自密实混凝土翻译资料英语Word文件下载.docx
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自密实混凝土翻译资料英语Word文件下载.docx
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Received27May2010;
accepted17September2010.
Availableonline16October2010.
Abstract
Thepresentworkresumestheexperimentalandnumericalresearchcarriedoutforthedevelopmentofanumericaltoolableofsimulatingthetensilebehaviourofsteelfibrereinforcedself-compactingconcrete(SFRSCC).SFRSCCisassumedasatwophasematerial,wherethenonlinearmaterialbehaviourofSCCmatrixismodelledbya3Dsmearedcrackmodel,andsteelfibresareassumedasembeddedshortcablesdistributedwithintheSCCmatrixaccordingtoaMonteCarlomethod.Theinternalforcesinthesteelfibresareobtainedfromthestress–sliplawsderivedfromtheexecutedfibrepullouttests.Theperformanceofthisnumericalstrategywasappraisedbysimulatingthetensiletestscarriedout.Thenumericalsimulationsshowedagoodagreementwiththeexperimentalresults.
Keywords:
Steelfibrereinforcedself-compactingconcrete;
Micromechanics(C);
Tensileproperties(C);
Finiteelementanalysis(C)
ArticleOutline
1.Introduction
Insteelfibrereinforcedconcrete,SFRC,steelfibresandmatrixarebondedtogetherthroughaweakinterface,whichbehaviourisimportanttounderstandandaccuratelymodelthemechanicalbehaviourofSFRC,sincethepropertiesofthiscompositearegreatlyinfluencedbytheinterfacezonebetweenfibre/matrixand,consequently,bythemicro-mechanicalfibrereinforcementmechanismsthataremobilized.Whenthesecompositesarereinforcedwithlowfibrevolumeratios,thefibrecontributionbenefitsarise,mainly,nottosayalmostexclusively,afterthecrackinitiation.
Thepost-crackingbehaviourofrandomdiscontinuousfibrereinforcedcompositescanbepredictedbytheuseofastress–crackopeningdisplacementrelationship,σ−w.Severalauthorsdevelopedmicro-mechanicalmodelstoobtaintheσ−wrelationship,sinceforquasi-brittlematerials,thestress–crackopeningrelationshipthatsimulatesthestresstransferbetweenthefacesofthecrackhasasignificantimpactonthebehaviourofastructureafteritscrackinginitiation.InthecaseofFRC,theσ−wrelationshipcanbeapproximatedbyaveragingthecontributionsoftheindividualfibresbridgingthematrixcrackplane,definingforthispurposetheprobability–densityfunctionsofthecentroidaldistanceoffibresfromthematrixcrackplane,andoftheorientationangle[1],[2]and[3].Thesemodels,whicharebasedonanaveragingprocessofalltheforcesthatarecarriedoutbythefibresoveracrackplane,canprovidethegeneralmaterialcompositebehaviourwithreasonableaccuracybymodellingthemainmechanismsofasinglefibrepullout.However,ingeneral,theydonotaccountforsomeaspects,suchas,fibrebendingruptureandmatrixspallingattheexitpointsofinclinedfibres.
Anotherdifficultyonthepredictionofthepost-crackingbehaviourofaFRCinarealstructureisthatthematerialbehaviourinatestspecimenmaydifferfromthebehaviourofarealstructuralelement.Itiswelldescribedinliteraturethatvariouscastingproceduresandstructuralshapesmayresultinpredominantfibreorientationintoparallelplanes[4]and[5].Inthecaseofsteelfibrereinforcedself-compactingconcrete,SFRSCC,thepredominantfibreorientationcanbealongtheflowitself(inthefreshstate)andalongtheboundarysurfacesduetothewall-effect[6]and[7].Apredefinedorientationofthesteelfibresparalleltothetensiledirectioninatestspecimenmayresultinoverestimatingthepost-crackingmechanicalpropertiesofthesteelfibrereinforcedconcrete,whencomparedwithspecimenswithequalamountoffibres,howeverwitharandomfibreorientation.
Havinginmindtheaforementionedaspectsandfactorsthatinfluenceandcontributetothepost-crackingbehaviourofaFRC,approachingtheFRCasacontinuummaterialmayleadtoaroughestimationofthemechanicalbehaviourofacertainFRCstructuralelement.Eventhough,materialbehaviourlawsforFRCcanbeobtainedwithgreataccuracybyinverseanalysisproceduresoftestspecimens,theselawsmaynottranslatetheaccuratematerialbehaviourwithinaspecificstructuralelement[8].ItisfeasibletoassumeFRCasatwophasematerial,namely,anunreinforcedconcretematrixphaseandafibrephase,withthelatteronecomprisinginformationaboutfibredensityandorientationdependingonwhereandhowthematerialisapplied.Hence,thisapproachcansomehowenhancethenumericalsimulationofFRCstructures,thusexcludingtheuseofbiasedmaterialbehaviourlaws,i.e.fromamacro-mechanicalbehaviourpointofview,obtainedfromtheinverseanalysisofexperimentaltests.
Therefore,basedonthepriorreasoning,thepresentworkispresentedwithanumericalapproachwhereSFRCistreatedasaheterogeneousmediumcomprisedofonehomogeneousphase(aggregatesandpaste),andanotheronecomposedofthesteelfibres.Thefractureprocessofthecementitiousmatrix(unreinforced)ismodelledwitha3Dmulti-directionalfixedsmearedcrackmodel.Thisunreinforcedconcretephaseisdiscretizedbysolidfiniteelements.Ontheotherhand,thestresstransferbetweencrackplanesduetothefibresbridgingactivecracksismodelledwith3Dtrusselements.Anonlinearbehaviourlawisassignedtotheselastelementsinordertoaccountthefibre/matrixinterfaceproperties.Theselawsarebaseduponthemicro-mechanicalbehaviourofthefibres.Therandomfibredistribution,overthematrix,issimulatedwithanalgorithmbasedontheMonteCarlomethod,providingarealisticdistributionofthefibresoverabulkelement.Thedevelopedalgorithmenablestotakeintoaccountfactorsthatinfluencethefibrestructure,suchas:
theso-calledwall-effectandthehighflowabilityoftheSFRSCC[8].Thegeometry,positioningandorientationofthefibresaresubsequentlyinsertedinathree-dimensionalfiniteelementmesh.Thecableelementsrepresentingthefibresareconsideredasembeddedelements.Withinafirststageoftheresearch,asasimplification,theembeddedelementismodelledwithaperfectlybondedformulation.Hence,thebond–slipbehaviourissimulatedinanindirectfashionfromthetransformationofaload–sliprelationshiptoatensilestress–strainrelation.Moreover,totheauthor'
sknowledgethiskindofapproachisquitenovel,andwithinnumericalmodelsfortheFRCwiththesamephilosophyonlymeso-levelmodelsusinglatticestructuresareknown,e.g.[9],[10]and[11].
2.Materials
ThematerialsusedinthecompositionoftheSFRSCC,were:
cement(C)CEMI42.5R,limestonefiller(LF),superplasticizer(SP)ofthirdgenerationbasedonpolycarboxilates(Glenium®
77SCC),water(W),threetypesofaggregates(fineriversand,FS,coarseriversand,CS,andcrushedgranite5–12
mm,CA)andDRAMIX®
RC-80/60-BNhookedendsteelfibres(length,lf,of60
mm,diameter,df,of0.75
mm,aspectratio,lf/df,of80,andyieldstressof1100
MPa).ThemethodusedtodefinetheSFRSCCcomposition,themixingprocedureandotherpropertiesoftheSFRSCCinthefreshstatecanbefoundelsewhere[12].
TostudytheSFRSCCtensilepost-crackingbehaviour,twobatcheswithdistinctfibrecontents(Cf),30and45
kg/m3wereused.Table
1includesthecompositionsthathavebestfittedself-compactingrequirementsfortheadoptedtwofibrecontents.RemarkthatinTable
1,WSisthewaternecessarytosaturatetheaggregates,andW/Cisthewater/cementratio.TheWSparcelwasnotusedtocomputetheW/Cratio.ThefibrepullouttestswereperformedontheSCCmediumwithafibrecontentof30
kg/m3.
Table
1.Compositionsfor1
m3ofSFRSCC.
CementtypeI42.5R
Limestonefiller
Water
Watertosaturateaggregates
Superplasticizer
Finesand
Coarsesand
Crushedcalcareous
Steelfibres
W/C
(C)
(LF)
(W)
(WS)
(SP)
(FS)
(CS)
(CA)
(Cf)
[kg]
[dm3]
359.4
312.2
96.9
64.7
6.9
108.2
709.4
665.2
30
0.29
401.7
344.2
117.3
65.4
7.6
178.3
668.1
45
0.31
Full-sizetable
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FordeterminingtheSFRSCCpropertiesinthefreshstate,theAbramsconewasusedininvertedposition(concreteflowedthroughthesmallorificeofthecone).Atotalspreadover700
mmwasmeasuredandnosignofsegregationwasdetectedasthemixtureshowedgoodhomogeneityandcohesion.
3.Experimentalresearch
3.1.Fibrepullouttests
3.1.1.Seriesoftests,preparationofspecimensandSCCproperties
Thepullouttestsweredividedintotwomaingroups,accordingtothegeometrytypeofusedfibres:
hookedendsandsmooth.Theinfluenceofthefibre'
sembeddedlength,Lb,(10,20and30
mm)andfibre'
sorientation(0,30and60°
)onthepulloutresponsewasassessedinbothgroups.Eachseriesofthesmoothfibrescomprisesthreespecimens,whereassixspecimenscomposeeachseriesofthehookedfibres.SmoothfibreswereobtainedbycuttingthehookedendsoftheRC-80/60-BNfibreswithpliers.Codenamesweregiventothetestseries,whichconsistonalphanumericcharactersseparatedbyunderscores.Thefirstcharacterindicatesthefibretype(S—smooth;
H—hooked),thesecondstringindicatestheembeddedlengthinmm(forinstance,Lb10representsafibreembeddedlengthof10
mm)andfinallythelastnum
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