用低变形传感器监测民用工程结构变形的一致性毕业设计外文翻译

1、X0.5Low-coherence deformation sensors for themonitoring of civil-engineering structuresD. Inaudi a, A. Elamari b, L. Pflug a, N. Gisin b, J. Breguet b, S. Vurpillot a“ IMAC, Laboratoryof Stress Analysis, Swiss Federal Instituteof Technology, CH- 1015 Lausanne, Switzerland GAP, Group ofApplied Physic

2、s -Optical Seciion, Geneva University CH-1205 Geneva, SwitzerlandRcccivcd 25 January 1993; in revised form 8 March 1994; accepted 25 March 1994AbstractAn optical-fiber deformation sensor with a resolution of 10 pm and an operational range of 60 mm has been realized. The system is based on low-cohere

3、nce interferometry in standard single-mode telecommunication fibers. It allows the monitoring of large structures over several months without noticeable drift. No continuous measurement is needed and the system is insensitive to variations of the fiber losses. This technique has been applied tothe m

4、onitoring of a 20 mX5 mm, 120 ton concrete slab over six months. It is possible tomeasure the shrinkage of concrete and its elastic coefficient during pre-straining, giving reproducible results in good agreement with theoretical calculations and measurements performed on small concrete samples. This

5、 paper describes the optical arrangement andthe procedures used to install optical fibers in concrete.Keywor&:Ikformation sensors; Civil-engineering structures1. IntroductionBoththesecurityofcivil-engineeringworksandthe lawrequireaperiodicmonitoringofstructures.Themethodsusedforthispurpose,such astr

6、iangulation, waterlevels orvibratingstrings,areoftenoftedious applicationand require one or many specializedoperators.Thiscomplexityandtheresultingcosts limit thefrequencyofthemeasurements. Furthermore,the spatialresolutionisoften poorandthe observationisusuallyrestrictedtothesurfaceoftheobject.Ther

7、e is thus a realdemandfora toolallowinganinternal,automaticand permanentmonitoringof structureswithhighaccuracy andstabilityoverperiods typicallyoftheorderof100yearsforbridges. Inthisframework,fiber-opticsmartstructures(i.e.,structureswithself-testingcapabilities)are gaininginimportanceinmanyfieldsi

8、ncludingaeronauticsandcompositematerialmonitoring.Thistechnologycanbeappliedincivil1engineeringandinparticularforthe short-andlong-timeobservationoflargestructuressuchasbridges,tallbuildingframes,dams, tunnels, roads,airportrunways,domes,pre-stressingandanchorage cables. The monitoringofsuch structu

9、resrequiresthedevelopmentof a measuring techniquewithhighaccuracy,stabilityandreliabilityoverlong periods. Ithas tobeindependentofvariations in the fiber losses and adapted to the adverse environmentof a building site.To reduce thecostoftheinstrumentation,itis furthermoredesirabletousethesame portab

10、lereadingunitforthe monitoringof multiplestructures.Wedescribe hereasystem based onlow-coherenceinterferometryrespondingtoallthese requirements.Experimental arrangementThemeasuring technique relies on an arrayofstandardtelecommunicationopticalfibersinmechanicalcontactwithconcrete.Anydeformationofthe

11、hoststructureresults jna change intheopticallengthof he fibers.Each sensor lineconsistsoftwosingle-modeibers:onemeasurementfiberinmechanicalcontactwiththestructure(gluedor cemented) and a referenceiberplacedloosenearthefirstone(ina pipe)inordertobeatthesame temperature.Since themeasurementtechniquem

12、onitorsthelengthdifferencebeweenthesetwo fibers, only the mechanical deformation willhavean effecton theresults whileall otherperurbations,such as thermallyinducedchanges inthe refractiveindexofthefibers,willaffectthetwoinanidenticalwayandcanceleachanotherout. Tomeasuretheopticalpathdifferencebetwee

13、nthetwofibers, alow-coherencedoubleinterferometerintandemconfigurationhasbeenused(Fig.1)l.ThesourceisanLED(light-emittingdiode)workingaround1.3pmwithacoherencelengthL,of30pmandaratedpowerof200pW.Theradiationislaunchedinto a single-modefiberandthendirectedtowardthemeasurement and the reference fibers

14、 by meansofa50:50single-modedirectionalcoupler.Attheendsofthefiberstwomirrorsreflectthelightbacktothecoupler,wherethebeamsarcrecombinedwitharelativedelayduetothelengthdifferenceAL,betweenthefibers, andthendirected towards the second (reference)interferometer. The referenceinterferometerisofMichelson

15、typewithoneofthearmsendedbyamobilemirrormountedonamicromctricdisplacementtablewitharesolution of 0.1 pm andanoperatingrange of50mm.Itallowstheintroductionofanexactly knownpathdifFcrenceAL,betweenitstwoarms.Thisfiberinterferometerisportableandneedsnoopticaladjustmentaftertransportation.Ithasbeendevel

16、opedbytheGAPwiththesupportoftheSwissPTTfor opticalcabletesting2.2The intensity at the output of the reference inter- ferometer is measured with a pig-tail photodiode and is then given by 3wherezz,r istheeffectiverefractiveindexofthefiber,zzgthegrouprefractiveindex(about1%higherthan nefrinsilica), A,

17、thecentralvacuumwavelengthofthelight,zi,theautocorrelationfunctiontakingthespectralcharacteristicsoftheemissionintoaccountand ALthephysicalpathdifferencebetweenthetwointerfering paths. Furthersimilar interferenceterms appear in Eq.(1)in thespecial cases whenAL,L,orAL, L,. Whentheopticalpathdifferenc

18、ebetween thearms inthe reference interferometercorresponds to the oneinducedbythetwofibersinstalledinthestructure(withinthe coherencelength of the source), interference fringesappear.ScanningAL,withthemirrorofthe referenceinterferometeritis possible to obtain AL = 0eitherwithAL,= AL,orwithAL,=-AL,an

19、dthustwointerferencefringepackets as described by Eq. (1). The mirrorposition correspondingto AL,=0 also produces an interferenceand is used as a reference. These threefringepacketsarcdetectedbymeansofalock-inamplifiersynchronized withthe mirrordisplacements. Themirrordisplacementsandthedigitalizati

20、onofthelock-inoutputare carriedoutbymeans ofa portablepersonal computer.Sincethereferencesignal is gcneratedseparatelyand does nothave a constant phase relationtotheinterferencesignal,onlytheenvelope ofthedemodulatedsignal has aphysicalmeaningandcorrespondstotheenvelopeofthefringepattern.Alock-inplo

21、tshowing thethreetypicalpeaks is shown in Fig. 2. Each peak has awidthofabout 30 pm. The calculationofits center ofgravitydetermines its positionwitha precisionbetterthan10pm.Thisprecisionis the limitingfactorofthewholemeasurement technique.SinceAL,isknownwithmicrometerprecision,itis possible tofoll

22、owAL,withthesame precision.3Fig. 1. Experimental setup of the low-coherence double Michelson interferomctcr. D. Innudi et al. 1 Semors andFig. 2. Typical fringe cnvclope as a function of the mirror position. The distance between the central and the lateral peaks corresponds to the length difference

23、between the measurement and the reference fibers mounted in the table. Any change in the length of the structure results in a change in the position of these peaks. Any change in the losses of the fibers will result in a change of the height of the peaks. The central peak is fixed and used as a refe

24、rence.The path difference AL, is proportional to the de-formation of the structure AL, with the relation between the two given by 4where p is Poissons ratio and pij is the strain optic tensor (Pockcls coefhcients). The coefficient 5 takes into account the variation of the effective index neff in a f

25、iber under strain. A degradation of one or both fibers (due to aging, for example) will result in a lower visibility4of the fringes but will not affect its position. The information about the deformation of the structure is encoded in the coherence properties of light and not in its intensity as in

26、the majority of the sensors applied to date in civil-engineering structures, mostly based on microbend losses and/or optical time-domain reflectometry (OTDR) techniques. Interference peaks resulting from reflections as low as -30 dB of the source power can be detected by our system without phase mod

27、ulators. By modulating the phase in one of the four arms of the two interferometers, one can increase the dynamic range of the device to more than 100 dB 5.Even if the polarization dispersion and bend-induced birefringence in the sensing fibers could reduce the visibility of the interference fringes

28、 or even split the fringe packets, none of those effects was observed in our experiment. No adjustment of polarization between the reference and the sensing arm was then necessary. A good mechanical contact between the measurement fiber and the structure under test is fundamental. In this study a nu

29、mber ofinstallation procedures have beentestedandoptimizedforthedifferentmeasurements(shrinkage,elasticitymodulus,etc.).Themounting techniques canbe divided into two main categories: full-lengthcouplingandlocalcoupling.During our tests five outofsixopticalfiberpairs witha0.9mm nyloncoating,beingmoun

30、tedonthe externalfaceofa 20m longplasticpipeandprotected onlywiththin rubberbands(seeFig.3(a),survived theconcreting process.Duringthesettingprocessthe concreteenvelopsthefiberandrealizesthedesired mechanicalcontact.Those fibers showed a minorincreaseinthescatteringlossesandtheappearanceof smallpara

31、sitepeaks.Themeasurementson thosefibers wereconsistentwiththeresultsobtainedwithotherinstallationtechniques(seebelow).Itseemsthatforfull-length coupling the nylon coatingtransmitsthe structuredeformations(extensionand shortening)entirelytothefibercore.Thisinstallationtechnique is verypromisingwhenco

32、mparedtotheusualprocedure, consistingofapipeprotectingthefibersduringthe pouringofconcreteandbeingremovedbeforethe settingprocessbegins.Thissecondmethodseemsmore adaptedtosmallsamplesthanto full-scalestructures. Elevenotherfiber pairsweregluedatthetwoends ofthetableafterremovinglocallytheprotectivec

33、oating layersofthefibers(seeFig. 3(b). The silica fiberwas ftxedwithepoxygluetoametallicplatemountedon theendfacesoftheconcretestructure.Thegluing lengthwas about 20 mm. Apre-strain(between0.1 and0.4%)hasbeengiventothosefibersduringthe gluingprocesstokeepthemunder tensionandallow the measurementofbo

34、thexpansionandshrinkageof thestructure.Thistypeoflocalcouplingprovedtobe themostreliable,butwasnotadaptedtofollowing the5deformation during the pre-stressing of the table because ofthe importantsurfacedeformations occurring during this operation.The problemhas beenovercome bygluingotherfibersinsidet

35、he pipesat abouttwometers fromthe surfaces,i.e.,far fromtheforceinsertion region(seeFig.3(c).Fig.3.Schematicrepresentationofthreeoftheinstallationtechniquesused:(a)directconcretingofthemeasurement fiber mounted on aplasticpipe;(b)fibergluedatthetablesurface; (c) fiber glued insidethe pipe at 2m from

36、 the pipeends.Fig. 4. Topandside viewsoftheconcretetablemeasuredinthe experimentandposition ofthesensing-fiberpairs A, B,CandD. Fibers A,B and C arcgluedat the surface ofthestructure,whilefiber D is gluedinside a pipe,2 mawayfromthe surface of the slab. Twelve morefihcr pairswereinstalled, but are n

37、ot shown for simplicity.6To study thepossibleeffectofcreepinstrained fibers6,one fiberhasbeenmountedonamechanicalsupportthatallowsthefibertobetightenedonlyatthetime of the measurement. No difference between this fiberand those permanentlystrained has beenobservedover a periodof sixmonths, confirming

38、 the assumptionthatnocreepoccursforfiberstrainsbelow1%.Sincethescanningrangeofthemirroris5mm,itwaseasyto cleavethe20mlong fiberswithinthismargin.TheFresnelreflectionofthecleavedfiberscombinedwiththehighdynamicofthesystemallowameasurementofAL,.ThisvalueofAL, can than be usedtocorrectthecuttingand obt

39、ain pairs with length differencesbelow1 mm.Twoferrulesweretheninstalledon the fiberendsandmountedinfront of a polished inoxsurface. Chemical silverdepositionwas also used to producemirrors on the cleaved fiber ends.Fig.6. Comparisonbetweenthemeasurementsperformedon thestructurebyopticalfibersandtheo

40、nesperformedon 360mmand500mmsamplesinamechanicalmicrometercomparator.Themeasurementonthesampleswaspossibleonlyduringthefirsttwo months.ResultsSeverallong-andshort-termmeasurementshave been carriedon a 20m x5m x0.5 m,120tonconcreteslab intended tobe used as a vibration-isolatedbase foropticalanalysis

41、(inparticular by holographic andspeckle interferometry) oflargestructures7.7Thisstructurehasbeenconcretedindoors,allowingcontrolledenvironmcntalconditionsandknownconcretecompositiontobeachieved.Sampleshavebeenpreparedwiththe samematerialcompositionand areunderpermanenttestfortheirmechanicalpropertie

42、s(resistance,shrinkageandelasticcoefficient).Thisallowsadirectcomparisonbetweentheresultsonthefull-scalestructureandthesamples.Thetablehasbeenpre-strained23daysafterconcretinginbothlengthandwidth. It was possibleatthistimetomeasuretheelasticcoefficient ofthematerialinfullscale.Fig.4showsaschematic r

43、epresentationofthetableandthepositionofthefibersreferredtointheexperimentalresults.Atthetimeofwriting,thetablehasbeenundertestforsixmonths.Overthisperiodtheshrinkageinthelongitudinaldirection(i.e.,over20m)hasbeenabout 6 mm.Weshowin Fig.5 theresultsof themeasurements forthree(glued)fibersover175days.

44、The tablehas aTprofile(Fig.4).ItisevidentfromFig.5thatthefibersmountednearthebordersofthetable,i.e.,werethethicknessissmaller,registeredalargershrinkage,asexpectedaccordingtotheconcretetheory.Adjacentfibersgiveconsistentresultsindependentlyoftheinstallationtechnique.Nodifferencehasbeennoticedbetween

45、thefibersunderpermanenttensionandthoseloosenedbetweenthemeasurements,suggestingthatnocreepofglass fibers occurred.Theshrinkagemeasuredwiththefibersystemhasbeencomparedduringthefirsttwomonths with the resultsobtainedwitha mechanicalcomparatormountedontwosamplesof360mmand500mm,respectively.Theobserved

46、deformationshavebeenscaledto20m andarecomparedinFig.6totheresultsobtained withfibersBandC.Verygoodagreementisfoundbetweenthetwomeasurements.AtheoreticalcomparisonbetweentheexperimentalresultsandtheSwisscivilengineeringstandardshasalsobeencarriedout.Theexperimentaldataandthestandardsareinagreementwit

47、hinf 10%.Amoreaccuratesimulationincludingthephysico-chemicalpropertiesoftheconcreteusedisunderdevelopment.Thetablewaspre-stressed23daysafterconcreting.Thefivesteelcablesrunningoverthelengthofthetableandthefortycablesrunningoveritswidthwerestretchedwithaforceof185kN(18.5Tons)each.Thefibersgluedtothes

48、urfaceandthoseindirectcontactwithconcreteoverthewholelengthmeasuredanexpansionofthetableinsteadoftheexpectedshrinkage.Thisisduetotheimportantsurfacedeformationsoccurringneartheforce-insertionpoints,i.e.,nearthepre-stressheadsthat wereplacednearthefiberends.FiberDgluedinsidetheplasticpipeat2mfromeach

49、end8wasnotsubjecttotheselocaleffectsandmeasuredashorteningof0.23 mm.The theoreticalcalculationbasedonanelasticcoefficientof30kN/mm 2gives ashorteningof 0.28mmatthebordersand0.19mmat thecenterofthetable.SincefiberDwasplacedin anintermediateposition,theexperimentalvaluecan beconsidered to be ingood ag

50、reementwiththe theory.ConclusionsA newdeformationsensoradaptedtothemonitoringofcivil-engineeringstructureshasbeenproposed.itisbasedonlow-coherenceinterferometryin standardlowcosttelecommunicationfibers.Theresolutionofthemeasurementsis10pm,theoperationalrangeis60mmandthestabilityhasbeentestedoversixm

51、onthswithoutnoticeabledrift.Thereadingunitiscompactandportable,needingnoopticalalignment beforethe measurements.Itiscontrolledby aportablepersonal computer,whichisalsoresponsibleforthedata trcatment.Thesamereadingunitcanbeusedtomonitormultiplefiberlinesbysimplemanualunplugging.Thistechniqueisfurther

52、morepracticallyinsensitivetoincreasedlossesduetodegradationofthefibers. A test studyhasbeencarriedoutona20m 5mX 0.5mconcreteslab,givingconsistentresultswhencomparedtoothermeasurementtechniquesbasedonsamplesor toconcretetheories.Itwaspossibletofollowconcreteshrinkageoversixmonths(thecxper-imentwillco

53、ntinueforaboutfiveyears)and tomeasuretheelasticcoefficienton the full-scalestructure.Differentfiber-installationtechniquesadaptedtothemeasurementofvariousparametershavebeentestedin building-siteconditions. Thistechniqueappearsverypromisingforthemon-itoringofcivil-engineeringstructuressuchasbridges,

54、damsandtunnels,allowing internal, automatic and permanentmonitoringwithhighprecisionandstability overlongperiods.AcknowledgmentsTheauthorsareindebtedtoR.PassyandR.Delezfortheirassistance,encouragementandhelpfuldis-cussion.WeacknowledgetheIMMInstituteinLugano(Switzerland)forplacingthetable atourdispo

55、salandforthe measurementscarriedoutonconcretesamples.WearegratefultoDrM.Pedrettiand IngR.Passerafortheir personalengagementintheproject.WealsothankCablopticinCortaillod (Switzerland) forsup-plyingalltheopticalfibers used in theexperiment. Thisresearchhasbeenperformedwiththefinancialsupportof CERS(Co

56、mmissionpour 1Encouragement delaRecherche Scientifique).9ReferencesA.Koch and R.Ulrich,Fiber optic displacement sensor with 0.02mm resolution buy white-light interferometry,sensors and actuators A,25-27(1991)201-207N.Gisin,J.-P.Von der weid and J.-P.Pellaux,Polarization mode dispersion ofshort and l

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58、ethod of integrated optics devices,Proc.2nd Opt. Fibre Meas. Conf: OFMC 93, Turin, Ztuly, Z993, pp.143-146.J.-P.Jaguin and A.Zaganiaris,La mecanique de rupture appliquee aux fibres optiques, Verres Refract, 34 (Jul-Aout)(1980).7L.PflugandM.Pedretti,Constructionof aloo-tonnesholographictable,ZS&TISPI

59、EZnt.Symp.ElectronicImaging,SanJose,CA,USA,1993,pp.50-54.10传感器和执行器A 44 （1994） 12.5-130用低变形传感器监测民用工程结构变形的一致性D.Inaudi a , A.Elamarib, L.Pflugb, N.Gisinb, J.Breguetb, S.VurpillotaaIMAC、实验室的应力分析 , 瑞士联邦理工学院 , CH-1015瑞士洛桑bGAP, 群应用物理 - 光学部分 ,日内瓦大学， CH-1205瑞士日内瓦举行1993 年 1 月 25 日实验 ;1994 年 3 月 8 日修订 ,1994 年

60、3 月 25 日发表文摘一个光纤变形的分辨率的传感器 ,10 m和运行范围的 60 毫米已经实现了。该系统是基于标准 low-coherence 干涉法在单模电信纤维。它允许的监测在几个月内大型结构没有明显的漂移。不需要连续测量的系统变化不敏感的纤维的损失。这种技术被应用到监测 20 米的 X0.5 X5 米混凝土板 120 吨米 , 为期 6 月。即可测量的收缩混凝土及其弹性系数在售前使劲地给可再生的结果吻合很好进行理论计算或测量小混凝土样品。本文阐述了光学安排和使用程序安装光纤有限公司。关键词 : 变形传感器 ; 民用工程结构1简介民用建筑的安全工作和法律需要定期监测结构。这方法用于此目的