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1、InternationalJournalofFracture95:195–219,1999.©1999KluwerAcademicPublishers.PrintedintheNetherlands.EffectofstraingradientsonthesizeeffectofconcreteinuniaxialtensionMARCELR.A.VANVLIETandJANG.M.VANMIERFacultyofCivilEngineeringandGeosciences,DelftUniversityofTechnology,P
2、.O.Box5048,2600GADelft,TheNetherlandsReceiving4July1998;acceptedinrevisedform18December1998Abstract.Aseriesofuniaxialtensionexperimentshasbeenconductedtoinvestigatethesizeeffectonstrengthandfractureenergyofquasibrittlematerialslikeconcreteandsandstone.Thispaperfocusesonth
3、eresultsoftheconcretetests,andspecificallydealswiththevariationofthenominalstrengthforspecimensofsixdifferentsizesinascalerangeof1:32.Itwasfoundthatundergivenexperimentalconditions,thenominalstrengthstronglydependedonthespecimensize.Moreimportanthowever,isthefactthatmostof
4、thissizeeffectcouldbeattributedtostraingradientswhichwerepresentinthecrosssectionofthespecimens.Thesestraingradientswerecausedbythespecimenshape,loadeccentricityandmaterialinhomogeneity.Throughacombinationofexperimentaldataandasimplelinearelasticanalysis,theimportanceofst
5、raingradientswithrespecttotheultimateloadlevelcouldbevisualized.Thisleadstotheconclusionthatstudyingamaterialsizeeffectisnotpossiblewithouttakingintoaccountstructuralstress/straingradients.Keywords:Concrete,sizeeffect,nominalstrength,materialinhomogeneity,materialbehaviou
6、r,structuralef-fects,stress/straingradients.1.IntroductionInthefieldofmaterialscience,sizedifferencesbetweenlaboratoryspecimensandpracticalapplicationsareofteninevitable.Thisisespeciallysoforapplicationsconcerningmaterialslikeconcreteandrock.Thatthissizedifferencecanhavean
7、effecton,forinstance,thenominal(oraverage)strengthhasbeenrecognizedfordecades.Severalresearchersconductedvarioustypesoftestsanddevelopedtheoriestryingto`predict'thesizeeffectforscalerangeswhichcannotbetestedunderlaboratoryconditions.BestknowninthisrespectistheworkofBažant
8、(1997)andCarpinteri(1994).Alltheseeffortshaveledtotheknowledgethatasizeeffectexists,andthatitvar
