《专业英语》课件Unit-5

Unit 5BuildingMaterialsText Asanengineer,onemustknowaboutthematerialsusedintheconstructionsite.Allstructuresareconstructedofmaterialsknownasengineeringmaterialsorbuildingmaterials.Itisnecessaryforanengineertobeconversantwiththepropertiesofsuchmaterials.Civilengineeringmaterialscanbenaturalandman-made.Theycontaincement,metals,timber,concrete,bituminousetc.Besidesthesetraditionalmaterials,newtypesofconstructionalmaterialsarealsoinvestigatedanddevelopedandwillbeappliedgradually.Nowgreencivilengineeringmaterialsandeveneco-materialsforcivilengineeringarerecommendedbasedontheconsiderationofsustainabledevelopment.Thishasthebenefitsofreducingenergy,savingresourcesandprotectingtheenvironment,havingminimumharmtohumanhealth. Materialsforbuildingmusthavecertainphysicalpropertiestobestructurallyuseful.Primarily,theymustbeabletocarryaload,orweight,withoutchangingshapepermanently.Whenaloadisappliedtoastructuremember,itwilldeform;thatis,awirewillstretchorabeamwillbend.However,whentheloadisremoved,thewireandthebeamcomebacktotheoriginalposition.Thismaterialpropertyiscalledelasticity.Ifamaterialwerenotelasticandadeformationwerepresentinthestructureafterremovaloftheload,repeatedloadingandunloadingeventuallywouldincreasethedeformationtothepointwherethestructurewouldbecomeuseless[1].TextAllmaterialsusedinarchitecturalstructuressuchasstone,brick,wood,steel,aluminum,reinforcedconcrete,andplastics,behaveelasticallywithinacertaindefinedrangeofloading.Iftheloadingisincreasedabovetherange,twotypesofbehaviorcanoccur:brittleandplastic.Intheformerthematerialwillbreaksuddenly.Inthelatter,thematerialbeginstoflowatacertainload(yieldstrength),ultimatelyleadingtofracture.Forexamples,steelexhibitsplasticbehavior,andstoneisbrittle.Theultimatestrengthofamaterialismeasuredbythestressatwhichfailure(fracture)occurs. Asecondimportantpropertyofabuildingmaterialisitsstiffness.Thispropertyisdefinedbytheelasticmodulus(E),whichistheratioofthestress(forceperunitarea,σ),tothestrain(deformationperunitlength,ε),E=σ/ε.Theelasticmodulus,therefore,isameasureoftheresistanceofamaterialtodeformationunderload.Fortwomaterialsofequalareaunderthesameload,theonewiththehigherelasticmodulushasthesmallerdeformation.Structuralsteel,whichhasanelasticmodulusof30millionpoundspersquareinch(psi),or2,100,000kilogramspersquarecentimeter,isthreetimesasstiffasaluminum,tentimesasstiffasconcrete,andfifteentimesasstiffaswood.TextMasonry Masonryconsistsofnaturalmaterials,suchasstoneormanufacturedproducts,suchasbrickandconcreteblocks(Fig5.1).Masonryhasbeenusedsinceancienttimes;mudbrickswereusedinthecityofBabylonforsecularbuildings,andstonewasusedforthegreattemplesoftheNileValley.TheGreatPyramidinEgypt,standing481feet(147meters)high,isthemostspectacularmasonryconstruction.Masonryunitsoriginallywerestackedwithoutusinganybondingagent,butallmodernmasonryconstructionusesacementmortarasabondingmaterial.Modernstructuralmaterialsincludestones,bricksandconcreteblocks. Masonryisessentiallyacompressivematerial;itcan'twithstandatensileforce,thatis,apull.Theultimatecompressivestrengthofbondedmasonrydependsonthestrengthofthemasonryunitandthemortar.Theultimatestrengthwillvaryfrom1,000to4,000psi(70to280kg/sqcm),dependingontheparticularcombinationofmasonryunitandmortarused.Fig5.1MasonryTextTimber

Timberisoneoftheearliestconstructionmaterialsandoneofthefewnaturalmaterialswithgoodtensileproperties.Hundredsofdifferentspeciesofwoodarefoundthroughouttheworld,andeachspeciesexhibitsdifferentphysicalcharacteristics.Onlyafewspeciesareusedstructurallyasframingmembersinbuildingconstruction.Thesearegenerallytheconifers,orsoftwoods,bothbecauseoftheirabundanceandbecauseoftheeasewithwhichtheirwoodcanbeshaped.ThespeciesoftimbermorecommonlyusedintheUnitedStatesforconstructionareDouglasfir,Southernpine,spruce,andredwood.Theultimatetensilestrengthofthesespeciesvariesfrom5000to8000psi(350to560kg/sqcm).Hardwoodsareusedprimarilyforcabinetworkandforinteriorfinishessuchasfloors. Becauseofthecellularnatureofwood,itisstrongeralongthegrainthanacrossthegrain.Woodisparticularlystrongintensionandcompressionparalleltothegrain,andithasgreatbendingstrength.Thesepropertiesmakeitideallysuitedforcolumnsandbeamsinstructures(Fig5.2).TextWoodisnoteffectivelyusedasatensilememberinatruss,however,becausethetensilestrengthofatrussmemberdependsuponconnectionsbetweenmembers.Itisdifficulttodeviseconnectionswhichdonotdependontheshearortearingstrengthalongthegrain,althoughnumerousmetalconnectorshavebeenproducedtoutilizethetensilestrengthoftimbers[2].Fig5.2TimberTextSteel

Steelisanoutstandingstructuralmaterial(Fig5.3).Ithasahighstrengthonapound-for-poundbasiswhencomparedtoothermaterials,eventhoughitsvolume-for-volumeweightismorethantentimesthatofwood.Ithasahighelasticmodulus,whichresultsinsmalldeformationsunderload.ItcanbeformedbyrollingintovariousstructuralshapessuchasI-beams,plates,andsheets;italsocanbecastintocomplexshapes;anditisalsoproducedintheformofwirestrandsandropesforuseascablesinsuspensionbridgesandsuspendedroofs,aselevatorropes,andaswiresforpre-stressedconcrete.Steelelementscanbejoinedtogetherbyvariousmeans,suchasbolting,riveting,orwelding.Carbonsteelsaresubjecttocorrosionthroughoxidationandmustbeprotectedfromcontactwiththeatmospherebypaintingthemorembeddingtheminconcrete.Abovetemperatureofabout371℃,steelrapidlylosesitsstrength,andthereforeitmustbecoveredinajacketofafireproofmaterialtoincreaseitsfireresistance.TextTheadditionofalloyingelements,suchassiliconormanganese,resultsinhigherstrengthsteelswithtensilestrengthupto250,000psi(17,500kg/sqcm)[3]Thesesteelsareusedwherethesizeofastructuralmemberbecomescritical,asinthecaseofcolumnsinaskyscraper.Fig5.3SteelTextAluminum

Aluminumisespeciallyusefulasabuildingmaterialwhenlightweight,strength,andcorrosionresistanceareallimportantfactors.Becausepurealuminumisextremelysoftandductile,alloyingelements,suchasmagnesium,silicon,zinc,andcopper,mustbeaddedtoittoimpartthestrengthrequiredforstructuraluse.Structuralaluminumalloysbehaveelastically.Theyhaveanelasticmodulusonethirdasgreatassteelandthereforedeformthreetimesasmuchassteelunderthesameload.Theunitweightofanaluminumalloyisonethirdthatofsteel,andthereforeanaluminummemberwillbelighterthanasteelmemberofcomparablestrength.Theultimatetensilestrengthofaluminumalloysrangesfrom20,000to60,000psi(1,400to4,200kg/sqcm).

Aluminumcanbeformedintoavarietyofshapes;itcanbeextrudedtoformI-beams,drawntoformwireandrods,androlledtoformfoilandplates.Aluminummemberscanbeputtogetherinthesamewayassteelbyriveting,bolting,and(toalesserextent)bywelding.Apartfromitsuseforframingmembersinbuildingsandprefabricatedhousing,aluminumalsofindsextensiveuseforwindowframes(Fig5.4)andfortheskinofthebuildingincurtain-wallconstruction.TextFig5.4AluminumTextConcrete

Concreteisamixtureofwater,sandandgravel,andPortlandcement(Fig5.5).Crushedstone,manufacturedlightweightstone,andseashellsareoftenusedinlieuofnaturalgravel.Portlandcement,whichisamixtureofmaterialscontainingcalciumandclay,isheatedinakilnandthenpulverized.ConcretederivesitsstrengthfromthefactthatpulverizedPortlandcement,whenmixedwithwater,hardensbyaprocesscalledhydration.Inanidealmixture,concreteconsistsofaboutthreefourthssandandgravel(aggregate)byvolumeandonefourthcementpaste.Thephysicalpropertiesofconcretearehighlysensitivetovariationsinthemixtureofthecomponents,soaparticularcombinationoftheseingredientsmustbecustom-designedtoachievespecifiedresultsintermsofstrengthorshrinkage.Whenconcreteispouredintoamoldorform,itcontainsfreewater,notrequiredforhydration,whichevaporates.Astheconcretehardens,itreleasesthisexcesswateroveraperiodoftimeandshrinks.Asaresultofthisshrinkage,finecracksoftendevelop.Inordertominimizetheseshrinkagecracks,concretemustbehardenedbykeepingitmoistforatleast5days.Thestrengthofconcreteincreasesintimebecausethehydrationprocesscontinuesforyears;asapracticalmatter,thestrengthat28daysisconsideredstandard.Text Concretedeformsunderloadinanelasticmanner.Althoughitselasticmodulusisonetenthofsteel,similardeformationswillresultsinceitsstrengthisalsoaboutonetenththatofsteel.Concreteisbasicallyacompressivematerialandhasnegligibletensilestrength.1-gravel；2-sand；3-cementpaste；4-pore Fig5.5ConcreteFig5.6ReinforcedconcreteTextReinforcedconcrete

Reinforcedconcretehassteelbarsthatareplacedinaconcretemembertocarrytensileforces.Thesereinforcedbars,whichrangeindiameterfrom0.25inch(0.64cm)to2.25inches(5.7cm)havewrinklesonthesurfacestoensureabondwiththeconcrete.Althoughreinforcedconcretewasdevelopedinmanycountries,itsdiscoveryisusuallyattributedtoJosephMonnier,aFrenchgardener,whousedawirenetworktoreinforceconcretetubesin1868.Thisprocessisworkablebecausesteelandconcreteexpandandcontractequallywhenthetemperaturechanges.Ifthiswerenotthecase,thebondbetweenthesteelandconcretewouldbebrokenbyachangeintemperaturesincethetwomaterialswouldresponddifferently.Reinforcedconcretecanbemoldedintoinnumerableshapes,suchasbeams,columns,slabs,andarches,andisthereforeeasilyadaptedtoaparticularformofbuilding[4](Fig5.6).Reinforcedconcretewithultimatetensilestrengthinexcessof10,000psi(700kg/sqcm)ispossible,althoughmostcommercialconcreteisproducedwithstrengthunder6,000psi(420kg/sqcm).TextPlastics

Plasticsarerapidlybecomingimportantconstructionmaterialsbecauseofgreatvariety,strength,durability,andlightness.Aplasticisasyntheticmaterialorwhichcanbemoldedintoanydesiredshapeandwhichusesanorganicsubstanceasabinder(Fig5.7).Organicplasticsaredividedintotwogeneralgroups:thermosettingandthermoplastic.Thethermosettinggroupbecomesrigidthroughachemicalchangethatoccurswhenheatisapplied;onceset,theseplasticscannotberemolded.Thethermoplasticgroupremainssoftathightemperatureandmustbecooledbeforebecomingrigid;thisgroupisnotusedgenerallyasastructuralmaterial.Theultimatestrengthofmostplasticmaterialsisfrom7,000to12,000psi(490to840kg/sqcm),althoughnylonhasatensilestrengthupto60,000psi(4,200kg/sqcm).Fig5.7PlasticsTextBitumen/bituminousEngineershavemadeuseoftheexcellentdurabilityandadhesivepropertiesofbituminousmaterials.Bituminousmaterialsareforthemostpartinmixtureswithmineralorotheraggregate.Theearliestknownusesofbitumenandtarrelatetohydraulicuses,forexample,bitumenisusedtowaterproofabuildingfloor(Fig5.8).Thincoatingofbitumenpaintsoremulsionsappliedtoabsorptivematerialshavetheeffectofsealingcapillariessothatbothwaterandwatervapourarepreventedfrommovingthroughthematerials[5].Nowadaysthemainuseofbitumenisinroadsurfaces,namedbitumenconcreteroad.Inordertoimprovethestrengthofbituminousmaterialsatthehightemperaturesandthetoughnessofthemattemperaturesbelowzero,polymermodifiedbitumen,suchasSBSrubbermodifiedbitumenandAPPplasticsmodifiedbitumenarewidelyused.Fig5.8BitumenNewWordsandPhrasesbrittlea.脆弱的，易碎的stiffnessn.刚度grainn.纹理sheetn.薄板boltn.螺栓连接rivetn.铆钉，连接；v.铆接，固定weldv.焊接ductilea.易变形的alloyn.合金magnesiumnn.锰siliconn.硅zincn.锌coppern.铜foiln.箔，金属薄片extrudev.挤压成形crushv.压碎calciumn.钙clayn.黏土kilnn.窑，炉pulverizev.使成粉末；研磨NewWordsandPhrasesingredientn.骨料shrinkagen.收缩hydrationn.水化作用evaporatev.蒸发，挥发finecrack微裂缝negligiblea.可以忽略的，无关紧要的，微不足道的bondv.黏结thermosettinga.热固性的thermoplastica.热塑性的bindern.黏结剂synthetica.合成的，人造的durabilityn.耐久性bitumenn.沥青Notes1.Ifamaterialwerenotelasticandadeformationwerepresentinthestructureafterremovaloftheload,repeatedloadingandunloadingeventuallywouldincreasethedeformationtothepointwherethestructurewouldbecomeuseless. 如果某种材料没有弹性，作用在结构上的荷载消失后，变形将仍然存在，反复的加载和卸载将加剧材料的变形，最终将导致结构不能再继续使用。2.Itisdifficulttodeviseconnectionswhichdonotdependontheshearortearingstrengthalongthegrain,althoughnumerousmetalconnectorshavebeenproducedtoutilizethetensilestrengthoftimbers. 虽然已经生产了许多利用木材抗拉强度的金属连接，但很难设计出与沿木材纹理方向抗剪强度和抗拉裂强度无关的接头。3.Theadditionofalloyingelements,suchassiliconormanganese,resultsinhigherstrengthsteelswithtensilestrengthupto250,000psi(17,500kg/sqcm). 添加像硅或锰这样的合金元素，会得到抗拉强度达250000磅/平方英寸（约1724兆帕---编者注）的高强钢筋。Notes4.Reinforcedconcretecanbemoldedintoinnumerableshapes,suchasbeams,columns,slabs,andarches,andisthereforeeasilyadaptedtoaparticularformofbuilding. 钢筋混凝土可以浇注成各种形状，如梁、柱、板和拱，因而适用于建筑物的具体形状。5.Thincoatingofbitumenpaintsoremulsionsappliedtoabsorptivematerialshavetheeffectofsealingcapillariessothatbothwaterandwatervapourarepreventedfrommovingthroughthematerials. 将薄的沥青涂料或乳液应用到吸收材料上，对封闭毛细管有影响，这样就可以阻止水和水蒸气从材料通过。Exercises（TranslatethefollowingChineseintoEnglish,orEnglishintoChinee）1.Cementisobtainedbyburningataveryhigh