土木工程专业英语 陈瑛 4.3. bond, anchorage, and development length新

在线教务辅导网HTTP/WWWSHANGFUWANGCOM更多课程配套课件资源请访问在线教务辅导网2018/4/17143BOND,ANCHORAGE,ANDDEVELOPMENTLENGTH粘结、锚固、基本锚固长度2018/4/172无粘结梁BEAMWITHUNBONDEDINTERFACEBETWEENREINFORCEMENTANDCONCRETEIFTHEREINFORCEDCONCRETEBEAMOFFIGURE417AWASCONSTRUCTEDUSINGROUNDREINFORCINGBARS,AND,FURTHERMORE,IFTHOSEBARSWEREGREASEDORLUBRICATEDBEFORETHECONCRETEWERECAST,THEBEAMWOULDBEONLYLITTLESTRONGERTHANIFITWEREBUILTOFPLAINCONCRETE,WITHOUTREINFORCEMENT41FUNDAMENTALSOFFLEXURALBOND2018/4/173NIFALOADWEREAPPLIED,ASSHOWNINFIGURE417B,THEBARSWOULDTENDTOMAINTAINTHEIRORIGINALLENGTHASTHEBEAMDEFLECTSTHEBARSWOULDSLIPLONGITUDINALLYWITHRESPECTTOTHEADJACENTCONCRETE,WHICHWOULDEXPERIENCETENSILESTRAINDUETOFLEXURE2018/4/174NFORREINFORCEDCONCRETE,ITISESSENTIALTHATBONDFORCESBEDEVELOPEDONTHEINTERFACE界面BETWEENCONCRETEANDSTEEL,SUCHASTOPREVENTSIGNIFICANTSLIPFROMOCCURRINGATTHATINTERFACE2018/4/175NFIGURE417CSHOWSTHEBONDFORCESTHATACTONTHECONCRETEATTHEINTERFACEASARESULTOFBENDING,WHILEFIGURE417DSHOWSTHEEQUALANDOPPOSITEBONDFORCESACTINGONTHEREINFORCEMENTNITISTHROUGHTHEACTIONOFTHESEINTERFACEBONDFORCESTHATTHESLIPINDICATEDINFIGURE417BISPREVENTED粘结应力BONDSTRESS钢筋与混凝土间具有足够的粘结是保证钢筋与混凝土共同受力变形的基本前提2018/4/176NSOMEYEARSAGO,WHENPLAINBARSWITHOUTSURFACEDEFORMATIONSWEREUSED,INITIALBONDSTRENGTHWASPROVIDEDONLYBYTHERELATIVELYWEAKCHEMICALADHESIONANDMECHANICALFRICTIONBETWEENSTEELANDCONCRETE粘附力摩擦力有滑移时粘附力即消失钢筋受力较大时粘结力主要由此二部分组成CHEMICALADHESIONFRICTION2018/4/177NONCEADHESIONANDSTATICFRICTIONWEREOVERCOMEATLARGERLOADS,SMALLAMOUNTOFSLIPLEDTOINTERLOCKINGOFTHENATURALROUGHNESSOFTHEBARWITHTHECONCRETEHOWEVER,THENATURALBONDSTRENGTHISSOLOWTHATINBEAMSREINFORCEDWITHPLAINBARS,THEBONDBETWEENSTEELANDCONCRETEWASFREQUENTLYBROKEN粘附力摩擦力有滑移时粘附力即消失钢筋受力较大时粘结力主要由此二部分组成CHEMICALADHESIONFRICTION机械咬合力（钢筋表面不平、微锈时可显著提高咬合力）INTERLOCKINGNATURALROUGHNESS2018/4/178N端布有锚固的无粘结梁BEAMWITHUNBONDEDINTERFACEBETWEENREINFORCEMENTWITHENDANCHORAGEANDCONCRETENTOPREVENTTHIS,ENDANCHORAGEWASPROVIDED,CHIEFLYINTHEFORMOFHOOKSIFTHEANCHORAGEISADEQUATE,SUCHABEAMWILLNOTCOLLAPSE,EVENIFTHEBONDISBROKENOVERTHEENTIRELENGTHBETWEENANCHORAGESENDANCHORAGE2018/4/179NTHISISSOBECAUSETHEMEMBERACTSASATIEDARCH,ASSHOWNINFIGURE418,WITHTHEUNCRACKEDCONCRETESHOWNSHADEDREPRESENTINGTHEARCHANDTHEANCHOREDBARSREPRESENTINGTHETIEDRODZ2018/4/1710NINTHISCASE,OVERTHELENGTHINWHICHTHEBONDISBROKEN,BONDFORCESAREZEROTHISMEANSTHATOVERTHEENTIREUNBONDEDLENGTHTHEFORCEINTHESTEELISCONSTANTANDEQUALTOSS常数BONDFORCESAREZEROUNBONDEDBONDSTRESSFORCEINTHESTEELISCONSTANTCZTMMAX2018/4/1711NASACONSEQUENCE,THETOTALSTEELELONGATIONINSUCHABEAMISLARGERTHANINBEAMSINWHICHBONDISPRESERVED,RESULTINGINLARGERDEFLECTIONSANDGREATERCRACKWIDTHSCZTSTEELELONGATIONT/ASESTCT2TBONDISPRESERVED2018/4/1712NTOIMPROVETHISSITUATION,DEFORMEDBARSARENOWUNIVERSALLYUSEDWITHSUCHBARS,THESHOULDERSOFTHEPROJECTINGPREJDVEKTIN伸出的RIBSBEARONTHESURROUNDINGCONCRETEANDRESULTINGREATLYINCREASEDINKRISTSTRENGTHITISTHENPOSSIBLEINMOSTCASESTODISPENSEWITH废除SPECIALANCHORAGEDEVICESSUCHASHOOKSINADDITION,CRACKWIDTHSASWELLASDEFLECTIONSAREREDUCEDSHOULDERS带肋钢筋DEFORMEDBARSRIBS2018/4/171342BONDSTRENGTHANDDEVELOPMENTLENGTHNBONDFAILURESDIRECTPULLOUTOFBARWHEN钢筋拔出NRELATIVELYSMALLDIAMETERBARS纵筋直径小NSUFFICIENTLYLARGECONCRETECOVERTHICKNESS混凝土的保护层较大NSUFFICIENTBARSPACING纵筋间距大SPLITTINGOFCONCRETEALONGBARWHEN顺钢筋方向混凝土劈裂NINSUFFICIENTCOVERCONFINEMENT混凝土的保护层较小NINSUFFICIENTBARSPACING纵筋间距小2018/4/1714NSPLITTINGOFCONCRETEALONGBAR顺钢筋方向劈裂裂缝THESECONDTYPEOFFAILUREISSPLITTINGOFTHECONCRETEALONGTHEBARWHENCOVERCONFINEMENTORBARSPACINGISINSUFFICIENTTORESISTTHELATERALCONCRETETENSIONRESULTINGFROMTHEWEDGINGEFFECTOFTHEBARDEFORMATIONS2018/4/1715MECHANICALINTERLOCKTHEEDGESTRESSCONCENTRATIONCAUSESCRACKINGTOOCCURNWEDGINGEFFECT2018/4/1716NWEDGINGEFFECTLATERALCONCRETETENSIONRESULTINGFROMTHEWEDGINGEFFECT楔入效应OFTHEBARDEFORMATIONSRIBS变形钢筋受力后，其凸出的肋对混凝土产生斜向挤压力BEARINGPRESSURE其水平分力HORIZONTALPROJECTION使钢筋周围的混凝土轴向受拉、受剪，径向分力RADIALFORCE使混凝土产生环向拉力HOOPTENSION。轴向拉力和剪力使混凝土产生内部斜向锥形裂缝环向拉力使混凝土产生内部径向裂缝。LATERALCONCRETETENSIONAXIALFORCESHEARFORCEHOOPTENSIONBEARINGPRESSURE2018/4/1717N1BONDSTRENGTH变形钢筋粘附力摩擦力机械咬合力主要作用CHEMICALADHESIONFRICTIONMECHANICALINTERLOCKFROMBARDEFORMATIONSFORMODERNDEFORMEDBARS,ADHESIONANDFRICTIONAREMUCHLESSIMPORTANTTHANTHEMECHANICALINTERLOCKOFTHEDEFORMATIONSWITHSURROUNDINGCONCRETE2018/4/1718NDIRECTPULLOUTOFBARS如果纵筋间距大且混凝土的保护层较大，径向裂缝很难发展达到构件表面，则肋前部的混凝土在水平分力和剪力作用下最终将被挤碎，发生沿肋外径圆柱面的剪切破坏，形成所谓的“刮梨式”破坏，是变形钢筋与混凝土粘结强度的上限。刮出式破坏PULLOUTIFTHEBARISSUFFICIENTLYCONFINEDBYAMASSOFSURROUNDINGCONCRETE,THEN,ASTHETENSILEFORCEONTHEBARISINCREASED,ADHESIVEED5HISIV粘的BONDANDFRICTIONAREOVERCOME,THECONCRETEEVENTUALLYCRUSHESLOCALLYAHEADOFTHERIBSIMMEDIATELYADJACENTTOTHEBARINTERFACE,ANDBARPULLOUTRESULTSTHESURROUNDINGCONCRETEREMAINSINTACTSURROUNDINGCONCRETEREMAINSINTACT2018/4/1719变形钢筋纵向分量径向分量构件纵向开裂NSPLITTINGOFCONCRETEALONGBAR顺钢筋方向劈裂裂缝BONDFAILURERESULTINGFROMSPLITTINGOFTHECONCRETEISMORECOMMONINBEAMSTHANDIRECTPULLOUTSUCHSPLITTINGCOMESMAINLYFROMWEDGINGACTIONWHENTHERIBSOFTHEDEFORMEDBARSBEARAGAINSTTHECONCRETE当混凝土保护层和钢筋间距较小时，径向裂缝可发展达到构件表面，产生劈裂裂缝，机械咬合作用将很快丧失，产生“劈裂式”粘结破坏LATERALCONCRETETENSION2018/4/1720SPLITTINGFAILUREMAYOCCUREITHERINAVERTICALPLANEASINFIGURE420AORHORIZONTALLYINTHEPLANEOFTHEBARSASINFIGURE420BTHEHORIZONTALTYPEOFSPLITTINGFREQUENTLYBEGINSATADIAGONALCRACKTHEDOWELACTIONINCREASESTHETENDENCYTOWARDSPLITTINGTHISINDICATESTHATSHEARANDBONDFAILUREAREOFTENINTRICATELYINTERRELATEDSPLITTINGFAILUREINHORIZONTALPLANESPLITTINGFAILUREINVERTICALPLANEDIAGONALCRACK2018/4/1721NCOMPLETEKEM5PLITFAILURE完全失效OCCURSWHENPULLOUTRESISTANCEISOVERCOMESPLITTINGHASSPREADALLTHEWAYTOTHEENDOFANUNANCHOREDBAR,NSLIDINGOFTHESTEELRELATIVETOTHECONCRETELEADSTOIMMEDIATECOLLAPSEOFTHEBEAM2018/4/1722DEVELOPMENTLENGTHLD基本锚固长度NTHEDEVELOPMENTLENGTHISDEFINEDASTHATLENGTHOFEMBEDMENTNECESSARYTODEVELOPTHEFULLTENSILESTRENGTHOFTHEBAR,CONTROLLEDBYEITHERPULLOUTORSPLITTINGNTHEDEVELOPMENTLENGTHISTHESHORTESTLENGTHOFBARINWHICHTHEBARSTRESSCANINCREASEFROMZEROTOTHEYIELDSTRENGTH钢筋屈服时正好发生粘结破坏（钢筋拔出或混凝土劈裂）原则2018/4/1723NTHEDEVELOPMENTLENGTHOFTHEBARISESTABLISHEDBYPULLOUTTESTSLA拔出试验SSLLDBONDFORCES2018/4/1724NWHENREFERENCETO参考FIGURE421,THEMOMENT,ANDTHEREFORETHESTEELSTRESS,ISMAXIMUMATPOINTANEGLECTINGTHEWEIGHTOFTHEBEAMANDZEROATTHESUPPORTSIFTHEBARSTRESSISSSASATA,THENTHETOTALTENSIONFORCEMUSTBETRANSFERREDFROMTHEBARTOTHECONCRETEINTHEDISTANCELBYBONDFORCES2018/4/1725NTOFULLYDEVELOPTHESTRENGTHOFTHEBAR,THEDISTANCELMUSTBEATLEASTEQUALTOTHEDEVELOPMENTLENGTHOFTHEBAR,ESTABLISHEDBYPULLOUTTESTSLA拔出试验SSLLDBONDFORCES2018/4/1726NINTHEBEAMOFFIGURE421,IFTHEACTUALLENGTHLISEQUALTOORGREATERTHANTHEDEVELOPMENTLENGTHLD,NOPREMATUREBONDFAILUREWILLOCCURNWHENLLD,THEBEAMWILLFAILINBENDING,ORFAILINSHEARNOBONDFAILURE2018/4/1727NTHISWILLBESOEVENIFINTHEVICINITYOFCRACKSLOCALSLIPMAYHAVEOCCURREDOVERSMALLREGIONALONGTHEBEAM2018/4/1728NMAINREQUIREMENTFORSAFETYAGAINSTBONDFAILURELENGTHOFTHEBARNFROMANYPOINTOFGIVENSTEELSTRESSSSASORATMOSTFYASTOITSNEARBYFREEENDMUSTBEATLEASTEQUALTOITSDEVELOPMENTLENGTHLLDSPECIALANCHORAGEHOOKSNIFTHEACTUALAVAILABLELENGTHISINADEQUATEFORFULLDEVELOPMENT2018/4/17293FACTORSINFLUENCINGDEVELOPMENTLENGTHNEXPERIMENTALRESEARCHHASIDENTIFIEDTHEFACTORSTHATINFLUENCEDEVELOPMENTLENGTH,ANDANALYSISOFTHETESTDATAHASRESULTEDINTHEEXPERIMENTALEQUATIONSUSEDINPRESENTDESIGNPRACTICENFACTORSINFLUENCINGDEVELOPMENTLENGTHCONCRETETENSILESTRENGTH混凝土强度COVERTHICKNESS保护层厚度SPACINGOFTHEREINFORCINGBARS钢筋净间距TRANSVERSE5TRANZVESSTEELREINFORCEMENT横向配筋2018/4/17303FACTORSINFLUENCINGDEVELOPMENTLENGTHNCONCRETETENSILESTRENGTH混凝土强度THETENSILESTRENGTHOFTHECONCRETEISIMPORTANTBECAUSETHEMOSTCOMMONTYPEOFBONDFAILUREINBEAMSISTHETYPEOFSPLITTINGTHEDEVELOPMENTLENGTHISINVERSEPROPORTIONALTOTHEAXIALTENSILESTRENGTHOFCONCRETE,FT,BUTISNOTINVERSEPROPORTIONALTOTHECUBECOMPRESSIVESTRENGTHOFCONCRETE,FCU2018/4/17313FACTORSINFLUENCINGDEVELOPMENTLENGTHNCOVERTHICKNESS保护层厚度IFTHEHORIZONTALORVERTICALCOVERISINCREASED,MORECONCRETEISAVAILABLETORESISTTHETENSIONRESULTINGFROMTHEWEDGINGEFFECTOFTHEDEFORMEDBARS,RESISTANCETOSPLITTINGISIMPROVED,ANDDEVELOPMENTLENGTHISLESS2018/4/17323FACTORSINFLUENCINGDEVELOPMENTLENGTHNBARSPACINGIFTHEBARSPACINGISINCREASEDEG,IFONLYTWOINSTEADOFTHREEBARSAREUSED,MORECONCRETEPERBARWOULDBEAVAILABLETORESISTHORIZONTALSPLITTINGINBEAMS,BARSARETYPICALLYTIPIKELISPACEDABOUTONEORTWOBARDIAMETERSAPARTONTHEOTHERHAND,FORSLABS,FOOTINGS基础）,ANDCERTAINTYPESOFMEMBERS,BARSPACINGSARETYPICALLYMUCHGREATER,ANDTHEREQUIREDDEVELOPMENTLENGTHISREDUCED2018/4/17333FACTORSINFLUENCINGDEVELOPMENTLENGTHNTRANSVERSESTEELREINFORCEMENT横向配筋TRANSVERSEREINFORCEMENTIMPROVESTHERESISTANCEOFTENSILEBARSTOBOTHVERTICALFAILUREORHORIZONTALSPLITTINGFAILUREBECAUSETHETENSIONFORCEINTHETRANSVERSESTEELTENDSTOPREVENTOPENINGOFTHEACTUALORPOTENTIALCRACK2018/4/1734DEVELOPMENTLENGTHNBASEDONTHERESULTOFASTATISTICALSTE5TISTIKEL统计的ANALYSISOFPULLOUTTESTSDATA,WITHAPPROPRIATEE5PREUPRIITSIMPLIFICATIONS,THELENGTHNEEDEDTODEVELOPSTRESSFYINAREINFORCINGBARMAYBEEXPRESSEDASAPPARENTCOEFFICIENTOFSTEELBARBARDIAMETER2018/4/1735ANCHORAGEOFTENSIONBARSBYHOOKSNSTANDARDDIMENSIONSINTHEEVENTTHATTHEDESIREDTENSILESTRESSINABARCANNOTBEDEVELOPEDBYBONDALONE,ITISNECESSARYTOPROVIDESPECIALANCHORAGEATTHEENDOFTHEBAR,USUALLYBYMEANSOFA90DEGREESORA180DEGREESHOOKTHEDIMENSIONSANDTHEBENDRADII5REIDIAIFORSUCHHOOKSHAVEBEENSTANDARDIZED5STANDE7DAIZD使标准化INCODERADIIAPLURAL5PLUERELOFRADIUS2018/4/1736NA180DEGREESBENDPLUSANEXTENSIONOFATLEAST3BARDIAMETERSATTHEFREEENDOFTHEBAR2018/4/1737N2A90DEGREESBENDPLUSANEXTENSIONOFATLEAST15BARDIAMETERSATTHEFREEENDOFTHEBAR2018/4/1738NFORSTIRRUPANDTIEANCHORAGE,A135DEGREESBENDPLUSANEXTENSIONOFATLEAST5BARDIAMETERS,BUTNOTLESSTHAN50MM,ORA90DEGREESBENDPLUSANEXTENSIONOFATLEAST10BARDIAMETERSATTHEFREEENDOFTHEBAR2018/4/1739MECHANICALANCHORAGE机械锚固NFORSOMESPECIALCASES,EG（EXEMPLIGRATIAI5ZEMPLAI5REIFIE例如FOREXAMPLE）,ATTHEENDSOFMAINFLEXURALREINFORCEMENTINDEEPBEAMS,THEREISNOROOMFORHOOKSORTHENECESSARY5NESESERI5NESESERICONFINEMENTSTEEL,ANDSPECIALMECHANICALANCHORAGEDEVICESMUSTBEUSEDTHEYMAYCONSISTOFWELDEDSHORTTRANSVERSEBAR,WELDEDPLATE,ORTHEADEDBARWELDEDSHORTTRANSVERSEBARWELDEDPLATETHEADEDBAR2018/4/1740NTHECONNECTIONOFSTEELBARSCANBEDIVIDEDINTOTWOTYPESCOLLIGATIONANDMECHANICALCONNECTIONORWELDINGNTHEREARETHREECHOICESFORJOININGBARSTOGETHER1MECHANICALDEVICE,2WELDING,AND3LAPSPLICESNWELDINGJOINTSHOULDSATISFYTHESTIPULATIONSINRELATEDEXISTINGSTANDARDSOFTHESTATENWELDEDSPLICESMUSTCONFORMTOSTRUCTURALWELDINGCODEFORREINFORCINGSTEELWHICHISBETTER434钢筋的连接BARSPLICES搭接长度2018/4/1741N翻译受力钢筋的接头宜设置在受力较小处。NITISADVISABLETOSETTHEJOINTOFAREINFORCINGBARWHERETHEBORNEFORCEISRELATIVELYSMALLERNSPLICESINTHEREINFORCEMENTATPOINTSOFMAXIMUMSTRESSSHOULDBEAVOIDEDWHICHISBETTER2018/4/1742434钢筋的连接BARSPLICES绑扎搭接LAPSPLICES机械连接MECHANICALDEVICE钢筋连接形式焊接WELDINGTHREECHOICESFORJOININGBARSTOGETHERLAPSPLICES2018/4/1743NTHEMECHANICALANDWELDEDSPLICESMUSTBETESTEDTOSHOWTHEDEVELOPMENTINTENSIONORCOMPRESSIONOFATLEAST125OFTHESPECIFIED5SPESIFAIYIELDSTRENGTHOFTHEBARNWELDEDSPLICESMUSTCONFORMTOSTRUCTURALWELDINGCODEFORREINFORCINGSTEELNSINCESPLICESINTRODUCEWEAKLINKSINTOTHESTRUCTURE,THEYSHOULDBELOCATEDASMUCHASPOSSIBLEAWAYFROMPOINTSOFMAXIMUMFORCEANDCRITICALLOCATIONSSPECIFYTOSTATEEXPLICITLYORINDETAIL明确说明2018/4/1744适用范围SPLICESFORBARSSMALLERTHAN16MMINDIAMETERAREUSUALLYMADESIMPLYBYLAPPINGTHEBARSASUFFICIENTDISTANCETOTRANSFERSTRESSBYBONDINGFROMONEBARTOTHEOTHER通过钢筋与混凝土之间的粘结强度来传递钢筋的内力。THELAPPEDBARSAREUSUALLYPLACEDINCONTACTANDTIGHTLYWIREDSOTHATTHEYSTAYINPOSITIONASTHECONCRETEISPLACEDLAPSPLICESSUFFICIENTDISTANCETIGHTLYWIREDPLACEDINCONTACT2018/4/1745适用范围DESIGNCODEPROHIBITSPRE5HIBITTHEUSEOFLAPPEDSPLICESFORMAINREINFORCEMENTINAXIALLYLOADEDTENSIONMEMBERSANDTENSIONMEMBERSWITHSMALLECCENTRICITYEKSEN5TRISITI,TENSIONBARSTHATAREGREATERTHAN28MMINDIAMETER,ORCOMPRESSIONBARSTHATAREGRE