《專業(yè)英語(yǔ)》課件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.剛度grainn.紋理sheetn.薄板boltn.螺栓連接rivetn.鉚釘，連接；v.鉚接，固定weldv.焊接ductilea.易變形的alloyn.合金magnesiumnn.錳siliconn.硅zincn.鋅coppern.銅foiln.箔，金屬薄片extrudev.擠壓成形crushv.壓碎calciumn.鈣clayn.黏土kilnn.窯，爐pulverizev.使成粉末；研磨NewWordsandPhrasesingredientn.骨料shrinkagen.收縮hydrationn.水化作用evaporatev.蒸發(fā)，揮發(fā)finecrack微裂縫negligiblea.可以忽略的，無(wú)關(guān)緊要的，微不足道的bondv.黏結(jié)thermosettinga.熱固性的thermoplastica.熱塑性的bindern.黏結(jié)劑synthetica.合成的，人造的durabilityn.耐久性bitumenn.瀝青Notes1.Ifamaterialwerenotelasticandadeformationwerepresentinthestructureafterremovaloftheload,repeatedloadingandunloadingeventuallywouldincreasethedeformationtothepointwherethestructurewouldbecomeuseless. 如果某種材料沒(méi)有彈性，作用在結(jié)構(gòu)上的荷載消失后，變形將仍然存在，反復(fù)的加載和卸載將加劇材料的變形，最終將導(dǎo)致結(jié)構(gòu)不能再繼續(xù)使用。2.Itisdifficulttodeviseconnectionswhichdonotdependontheshearortearingstrengthalongthegrain,althoughnumerousmetalconnectorshavebeenproducedtoutilizethetensilestrengthoftimbers. 雖然已經(jīng)生產(chǎn)了許多利用木材抗拉強(qiáng)度的金屬連接，但很難設(shè)計(jì)出與沿木材紋理方向抗剪強(qiáng)度和抗拉裂強(qiáng)度無(wú)關(guān)的接頭。3.Theadditionofalloyingelements,suchassiliconormanganese,resultsinhigherstrengthsteelswithtensilestrengthupto250,000psi(17,500kg/sqcm). 添加像硅或錳這樣的合金元素，會(huì)得到抗拉強(qiáng)度達(dá)250000磅/平方英寸（約1724兆帕---編者注）的高強(qiáng)鋼筋。Notes4.Reinforcedconcretecanbemoldedintoinnumerableshapes,suchasbeams,columns,slabs,andarches,andisthereforeeasilyadaptedtoaparticularformofbuilding. 鋼筋混凝土可以澆注成各種形狀，如梁、柱、板和拱，因而適用于建筑物的具體形狀。5.Thincoatingofbitumenpaintsoremulsionsappliedtoabsorptivematerialshavetheeffectofsealingcapillariessothatbothwaterandwatervapourarepreventedfrommovingthroughthematerials. 將薄的瀝青涂料或乳液應(yīng)用到吸收材料上，對(duì)封閉毛細(xì)管有影響，這樣就可以阻止水和水蒸氣從材料通過(guò)。Exercises（TranslatethefollowingChineseintoEnglish,orEnglishintoChinee）1.Cementisobtainedbyburningataveryhigh