2Research on Horizontal Bearing Capacity of Precast0331.docx
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2Research on Horizontal Bearing Capacity of Precast0331.docx
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2ResearchonHorizontalBearingCapacityofPrecast0331
ResearchonHorizontalBearingCapacityofPrecastThin-wallSteelandspunConcretecompositePile
WANGXinquan1,ZHANGShimin1,LIAOJuan1,HUANGYingsheng1,LiuHong2
1.DepartmentofCivilEngineering,ZhejiangUniversityCityCollege,Hangzhou310015,China
2.CollegeofHarborCoastalandOffshoreEngineering,HohaiUniversity,Nanjing210098,China
Abstract:
Precastthin-wallsteelandspunconcretecompositepile(TSCpile)isanewtypeofsteel-concretecompositefoundationpilewhoseperformanceisbetweensteelpileandconcretepile.3DnumericalanalysismodelofTSCpilewasestablishedbyFEMsoftwareinthispaper.Bycomparedwiththelaboratorybendingtestresults,themodel’sreliabilitywasverified,andthenthebearingcapacityofTSCpileunderhorizontalloadwascalculated,moreover,influencesofdifferentcrosssectionparameters(diameter,wallthickness,steelpipethickness,pile’slength)onthehorizontalbearingcapacityofTSCpilewerestudied.Theresultsshowthat:
withtheincreaseofpile’soutsidediameter,wallthicknessofsteelpipe,wallthicknessofconcretepipeandlengthofpile,thehorizontalbearingcapacityofTSCpileisincreased.TheoutsidediameterhasabiggestimpactonthehorizontalbearingcapacityofTSCpile,thenpile’slength,steelpipe’swallthickness,andtheinfluencesofconcretepipe’swallthicknessaretheleast.
Keywords:
TSCpile;Horizontalload;Bearingcapacity
1.Introduction
PrecastThin-wallSteelandspunConcretecompositePile(theabbreviationisTSCpile[1])isakindofnewtypeoffoundationpilewhichismadebypouringconcreteintothecurlformedsteelpipe,madebyQ235BorQ345Bsteelplate(steelbelt),andthencentrifugingincentrifugetoformtheshape.Concretecompressionstrengthisnotlowerthan80MPa,whichcanbearlargeverticalloadandhorizontalload.TSCpileisanewtypeofsteel-concretecompositestructurewhosebearingperformanceisbetweensteelpileandconcretepile,anditowestheadvantagesofsteelpileandconcretepile,andcanavoidthedefectsofthesetwokindsofpileswhentheyareusedalone:
outsidesteelpipe’sstabilitywillbeincreasedbyinsideconcretepipe;Insideconcretepipe’scompressioncapacitywillbegreatlyincreasedbythe“lockringeffect”ofoutsidesteelpipe,whichturnthestressstateofconcretepipefromone-waytothree-dimensionalstressstate[2].TSCpileoweslotsofadvantages:
highanti-hammeringcapacity,highpenetratingpower,fastdrivingspeed,goodendurancequality,goodformingequality,lowmaterialcostandsoon[3].
TSCpilehasalreadysuccessfullybeenusedinpracticalengineeringprojectsinindustry,electricitypower,transportationandsomeotherfields[4].Harborengineeringprojectsusuallyusepileswithlargediameter,andcommonly,thepileobviouslybearstheeffectofwind,waveandsomeotherhorizontalloadseffect,whichneedhighflexuralcapacity.Now,therewerealreadymanyscholarsstudiedtheflexuralperformanceofTSCpilethroughlaboratorytestsmethod[5],theresultsshowedthatTSCpile’sflexuralcapabilityisgood,andalsoindicatedthatcrosssectionpropertiesofpilehadagreaterimpactonitsbendingperformance,butinactualengineeringprojects,TSCpilebearstheloadeffectwithsoiltogether.Modeltestandnumericalcomputationareusuallythemostusefulmethodstostudythepileloadingbehavior[6-8].ForthepopularizationofapplicationofTSCpile,thefullyplayofperformanceofsteelpipeandconcretematerialinTSCpile,andstudyingtheinfluencesofdifferentcrosssectionparameters(outsidediameter,pile’slength,concretepipe’swallthicknessandsteelpipe’swallthickness)onthehorizontalbearingcapacity,numericalmodelingofTSCpilewasusedtostudythehorizontalbearingcapabilityofTSCpile,theresultswerevaluedforTSCpile’sdesigningandproducing.
2.Analysismethod
TheanalysisusedFEMsoftwareAbaqus.Abaqusisoneofthemosteffectiveandreliablesoftwarewhichcontainsnonlinearfunctionsatpresentintheworldandithasobviousadvantagesforsolvingavarietyofnonlinearproblemsincivilengineeringprojects.Atthesametime,Abaqusalsoprovidesavarietyofmaterialconstitutivemodels.Inthispaper,thesoilbetweenpilesadoptedMohr-CoulombmodelprovidedbyAbaqus.
TSCpile’spurebendingtestdatawereusedtoverifythereliabilityofthemodel,becausefieldhorizontalbearingcapacitytestofTSCpilehasnotbeencarriedoutyet.Inlaboratorytest,TSCpile’sdiameteris1000mm,pilelengthis13m,totalwallthicknessis130mm,theoutsidesteelpipeusesQ235steelanditswallthicknessis10mm,insideconcreteisC80concrete.Theloadingsketchmapofprototypeisshowedinthefigure1.Lispile’slength(valueintestis13m),ais1/2loadingspan(valueintestis0.5m).Innumericalsimulation,soilusedMohr-Coulompmodel,thepilematerial(thesteelpipeandconcretepipe)usedelasticmodel.
Figure1istheTSCpileload–mid-spandeflectioncurvesmeasuredinlaboratorytestandcalculatedinnumericalmodeling.Ascanbeseenfromthegraph,theresultsofnumericalsimulationresultsandmeasuredresultsareclosetoeachother.Thenumericalsimulationmethodcanreflectthedeformationcharacteristicsofthematerialintheplasticphase,provedthatitisfeasibletousethefiniteelementanalysismethod.
Fig.1.TSCpileload-acrossdisplacementcurve
WhatnextdoisthebearingcapacitycalculationsandanalysisofTSCPilewhichisunderthehorizontalloadinthefoundation,andtheinfluencesofdifferentpileparameterswerediscussed.Inthenumericalmodel,thetypicaldouble-layeredfoundationwereused,namelytheupperforclay,thelowerforsandysoil.PilematerialsareQ235steelpipeandC80concretepipe,thespecificmaterialparametersareshownintable1.
Table1.Materialparametersusedinnumericalmodel
Sorts
Youngmodulus
E(MPa)
Poissonratio
υ
Weight
γ(kN/m3)
Cohesion
c(kPa)
Internalfrictionangle
Φ(º)
Dilationangle
ψ(º)
Clay
5.0
0.35
18
3
20
0.1
Sand
5.0
0.3
18
0.1
35
10
Concrete
2.8×104
0.167
23
-
-
-
Steelpipe
2.0×105
0.3
78
-
-
-
Inordertoanalyzetheinfluencesofpile’scrosssectionparametersonthehorizontalbearingperformance,differentpilesectionparameters(diameter,concretepipe’swallthickness,steelpipe’swallthickness,pile’slength)wereusedinnumericalcalculationstoanalyzeeachparameter’sinfluenceonthebearingcapability,thespecificcalculationparametersareshownintable2.
Table2.Calculationparametersinnumericalsimulation
Sorts
Parameters
OutsidediameterD/mm
600、800、1000、1200
Concretepipe’swallthicknesst/mm
100、120、140
Steelpipe’sthicknessts/mm
8、10、16、20
Pile’slengthL/m
8、10、15
Inordertoreducetheeffectofboundaryconditiononthecalculationresult,soil’sdiameterwaschosenas20timesofpile’sdiameterinthecalculation,andthethicknessofbottomsoillayerwas1timespile’slength.Concentratedforce,withagradualincrease,isappliedtothetopofthepileinthecalculation.Finiteelementmodelingisshowedinthefigure2.
Fig.2.Numericalmodel
3.Analysisofcalculationresults
3.1.Theinfluencesofpile’sdiameteronthehorizontalbearingcapacityofTSCpile
Figure3reflectstheinfluencesofdifferentpilediametersonload-horizontaldisplacementcurvesofthepile.Incomparisoncalculations,thetotalwallpilesectionthickness,steelpipe’swallthicknessandpile’slengthisconstant(t=110mm,ts=10mm,L=15m),andthematerialisthesame,thepilediameteristheonlyadjustedparameter.Ascanbeseenfromthegraph,withtheincreasingoftheTSCpile’sdiameter,thehorizontalbearingcapacityisincreasedobviously.Whenthehorizontalloadincreasesto250kN,horizontaldisplacementofTSCpile’stopisabout51.2mmwhenthepile’sdiameteris600mm,however,whenthepile’sdiameteris1000mm,horizontaldisplacementofTSCpile’stopisabout14.3mm,about27.9%oftheformer.Fromtheload–horizontaldisplacementcurvesshapealsocanbeseenthatwhentheloadincreasesto250kN,forTSCpilewithdiameter600mmhasclearlyenteredthestageofplasticdeformation,whilefortheTSCpilewithdiameter1000mmisstillinthestageofelasticdeformation.Andalsocanbeseenfromthegraph,withtheincreaseofdiameter,thehorizontalbearingcapacityofpileisalsoincreasing,buttheincreasingamplitudeissmallergradually.
Fig.3.Horizontalload-horizontaldisplacementcurvesofpileswithdifferentpilediameters
Figure4reflectstheinfluencesofdifferentpilediameteronhorizontaldisplacementcurveofthepilebody.Ascanbeseenfromthegraph,underthesameload,thechangeofthepilediameterstillhaseffectonitshorizontaldisplacement,especiallyforthehorizontaldisplacementoftheupperpilebody,theinfluenceisveryremarkable.Withtheincreaseofthediameter,thehorizontaldisplacementisreducedgradually,andinthiscalculation,thepilebodydisplacementdifferenceisobviousmainlyinmorethan5m.Withtheincreaseofdiameter,theflexuralcapacityisalsoincreasing,whichhaseffectonthehorizontaldisplacementofpilebodyaswellastheinfluenceonthemodeofactionbetweenpileandsoil.Whentheloadincreasesto250kN,forpilewith600mmdiameter,zerodisplacementappearsatabout7m,namelythedisplacementofpilehasthesamedirectionwiththehorizontalloadabove7m,whilethedisplacementofpileandhorizontalloadareintheoppositedirectionbelow7m,italsoledtothechangeoftheactiveearthpressureandpassiveearthpressure
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