................................. 36

4.3 LengthofSimulatedCorrosionCharacterization...........................................................45

4.3.1 ChangeinFrequencyContentofBackEchoforLengthofSimulatedCorrosion...46


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1 IntroductionandObjectivesIn2002,justeastofdowntownCleveland,Ohio,severaltiebackrodsinasheetpileearth

retainingwallfailed(Esser&Dingeldein,2007). Thefailurewasduetocorrosionandcauseda

nearcollapseofthewall. Corrosioninstructuralsteeltiebackrodscausesadecreaseincross

sectionalarea,limitingtensileloadcapacity. Tiebackrodsaretypicallyburiedinsoil,

eliminatingtheoptionofvisualinspectionwithoutexcavation. Theresearchinthisstudy

evaluatedultrasonictestingasamethodofdetectingsimulatedcorrosioninsteelrods.

1.1 TiebackRodsTiebackrodsareavitalcomponentofsheetpile retainingwalls. Therodsconnecttheouter

supportstructuretoanchors(ordeadman)buriedinthesoil(Figure1.) Thefirsttiebackrods

Figure1. Sheetpileearthretentionwalls(USArmyCorpsofEngineers,1994)

Wale

SheetPiling

Wale TieRod

TieRodConcrete

Deadman

SheetPiling

Anchor

SheetPiling

a.Tierodsanddeadman

b.Tierodsandanchorwall


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2 BackgroundandLiteratureReviewThischapterpresentsabackgroundofultrasonicwaves. Anoverviewoffundamentalwave

propagationprovidesthebasisforunderstandingultrasonicwaves. Theuseofultrasonic

wavesinnondestructivetesting(NDT)ispresented,includingpreviousresearchpertaining

specificallytosteelrods.

2.1 PressureWavePropertiesAwaveisadisturbancethatpropagatesthroughtimeandspace. Energyistransferredfrom

onepointtoanotherviawaves. Asinglefrequencybulkwaveischaracterizedmathematically

bythewavelength()andamplitude(A)ofthesignal(Figure2). Thewavelengthisthedistance

betweentwoadjacentpeaksinthewavecycleandtheamplitudeisthemaximumdisplacement

ofthedisturbancefromtheundisturbedposition. Thefrequency(f)ofthewaveisdefinedas

Figure2. Mathematical wavecharacterization


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thenumberofoscillationsthatoccurinonesecondandtheperiod(T)isthetimetocomplete

oneoscillation.

Phase

Velocity

Thespeedatwhichthebulkwavetravelsthoughamediumiscalledthephasevelocity(p)and

iscalculatedwiththefollowingequation(Main,1988).

Equation1Thephasevelocityisdependentuponthetypeofwavetravelinginthemedium. Longitudinal

andshearwaveswillbeconsideredinthisresearch. Longitudinalwavesexhibitparticlemotion

inthedirectionofwavepropagation. Shearwavesexhibitparticlemotionorthogonaltothe

directionofwavepropagation.

Snell'sLaw

Whenalongitudinalwaveencountersaboundarysurface,longitudinalandshearwavesare

reflectedbackintothemediumatanglesdeterminedbySnell'sLaw(Figure3). Theresulting

longitudinalwavereflectsatanangleequaltotheincidentangle. Thereflectedshearwavehas

1

2

1

Figure3. DiagramofSnell'sLaw


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willestablishthetheoreticalfoundationthatwillbebuiltupontocompileamorecomplete

understandingofultrasonicwavesinrods.

2.3.1 UltrasonicWaveUltrasonicwavescanbeinitiatedinsteelrodsusingapiezoelectrictransducer. Anelectric

signalwassenttothetransducerconvertingelectricalenergytomechanicalenergyintheform

ofapressurewave. Whencoupledtotheendofasteelrodthewaveisgeneratedinthesteel

rodandproceedstotravelthelengthoftherod. Atthispointareceivingtransducercandetect

thesignalattheotherendoftherod,oriftheendoftherodisnotaccessible,thewave

reflectsfromtheendsurfaceoftherodandtravelsbacktothetransducer. Asthewave

returnstothefrontend,thetransducerconvertsthemechanicalenergyintoelectricalenergy,

andtheelectricalsignalisrecordedbythecomputer. Theultrasonicsignalforastraightrod

withoutanyflawsisshownbelow(Figure6).Themainbangrepresentsthegenerationofthe

ultrasonicwave. Thesmallsignalfollowingthemainbangisaringingoutofthepiezoelectric

transducer. Thenextsignalthatappearsisthefirstbackecho,whichrepresentsthefrontof

Figure6. Standardultrasonicsignalfrom1.0ft.long1.0in.diametercircularrod


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inspections. Themainvariablesincommercialtransducersarethediameterofthetransducer

andthefrequencyoftheultrasonicsignalgenerated. Thefollowingisalistoftransducers

availablefortestingofthesteelrodsinthisresearch(Table1.) Usinga1.0in.diameterrod

threefeetlongwithnoflaws,themaximumamplitudeofthebackechoforeachtransducer

wasrecorded(Figure15.) Thedatashowsthatthe5MHztransducerswith0.5in.diameter

providedthelargestamplitude. Transducerswhichproducelargeechoamplitudeswill

Figure15. Transduceramplitudecomparisononarodwithnosimulatedcorrosion

increasethemaximumdetectablelengthofrod. Thetransducerswerealsotestedtomake

suretheycandetectareductionindiameterfrom1.0in.to0.75inlocated2in.alonga6in.

longrodwitha1in.diameter. Thesignalresponsewasmeasuredtofindthemaximum

amplitudeoftheflawechoandbackecho(Figure16). The0.5in.diameter5MHz

transducersprovidedthemaximumflawechoandbackechoamplitudesata40dBgainsetting


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wasappliedbeforethetransducerwascoupledtotheendoftherod. Withoutthegel,the

transducercouldnoteffectivelycoupletheultrasonicsignalintotherod,resultinginan

extremelypoorultrasonicwave,ifanyatall. Amagnetictransducerwasusedinmostteststo

provideaconsistentadheringforcebetweenthetransducerandtheendoftherod.

3.6 SteelRodsUsedinTestingTwotypesofsteelrodswereusedinthisresearch(Figure18). 12L14steelrodswereusedfor

fabricatingandtestingvariousgeometriesofsimulatedcorrosion. Williams75ksiallthread

tiebackrodswereusedtoconfirmdetectionofultrasonicwavesinactualtiebackrods. The

propertiesofthe12L14steelandWilliamsgrade75steelareshowninTable2.

Williams tieback rod 12L14 cold drawn rod stock

Figure18. Williamscommercialtiebackrodand12L14rodstockusedintesting

12L14Steel

Thesimulatedcorrosiongeometriesweremachinedfrom1in.diametercoldrolled12L14steel.

12L14isaleadbasedsteelwithasmoothsurfacethatisidealformachining. Thesteeliscold

drawnandfabricatedaccordingtoASTMA108(ASTMStandardA108,2007)orASTMA29

(ASTMStandardA29,2005).


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WilliamsGrade75AllThreadTiebackRods

Williams1in.diametertiebackrodswereusedtoevaluatethedetectionofultrasonicwavesin

commercialrods. Thegrade75allthreadrodswereacontinuouslythreadedrodspecially

designedtobeusedasconcreteformingtierodsandanchors. Allthreadtiebackrodsare

availableinlengthsupto50feet.Therodsaremanufacturedwithaspecialthreaddesignedto

meettherequirementsofASTMA615(ASTMStandardA615,2008).

Table2.Propertiesfor12L14steelandWilliamsgrade75tiebackrod

Property 12L14 Williams tieback rod

Density (lbs/ft3) 481 - 501 481 - 501

Poisson's Ratio 0.27 - 0.30 0.27 - 0.30

Elastic Modulus (ksi) 27,560 - 30,460 27,560 - 30,460

Tensile Strength (ksi) 78 100

Yield Strength (ksi) 60 75

3.7 VelocityCalculationforSteelRods

Determiningthewavespeedinthesteelspecimenswasnecessaryforcalculatingspecific

geometriesofthesteel. Ultrasonicsignalswererecordedfor1.0ft.longsectionsof12L14steel

andgrade75Williamstiebackrods. Itwasnecessarytodeterminethewavespeedusingthe


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firstandsecondbackecho. Apotentialdelayinthesignalcanoccuratthemainbang,because

thesignalismeasuredastheelectricalimpulseentersthetransducer,butthebackechoesare

measuredwhentheultrasonicwaveimpactsthetransducer. Afullsignal,containingtwoback

Figure19.Fullultrasonicsignalfor1.0ft.long1.0in.diameter12L14steelrodforcalculatingwavespeed

echoeswasrecorded(Figure19).Todeterminethearrivaltimeofthebackecho,itwas

necessarytodeterminewhenthebackechosignalfirstrisesabovethenoise. Thegraphsofthe

firstandsecondbackechoesareshownbelowtodeterminethestarttimeofeachbackecho

(Figure20.) Tofindthestarttime,itwasfirstnecessarytoinspectthemainbangsignal. The

directionthatthesignalamplitudefirsttravelsaboveorbelowthehorizontaltimeaxis

determinesthedirectionofthearrivalofthebackechoes. Inthecaseshown,themainbang

travelsinthenegativedirectionfirst;thusthearrivalofthefirstandsecondbackechoeswill

occurinthenegativedirection. Individualpointswereplottedinthegraphstovisualizethe

departureoftheechoesfromthesignalnoise.Thearrivaltimesofthemainbangandfirstand


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Figure20. Mainbangandfirstandsecondbackechoesfor1.0ft.long1.0in.diametersteelrod

secondbackechoeswererecorded(Table3). Then,thetimebetweenthefirstandsecondback

echoeswasdividedbytwotofindthewavespeedperfootofrod. Twolengthsarenecessary

toaccountforthewavetravelingdowntherodandthenreturningtothetransducer. Thebulk

longitudinalwavespeedsforthesteelusedinthefollowingresearchareshownbelow(Table

4.) The12L14SteelusedforthesimulatedcorrosionrodsandtheWilliamstiebackrods


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Figure24.Ultrasonicsignalsforsimulatedcorrosionlocatedat8.94in.,16.06in.,and23.03in.fromtheendof

therod.

Thelength,L,fromthetransducertotheleadingedgeofsimulatedcorrosioncanbecalculated

usingthefollowingformula:

Equation27

whereC1isthebulklongitudinalwavespeedofthematerial,andtisthetimebetweenthe

mainbangandtheleadingedgeoftheflawecho. Thetimewasdividedbytwobecausethe

ultrasonicpulsepassesdownthelengthoftherodtotheflawandthenreturnsbacktothe


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Thesecondsetofrodsincludeda3ft.long1.0in.diameterrodwitha2.0in.lengthof0.5in.

diametersimulatedcorrosion,a3ft.long0.5in.diameterrodwithoutsimulatedcorrosionand

a3ft.long1.0in.diameterrodwithoutsimulatedcorrosion(Figure28). A45transitionwas

includedateachendofthesimulatedcorrosiontoaddresstheconcernthatcorrodedregions

donottypicallyexhibitanabrupttransition. The45transitionalsoreducedtheamplitudeof

thesecondflawechothatoccuredcoincidentwiththebackechointheultrasonicsignal. These

rodswereusedtoinvestigatetheeffectof0.5in.diametersimulatedcorrosiononthe

ultrasonicsignal. Thebackechoandsuccessivetrailingechoeswererecordedforeachrod

(Figure29). Thetimebetweenthetrailingechoes(t)foreachofthethreerodswasrecorded

3ft.

0.50 in.

36in.

1.00in.

Figure28. 1.0in.diameterrodwith 0.5in.simulatedcorrosiondiametercomparedwith0.5in.diameter and

1.0in.diameterrods

*Transducerwasmounted

onleftendoftherod.

*Thetransitionindiameterwas45asshown

atright

45

16.0625in.

3ft.

0.500 in. 1.00 in.

2.0 in.


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outerdiameterisamultipleofthesimulatedcorrosiondiameterthesuperimposedtrailing

echoesarriveatthesametimeappearingasasingletrailingechoes. Thetimebetweentrailing

Table8. Calculateddiameterfor1.0in.diameterrodwith0.5in.and0.75in.diametersimulatedcorrosion

Specimen

Smallest

Diameter (in.)

Measured

t(s)

Calculated

Diameter(in)

%

Difference

0.5in.Simulated

CorrosionDiameter0.5 3.50 0.53 6.6%

0.75in.Simulated

CorrosionDiameter0.75 4.76 0.73 3.2%

echoeswasmeasuredandthecorrespondingsimulatedcorrosiondiameterwascalculatedas

0.53in. Theseresultsshowedthat0.5in.diameterand0.75in.diametersimulatedcorrosion

canbecalculatedin1.0in.diameterrodsusingEquation25. Thetimebetweentrailingechoes

mustbemeasuredfromthebackechotothefirsttrailingechotodetectthesmallestreduced

Figure32. Percentreductionoforiginalloadcapacityforsimulatedcorrosionina1in.diameterrod


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diameter. Thereductionindiameterofasteelrodcorrelatesdirectlywithareductionofload

capacity. Thetensileloadcapacityofasteelrodisdependentuponthesmallestcrosssectional

areaoftherodperpendiculartothelongitudinalaxis. Thereductioncanbecalculatedin

percentoforiginalloadcapacitybasedupontheoriginaldiameter(do)andthecorroded

diameter(dc). Thepercentreductioninloadcapacityfora1in.diameterrodwithreduced

crosssectionisplottedinFigure32. The0.75in.diametersimulatedcorrosionrepresentsa

43.75%reductioninloadcapacityandthe0.5in.diameterrepresentsa75%reductioninload

capacity.

% Equation28

4.3 LengthofSimulatedCorrosionCharacterizationInordertoinvestigatetheeffectoflengthofsimulatedcorrosionontheultrasonicsignalthe

backechoandfirsttrailingechowereexamined. Thefrequencycontentofthebackechowas

inspectedforashiftofthepeakfrequencywithachangeinthelengthofsimulatedcorrosion.

Also,theratioofmaximumamplitudesofthetrailingandbackechoeswereexaminedfora

changewiththelengthofsimulatedcorrosion. Allultrasonicsignalspresentedinthissection

weregeneratedwiththeM1042OlympusNDT5MHztransducer.Thesignalwaveformand

frequencycontentareshowninFigure33.


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Figure33. Signalwaveformandfrequencycontentfor5MHzM1041OlympusNDTtransducer

4.3.1 ChangeinFrequencyContentofBackEchoforLengthofSimulatedCorrosionThefrequencycontentofthebackechowasinvestigatedtoidentifyanytrendsassociatedwith

thelengthofsimulatedcorrosion.Thebackechoesofseveralrodswithvariouslengthof

simulatedcorrosionwereevaluatedusingaFastFourierTransform(FFT). TheFFTanalysisof

thebackechoshowsthefrequencycontentofthetimedomainsignal. AnFFTrequiresthe

numberofdatapointsbe2NwhereNisaninteger. Todecreasetheeffectofnoiseonthe

signalonlytheoscillationswhichcrossthexaxiswereconsideredintheanalysis,andthe

remainderofthesignalwasreplacedwithzeros(Figure34.) Beforethefrequencyofthesignal

wasanalyzedforsimulatedcorrosion,twotestswereperformedtoinvestigatetheeffectof

lengthanddiameteroftherodonthefrequencyoftheultrasonicsignal. Thefirsttestincluded


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Figure34. Backechoof1.0ft.longrodwitha0.5in.simulatedcorrosiondiameterwithandwithoutzeros

threerods3.0ft.inlengthwithdiametersof0.5in.,1.0in.,and1.5in. AnFFTwascalculated

forthebackechoineachrod. Thepeakfrequenciesforthe0.5in.,1.0in.,and1.5in.diameter

rodswere6.10MHz,3.91MHz,and4.39MHzrespectively(Figure35). Thesecondtest

includedthreerods1.0in.indiameterwithlengthsof1.0ft.,3.0ft.,and10.0ft. AnFFTwas

calculatedforthebackechoineachrod. Theresultsshowedthatthepeakfrequenciesforthe

1.0ft.,3.0ft.,and10.0ft.longrodswere4.39MHz,3.66MHz,and4.64MHz(Figure36.)

Figure35andFigure36showthatthepeakfrequencyofthebackechocanvarywithbothrod

diameterandrodlength. However,adefiniterelationshipbetweenpeakfrequency,rod

diameterandrodlengthwasnotestablishedinthisstudy.


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Figure35. FFTfor3.0ft.longrodswith0.5in.,1.0in.,and1.5in.diameters

Figure36. FFTforbackechoof1.0in.diameterrodswith1.0ft.,3.0ft.,and10.0ft.lengths


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Twosetsofrods1.0in.indiameterand1.0ft.and3.0ft.inlengthweretestedtoidentifyany

correlationforeachspecificlengthanddiameterofrods. Thefirstsetofrodsincludedfive1.0

ft.longsteelrodswith0.5in.simulatedcorrosiondiameterforlengthsof0.5in.,1in.,2in.,4

in.,and8in.(Figure37). A90transition,fromtheoriginalroddiametertothesimulated

corrosiondiameter,wasusedoneachrod. Thelocationofthesimulatedcorrosionwas2.0in.

fromtheendofeachrod. TheFFTforthebackechowascomparedforeachofthefiverods

Figure37. 1.0in.diameter1.0ft.longrodswithdifferentlengthsofsimulatedcorrosion

8in.

12in.0.500

1.00

2.0in.

9in.

12in.0.500

1.0

1.00

9.5in.

12in.0.500

0.5in.

1.00

6.0in.

12in.0.500

4.0

1.00

2in.

12in.0.500

8.0in.

1.00


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9.0in.

36in.

0.500in. 1.00 in.

2.0in.

9.0in.

36in.

0.500 in. 1.00 in.

6.0in.

9.0in.

36in.

0.500 in. 1.00in.

10.0 in.


onleftendoftherod.

*Alltransitionswere90

asshownatright

90

Figure39. 3.0ft.long1.0in.diameterrodswith2.0in.,6.0in.,and8.0in.lengthsofsimulatedcorrosion

startingat9in.alongtherod


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Figure40. Peakfrequencyofthebackechofor3.0ft.longrodswith2.0in.,6.0in.,and10.0in.lengthsof

simulatedcorrosion.

percentageoftotalrodlength(Figure40). Theresultsshowanincreaseinpeakfrequencywith

anincreaseinpercentsimulatedcorrosion. The0.5in.and1.0in.diameterrodswithout

simulatedcorrosioncreatetheupperandlowerboundofthefrequencyshift. The1.0in.

diameterrodrepresentsarodwithoutanysimulatedcorrosionandformsthelowerboundof

thepeakfrequency. The0.5in.diameterrodrepresentsarodwithfull0.5in.diameter

simulatedcorrosionandformstheupperboundofthepeakfrequency. Theshiftinpeak

frequencyshowsthattheincreaseinsimulatedcorrosionlengthactsasafilterforcertain

frequenciesintheultrasonicsignal.


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Overall,theresultsindicatethatanincreaseinpeakfrequencyofthebackechooccurswithan

increaseinthelengthofsimulatedcorrosionfor1.0ft.and3.0ft.longrodswitha1.0in.

diameter. The3.0ft.longrodsexhibitedastrongercorrelationthanthe1.0ft.longrods,but

thenumberofdatapointsforeachrodlengthwaslimited.

4.3.2 ChangeinBackEchoAmplitudewithLengthofSimulatedCorrosionThemaximumamplitudesofthebackechoandthefirsttrailingechowereinvestigatedto

identifyarelationshipwiththelengthofsimulatedcorrosion.Thebackechorepresentsan

ultrasonicpulseundergoingdirectreflectionfromtheendoftherod,whilethefirsttrailing

echoincludesonemodeconversionwithshearwavepropagationacrosstheminimum

diameteroftherod.

Thesetof1.0ft.(Figure37)longrodswereusedfortesting. Thebackechoandfirsttrailing

echowererecordedforeachrod(Figure41).Themaximumamplitudesofthebackechoand

thefirsttrailingechowererecordedinTable9. Theratiooftheamplitudeofthefirsttrailing

echotothebackechoincreaseswiththelengthofsimulatedcorrosion. Theamplituderatiofor

eachlengthofsimulatedcorrosionwasplottedinFigure42. Theresultsshownastrong

correlationbetweenthepercentlengthofsimulatedcorrosionandtheratioofpeaktrailing

echotothebackecho. Theincreaseinamplitudeofthetrailingechorelativetotheamplitude

ofthebackechowasduetotheincreasedlengthofsimulatedcorrosion. Assumingapoint

sourceforatransducer,Figure43showsacrosssectionoftheultrasonicwavethatreflects

fromthesimulatedcorrosionregionfora0.5in.and8in.lengthofsimulatedcorrosion.


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Figure41. Backechoandfirsttrailingechofor1.0 ft.longrodswithmultiplelengthsofsimulatedcorrosion


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0.5in.lengthofsimulatedcorrosion

8.0in.lengthofsimulatedcorrosion

Portionofwavethat

reflectsfromthesimulated

corrosionsurface

Figure43. Comparisonofreflectionfromthesimulatedcorrosionsurface


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Figure46. Ultrasonicsignalfor90,45,30,15,10and5 transitionangles


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Figure47. Delayindetectableflawechoversustransitionangle

theflawechodoesnotdecreaseconsistentlywiththetransitionangle. Thisphenomenonwas

investigatedmorethoroughlybymachiningrodswithamorecompleterangeoftransition

angles. Tocompareamplitudesbetweenvariousrods,thedatawasnormalizedusingnotches

tocomparetwoamplitudeswithinasingleultrasonicsignal. Multiplevariablesaffect

consistenttransducercoupling.Theseinclude:forceappliedtothetransducer(couplingforce),

surfaceconditionoftherodend,amountofcouplinggel,andthepresenceofparticles

betweenthetransducerandthesurfaceofthespecimen. Thesevariablesaredifficultto

controlconsistently. Tomaintainaconsistentcomparison,anotchwasaddedtoeachrodto

createarepeatablebaselineechoineveryultrasonicsignal. Thesignalechoassociatedwith

thereflectionfromthisnotchwascomparedtotheamplitudesofanyechoesofinterestin

ordertonormalizethedata. Threenotchlocationswereevaluatedtoselectanappropriate

baselinenotchlocation. Eachnotchwascutintoa1in.diameter,6in.longrod. Thenotchwas


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made0.125in.deeparoundthecircumferenceoftherodandwas0.25in.wide(Figure48).

Thenotcheswerecutatthreedifferentdistancesfromtheleadingedgeoftherod:0.5in.,1.0

in.,and1.5in. Therodsweretestedwiththe5MHzmagnetictransducer,andtheultrasonic

signalwasrecorded(Figure49). Thenotchlocated1in.awayfromtheultrasonictransducer

wasselectedbecauseitprovidedanechothatcouldbemeasuredinthesameorderof

magnitudeastheflawechoesfoundinFigure46,anddidnotaddextranoisetotheultrasonic

signal. Incontrast,thenotchlocated2in.fromthetransducerprovidedincreasednoise

followingthebackecho,whilethenotchlocated0.5in.fromthetransducerprovidedapulse

withanegligibleamplitude.

0.5in.

6in.

0.75in.

0.25in.

1.00in.

1.0in.

6in.

0.75in.

0.25in.

1.00in.

0.5in.

6in.

0.75in.

0.25in.

1.00in.

Figure48. 6.0in.long1.0in.diameterrodswith0.125in.deep0.25in.widenotches

located0.5in.,1.0in.,and2.0in.fromtheendoftherod

Ultrasonic

Transducer


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Figure51. Normalizedmaximumamplitudeofflawechoversustransitionangle

echo. Thenormalizedamplitudedecreasedsharplyfromatransitionangleof90to75.

However,insteadofcontinuingtodecline,thenormalizedamplitudeleveledoffandthen

showedseveralsmallpeaksalongwithasignificantpeakatatransitionangleof30anda

smallerpeakatatransitionangleofapproximately43. Thepeakswereinvestigatedusingthe

raymethod,assumingapointsourceattheendoftherod. Twopossiblescenarioswere

considered.

Thefirstscenarioconsideredwasthedirectlongitudinalwavereflectionfromthetransition

surface. AccordingtoSnell'slaw(Figure3),alongitudinalwavereflectsattheangleof

incidenceofthelongitudinalwavearrivalatthesurface,becausethewavespeedsarethesame

(Figure52). Table10documentstheangleoftravelofthereflectedlongitudinalwavewith


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Table10. Angleoflongitudinalwavereflectionfromtransitionsurface

TransitionAngle InitialWaveAngle IncidentAngle ReflectedWaveRelativetoRodAxis

transition initial 1 axis

5

4.76

80.24 165.2410 4.76 75.24 155.24

15 4.75 70.25 145.25

20 4.73 65.27 135.27

25 4.71 60.29 125.29

30 4.69 55.31 115.31

35 4.67 50.33 105.33

40 4.64 45.36 95.36

42.5 4.62 42.87 90.00

45 4.61 40.39 85.39

50 4.58 35.42 75.42

55 4.55 30.45 65.45

60 4.51 25.49 55.49

65 4.48 20.52 45.52

70 4.44 15.56 35.56

75 4.40 10.60 25.60

80 4.36 5.64 15.64

85 4.33 0.67 5.67

90 4.29 4.29 4.29

Thesecondscenarioconsideredwasthedirectshearwavemodeconversionfromthetransition

surface. Theinitiallongitudinalwavemodeconvertsatthetransitionsurfaceproducingashear

wavereflection. AccordingtoSnell'slaw,theshearwavereflectsatanincidentanglethatis

dependentuponthearrivalincidentangleandthespeedsofthelongitudinalwave(C1)and

shearwave(C2)(Figure53). Table11documentstheangleoftravelofthereflectedshearwave

withrespecttotheaxisoftherod. Whentheshearwavereflectsfromthetransitionsurface


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ata90angletothelongitudinalaxisoftherod,thewavereflectsfromtheoppositetransition

surfaceonemoretimeandreturntothepointsource,duetosymmetry. This90reflection

occursata27.8transitionangle. Thisrepresentsthelargepeakatapproximately28in

Figure51. Thevaluewasapproximatebecausethetransducerwasapproximatedasapoint

source.

Figure53. Shearwavereflectionfromtransitionsurface

initial

tansition

1

2


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Table11. Angleofshearwavereflectionfromtransitionsurface

Transition

Angle

Initial Wave

Angle

Incident

Long.Angle

Incident

ShearAngle

ReflectedWave

RelativetoRodAxis

transition initial 1 2 axis

5 4.76 80.24 32.95 117.95

10 4.76 75.24 32.26 112.26

15 4.75 70.25 31.30 106.30

20 4.73 65.27 30.09 100.09

25 4.71 60.29 28.64 93.64

27.8 4.70 57.50 27.71 90.00

30 4.69 55.31 26.99 86.99

35 4.67 50.33 25.14 80.14

40 4.64 45.36 23.12 73.12

45 4.61 40.39 20.95 65.95

50 4.58 35.42 18.66 58.6655 4.55 30.45 16.24 51.24

60 4.51 25.49 13.74 43.74

65 4.48 20.52 11.16 36.16

70 4.44 15.56 8.51 28.51

75 4.40 10.60 5.83 20.83

80 4.36 5.64 3.11 13.11

85 4.33 0.67 0.37 5.37

90 4.29 4.29 2.37 2.37

Overall,theresultsprovideevidencetosupporttwoconclusions. First,exceptforthe27.5

transitionangle,theflawechoexperiencedasignificantdecreaseinamplitudebelow80but

wasstilldetectable. Theflawechowasdetectableforgradualtransitionsaslowas5.

Second, transitionscauseadelayintheultrasonicsignalbetweenthemainbangandtheflaw

echo. Themoregradualthetransition,thelongerthedelay. Thelargestdelaywas23.8sfor

the5transitionwhichcorrespondstoa5.5in.insteelrods. Thus,thelocationofsimulated

corrosionmustbeadjustedbaseduponthetransitionangleofthesimulatedcorrosion.


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5 WilliamsCommercialTiebackRodTestingTherodstestedtoevaluatethephysicalgeometryofsimulatedcorrosionweremachinedfrom

12L14smoothrodstock. Commerciallyavailabletiebackrodsaretypicallyfabricatedwithan

allthreadsurface.Williamscommercialtiebackrodswereselectedfortestingtoevaluate

differencesintheultrasonicsignalduetothethreadedsurface.

5.1 TypesofTiebackRodsUsedinGeotechnicalApplicationsVariousstylesoftiebackrodshavebeenusedinconstructionofsheetpilesystems. Thetwo

mostcommonstylesareshownbelow(Figure54). Theupsetthreadstylewascommonin

previousconstruction. Upsetthreadsarerolledintothesteelrod,ratherthancut,toensure

theminordiameterofthethreadsisgreaterthantheouterdiameteroftherod. These

tiebackrodsweretypicallyfabricatedfromsmoothA36steelrod. Themajorityofcurrent

geotechnicalpracticesuseallthreadtiebackrods. Thesetiebackrodsarefabricatedfroma

highgradesteelwiththreadsformedalongtheentirelengthoftherod.

Rods used in old construction

(Upset Threads)

Rods used in new construction

(All-Thread)

Figure54. Upsetthreadandallthreadrods


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Theultrasonicsignalsfor12L14smoothrodstockandWilliamsallthreadrodswerecompared.

Therodstestedwere10feetlongwitha1.0in.majordiameter. Thefullultrasonicsignalfor

eachtypeofrod,includingmultiplebackechoes,isprovidedinFigure55. Adistinctdifference

Figure55. Comparisonof10ft.longWilliamsthreadedrodand12L14smoothsteelrod

isevidentin theportionofthesignalfollowingeachbackechoforthetworods. Figure56

providesacloserlookatthebackechoandsubsequenttrailingechoesofeachrod.The

ultrasonicsignalforthe12L14steelrodshowsseveraldistincttrailingechoesaftertheback

echo.TheWilliamstiebackrodshowsadistinctbackechowithonlyonedistinguishabletrailing


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echo. Thetimebetweenthebackechoandthetrailingechowasdifficulttomeasureinthe

Williamsthreadedrodduetoincreasednoiseintheultrasonicsignal. ThreadsintheWilliams

rodcausedispersionoftheultrasonicwaveduetospuriousreflectionsfromthethreaded

surfaces. Sincetrailingechoesinvolveatleastonereflectionfromthesurfaceoftherod,

detectingtrailingechoesfromathreadedsurfaceprovestobedifficult. Thisimpliesthat

calculatingtheexactouterdiameterofathreadedrodmaynotbepossibleusingthetime

betweentrailingechoes(t). Anapproximationofthediametermaybecalculatedusingthe t

betweenthepeaks,insteadoftheleadingedge,ofbackechoandthefirsttrailingecho.

Figure56. Trailingechocomparisonfor12L14smoothrodandWilliamsthreadedrod


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evaluatingthepeakvaluesofsuccessivebackechoesineachrod. ArectifiedAscan,which

acquirestheabsolutevalueoftheultrasonicsignalamplitude,includingalldetectableback

echoes,wasrecorded(Figure57). Theattenuationofthewaveamplitudealongtherodwas

definedbyEquation29(Kolsky,1963)

Equation29

whereaoistheinitialamplitude, isthecoefficientofattenuation,andxisthedistancealong

therod. TheunitsofthecoefficientofattenuationareNepers(Np)perlength,whereaNeper

isadimensionlessquantity. Thepeakamplitudeofeachbackechowasplottedwithrespectto

thedistancetraveled(Figure58.) Thebestfittrendlinewascalculatedanddisplayedwiththe

Figure58. Signalattenuationfor1.0ft.,3.0ft.,and6.0ft.longWilliamsrods.


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equationandR2value. Theattenuationcoefficients()forthe1ft.,3ft.,and6ft.rodswere

0.177Np/ft.,0.120Np/ft.,and0.096Np/ft.respectively. Thedifferencesinmagnitudeof

wereduetoscatteringwhichoccurredeachtimetheultrasonicwavereflectedfromanendof

therod. Whentheultrasonicwavetraveledanequivalent12feetalongthe1ft.longrod,the

wavereflectedfromanendsurface11times. Forthe3ft.and6ft.longrods,thesame12ft.

equivalentlengthincluded3and1endreflectionsrespectively. Theresultsshowadecreasein

attenuationcoefficientwithadecreaseinthenumberofendsurfacereflections. Longerrods

havefewerreflectionsresultinginasmallerattenuationcoefficient.

Figure55showsthata10ft.long1.0in.diameterWilliamstiebackrodexhibits4distinctback

echoesintheultrasonicsignal. Thisshowsthatthepulseechomethodusinga5MHzprobe

couldbeusedtodetectabackechoina1.0in.diameter40ft.longWilliamstiebackrod. This

wasaconservativeestimatesinceanactual40ft.rodwouldnotincludetheattenuationfrom

themultipleendreflectionsinthe10ft.rod.

5.3 SignalAttenuationforWilliamsRodsinSoilTheeffectofultrasonicsignalattenuationinsoilwasimportantfortestingWilliamscommercial

tiebackrods. Theamountofenergytransmittedintothesurroundingmediumduringultrasonic

inspectionofatiebackrodisdependentuponthepropertiesofthatmedium. Williamstieback

rodswithvarioussurroundingmediaweretestedtoinvestigatetheeffectonsignal

attenuation. Threesectionsof3ft.longWilliamstiebackrodswereplacedinplywoodboxes

withapproximately5.5in.ofcoverineachdirection. Anultrasonictransducerwascoupledto


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oneendofthetiebackrodwhichprotrudedthroughtheendofthebox(Figure59). Eachbox

wasfilledwithoneofthreesoils: sand,loosesoil,andcompactedsoil.

Figure59. Boxesconstructedforsignalattenuationtestsinsoils

5.3.1 SoilCharacterizationTwosoils,sandandPalousesoil,wereusedinthetests. Thesandwascollectedfromaquarry

runbyAtlasConcretecompanyinLewiston,Idaho. ThePalousesoilwascollectedfromtopsoil

inthePalouseregionofWashingtonState. Thesoilswerecharacterizedaccordingtothe

protocoldevelopedbytheArmyCorpsofEngineersforearthretentionssystems,including

grainsizedistributionandAtterberglimittests(USArmyCorpsofEngineers,1994).

AgrainsizedistributiontestwasperformedaccordingtoASTMD422(ASTMStandardD422,

2007). TheresultswereplottedforeachsoilinFigure60andthecoefficientofuniformity(Cu)

andcoefficientofcurvature(Cc)werecalculatedforeachsoil. Theresultswererecordedin

Table12.


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Figure61. AtterberglimittestofPalousesoil

experimentaldatausedtodeterminetheliquidlimit(LL). Theplasticlimit(PL)wasmeasured

experimentallyandtheplasticityindex(PI)andtheflowindexwerecalculatedusingLLandPL.

TheresultswereprovidedinTable13.

Table13. ResultsofAtterberglimittestforPalousesoil

PL 23.4

LL 35.3

PI 11.9

Flow Index -1.33

Usingthesoilpropertiesmeasured,theUSCSsoilclassificationwasdeterminedforsandand

Palousesoil. Thesandusedwasapoorlygradedsand(SP)and thePalousesoilwasasiltysand

(SM).

5.3.2 SoilPreparationThesandandloosesoilwereplacedintheboxescompletelysurroundingtheWilliamstieback

rods. Forthesandandloosesoilnocompactionwasused. Forthecompactedsoila25lb.


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Table15. AttenuationcoefficientsoftheultrasonicsignalforWilliamstiebackrodsinsoils

Sand LooseSoil CompactedSoil

Control Baseline Wet Control Baseline Wet Control Baseline Wet

0.081 0.075 0.078 0.072 0.069 0.065 0.095 0.076 0.0830.074 0.084 0.08 0.068 0.069 0.074 0.094 0.076 0.082

0.084 0.083 0.087 0.066 0.073 0.073 0.083 0.079 0.071

0.079 0.082 0.085 0.065 0.072 0.07 0.083 0.076 0.07

0.079 0.08 0.079 0.064 0.076 0.075 0.093 0.095 0.089

0.083 0.08 0.078 0.077 0.075 0.067 0.081 0.09 0.089

0.08 0.083 0.081 0.073 0.075 0.061 0.088 0.08 0.083

0.079 0.073 0.081 0.073 0.073 0.073 0.089 0.081 0.083

0.083 0.079 0.086 0.075 0.086 0.076 0.093 0.075 0.09

0.081 0.067 0.082 0.072 0.086 0.067 0.084 0.075 0.091

Average Average Average Average Average Average Average Average Average

0.0803 0.0793 0.0817 0.0705 0.0754 0.0701 0.0883 0.0803 0.0831

Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev.

0.0029 0.004 0.0033 0.0045 0.0061 0.0049 0.0053 0.0069 0.0074

CoV CoV CoV CoV CoV CoV CoV CoV CoV

0.0361 0.0504 0.0404 0.0638 0.0809 0.0699 0.0600 0.0859 0.0890

zTest zTest zTest zTest zTest zTest

0.640 1.008 2.044 0.190 2.908 1.807

theloosesoilthecoefficientsofattenuationswere0.0705Np/ft.,0.0754Np/ft.,and0.0701

Np/ft.forthecontrol,"baseline",and"wet"samples. Again,therewasnosignificantincrease

inattenuationfromthecontroltothe"baseline"or"wet"condition. Forthecompactsoilthe

coefficientsofattenuationwere0.0883Np/ft.,0.0803Np/ft.,and0.0831Np/ft.forthecontrol,

"baseline",and"wet"samples.Inthiscasetheattenuationcoefficientsforthe"baseline"and

the"wet"conditionwereslightlylessthanthecoefficientofattenuationforthecontrol. Thez

Testforeach"baseline"and"wet"testcomparedwiththecontrolshowedthatalltests,except

the"baseline"forthecompactedsoil,werewithina99%confidenceinterval (2.58z2.58).

NormalizeddataisalsoshowninTable16whichiscalculatedbydividingeachofthe"baseline"


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and"wet"conditiontestsbytheaveragecontrolvalueforeachrod. Forexample,theaverage

"baseline"valueforsandof0.979showsthattheattenuationcoefficientwas97.9%ofthe

averagecontrolvalue. Theseresultsshowthattheattenuationcoefficientforthe"baseline"

and"wet"conditionoftheultrasonicsignalforsand,loosePalousesoil,andcompactPalouse

soilwaswithinplusorminus9.1%forpercentwatercontentsupto7.74%,28.21%,and29.50%

respectivelyforWilliamstiebackrods.

Table16. NormalizedattenuationcoefficientsoftheultrasonicsignalforWilliamstiebackrodsinsoils

Sand

LooseSoil Compacted

Soil

Baseline Wet Baseline Wet Baseline Wet

0.934 0.971 0.979 0.922 0.861 0.940

1.046 0.996 0.979 1.050 0.861 0.929

1.034 1.083 1.035 1.035 0.895 0.804

1.021 1.059 1.021 0.993 0.861 0.793

0.996 0.984 1.078 1.064 1.076 1.008

0.996 0.971 1.064 0.950 1.019 1.008

1.034 1.009 1.064 0.865 0.906 0.940

0.909 1.009 1.035 1.035 0.917 0.940

0.984 1.071 1.220 1.078 0.849 1.0190.834 1.021 1.220 0.950 0.849 1.031

Average Average Average Average Average Average

0.979 1.017 1.070 0.994 0.909 0.941

Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev. Std.Dev.

0.067 0.041 0.086 0.070 0.078 0.084

CoV CoV CoV CoV CoV CoV

0.069 0.040 0.080 0.070 0.085 0.090

Thepercentoftheincidentwavethatistransmittedtothesurroundingmediaduringa

reflectionisdependentupontheimpedanceofthetwomaterialsincontact(Krautkramer&

Krautkramer,1990). Ifthetwomaterialshavethesameimpedanceandareinperfectcontact,


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thenalltheenergywilltransferthroughtheboundary. Thetransmittancepercentfortwo

dissimilarimpedancesisgivenby

Equation30

whereZ1istheimpedanceofthesteel(Z=46.0MRayls)andZ2istheimpedanceofthe

surroundingmedia,forthematerialsinthisstudy. Figure63showsthetransmittanceofasteel

rodembeddedinseveral surroundingmediaincludingwater(Z=1.48MRayls)andconcrete(Z

=8.0MRayls). Foratiebackrodinsoil,partofthesurroundingmediais air(Z=0.000429

MRayls),whichdrasticallydecreasesthetransmittanceoftheincidentwavetothesurrounding

media. Consideringthataportionofthesurroundingmediaisairandthefirstbackechoonly

hasonereflection,thetransmittanceisnegligible. Thus,theinspectablelengthsoftiebackrods

willnotvarywhentherodsareembeddedinsoils.

Figure63. Transmittanceforsteelwithwaterandconcretesurroundingmedia


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5.4 ActualTiebackRodswithFlawsSimulatedcorrosionwasmachinedin3ft.Williamstiebackrodsectionstodetermineifspecific

geometriescouldbedetectedincommercialtiebackrods. Theseincludedlocationof

simulatedcorrosion,diameterofsimulatedcorrosion,lengthofsimulatedcorrosion,andthe

transitionofsimulatedcorrosion.

5.4.1 LocationofSimulatedCorrosionThreeWilliamssteelrods,3ft.longand1in.indiameter,weremachinedwithsimulated

corrosionatvariouslocationstovalidatethepulseechomethodforlocationtheleadingedge

ofsimulatedcorrosioninaWilliamstiebackrod. Simulatedcorrosionwitha0.5in.diameter

9.28in.

36in.

0.500in. 1.00 in.

2.0in.

15.97in.

36in.

0.500 in. 1.00 in.

2.0 in.

22.84in.

36in.

0.500 in. 1.00in.

2.0 in.


onleftendoftherod.

*Alltransitionswere90

asshownatright

90

Figure64. 3.0ft.long1.0in.diameterWilliamstiebackrodswith2.0in.lengthof0.5in.simulatedcorrosion

diameterat9.28in.,15.97in.,and22.84in.alongtherod


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and 2.0in.lengthwasmachinedat9.28in.,15.97in.,and22.84in.alongthelengthofthe

steelrods(Figure64).Thelocationofsimulatedcorrosionwaseasilydetectablebasedonthe

timebetweenthemainbangandtheleadingedgeoftheflawecho. Thefollowingsignals

(Figure65)showaflawechoappearingintheultrasonicsignalthatcorrelatesdirectlywiththe

locationoftheflaw. Theformulaforlength(Equation27)wasusedtodeterminethelocation

oftheflaw(Table17)foreachofthethreerodsinFigure65. Thethreerodsshoweda

maximumpercentdifferenceof1.59%betweenmeasuredandcalculatedflawlocation. The

Figure65.Ultrasonicsignalsfrom3.0ft.long1.0in.diameterWilliamstiebackrodswith2.0in.lengthof0.5in.

diametersimulatedcorrosionat9.28in.,15.97in.,and22.84in.alongtherod.


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resultsshowthattheabilitytolocatetheflawpositionwasnotaffectedbythethreadsofthe

Williamsrods.

Table17. Comparisonofmeasuredandcalculatedlocationofsimulatedcorrosion

MeasuredFlawLocation

(in.) FlawTime(s) CalculatedFlawLocation(in) %Difference

9.28 79.3 9.13 1.59%

15.97 138.3 15.93 0.27%

22.84 197.4 22.73 0.47%

5.4.2 DiameterofSimulatedCorrosionToverifythedetectionofsimulatedcorrosiondiameteronWilliamstiebackrods,two3ft.long

rodsweremachinedwith0.5in.diameterand0.75in.diametersimulatedcorrosionregions

16.0in.

36in.

0.500 in. 1.00 in.

2.0 in.

*Transducerismounted

onleftsideofrod.

*Alltransitionsare90asshownatright

90

Figure66. 3.0ft.long1.0in.diameterWilliamsrodswith2.0in.lengthsof0.5in.and0.75in.diameter

simulatedcorrosion

16.0in.

36in.

0.750 in. 1.00 in.

2.0 in.


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Figure67. ComparisonofWilliamsrodswith0.5in.and0.75in.diameterofsimulatedcorrosion

(Figure66). Thefirstbackechowitheachdistinguishabletrailingechoeswasprovidedin

Figure67. Thetimebetweenthetrailingechoeswasmeasured(Table18.) UsingEquation25

thediameterwascalculatedfromthespacingofthetrailingechoes. The0.5in.simulated

corrosiondiameterrodhadacalculateddiameterof0.51in.resultingina1.9%difference. The

0.75in.simulatedcorrosiondiameterrodhadacalculateddiameterof0.73resultingina2.6%

difference. Thisprovidesaverystrongcorrelationbetweentheminimumdiameter(or

simulatedcorrosiondiameter)andthetimebetweentrailingechoesfortheWilliamsrod.

Table18. Timebetweentrailingechoesfor0.5in.and0.75in.simulatedcorrosiondiameter

RodSmallest

Diameter(in.)

Measured

Time(s)

Calculated

Diameter(in.)

%Difference

0.5in.SimulatedCorrosion 0.50 3.34 0.51 1.9%

0.75in.SimulatedCorrosion 0.75 4.79 0.73 2.6%


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5.4.4 TransitionofSimulatedCorrosionFinally,a3ft.longWilliamsrodwasmachinedwitha0.5in.simulatedcorrosiondiameteranda

45transitionangle(Figure71). Thisrodwasusedtoinvestigatetheabilitytodetectthe

location,diameter,andlengthofsimulatedcorrosionforarodwitha45transitionangleina

Williamsrod. ThefullultrasonicsignalfromthepulseechotestwasrecordedfortheWilliams

rodwitha45transition(Figure72). Thesignalshowsadistinctflawandbackecho. Theflaw

andbackechowereeachfollowedbyfourdistincttrailingechoes.

Figure72. Fullultrasonicsignalfor2in.lengthof0.5in.diametersimulatedcorrosionwith45transitionangle

forWilliamstiebackrod

*Transducerismounted

onleftsideofrod.

45o

36in.

15.75in. 0.500 in. 1.00 in.

2.0 in.

Figure71. Rodusedforsimulatedcorrosiondetectionwitha45transitionangle


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Thearrivaltimeoftheflawechowas138.7s. Usingthelongitudinalwavespeedofthe75ksi

steel,theflawlocationwascalculatedtobe15.97in,whichhasa1.41%differencefromthe

measured15.75in.tothebeginningofthetransitionoftheflaw(Table19). Thisshowsthatthe

methodusedinthepreviouschapterforlocatingthepositionofsimulatedcorrosioncanbe

usedinWilliamsrodswitha45transitionangle.

Table19. CalculatedsimulatedcorrosionlocationforWilliamsrodwith45transitionangle

MeasuredFlawLocation

(in.) FlawTime(s) CalculatedFlawLocation(in) %Difference

15.75 138.7 15.97 1.41%

ThebackechoandsubsequenttrailingechoeswererecordedfortheWilliamsrodwitha45

transitionangle. Thebackechoandfourtrailingechoeswerevisible(Figure73.) Thearrival

timeofthefirstbackechoandtwotrailingechoeswereusedtocalculatethetimebetween

echoes. Thistimebetweentrailingechoeswasusedtocalculatethediameterofthesimulated

Figure73. Firstbackechoandsuccessivetrailingechoesfor2in.simulatedcorrosionwith45transition


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corrosionaccordingtoEquation25(Table20). Thecalculateddiameterwas0.502in.whichhad

a0.4%differencefromthemeasuredvalueof0.500in. Thisshowsthatthemethodfor

detectingthediameterofsimulatedcorrosioncanbeusedforWilliamsrodswitha45

transitionangle.

Table20. ComparisonofmeasuredandcalculateddiameterofsimulatedcorrosionforWilliamsrodwith45

transitionangle

RodSmallest

Diameter(in.)

MeasuredTime

(s)

Calculated

Diameter(in.)%Difference

0.5in.simulatedcorrosion 0.500 3.27 0.502 0.4%

TheFFTofthefirstbackechowasrecordedfortheWilliamsrodwitha2in.lengthofsimulated

corrosionanda45transitionangle. TheresultwasplottedwiththeFFTsignalsfroma0.5in.

diameterand1.0in.diameter3.0ft.longrodsof12L14steel. Theresultsshowthatthe

Figure74.Frequencyofbackechoof2in.long0.5in.diametersimulatedcorrosionwith45

transitioninWilliamsrod


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measuredfromtheleadingedgeofthemainbangtotheleadingedgeoftheflawecho. The

leadingedgeforeachechoisdefinedasthefirstpointthatappearsoutsidetheboundsofthe

signalnoise. Figure77plotseachpointoftheultrasonicsignalintherangeofthemainbang

andtheflawechotoidentifytheleadingedge. Forrodswithatransitionfromtheoriginal

diametertotheflawdiameter,themeasuredtimemayincludeadelayfromtheactualflaw

location. Themaximumdelayfora5transitionangleina1.0in.diameterrodwith0.5in.

diametersimulatedcorrosionwas23.8s,whichcorrespondstoanerrorof0.44in.for

determiningthelocationoftheflaw.

Figure78depictsthebackechoandtrailingechoesfora3.0ft.long1.0inchdiameter12L14

smoothsurfacerodandaWilliamscommercialtiebackrod,bothwitha2.0in.longsectionof

0.5in.diametersimulatedcorrosionstarting17.0in.fromtheleftendoftherod. Thetime

betweenthetrailingechoesfollowingthefirstbackechocanbedirectlyrelatedtothediameter

Figure78. Firstbackechoandsubsequenttrailingechoesforinspectionofsimulatedcorrosiondiameter

inspectionin1.0in.diameter12L14steelrodand1.0in.diameterWilliamsrod

12L14SteelRod

WilliamsTiebackRod


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ofsimulatedcorrosion. Equation31correlatesthediameteroftherod(d)tothetimebetween

echoes(t),baseduponthespeedoflongitudinalwavepropagation(C1)andthespeedof

transversewavepropagation(C2). Thetimebetweentrailingechoesismeasuredinthesame

Equation32

mannerasthetimebetweenthemainbangandtheflawecho. Theindividualpointsofeach

echoareplottedtoidentifytheleadingedgewhichisthefirstpointtoraiseaboveorbelowthe

noiseofthesignal. TypicalvaluesforthelongitudinalandshearwavespeedinsteelareC1=

19,190ft/sandC2=10,597ft/s. Thediameterofsimulatedcorrosioncanbeusedin

conjunctionwiththeoriginaldiametertodeterminethereductioninloadcapacity. Equation

32depictsthepercentloadcapacityfora rodwithsimulatedcorrosion.

%

Equation33

Theloadcapacityisdependentuponthediameterofthecorrodedregion,dc,andtheoriginal

roddiameter,do. Theabilitytoidentifythelocationanddiameterofcorrosionprovidesan

inspectorwiththeabilitytoapproximatethestructuralintegrityofatiebackrod.

Theselectionoftheultrasonictransduceriscriticalwheninspectingatiebackrod. Themain

variables toconsiderincommercialtransducersarethediameterofthetransducerandthe

frequencyoftheultrasonicsignalgenerated. Thetransducerdiametershouldbeaslargeas

possiblewithoutexceedingthediameteroftherod. Anincreaseinthediameterofthe


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transducerresultsinanincreaseintheenergygeneratedintheultrasonicwavewhichinturn

increasestherangeofinspection.Thetransducerwavelengthisdependentuponthediameter

ofthetiebackrodandthesmallestexpectedflawdimension. Toensurebulkwavepropagation

thetransducerwavelengthshouldbeatleastoneorderofmagnitudelessthanthediameterof

therod. Thewavelengthoftheultrasonicsignalwilldeterminetheminimumflawdetectablein

thespecimen. Theminimumdetectableflawdimensionisapproximatelythewavelengthofthe

ultrasonicpulsefrequencyintroducedintothemedium(Figure17). Thesetwocriteriawill

determinethetransducerfrequencyselection.

Figure79. Minimumdetectableflawdimensioninsteel

6.2

Endpreparation

and

Transducer

Coupling

Asignificantvariationintheamplitudeofthesignalcanoccurduetotheconditionoftherod

end. Ifthesurfaceisnotplanar,thewavewillexperiencedispersionfromareflectionfromthe


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endoftherod. Anothersourceofamplitudelosscanoccurinthecouplingofthetransducerto

therod. Itisimperativetohaveasmoothplanarsurfacetoattachthetransducer. Thus,itmay

benecessarytocutanewsurfaceattheendoftherod. Also,contaminantslocatedbetween

thetransducerandtheendoftherodmayresultinpoortransferofenergytotherod.

Therefore,theendofeachrodmustbecleaned,andacouplantgelappliedbeforethe

transduceriscoupledtotheendoftherod. Withoutthegel,thetransducerwillnoteffectively

coupletheultrasonicsignalintotherod,resultinginanextremelypoorultrasonicwave,ifany

atall. Amagnetictransducerisalsorecommendedtoprovideaconsistentadheringforce

betweenthetransducerandtheendoftherod.

6.3 CommercialTiebackRodTestingThefollowingguidelinesarepresentedtoassistindevelopinganinspectionprocedurefor

tiebackrodsinthefield. Transitioningfromtestingsmooth12L14samplestoinsitutestingof

commercialtiebackrods introducesseveralpotentiallimitations. First,turnbucklesareoften

usedwhenadesigncallsforrodslongerthan50ft. Anultrasonicsignalisnotabletopropagate

throughtheturnbuckle,thusonlythefirstsectionofrodisinspectable. Second,actual

corrosionwillnothaveasmoothsurface,orasinglediameter. Theirregularsurfaceofactual

corrosionwillincreasescatteringoftheultrasonicwaveduringreflection. Third,curvaturein

thetiebackrodmayeliminatethedetectionofthebackecho.Ifadirectlineofsightthrough

therodfromthefronttothebackoftherodiseliminatedthendetectionofadirectbackecho

isnotpossible. Thesefactorsmaylimittheeffectivenessofultrasonicinspectioninsome

scenarios. Thefollowingchartsprovideguidelinesfortheuseoftheultrasonicpulseecho


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methodforinspectingtiebackrods. Theguidelinesaredividedintotwosections. Thefirst

sectioncoversinspectionsofnewconstruction. Theseguidelinesassumethatinitialultrasonic

pulseechomeasurementswillbeperformedaftertheplacementoftherodsandpriortothe

facadeconstruction,whichcoverstheendsofthetiebackrods. Thesecondsectioncovers

inspectionofexistingconstruction. Thissectionisdividedintotwosections. Thefirstsub

sectionincludestiebackrodlengthsthatarerecordedinthedesignplans. Thesecond section

isforinspectionoftiebackrodswithunknownlength.

6.3.1 NewConstruction

Thissectionintroducesinspectionguidelinesfortiebackrodsinnewconstruction. Performing

severalmeasurementsduringtheconstructioncansignificantlyincreasetheabilitytomonitor

corrosioninsteeltiebackrods. Anultrasonicpulseechomeasurementperformedafterthe

placementoftherods,andpriortothefaadeconstructiongeneratesa"controlsignal"to

comparewithsubsequentmeasurementsduringthelifeoftherod. Thecontrolsignalshould

includetwoseparateinspections. First,afullsignalshowingalldetectablebackechoes,and

secondthefirstbackechowithalldetectabletrailingechoes. Thefullsignalcanbeusedto

calculatetheactuallongitudinalwavespeedofeachrod,usingthetimebetweenthemain

bangandthefirstbackecho. Apublishedvaluefortheshearwavespeed,C2=10,597ft/swill

beused. Thefollowingisaseriesofstepstoaidinfutureinspections:


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6.3.2 ExistingConstructionInterpretationofinspectionofexistingconstructionismoredifficultthannewconstruction.

Sincethereisnotacontrolsignalgeneratedduringtheconstructionprocess,theseguidelines

mustbedividedintotwosubcategories. Thefirstapproachassumesthattheoriginalplansare

availablewhichidentifytheoriginalrodlength. Thesecondapproachisforinspectionofrods

ofunknownlength.

6.3.2.1 OriginalrodlengthisknownRodswithaknownlengthprovidedimensionstoidentifythebackechointheultrasonicsignal.

Thefollowingisseriesofstepstoaidininspectionoftiebackrodsofknownlength:

Step#1: Calculatethetimebetweenthemainbangandthebackecho

UsingthelengthoftherodandalongitudinalwavespeedofC1=19,190ft/scalculatethe

expectedtimebetweenthemainbangandthebackechousingEquation30.

Step#2:Performapulseechoinspectiononthetiebackrod

Recordthreedifferentsectionsoftheultrasonicsignal. First,recordthefullsignal,extendingto

thefirstbackwithalldetectabletrailingechoes. Usetheexpectedtimefromthemainbangto

thetrailingechofromStep#1toapproximatethetimewindownecessarytocapturetheentire

signal. Second,recordthebackechowithalldetectabletrailingechoes. Third,recordanyflaw

echothatappearsbeforethebackechoandalldetectabletrailingechoes.


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Step#3: Verifythelengthofthetiebackrod

Measurethetimebetweenthemainbangandthebackechointheultrasonicsignal. Usethis

measurementtocalculatethelengthoftherod,usingalongitudinalwavespeedofC1=19,190

ft/swithEquation30. Comparethecalculatedrodlengthwiththeoriginalrodlengthtoensure

thattherearenocompletebreaksintherod.

Step#4: Verifytheouterdiameterofthetiebackrod

Ifaflawechodoesnotexist,calculatethetimebetweentrailingechoesafterthebackecho. If

aflawechoexists,calculatethetimebetweentrailingechoesaftertheflawecho. Usingthe

appropriatetimebetweentrailingechoesandEquation31,calculatethediameteroftherod.

Measuringthetimebetweentrailingechoesmaybedifficultforthreadedrods,becausethe

threadscausedispersionoftheultrasonicwavewhenitreflectsandmodeconvertsfromthe

outerdiametertocreatethetrailingechoes.

Step#5: Calculatethelocationoftheflaw(ifaflawechoexists)

Measurethetimebetweenthemainbangandthefirstflawecho. Usethismeasurementto

calculatethedistancetotheflaw,usingalongitudinalwavespeedofC1=19,190ft/swith

Equation30. Repeatthisstepforeachdistinctflawecho. Becarefulnottomistakeasecond

flawechoassecondflaw. Anechothatappearsattwicethedistanceofthefirstflawismost

likelyasecondflawechoandnotasecondflaw.


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Step#6Determinetheminimumdiameterofthetiebackrod(ifaflawexists)

Measurethetimebetweenthebackechoandthefirsttrailingecho. Usethismeasurementto

calculatetheminimumdiameteroftherod,usingthelongitudinalwavespeedofC1=19,190

ft/s,andashearwavespeedofC2=10,597ft/s withEquation30.

6.3.2.2 UnknownlengthofrodArodwithunknownlengthrequiresacloseinspectionofthetrailingechoestoidentifypossible

flawsintherod. Thefollowingisseriesofstepstoaidininspectionoftiebackrodsofunknown

length:

Step#1:Performapulseechoinspectiononthetiebackrod

Recordthreedifferentsectionsoftheultrasonicsignal. First,recordthefullsignal,includingall

detectableechoes. Second,recordthefurthestechowithalldetectabletrailingechoes. Third,

recordanyotherechothatappearsinthesignalwith alldetectabletrailingechoes.

Step#2:Determineifnodetectableflawsarepresent

Measurethetimebetweentrailingechoesforeachechorecorded. Usingthetimebetween

trailingechoes,alongitudinalwavespeedofC1=19,190ft/s,ashearwavespeedof10,597ft/s

andEquation31calculateadiameterforeachsetoftrailingechoes. Ifthecorresponding

diameterforthefirsttwosetsoftrailingechoesisapproximatelyequaltotheoriginaldiameter

oftherod,thentheechoesrepresentthefirstandsecondbackechoes. Sincenoflawechoes


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7 SummaryandConclusionsThisdissertationconcentratedonthedetectionofsimulatedcorrosioninsteeltiebackrods.

Ultrasonicsignalswereusedtodeterminethephysicalgeometryof0.25in.,0.50in.,and0.75

in.diametersimulatedcorrosionin1.0in.diametersteelrods. Researchwasalsoperformedto

investigatetheuseofultrasonicwavesinWilliamscommercialtiebackrods. Guidelineswere

developedforinspectingtiebackrodswithactualcorrosioninfieldapplications.

Thelocation,diameter,length,andtransitionofconcentricsimulatedcorrosionwere

investigatedforstraightsteelrods. Fora90transitionangle,thelocationofsimulated

corrosionwasdetectablebaseduponthetimebetweenthemainbangandtheflawechointhe

ultrasonicsignalandthelongitudinalwavespeedofthesteel. Adecreaseinthetransition

angleresultsinadelayinthearrivaltimeoftheflawecho. Thelargestdelaywas23.8sfor

the5transitionwhichrepresentsapotentialerrorof5.5in.whenestimatingthelocation.

Theminimumdiameterofconcentricsimulatedcorrosioninastraightrodwasdetectable

baseduponthedistancebetweenthebackechoandthefirsttrailingecho,andthelongitudinal

andshearwavespeedsofthesteelinaccordancewithpreviousresearchbyLight&Joshi(Light

&Joshi,1987). Thetimebetweenthebackechoandfirsttrailingechoisexclusivelydependent

upontheminimumdiameteroftherod,andisnotdependentuponthetransitionangleofthe

simulatedcorrosion.

Thelengthofconcentricsimulatedcorrosioninastraightrodwasdetectablebasedontwo

differenttechniques. First,anincreaseinthepeakfrequencyofthebackechocorrelatedwith


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anincreaseinthelengthofsimulatedcorrosion. Second,theratiooftheamplitudeofthefirst

trailingechoandthebackechocorrelatedwithanincreaseinthelengthofsimulated

corrosion.

Theinvestigationofthetransitionofthesimulatedcorrosionconcludedthattheflawechois

detectableforabrupttransitionsof90downtoassmallas5. Theflawechoexperienceda

decreaseinamplitudebelowa80transitionanglebutwasstilldetectable. Twopeakswere

evidentat transitionanglesof27.5and45. Thesepeakscorrelatetoashearandlongitudinal

wavereflectiondirectlyacrosstherodfromthetransitionsurface.

Williamsallthreadtiebackrodswereinvestigatedincludingprojecteddetectablerodlength,

signalattenuationduetosurroundingmedia,andsimulatedcorrosionintiebackrods. The

signalsintiebackrodsshowedadistinctbackecho,withlowsignalamplitudefollowing,dueto

thedispersionofthewavefromthethreads. Sincethebackechodidnotreflectfromthe

threads,theamplitudewasnotaffected. Thesignalattenuationtestsrevealedthattherewas

nosignificantamplitudelossinthebackechoforsand,loosesoil,orcompactsoil. Aprojected

detectablerodlengthwasfoundtobe40feetwiththepulseechomethod. Finally,simulated

corrosioninWilliamstiebackrodsshowedthatlocationanddiameterofsimulatedcorrosion

weredetectableinthreadedrodswitha90anda45transitionangle.

Theworkpresentedinthisdissertationformsoriginalresearchthatcontributestothefollowing

fields:

1. SafetyofstructureswithinthefieldofCivilEngineering

2. AddingtothecurrentliteratureofNDTtesting


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Thesecontributionsinclude:

1. Effectoftransitionsontheultrasonicsignal

2. Effectoflengthofcorrosionontheultrasonicsignal

3.

Effectofsoilontiebackrodsignalattenuation4. DetectionofsimulatedcorrosioninWilliamstiebackrods

Basedontheresearchpresented,thefollowingrecommendationsweremadeforfuture

research.

1. Investigatetheminimumdetectablecrosssectionlossin1.0in.diametertiebackrods.

Forexample,machinerodswith0.8125in.,0.875in,0.9375in.diameterofsimulated

corrosionandidentifythesmallestsimulatedcorrosionthatexhibitsaflawecho.

2. Investigatethedetectabilityofsimulatedcorrosioninlargerdiametertiebackrods. For

example,machinesimulatedcorrosionin2.0in.and3.0in.diameterWilliamsrods,and

identifythedetectablegeometries.

3. Investigatethedetectabilityofadditionalgeometriccharacteristicsofsimulated

corrosionontheultrasonicsignalforthepulseechomethod. Forexample:

machinesimulatedcorrosionwithavariationindiameterinthecorrodedregion,

insteadofuniformreduceddiameter.

machinenonconcentriclossofcrosssectioninsteelrods.

4. Investigatethedetectionofultrasonicsignalsinrodswithcurvaturetomimicrodsthat

havebentduringsettlement. Bendmultiplecommercialtiebackrodstovariousradii

andmonitortheultrasonicsignal.


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ReferencesCited:

ASTMStandardA108.(2007).StandardSpecificationforSteelBar,CarbonandAlloy,Cold

Finished,DOI:10.1520/A010807.WestConshohocken,PA:ASTMInternational.

ASTMStandardA29.(2005).StandardSpecificationforSteelBars,CarbonandAlloy,Hot

Wrought,GeneralRequirementsfor,DOI:10.1520/A0029_A0029M05.WestConshohocken,

PA:ASTMInternational.

ASTMStandardA615.(2008).StandardSpecificationforDeformedandPlainCarbonSteelBars

forConcreteReinforcement,DOI:10.1520/A0615_A0615M08B.WestConshohocken,PA:

ASTMInternational.

ASTMStandardD2216.(2005).StandardTestMethodsforLaboratoryDeterminationofWater

(Moisture)ContentofSoilandRockbyMass,DOI:10.1520/D221605.WestConshohocken,

PA:ASTMInternational.

ASTMStandardD422.(2007).StandardTestMethodforParticleSizeAnalysisofSoils,DOI:10.1520/D042263R07.WestConshohocken,PA:ASTMInternational.

ASTMStandardD4318.(2005).StandardTestMethodsforLiquidLimit,PlasticLimit,and

PlasticityIndexofSoils,DOI:10.1520/D431805.WestConshohocken,PA:ASTMInternational.

Beard,M.,Lowe,M.,&Cawley,P.(2001).InspectionofRockboltsusingGuidedUltrasonic

Waves.ReviewofProgressinQuantitativeNondestructive Evaluation,11561163.

Bray,D.E.,&Stanley,R.K.(1989).NondestructiveEvaluation.NewYork:CRCPress.

Davies,R.(1948).ACriticalStudyoftheHopkinsonPressureBar.Phil.Transactions,375457.

Esser,A.J.,&Dingeldein,J.E.(2007).FailureofTiebackWallAnchorsDuetoCorrosion.Geo

Denver2007,(pp.110).Denver.

Hudson,G.(1943).DispersionofElasticWavesinSolidCircularCylinders.PhysicsReview,46

51.

Kolsky,B.(1963).StressWavesinSolids.NewYork:DoverPublicationsInc.

Krautkramer,J.,&Krautkramer,H.(1990).UltrasonicTestingofMaterials.Berlin:Springer

Verlag.

Light,G.M.,&Joshi,N.R.(1987).UltrasonicWaveguideTechniqueforDetectionofSimulated

CorrosionWastages.NondestructiveTestingCommunications ,1327.

Main,L.G.(1988).VibrationsandWavesinPhysics.NewYork:CambridgeUniversityPress.

Niles,G.B.(1996).InSituMethodforInspectingAnchorRodsforSectionLossUsingthe

CylindricallyGuidedWaveTechnique.IEEETransactionsofPowerDelivery,16011605.


123/123

Pochhammer,J.(1876).Aboutthereproductionspeedsofsmallvibrationsinaninfinite

isotropiccircularcylinder.JournalofPureandAppliedMath,324336.

Pollock,D.G.(1997).ReliabilityAssessmentofTimberConnectionsThroughUltrasonic

InspectionofBolts.TexasA&MUniversity.

USArmyCorpsofEngineers.(1994,March31).RetrievedJanuary18,2009,fromDesignof

SheetPileWalls:http://140.194.76.129/publications/engmanuals/em111022504/

WilliamsFormEngineeringCorp.(2008).RetrievedApril2,2009,fromTieRodInformation:

http://www.williamsform.com/

ultrasonic detection of simulated corrosion in 1 inch diameter steel tieback rods

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