Unit 6ReinforcedconcreteText Concreteandreinforcedconcreteareusedasbuildingmaterialsineverycountry.InmanyincludingtheUniteStateandCanada,reinforcedconcreteisadominantstructuralmaterialinengineeredconstruction.Theuniversalnatureofreinforcedconcreteconstructionstemsfromthewideavailabilityofreinforcingbarsandtheconstituentsofconcrete,gravel,sand,andcement,therelativelysimpleskillsrequiredinconcreteconstruction,andtheeconomyofreinforcedconcretecomparedtootherformsofconstruction.Concreteandreinforcedconcreteareusedinbridge,buildingsofallsorts,undergroundstructures,watertanks,televisiontowers,offshoreoilexplorationandproductionstructures,dams,andeveninships. Asweknow,concretehascomparativelylowtensileandbendingstrengthcomparedtoitshighcompressivestrength,andconcreteiseasytocrackevenunderaverylowstress.Forstructuralapplicationsitisnormalpracticetoincorporatesteelbarstoresistanytensileforces.Steelreinforcementisusedintheconcrete,canovercomethedeficienciesinthetensileandbendingstrengthsofconcrete.Concretecanbepoured,pumped,orevensprayedintoallkindsofshapes.Andwhereassteelhasgreattensilestrength,concretehasgreatstrengthundercompression.Thus,thetwosubstancescomplementeachother.Text Comparedwithconcrete,theenormousadvantageofsteelisitstensilestrength;thatis,itdoesnotloseitsstrengthwhenitisunderacalculateddegreeoftension,aforcewhich,aswehaveseen,tendstopullapartmanymaterials[1].Theusefulstrengthofordinaryreinforcingsteelsintensionaswellascompression,i.e.theyieldstrength,isabout15timesthecompressivestrengthofcommonstructuralconcrete,andwellover100timesitstensilestrength.Thesteelisthevitalpartofthestructure,sinceconcreteisdeficientintensilestrength.Itispossibletobuildastructureframefromsteelwithoutconcrete,butnotfromconcretewithoutsteel.Ontheotherhand,steelisahigh-costmaterialcomparedwithconcrete.Althoughsteeloccupiesonlyasmallpartofthevolumeofreinforcedconcrete(ontheaverageabout2percent),itisamajorpartofthecost.Asaveryroughguide,thecostoftheformwork,thecostoftheconcreteandthecostofthesteelareapproximatelythesame,i.e.onethirdofthetotal. Itfollowsthatthetwomaterialsarebestusedincombinationiftheconcreteismadetoresistthecompressivestressesandthecompressiveforce,longitudinalsteelreinforcingbarsarelocatedclosetothetensionfacetoresistthetensionforce,andusuallyadditionalsteelbarsaresodisposedthattheyresisttheinclinedtensionstressesthatarecausedbytheshearforceinthebeams.[2]TextHowever,reinforcementisalsousedforresistingcompressiveforcesprimarilywhereitisdesiredtoreducethecross-sectionaldimensionsofcompressionmembers,asinthelower-floorcolumnsofmultistorybuildings.Evenifnosuchnecessityexist,aminimumamountofreinforcementisplacedinallcompressionmemberstosafeguardthemagainsttheeffectsofsmallaccidentalbendingmomentsthatmightcrackandevenfailanunreinforcedmember[3]. Theyalsocomplementeachotherinanotherway:theyhavealmostthesamerateofcontractionandexpansion.Theythereforecanworktogetherinsituationswherebothcompressionandtensionarefactors. Steelrodsareembeddedinconcretetomakereinforcedconcreteinconcretebeamsorstructureswheretensionwilldevelop.Theproperadhesionbetweenthesteelandtheconcreteisofthegreatestimportance,andbarsshouldbeofasufficientlysmalldiametertoofferanadequateareaofcontactwiththeconcrete;notethatthesmallerthediameterofthebars,thegreatertheirsurfaceareaforanygivenpercentageofreinforcement.Thepracticallimitisreachedwhenthebarsbecomesonumerousthattheyobstructtheproperplacingofconcrete.Text Concreteandsteelformsuchastrongbond－theforcethatunitesthem－thatnorelativemovementsofthesteelbarsandthesurroundingconcreteoccur.Thisbondisprovidedbytherelativelylargechemicaladhesionwhichdevelopsatthesteel-concreteinterface,bythenaturalroughnessofthemillscaleofhot-rolledreinforcingbars,andbythecloselyspacedrib-shapedsurfacedeformationswithwhichreinforcingbarsarefurnishedinordertoprovideahighdegreeofinterlockingofthetwomaterials[4]. Stillanotheradvantageisthatthesteelisthereforecompletelysurroundedbytheconcreteandthesteeldoesnotrustinconcrete.Acidcorrodessteel,whereasconcretehasanalkalinechemicalreaction,theoppositeofacid.Inordertominimizecorrosionofreinforcementandconsequentspallingofconcreteundersevereexposureconditionssuchasinbridgedeckssubjectstodeicingchemicals,galvanizedorepoxy-coatedrebarmaybespecified[5]. Althoughthestructureismadeinonepiece,thereinforcingbarsarenot.Thecomponentpiecesofarigidstructuralsteelframearejoinedtogetherbyweldingofothermeans,andthesamecouldbedonetothebarsinaconcretestructuretoproducearigidframeofreinforcement.Thiswould,however,beaconsiderableandunnecessaryexpense.TextWearethereforedealingwithindividualreinforcingbarswhichgenerallydonotexceed12m(39ft)inlengthbecauselongerbarsaredifficulttotransport.Thesebarsarejoinedbybondingthemtotheconcrete.Thesteelstressisthustransmittedtotheconcretebybondoranchorage,anditisthentransmittedtoanotherbarbythesamemeans.Itisthusnecessarytoprovideadequatespaceforthereinforcementtodevelopmentthestressbytransmissionfromtheconcrete. Theadoptionofstructuralsteelandreinforcedconcretecausedmajorchangesintraditionalconstructionpractices.Intheearliersteelofconcreteframebuilding,thecurtainwallsweregenerallymadeofmasonry,theyhadthesolidlookofbearingwalls.Today,however,curtainwallsareoftenmadeoflightweightmaterialssuchasglass,aluminum,ofplastic,incariouscombinations.Itwasnolongernecessarytousethickwallsofstoneorbrickformultistorybuildings,anditbecamemuchsimplertobuildfire-resistantfloors.Boththesechangesservedtoreducethecostofconstruction.Italsobecamepossibletoerectbuildingswithgreaterheightsandlongerspans.NewWordsandPhrasescrackv.開(kāi)裂；n.裂縫，裂紋pourv.澆注，傾倒pumpv.抽吸，泵送sprayv.噴涂complementn.補(bǔ)充，補(bǔ)充物reinforcingsteel=Reinforcingbar鋼筋longitudinala.長(zhǎng)度的，縱向的，軸向的shearforce剪力multistorybuilding多層建筑rateofcontraction收縮率rateofexpansion膨脹率embedv.放入，埋入，嵌入reinforcedconcrete鋼筋混凝土adhesionn.附著力，黏合（力）bondn.結(jié)合力，黏結(jié)力；v.握裹，黏結(jié)interfacen.界面，接觸面，交界面milln.制造廠(chǎng)，粉碎機(jī)hot-rolledreinforcingbar熱軋鋼筋NewWordsandPhrasesrib-shapedsurface肋形表面interlockn.連動(dòng)，聯(lián)結(jié)，結(jié)合；相互關(guān)系alkalinea.堿性的；n.堿性corrosionn.腐蝕，侵蝕spallingn.剝落，層裂galvanizeda.鍍鋅的epoxy-coated環(huán)氧涂層的rigida.剛性的framen.框架anchoragen.錨固；錨具curtainwall幕墻bearingwall承重墻Notes1.Comparedwithconcrete,theenormousadvantageofsteelisitstensilestrength;thatis,itdoesnotloseitsstrengthwhenitisunderacalculateddegreeoftension,aforcewhich,aswehaveseen,tendstopullapartmanymaterials. 與混凝土相比，鋼筋的最大優(yōu)點(diǎn)是抗拉強(qiáng)度；也就是說(shuō)，它在一定的拉力作用下，鋼的強(qiáng)度不損失，正如我們看到的，這個(gè)拉力能夠使得許多材料被拉開(kāi)。2.Itfollowsthatthetwomaterialsarebestusedincombinationiftheconcreteismadetoresistthecompressivestressesandthecompressiveforce,longitudinalsteelreinforcingbarsarelocatedclosetothetensionfacetoresistthetensionforce,andusuallyadditionalsteelbarsaresodisposedthattheyresisttheinclinedtensionstressesthatarecausedbytheshearforceinthebeams. 如果混凝土被用來(lái)抵抗壓應(yīng)力和壓力，縱向鋼筋被放在受拉力一側(cè)用來(lái)抵抗拉力，其他的附加鋼筋用來(lái)抵抗由剪力引起的斜向拉應(yīng)力，這樣兩種材料組合使用最佳，如鋼筋混凝土梁。3.Evenifnosuchnecessityexist,aminimumamountofreinforcementisplacedinallcompressionmemberstosafeguardthemagainsttheeffectsofsmallaccidentalbendingmomentsthatmightcrackandevenfailanunreinforcedmember. 即使沒(méi)有這種必要，少量鋼筋被用在所有的受壓構(gòu)件中可以保證它們免受小的附加彎矩的影響，這個(gè)彎矩能使得構(gòu)件開(kāi)裂甚至可能使得無(wú)筋構(gòu)件破壞。Notes4.Thisbondisprovidedbytherelativelylargechemicaladhesionwhichdevelopsatthesteel-concreteinterface,bythenaturalroughnessofthemillscaleofhot-rolledreinforcingbars,andbythecloselyspacedrib-shapedsurfacedeformationswithwhichreinforcingbarsarefurnishedinordertoprovideahighdegreeofinterlockingofthetwomaterials. 這種黏合力是由產(chǎn)生在鋼筋混凝土表面的相對(duì)較大的化學(xué)附著力、熱乳鋼筋工廠(chǎng)的原始粗糙度以及帶肋鋼筋表面的間隔較小的變形所提供的，這種帶肋鋼筋主要是為了使兩種材料有很高的聯(lián)結(jié)。5.Inordertominimizecorrosionofreinforcementandconsequentspallingofconcreteundersevereexposureconditionssuchasinbridgedeckssubjectstodeicingchemicals,galvanizedorepoxy-coatedrebarmaybespecified. 在嚴(yán)重的暴露環(huán)境下，例如易遭受除冰鹽的橋面，為了減小鋼筋的腐蝕和隨之而來(lái)的混凝土剝落，一些鍍鋅或環(huán)氧涂層鋼筋被指定使用。Exercises（TranslatethefollowingChineseintoEnglish,orEnglishintoChinese）1.Asaresult,cracksdevelopwheneverloads,orrestrainedshrinkageortemperaturechanges,giverisetotensilestressesinexcessofthetensilestrengthoftheconcrete.2.Thisisparticularlytrueifdense,air-entrainedconcretehasbeenusedforsurfacesexposedtotheatmosphere,andifcarehasbeentakeninthedesigntoprovideadequatedrainageoffandawayfromthestructure.3.Ontheotherhand,concreteundergoesdrying