1、WORD格式PAGE1 / NUMPAGES4Theapplicationofconstructionalmaterial建筑材料的應(yīng)用Theavailabilityofsuitablestructuralmaterialsisoneoftheprincipallimitationsontheaccomplishmentofanexperiencedstructuralengineer.Earlybuildersdependedalmostexclusivelyonwood,stone,brick,andconcrete.Althoughironhadbeenusedbyhumansatlea

2、stsincethebuildingoftheEgyptianpyramids,useofitasastructuralmaterialwaslimitedbecauseofthedifficultiesofsmeltingitinlargequantities.Withtheindustrialrevolution,however,cameboththeneedforironasastructuralmaterialandthecapabilityofsmeltingitinquantity.JohnSmeaton,anEnglishcivilengineer,wasthefirsttous

3、ecastironextensivelyasastructuralmaterialinthemid-eighteenthcentury.After1841,malleableironwasdevelopedasamorereliablematerialandwaswidelyused.Whereasmalleableironwassuperiortocastiron,therewerestilltoomanystructuralfailuresandtherewasaneedforamorereliablematerial.Steelwastheanswertothisdemand.Thein

4、ventionoftheBessemerconverterin1856andthesubsequentdevelopmentoftheSiemens-Martinopen-hearthprocessformakingsteelmadeitpossibletoproducestructuralsteelatcompetitivepricesandtriggeredthetremendousdevelopmentsandaccomplishmentsintheuseofstructuralsteeloverthenexthundredyears.Themostseriousdisadvantage

5、ofsteelisthatitoxidizeseasilyandmustbeprotectedbypaintorsomeothersuitablecoating.Whensteelisusedinanenclosurewhereafirecouldoccur,thesteelmembersmustbeencasedinasuitablefire-resistantenclosuresuchasmasonry,concrete.Normally,steelmemberswillnotfailinabrittlemannerunlessanunfortunatecombinationofmetal

6、lurgicalcomposition,lowtemperature,andbi-ortriaxialstressexists.Structuralaluminumisstillnotwidelyusedincivilengineeringstructures,thoughitsuseissteadilyincreasing.Byaproperselectionofthealuminumalloyanditsheattreatment,awidevarietyofstrengthcharacteristicsmaybeobtained.Someofthealloysexhibitstress-

7、straincharacteristicssimilarthoseofstructuralsteel,exceptthatthemodulusofelasticityfortheinitiallinearlyelasticportionisabout10,000,000psi(700,000kgf/cm*cm)oraboutone-thirdthatofsteel.Lightnessandresistancetooxidationare,ofcourse,twoofthemajoradvantagesofaluminum.Becauseitspropertiesareverysensitive

8、toitsheattreatment,caremustbeusedwhenrivetingorweldingaluminum.Severaltechniqueshavebeendevelopedforprefabricatingaluminumsubassembliesthatcanbereadilyerectedandboltedtogetherinthefieldtoformanumberofbeautifulandwell-designedshellstructures.Thisgeneralprocedureofprefabricationandheldassemblybyboltin

9、gseemstobethemostpromisingwayofutilizingstructuralaluminum.Reinforcedandprestessesconcretesharewithstructuralmaterial.Naturalcementconcreteshavebeenusedforcenturies.Modernconcreteconstructiondatesfromthemiddleofthenineteenthcentury,thoughartificialPortlandcementwaspatentedbyAspidin,anEnglishman,abou

10、t1825.Althoughseveralbuildersandengineersexperimentedwiththeuseofsteel-reinforcedconcreteinthelasthalfofthenineteenthcentury,itsdominantuseasabuildingmaterialdatesfromtheearlydecadesofthetwentiethcentury.Thelastfiftyyearshaveseentherapidandvigorousdevelopmentofprestressedconcretedesignandconstructio

11、n,foundedlargelyonearlyworkbyFreyssinetinFranceandMagnelinBelgium.Plain(unreinforced)concretenotonlyisaheterogeneousmaterialbutalsohasoneveryseriousdefectasastructuralmaterial,namely,itsverylimitedtensilestrength,whichisonlyoftheorderofone-tenthitscompressivestrength.Notonlyistensilefailureinconcret

12、eofabrittletype,butlikewisecompressionfailureoccursinarelativelybrittlefashionwithoutbeingprecededbytheforewarningoflargedeformations.(Ofcourse,inreinforced-concreteconstruction,ductilebehaviorcanbeobtainedbyproper1selectionandarrangementofthereinforcement.)Unlesspropercareisusedintheselectionofaggr

13、egatesandinthemixingandplacingofconcrete,frostactioncancauseseriousdamagetoconcretemasonry.Concretecreepsunderlong-termloadingtoadegreethatmustbeconsideredcarefullyinselectingthedesignstressconditions.Duringthecuringprocessanditsearlylife,concreteshrinksasignificantamount,whichtoadegreecanbecontroll

14、edbyproperlyproportioningthemixandutilizingsuitableconstructiontechniques.Withallthesepotentiallyseriousdisadvantages,engineershavelearnedtodesignandbuildbeautiful,durable,andeconomicalreinforced-concretestructuresforpracticallyallkindsofstructuralrequirements.Thishasbeenaccomplishedbycarefulselecti

15、onofthedesigndimensionsandthearrangementofthesteelreinforcement,developmentofpropercements,selectionofproperaggregatesandmixproportions,carefulcontrolofmixing,placing,andcuringtechniquesandimaginativedevelopmentofconstructionmethods,equipmentandprocedures.Theversatilityofconcrete,thewideavailability

16、ofitscomponentmaterials,theuniqueeaseofshapingitsformtomeetstrengthandfunctionalrequirements,togetherwiththeexcitingpotentialoffurtherimprovementsanddevelopmentofnotonlythenewerprestressedandprecastconcreteconstructionbutalsotheconventionalreinforcedconcreteconstruction,combinetomakeconcreteastrongc

17、ompetitorofothermaterialsinaverylargefractionofstructures.Inmoderntimes,withtheincreaseduseofsteelandreinforced-concreteconstruction,woodhasbeenrelegatedlargelytoaccessoryuseduringconstruction,touseintemporaryandsecondarystructures,andtouseforsecondarymembersofpermanentconstruction.Moderntechnologyi

18、nthelastsixtyyearshasrevitalizedwoodasastructuralmaterial,however,bydevelopingvastlyimprovedtimberconnectors,varioustreatmentstoincreasethedurabilityofwood,andlaminatedwoodmadeofthinlayersbondedtogetherwithsyntheticgluesusingrevolutionarygluingtechniques.Plywoodwithessentiallynondirectionalstrengthp

19、ropertiesisthemostwidelyusedlaminatedwood,buttechniqueshavealsobeendevelopedforbuildinglargelaminatedwoodmembersthatforcertainstructuresarecompetitivewithconcreteandsteel.Materialswithfuturepossibilitiesaretheengineeringplasticsandtheexoticmetalsandtheiralloys,suchasberyllium,tungsten,tantalum,titan

20、ium,molybdenum,chromium,vanadium,andniobium.Therearemanydifferentplasticsavailable,andthemechanicalpropertiesexhibitedbythisgroupofmaterialsvaryoverawiderangethatencompassestherangeofpropertiesavailableamongthemorecommonlyusedstructuralmaterials.Thusinmanyspecificdesignapplicationsitispossibletosele

21、ctasuitableplasticmaterialforanalternativedesign.Experiencewiththeuseofplasticsoutdoorsislimited.Generallyspeaking,however,plasticsmustbeprotectedfromtheweather.Thisaspectofdesignisthereforeamajorconsiderationintheuseofplasticsforprimarystructuralelements.Oneofthemostpromisingpotentialusedofplastics

22、isforpanelandshell-typestructures.Laminatedorsandwichpanelshavebeenusedinsuchstructureswithencouragingresultsthatindicateanincreaseduseinthistypeofconstructioninthefuture.Anothermaterialsdevelopmentwithinterestingpossibilitiesisthatofcompositesconsistingofamatrixreinforcedbyfibersorfiberlikeparticle

23、s.Althoughglass-fiber-reinforcedcompositeswithaglassorplasticmatrixhavebeenusedforyears,theyappeartohavemuchbroaderpossibilitiesforalargevarietyofsecondarystructuralcomponents.Fiber-reinforcedconcreteisanothercompositebeingactivelystudiedanddeveloped.Severalexperimentalapplicationsarebeingobservedun

24、derserviceconditions.Experimentshavebeenconductedwithbothsteelandglassfibers,butmostoftheserviceexperiencehasbeenwithsteelfibers.2建筑材料的應(yīng)用適當(dāng)有效的建筑材料是限制富有經(jīng)驗(yàn)的結(jié)構(gòu)工程師成就的主要原因之一。早期的建筑者幾乎都只使用木材，石頭，磚塊和混凝土。盡管鑄鐵在修建埃及的金字塔中已被人們使用,但是把它作為建筑材料卻由于大量熔煉它比較困難而被限制。藉由產(chǎn)業(yè)革命，然而，受到把鑄鐵作為建筑材料和在大量融煉它的能力的兩者對(duì)其雙重需要的影響。JohnSmeaton，一個(gè)

25、英國(guó)土木工程師,在十八的世紀(jì)中時(shí)，是第一廣泛地使用鑄鐵作為建筑材料的。在1841之后，可鍛金屬被發(fā)展成更可靠的材料并且廣泛地被應(yīng)用。盡管可鍛金屬優(yōu)于鑄鐵,但仍有很多結(jié)構(gòu)破壞從而需要有更可靠的材料。鋼便是這一需要的答案。1856年的貝色麥轉(zhuǎn)轉(zhuǎn)爐煉鋼法和后來(lái)發(fā)展的馬丁平爐煉鋼法的發(fā)明使以競(jìng)爭(zhēng)的價(jià)格形成了生產(chǎn)建筑用鋼并且興起了建筑用鋼在下個(gè)百年的快速發(fā)展。鋼的最嚴(yán)重缺點(diǎn)是它容易被氧化而需要被油漆或一些其他的適當(dāng)涂料保護(hù)。當(dāng)鋼被用于可能發(fā)生火災(zāi)環(huán)境時(shí),鋼應(yīng)該包圍在一些耐火的材料中,例如石料或混凝土。通常，鋼的組合結(jié)構(gòu)不易被壓碎除非是在冶金成分不好，低溫的不利組合,或空間壓力存在的情況下。建筑用鋁仍然不

26、廣泛被在土木工程結(jié)構(gòu)中用,雖然它的使用正在穩(wěn)定地增加。藉著鋁合金作為一個(gè)適當(dāng)?shù)倪x擇和對(duì)其進(jìn)行熱處理,可獲得各式各樣的強(qiáng)度特性。一些合金所展現(xiàn)的抗壓強(qiáng)度特性相似于鋼,除線形彈性模量大約是7,000,000牛/平方厘米，相當(dāng)于剛的三分之一。質(zhì)量輕和耐氧化是鋁的兩個(gè)主要優(yōu)點(diǎn)。因?yàn)樗奶匦詫?duì)熱處理是非常敏感的,當(dāng)鉚接或焊接鋁的時(shí)候，一定要小心仔細(xì)。一些技術(shù)已為制造預(yù)制鋁組合配件及形成若干的美麗的設(shè)計(jì)良好的外型結(jié)構(gòu)的鋁制結(jié)構(gòu)而發(fā)展起來(lái)。組合房屋配件制造的一般程序藉由螺栓連接，這似乎是利用建筑用鋁的最有前途的方法。加強(qiáng)和預(yù)應(yīng)力混凝土是主要的建筑材料。天然的水泥混凝土已經(jīng)被使用長(zhǎng)達(dá)數(shù)世紀(jì)之久?，F(xiàn)代的混凝土建

27、筑興起于十九世紀(jì)中葉,盡管人造水泥被Aspidin，一個(gè)英國(guó)人于1825年申請(qǐng)了專(zhuān)利.雖然一些建筑者和工程師在十九世紀(jì)后期用鋼筋混凝土作實(shí)驗(yàn),但作為一種建筑材料它占統(tǒng)治地位是在二十世紀(jì)初期。后五十年鋼筋混凝土結(jié)構(gòu)設(shè)計(jì)和建筑得到迅速發(fā)展,早期在法國(guó)的Freyssinet和比利時(shí)的Magnel被大量使用。素混凝土作為建筑材料有一個(gè)非常嚴(yán)重的缺點(diǎn)：就是它的抗拉強(qiáng)度非常有限,只是它的抗壓強(qiáng)度的十分之一。素混凝土不僅受拉破壞是脆性破壞，而且受壓破壞也是在沒(méi)有多大變形預(yù)兆的情況下發(fā)生的準(zhǔn)脆性破壞。(當(dāng)然,在鋼筋混凝土建筑中,可以得到適當(dāng)?shù)难有?。只有進(jìn)行適當(dāng)?shù)酿B(yǎng)護(hù)和合理的選擇并且摻加適當(dāng)?shù)幕旌咸旒觿?否則霜凍破壞能?chē)?yán)重的損害混凝土。在長(zhǎng)期荷載作用下混凝土在選擇設(shè)計(jì)受壓情況方面要仔細(xì)考慮。在硬化的時(shí)候和它的早期養(yǎng)護(hù)下,混凝土收縮占主要地位,因此需要添加