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英语

有限元分析的剪力滞后效应对复合材料与钢桁架梁网

拉拔力的行为在钢纤维混凝土预应力链

净截面抗弯承载力的冷轧薄钢板通道括号螺栓在Web

预测剩余抗拉强度七线链使用单一的电线暴露于氯环境

试验研究钢的疲劳行为与不同的纤维增强复合材料板梁加强

钢筋混凝土结构元素的小规模建模用于岩土离心机

案例研究条件评估和加强住宅单位

引起的预应力损失的新混凝土箱梁竖向预应力锚固系统网

比较实验桥面与粘贴层板的性能和钢预制面板

抗震性能的参数分析与钢丝网加固的钢筋混凝土柱

有限元分析钢筋混凝土梁的剪切行为的高强度钢丝网

分析研究横向间距的钢铁和列约束

迷因算法设计方法与钢纤维钢筋预制预应力混凝土公路桥梁

有限元建模的混合复合梁桥梁在密苏里州

修复的预应力混凝土梁结合内部链连接和外部保税碳纤维增强塑料技术

后张混凝土结构的腐蚀监测引导超声波的使用分形分析

案例研究使用超高性能混凝土预应力梁桥设计

行为的预制混凝土剪力墙抗震地区:

比较混合动力和好胜的标本

应用钢丝网水泥混凝土梁施工的概念将钢筋砂浆永久的形式

实验评价轴向的行为加强圆形钢筋混泥土列

闭环钢筋混凝土梁

钢应力再分配和疲劳寿命评估的部分预应力混凝土梁在疲劳载荷

实验研究玄武岩纤维加固的钢筋混凝土梁和预应力钢丝复合镀层使用混合锚固系统

试验研究钢筋混凝土梁的弯曲行为加强钢丝连续玄武岩纤维复合板材

行为无筋砌体棱镜和梁改造工程胶结复合材料

时变分析复合梁的剪力滞效应

使用永久钢丝网水泥混凝土梁施工形式

碳纤维增强塑料的行为,在持续荷载作用下预应力混凝土梁在较低的温度

高强度混凝土应力-应变模型限制焊接钢丝网

高效复合梁预应力提供中小跨度桥梁。

2:

有限元分析及试验研究

传感器监视碳纤维增强塑料/混凝土债券在梁使用电化学阻抗谱

时变预应力损失历史粘土砖砌体墙抗震加固使用无粘结后张

磁滞多配置组件的镍钛诺和钢铁股:

实验和现象学识别

腐蚀损害量化的预应力使用声发射链

与预应力钢筋混凝土短柱的抗震性能

研究钢筋混凝土梁强度钢丝使用非线性有限元方法

抗弯加固钢筋混凝土梁使用分布式预应力高强度钢丝绳:

理论分析

光纤光栅传感器封装到7钢丝钢绞线预应力钢筋束的张力监测

Closed-loopwirereinforcedconcretebeams

Abstract

Thepurposeofthispaperistoseekawaytoimprovethetransferofpostcrackforcesinconcreteusingfibretechnology.Whenstraightfibresareaddedtoaconcretemix,thedirectionofthefibrescanbeinfluencedbythemould,ballingtogetherandrandomorientation.Thismayresultinasmallerpercentageoffibresbeingeffectivewhencomparedtothatwhichitwasoriginallydesignedfor,whencopingwithpostcrackforcesinconcrete.Theclosedloopfibretechnologyisdesignedtoplacethefibresinanorientationandpositionwheretheywillbeofmostbenefit,thusreducingthelikelihoodofhavingfibresinconcretewheretheywillnotbeofstructuralbenefitandasaresultofthis,theywillmaximisetheengineeringqualitiesofthefibreaddition.

Beamsweremanufacturedwithafixedadditionoffibresbyweight,andthentheyweretestedfortoughness（energyabsorption）usingathreepointtest,recordingloadanddeflection.Asanadditionalmeasureofthebeamsabilitytoabsorbenergy,adrophammertestwasusedtoanalysetheenergyabsorbedandthetotalimpactenergydissipated.

Thefindingsshowedasignificantimprovementinperformancewhenclosedloopfibreswereused,whencomparedtoanequaldoseofstraightsteelfibres.

Thisworkissignificantinthattheclosedloopfibresarenotcommerciallyavailableatthispresenttimeandthisresearchassistsinanewproductdevelopment.Closedloopfibresuseloweramountsofsteelthanstraightfibresforanequivalentperformancetobeachieved.Theythereforehavesustainabilitycredentialswithregardtocarbonfootprintanduseofrawmaterialsinconstructionandbuilding.

1.Introduction

Concreteisawidelyusedmaterialwithinthebuiltenvironment,havingmanyvariedapplicationsthatutiliseitsinherentqualities.Whenconcreteissubjecttorapidorimpactloadingitcansufferfailureasitisinherentlyweakintension.Theinclusionoffibresmaygosomewaytomitigatethisweakness.Thispaperinvestigatesanewclosedloopfibredesignwithregardtoenergyabsorption.

Concretewithhighdegreesoftoughnessisvaluableinmanyareasofconstructionandinfrastructureprovision.Motorwaybarriers,blastandprojectileresistancebarriers,industrialfloors,airportrunwaysandearthquakeresistantdesignallbenefitfromhighlevelsoftoughness/energyabsorption.

Thepostcrackperformanceofreinforcedconcretecanbeimprovedwiththeuseofsteelrebar,steelfabricorfibres.Thefibresareusedtoprovidereinforcementwithinthefullconcretesectionandnotjustatdiscretepoints.Concretewithfibresdisplaysgreaterdegreesoftoughnessthanconcretewithout.Thispaperreportsuponthecomparativeinvestigationastohow2Dclosedloopsteelfibreswhencomparedtostraighthookedendcommercialsteelfibres,affecttheflexuralstrengthandtoughness（energyabsorption）ofconcrete.

Theaimof2DclosedloopsteelfibresistointerlockwiththeaggregateinthemixinordertoincreasethepulloutperformanceofthefibreandthiseffectisdisplayedinFig.1.TheaggregateashowninFig.1isnotrepresentativeoftheroundedmarineaggregateusedinthebatchingasthisaggregatehasalargedegreeofflakinessasdefinedinBS812-105.1andhasbeenusedtodisplaytheinterlockingcharacteristicsbetweenclosedloopfibreandaggregate.Thereisverylittleinformationinthepublicdomainabouthow2Dclosedloopsteelfibresbehave.

Fig.1.2Dclosedloopfibresinterlockingwithaggregate.

Theproblemwithusingstraightfibresisthatthefibresmaycongregatewithintheconcreteatpositionswheretheyprovidenousefulloadtransfer.Fibressticktothesidesofrotarydrummixersandarenotusedwithinthefinalproduct,thereforethereisaneffectivereductioninthedosageaddition.Finally,theorientationofthefibretotheruptureplaneisrandomandmanyfibresarenotusedeffectivelywithintheconcretemix.Closedloopfibretechnologycastsinarandomlayeroffibresinthetensionareaofabeam/slabandavibrationtablewasusedtoensuretheorientationofthefibresdidnotchangesignificantlyduetocompaction.

Itisgenerallyacceptedthestrengthoftheconcretehaslittleeffectonthefailureloadforthefibres,asitisthebondbetweentheconcreteandthefibrethatbreaksfirst[1].Thefinalpostcrackloadwillbeinfluencedbyfibredirection,totalnumberoffibres,fibretypeandconcretetype.ParvizandCha-DonLee[2]concludedthat,only65%ofthe“straight”fibresshouldbeconsideredforstructuralanalysis,andfrompreviousresearch[3]itshouldbeconsideredthatthisfiguremaybeslightlytoohighandcautionshouldbeexercisedwhenestablishingperformanceparameters.

1.1.Fibreuseinconcreteslabs

Forafibretobesuccessfulasreinforcementinfloorslabsitmusthavethefollowingattributes–beeasilyspreadevenlythroughoutthemix,shouldhavesufficientbondwiththeconcretetotransferanytensilestressesacrosstheconcreteruptureplane,shouldbesufficientlystiffandhaveasuitablemodulusofelasticitysoastolimitcrackingtoacceptablelimits,providefracturetoughness,shouldbesufficientlydurabletoprovideservicethroughoutthelifeoftheconcrete.Thepostcrackperformanceofreinforcedconcretecanbeimprovedwiththeuseofsteelrebar,steelfabricorfibres.Destrée[4]reportsthatitisnowpossibleinsomeapplicationstoreplacetraditionallyusedreinforcementwithconcretethatisreinforcedbyfibresalone.Concreteisusedwidelybecauseofitshighcompressivestrength,howeverconcretehaslowtensilestrength,crackingeasilyundertensileforces.Thereforeinordertocounteractthis,reinforcementisnecessarytopreventcracksandfailureofthematerial.Traditionally,reinforcingconcreteisachievedbyusingrebar,orsteelmesh,inquantitiesdependentuponthefunctionandapplicationoftheconcretememberorfloorslab.

Thepotentialbenefitofusingfibresisthattheyaresmallenoughtobeincludedintheconcretemixandthereforecanremovelabourassociatedwithplacingtraditionalreinforcementandprovidereinforcementthroughoutthemixinalldirections.Theotherpotentialbenefitisthat;iffibresarespreadevenlythroughouttheconcrete,thensoshouldthetensileforces,whichwouldleadtoalargenumberofsmallercracksratherthanfewerlargecracks.

1.2.Blastprojectiledamagemitigation

Whenanexplosionoccursadjacenttoaconcretewallaproportionoftheenergywilltravelthroughthewallasa‘compressivestresswave’.Asthewavemeetsthebackfaceofthewallitpartlyrebounds,withsomeenergytravellingbackthroughthewall,andsometravellingintotheair.Thereboundofthe‘compressivestresswave’withintheconcretecancauseatensionrebound.Astheconcretefailsintension,backfacespallingcanoccur,ejectingconcretefragmentsathighspeed[5].

GutierrezdeCeballosetal.[6]statethatshrapnelwoundsaccountedfor36%ofallinjuries.Thereisarequirementtoreduceconcretespallingandcracking,sothatthematerialdoesnotfragmentcreatinglethalprojectilesandforanequaldosage,closedloopfibresmayimprovetheperformanceofconcreteinthesesituationswhencomparedtostraightsteelfibres.

2.Materials

Theclosedloopfibresasusedwithinthistestwere50mm×50mmsquareloops.Theloopswerecreatedusingstainlesssteelwireofgrade316L,diameter1.2mm.Manufacturewasusingacomputernumericalcontrolled（CNC）machinewhichbentthewireintotheloopsoftherequireddimension.Thetwoendsofthewiresectionwerethenresistancelapweldedalongsideoneanother.Agoodaspectofthisclosedloopfibredesignisinitssimplicitytobemanufacturedfromastraightwirewithfourrightanglebendsandasinglefrictionweld.Thestraightsteelfibresusedwereofthecommercial,hookedendtype50mminlength,diameter0.75mm.AcomparisonbetweenthetwofibretypesasusedisshowninFig.2.Theclosedloopfibreshaveacrosssectionalarea2.57timesthatofthestraightsteelfibreandalengthfourtimesgreater.Intermsofstructuralperformancethenumberofstraightfibresexceedstheclosedloopfibresby1000%asthereare10straightfibresforoneclosedloopfibre.

Fig.2.Closedloopandstraightfibrecomparison

TheBSEN14845-1:

2007,mouldandfibresizeinformedtheconcretemixdesign,usingacharacteristicdesignstrengthC35withmaximumcementcontentandwatercementratiotohelpcoatthefibresintheplasticmatrix.TheconcretemixasusedisdisplayedinTable1.

Thequalityofthemixingwaterforproductionofconcretecaninfluencethesettingtime,thestrengthdevelopmentofconcreteandtheprotectionofreinforcementagainstcor