中英 建筑中的結(jié)構(gòu)設(shè)計(jì)及建筑材料

PAGE17StructureinDesignofArchitectureAndStructuralMaterialWehaveandthearchitectsmustdealwiththespatialaspectofactivity,physical,andsymbolicneedsinsuchawaythatoverallperformanceintegrityisassured.Hence,heorshewellwantstothinkofevolvingabuildingenvironmentasatotalsystemofinteractingandspaceformingsubsystems.Isrepresentsacomplexchallenge,andtomeetitthearchitectwillneedahierarchicdesignprocessthatprovidesatleastthreelevelsoffeedbackthinking:schematic,preliminary,andfinal.Suchahierarchyisnecessaryifheorsheistoavoidbeingconfused,atconceptualstagesofdesignthinking,bythemyriaddetailissuesthatcandistractattentionfrommorebasicconsiderations.Infact,wecansaythatanarchitect’sabilitytodistinguishthemorebasicformthemoredetailedissuesisessentialtohissuccessasadesigner.Theobjectoftheschematicfeedbacklevelistogenerateandevaluateoverallsite-plan,activity-interaction,andbuilding-configurationoptions.Todosothearchitectmustbeabletofocusontheinteractionofthebasicattributesofthesitecontext,thespatialorganization,andthesymbolismasdeterminantsofphysicalform.Thismeansthat,inschematicterms,thearchitectmayfirstconceiveandmodelabuildingdesignasanorganizationalabstractionofessentialperformance-spaceinteractions.Thenheorshemayexploretheoverallspace-formimplicationsoftheabstraction.Asanactualbuildingconfigurationoptionbeginstoemerge,itwillbemodifiedtoincludeconsiderationforbasicsiteconditions.Attheschematicstage,itwouldalsobehelpfulifthedesignercouldvisualizehisorheroptionsforachievingoverallstructuralintegrityandconsidertheconstructivefeasibilityandeconomicofhisorherscheme.Butthiswillrequirethatthearchitectand/oraconsultantbeabletoconceptualizetotal-systemstructuraloptionsintermsofelementaldetail.Suchoverallthinkingcanbeeasilyfedbacktoimprovethespace-formscheme.Atthepreliminarylevel,thearchitect’semphasiswillshifttotheelaborationofhisorhermorepromisingschematicdesignoptions.Herethearchitect’sstructuralneedswillshifttoapproximatedesignofspecificsubsystemoptions.Atthisstagethetotalstructuralschemeisdevelopedtoamiddlelevelofspecificitybyfocusingonidentificationanddesignofmajorsubsystemstotheextentthattheirkeygeometric,component,andinteractivepropertiesareestablished.Basicsubsysteminteractionanddesignconflictscanthusbeidentifiedandresolvedinthecontextoftotal-systemobjectives.Consultantscanplayasignificantpartinthiseffort;thesepreliminary-leveldecisionsmayalsoresultinfeedbackthatcallsforrefinementorevenmajorchangeinschematicconcepts.Whenthedesignerandtheclientaresatisfiedwiththefeasibilityofadesignproposalatthepreliminarylevel,itmeansthatthebasicproblemsofoveralldesignaresolvedanddetailsarenotlikelytoproducemajorchange.Thefocusshiftsagain,andthedesignprocessmovesintothefinallevel.Atthisstagetheemphasiswillbeonthedetaileddevelopmentofallsubsystemspecifics.Heretheroleofspecialistsfromvariousfields,includingstructuralengineering,ismuchlarger,sincealldetailofthepreliminarydesignmustbeworkedout.DecisionsmadeatthislevelmayproducefeedbackintoLevelIIthatwillresultinchanges.However,ifLevelsIandIIarehandledwithinsight,therelationshipbetweentheoveralldecisions,madeattheschematicandpreliminarylevels,andthespecificsofthefinallevelshouldbesuchthatgrossredesignisnotinquestion,Rather,theentireprocessshouldbeoneofmovinginanevolutionaryfashionfromcreationandrefinement(ormodification)ofthemoregeneralpropertiesofatotal-systemdesignconcept,tothefleshingoutofrequisiteelementsanddetails.Tosummarize:AtLevelI,thearchitectmustfirstestablish,inconceptualterms,theoverallspace-formfeasibilityofbasicschematicoptions.Atthisstage,collaborationwithspecialistscanbehelpful,butonlyifintheformofoverallthinking.AtLevelII,thearchitectmustbeabletoidentifythemajorsubsystemrequirementsimpliedbytheschemeandsubstantialtheirinteractivefeasibilitybyapproximatingkeycomponentproperties.Thatis,thepropertiesofmajorsubsystemsneedbeworkedoutonlyinsufficientdepthtoverytheinherentcompatibilityoftheirbasicform-relatedandbehavioralinteraction.ThiswillmeanasomewhatmorespecificformofcollaborationwithspecialiststhenthatinlevelI.AtlevelIII,thearchitectandthespecificformofcollaborationwithspecialiststhenthatprovidingforalloftheelementaldesignspecificsrequiredtoproducebiddableconstructiondocuments.OfcoursethissuccesscomesfromthedevelopmentoftheStructuralMaterial.Theprincipalconstructionmaterialsofearliertimeswerewoodandmasonrybrick,stone,ortile,andsimilarmaterials.Thecoursesorlayerswereboundtogetherwithmortarorbitumen,atarlikesubstance,orsomeotherbindingagent.TheGreeksandRomanssometimesusedironrodsorclapstostrengthentheirbuilding.ThecolumnsoftheParthenoninAthens,forexample,haveholesdrilledinthemforironbarsthathavenowrustedaway.TheRomansalsousedanaturalcementcalledpuzzling,madefromvolcanicash,thatbecameashardasstoneunderwater.Bothsteelandcement,thetwomostimportantconstructionmaterialsofmoderntimes,wereintroducedinthenineteenthcentury.Steel,basicallyanalloyofironandasmallamountofcarbonhadbeenmadeuptothattimebyalaboriousprocessthatrestrictedittosuchspecialusesasswordblades.AftertheinventionoftheBessemerprocessin1856,steelwasavailableinlargequantitiesatlowprices.Theenormousadvantageofsteelisitstensileforcewhich,aswehaveseen,tendstopullapartmanymaterials.Newalloyshavefurther,whichisatendencyforittoweakenasaresultofcontinualchangesinstress.Moderncement,calledPortlandcement,wasinventedin1824.Itisamixtureoflimestoneandclay,whichisheatedandthengroundintoapower.Itismixedatorneartheconstructionsitewithsand,aggregatesmallstones,crushedrock,orgravel,andwatertomakeconcrete.Differentproportionsoftheingredientsproduceconcretewithdifferentstrengthandweight.Concreteisveryversatile;itcanbepoured,pumped,orevensprayedintoallkindsofshapes.Andwhereassteelhasgreattensilestrength,concretehasgreatstrengthundercompression.Thus,thetwosubstancescomplementeachother.Theyalsocomplementeachotherinanotherway:theyhavealmostthesamerateofcontractionandexpansion.Theythereforecanworktogetherinsituationswherebothcompressionandtensionarefactors.Steelrodsareembeddedinconcretetomakereinforcedconcreteinconcretebeamsorstructureswheretensionswilldevelop.Concreteandsteelalsoformsuchastrongbond─theforcethatunitesthem─thatthesteelcannotslipwithintheconcrete.Stillanotheradvantageisthatsteeldoesnotrustinconcrete.Acidcorrodessteel,whereasconcretehasanalkalinechemicalreaction,theoppositeofacid.Theadoptionofstructuralsteelandreinforcedconcretecausedmajorchangesintraditionalconstructionpractices.Itwasnolongernecessarytousethickwallsofstoneorbrickformultistorybuildings,anditbecamemuchsimplertobuildfire-resistantfloors.Boththesechangesservedtoreducethecostofconstruction.Italsobecamepossibletoerectbuildingswithgreaterheightsandlongerspans.Sincetheweightofmodernstructuresiscarriedbythesteelorconcreteframe,thewallsdonotsupportthebuilding.Theyhavebecomecurtainwalls,whichkeepouttheweatherandletinlight.Intheearliersteelorconcreteframebuilding,thecurtainwallsweregenerallymadeofmasonry;theyhadthesolidlookofbearingwalls.Today,however,curtainwallsareoftenmadeoflightweightmaterialssuchasglass,aluminum,orplastic,invariouscombinations.Anotheradvanceinsteelconstructionisthemethodoffasteningtogetherthebeams.Formanyyearsthestandardmethodwasriveting.Arivetisaboltwithaheadthatlookslikeabluntscrewwithoutthreads.Itisheated,placedinholesthroughthepiecesofsteel,andasecondheadisformedattheotherendbyhammeringittoholditinplace.Rivetinghasnowlargelybeenreplacedbywelding,thejoiningtogetherofpiecesofsteelbymeltingasteelmaterialbetweenthemunderhighheat.Priestess’sconcreteisanimprovedformofreinforcement.Steelrodsarebentintotheshapestogivethemthenecessarydegreeoftensilestrengths.Theyarethenusedtopriestessconcrete,usuallybyoneoftwodifferentmethods.Thefirstistoleavechannelsinaconcretebeamthatcorrespondtotheshapesofthesteelrods.Whentherodsarerunthroughthechannels,theyarethenbondedtotheconcretebyfillingthechannelswithgrout,athinmortarorbindingagent.Intheother(andmorecommon)method,thepriestessessteelrodsareplacedinthelowerpartofaformthatcorrespondstotheshapeofthefinishedstructure,andtheconcreteispouredaroundthem.Priestess’sconcreteuseslesssteelandlessconcrete.Becauseitisahighlydesirablematerial.Progressedconcretehasmadeitpossibletodevelopbuildingswithunusualshapes,likesomeofthemodern,sportsarenas,withlargespacesunbrokenbyanyobstructingsupports.Theusesforthisrelativelynewstructuralmethodareconstantlybeingdeveloped.建筑中的結(jié)構(gòu)設(shè)計(jì)及建筑材料建筑師必須從一種全局的角度出發(fā)去處理建筑設(shè)計(jì)中應(yīng)該考慮到的實(shí)用活動(dòng)，物質(zhì)及象征性的需求。因此，他或他試圖將有相互有關(guān)的空間形式分體系組成的總體系形成一個(gè)建筑環(huán)境。這是一種復(fù)雜的挑戰(zhàn)，為適應(yīng)這一挑戰(zhàn)，建筑師需要有一個(gè)分階段的設(shè)計(jì)過(guò)程，其至少要分三個(gè)“反饋”考慮階段：方案階段，初步設(shè)計(jì)階段和施工圖設(shè)計(jì)階段。這樣的分階段涉及是必需的，它可使設(shè)計(jì)者避免受很多細(xì)節(jié)的困惑，而這些細(xì)節(jié)往往會(huì)干擾設(shè)計(jì)者的基本思路。實(shí)際上，我們可以說(shuō)一個(gè)成功的建筑設(shè)計(jì)師應(yīng)該具備一種從很多細(xì)節(jié)中分辨出更為基本的內(nèi)容的能力。概念構(gòu)思階段的任務(wù)時(shí)提出和斟酌全局場(chǎng)地規(guī)劃，活動(dòng)相互作用及房屋形式方案。為實(shí)現(xiàn)這些，建筑師必須注意場(chǎng)地各部分的基本使用，空間組織，并應(yīng)用象征手法確定其具體形式。這就要求建筑師首先按照基本功能和空間關(guān)系對(duì)一項(xiàng)建筑設(shè)計(jì)首先構(gòu)思并模擬出一個(gè)抽象的建筑物，然后再對(duì)這一抽象的總體空間進(jìn)行深入探究。在開(kāi)始勾畫(huà)具體的建筑形似時(shí)，應(yīng)考慮基本的場(chǎng)所跳進(jìn)加以修改。在方案階段，如果設(shè)計(jì)者能夠形象的預(yù)見(jiàn)所作方案的結(jié)構(gòu)整體性，并要考慮施工階段可行性及經(jīng)濟(jì)性，那將是非常有幫助的。這就要求建筑師或者過(guò)問(wèn)工程是能夠從主要分體系之間的關(guān)系而不是從構(gòu)建細(xì)節(jié)去構(gòu)思總體結(jié)構(gòu)方案。這種能夠易于反饋以改進(jìn)空間形式方案。在初步設(shè)計(jì)階段，建筑師的重點(diǎn)工作應(yīng)是詳細(xì)化可能成為最終方案的設(shè)計(jì)，這是建筑師對(duì)結(jié)構(gòu)的要求業(yè)轉(zhuǎn)移到做分體系具體方案的粗略設(shè)計(jì)上。在這一階段應(yīng)該完成對(duì)結(jié)構(gòu)布置的中等程度的確定，重點(diǎn)論證和設(shè)計(jì)主要分體系已確定它們的主要幾何尺寸，構(gòu)件和相互關(guān)系。這樣就可以依據(jù)全局設(shè)計(jì)方案，確定并解決各分體系的相互影響以及設(shè)計(jì)難題。顧問(wèn)工程師在這一過(guò)程中作用重大，但各細(xì)部的考慮還留有選擇余地。當(dāng)然，這些初步設(shè)計(jì)階段所作的決定仍可以反饋回取使方案概念進(jìn)一步改善，或甚至可能有重大變化。當(dāng)設(shè)計(jì)者和顧問(wèn)工程師對(duì)初始階段設(shè)計(jì)方案的可行性滿意時(shí)，就意味著全部設(shè)計(jì)的基本問(wèn)題已經(jīng)解決，不會(huì)再因細(xì)節(jié)問(wèn)題而發(fā)生大的變化。這是工作重點(diǎn)將再次轉(zhuǎn)移，進(jìn)入細(xì)部設(shè)計(jì)。在這一階段將重點(diǎn)完善各分體系的細(xì)節(jié)設(shè)計(jì)。此時(shí)包括結(jié)構(gòu)工程在內(nèi)的各個(gè)領(lǐng)域的專(zhuān)家的作用將十分突出，應(yīng)為所有施工的細(xì)節(jié)都必須設(shè)計(jì)出來(lái)。這一階段的決定，可能會(huì)反饋到第二階段并導(dǎo)致一些變化。如果第一階段和第二階段的設(shè)計(jì)做的深入，那么在最初兩個(gè)階段所得到的總體結(jié)論和最后階段的細(xì)節(jié)的重新設(shè)計(jì)不再是問(wèn)題。當(dāng)然，整個(gè)實(shí)際過(guò)程應(yīng)該是逐步發(fā)展的過(guò)程，從創(chuàng)造和細(xì)化（改進(jìn)）總體設(shè)計(jì)概念直到做出精確的結(jié)構(gòu)設(shè)計(jì)和細(xì)部構(gòu)造。綜上所述：在第一階段，建筑師必須首先用概念的方式來(lái)確定基本方案的全部空間形式的可行性。在第一階段，專(zhuān)業(yè)人員的合作是有意義的，但僅限于行程總的構(gòu)思方面；在第二階段，建筑師應(yīng)該能夠用圖形來(lái)確定各分體系的需求，并且通過(guò)估計(jì)關(guān)鍵構(gòu)件的性能來(lái)證明其相互作用的可行性。也就是說(shuō)，主要分體系的性能只須做到一定深度，需要驗(yàn)證他們的基本形式和相互關(guān)系是協(xié)調(diào)一致的。這需要與工程師進(jìn)行更加詳細(xì)與明確的合作；在第三階段，建筑師和專(zhuān)業(yè)人員必須繼續(xù)合作完成所有構(gòu)件的設(shè)計(jì)細(xì)節(jié)，并制定良好的施工文件。當(dāng)然，這些設(shè)計(jì)的成功來(lái)源于建筑材料的發(fā)展與革新。早期的建筑材料主要是木材和砌塊,如磚塊、石材或瓦片及其它類(lèi)似的材料。磚和磚之間是由砂漿或者焦油狀的瀝青或其它粘合物粘結(jié)在一起。希臘人和羅馬人有時(shí)利用鐵棒或夾鉗來(lái)加固他們的建筑。例如,在雅典的帕臺(tái)農(nóng)神廟的柱子,就是由在水中也能變得如石材般堅(jiān)硬的火山灰建成的。鋼材和水泥─現(xiàn)代最重要的兩種建筑材料,在1