Itissaidthatnecessityisthemotherofallinvention.Ifthatisthecase,thentheneedforstriking,elegantcable-stayedbridgesthatcanspangreaterlengthsandbemoreeasilymaintainedoverthecourseoflongerliveshasyieldedasignificantnewinventionthatmaywellbenefitbridgedesignerstheworldover.Drivenbyadesiretopushthedesignofsingle-planecable-stayedbridgesbeyondtheircurrentlimits—bothinspanlengthandinaestheticappeal—whilestilldeliveringaneconomicsolutionthatiseasytoconstructandmaintain,FIGG,anengineeringfirmbasedinTallahassee,Florida,hascreatedanovelsystemforroutingstaycablesfromoneendofabridgedeck,throughthebridge’spylon,andthendowntotheotherendofthedeckinawaythatprecludesthepossibilityofcable-to-cableinteractions.Theinnovationhasbeenemployedontwonewbridges—theVeterans’GlassCitySkywayBridge,whichcarriesInterstate280acrosstheMaumeeRiverinToledo,Ohio(see“OhioDOTEndorsesDesignforMaumeeRiverCrossing,”CivilEngineering,September2000,page12),andthePenobscotNarrowsBridgeandObservatory,whichcarriesU.S.Route1overthePenobscotRiverinsoutheastern(“downeast”)Mainenearthecoastline(see“ObservatorytoCapMaineCrossing,”CivilEngineering,April2004,pages15–17).Thecradleoffersbenefitsbothduringconstructionandoverthelifeofthebridges.Mostimportantofall,itpermitstheuseofthelargestnumberofstrandswithinasinglestaycableintheworld:156,anincreaseofmorethan70percentoverthesecond-highestnumberknowntohavebeenusedintheUnitedStates.Italsomakesitpossibletoincreasethedistancebetweenstaycablesbyapproximately50percentwhenusedwithprecastdeltaframestofacilitateasingleplaneofstaycables,resultinginaestheticallysuperiordesigns.Thisisaccomplishedbyhavingallthestrandsparallelastheytravelfromtheanchorsatthedecklevelthroughthecradleinthepylonandbacktothedeck.Individualsleevepipeslocatedwithinthecradlesystemenableeachstrandtoactindependentlyofadjacentstrands.Thisalsopermitsthecablestobemuchlargerandtobespacedfartherapart,whichtranslatesintolongerspans.Furthermore,thecradlesystemlowersinitialcostsbyreducingtheamountofmaterialsandlaborneededbecausenoanchoragesinthepylonarerequired.Thissimplifiesconstructionoperationsbyallowingallofthecable-stressingoperationstobeperformedatthebridgedecklevelratherthanwithinthe(oftenrestricted)confinesofthepylon,highabovethebridgedeck.Thesystemalsoincludesremovable“reference”strandsineachstaycablethatprovideasimple,reliablemethodforverifyingtheconditionofthestaycablesinthefuture.Becausethecradlesystemdoesnotrequirestrandstobegrouted,theycanbeindividuallyremoved,inspected,andreplaced,evenwhenthereistrafficonthebridge.Bridgeownerscanthussafelyandaccuratelyassesstheconditionsofthestaycablesatanytimeoverthecourseofthebridge’slife.InthecaseoftheMainebridge,newstrandmaterialscanbetestedside-by-sidewithtraditionalmaterialsinanactualsetting,asopposedtoaprocessofcomputersimulation.Whatismore,thecradlesystemmakespossibletheuseofawidervarietyofpylondesigns—somewithmuchsmallerandmoreelegantcross-sectionalshapes—thatcanbeconstructedmoreeconomically.Engineerscanthusdesignpylonsthatarefarmoreunusualandaestheticallypleasingthanhasbeenthecaseinthepast.Thecradledesignworkswiththenaturalflowofforcesbecausetheforcestransmittedthroughthecradlenaturallycompressthepyloninanefficientmanner,thestressesbeingappliedradiallyalongthecurveofthecradle(seetheillustrationsonpage41).Intraditionalsystems,anchorageswithinthepylonrequiredlargetensiontiestoresistthehighsplittingforcesthatwouldbegenerated.Usingthecradlesystemeliminatesthisrequirementandfurtherenhancestheeleganceofthepylonshapes.Thedevelopmentofthisnewtechniquebeganinearly2000.TheOhioDepartmentofTransportation(ODOT)andtheToledoMetropolitanAreaCouncilofGovernmentshadformedwhatwascalledtheMaumeeRiverCrossingTaskForceDesignCommitteetoassessandcommunicatethecommunities’perspectiveonthedevelopingdesign.Thetaskforcechoseglassasthethemeforthenewcable-stayedbridge.Meetingsinvolvingadiversecrosssectionofthecommunityhadmadethepublic’sviewsclear:thebridgewastofeatureglassinaveryvisibleandstrikingwayinrecognitionofToledo’sindustrialheritageasaleaderintheglassindustry.Manyfamiliesintheareahadworkedinthelocalglassindustryforgenerations,anditwasimportanttothemthatthecrossingbeasymbolofthe“GlassCity,”asToledohascometobeknown.Thepublicwasalsooftheopinionthatthebridgedesignshouldchampionaproductthathadbeenoftheutmostimportancetothearea’seconomy.Thetaskforcefurtherdeterminedthatresidentswantedthebridgedesigntobelight,simple,andelegant.FIGGledtwocommunityworkshops,ordesigncharettes,duringwhichthepublicwaspresentedwithavarietyofaestheticoptions.Communityvotingshowedaclearpreferenceforasingle-pylondesign.Theconsensuswasthatbycreatingasingletallpylon—403ft(123m)—usingglassonthetop196ft(60m)andonallfoursides,thenewbridgewouldbevisuallystunning.Inkeepingwiththisdirective,thetopofthepylontakesonaprismaticshape,itspanelsoftreatedglassreflectingsunlightduringthedayonallfoursides.Behindtheglassarelight-emittingdiodes(LEDS)thatenablethepylontostandasabeaconatnight.(Theledfixturesarecontrolledremotelyandcapableofliterallymillionsofcolorcombinations.Infact,variouscolorschemeshavebeenpreprogrammed,someschemesmarkingmajorholidaysandothersexhibitingteamcolorsforstatewidesportingevents.)有人說需求是一切發明的母親。如果真的是這樣，那么引人注目的，優雅的斜拉橋能夠橫跨更大的距離和使得橋梁在更長的使用壽命中的維護變得更簡單將是一項可以讓全球橋梁設計者都受益的重要的新發明。在推動單面斜拉橋超越現有極限（在跨度和美觀兩方面）的需求的驅使下，同時用一種在建造和維護過程中都經濟的解決方法，FIGG，一家位于Florida首府Tallahassee的工程公司，發明了一個新穎的體系。該體系的斜拉索的傳力路徑是將力從橋面板的一端通過橋塔傳下至橋面板的另一端。這種方法就可以排除斜拉索間互相作用的可能性。這種創新的方法被應用在兩座新橋上。一座是老兵玻璃城航線大橋，這座大橋連接著280洲際公路橫跨流經Toledo,Ohio的Maumee河；另一座是Penobscot紐約灣海峽大橋和天文臺，這座大橋連接著美國1號公路橫跨位于靠近海岸線的Maine洲東南面的Penobscot河。這個支架為橋梁的建造過程和其使用壽命中都帶來了好處。最重要的是，它使得一根拉索中繩的股數達到了世界范圍內的最大值：156。這個值比美國境內用過的第二多的股數多了70％。也使得當它用于預制的三角形框架（可使得單面斜拉索更方便）的斜拉索的距離增加大約50％成為了可能。這樣就可以實現美學上的非凡設計。這是通過在繩股從橋面板水平面的支座穿過橋塔中的支架然后返回到橋面板過程中使得所有的繩股平行來實現的。位于支架系統內的獨立套管使得每股繩都能不受相鄰繩股的影響而單獨作用。這也使拉索可以做得比以前大得多并且拉索間的距離也可以更大，也就是說橋梁可以橫跨更大的距離。而且，由于橋塔內不需要支座所以材料的用量和人力的使用都減少了，從而支架系統降低了橋梁的初始成本。由于拉索的張拉操作都在橋面板上進行而不是在高高的橋塔上那么局限的范圍內進行所以施工操作也變得簡化了。這個體系還包括在每個斜拉索中都有可移動的參考繩股，這樣為將來檢驗拉索的使用情況提供了一個簡單可靠的方法。因為支架系統不要求用水泥漿添塞繩股，所以即使是在橋上有車輛和行人的情況下它們可以被單獨地移除，檢查和替換。這樣一來橋梁的業主在橋梁的使用壽命期間隨時都可以安全地，準確地對拉索的