中英改造現(xiàn)有的結(jié)構(gòu)

山東建筑大學(xué)畢業(yè)設(shè)計外文文獻(xiàn)及譯文PAGEPAGE23外文翻譯：RETROFITOFEXISTINGSTRUCTURES2.1IntroductionManystructureshavehistoricallybeenconstructedusingreinforcedconcrete.Typicalordinaryconcreteconsistsoffourconstituents:gravel,sand,water,andcement.Reinforcedconcretehassometypeofreinforcement,typicallysteel,combinedwithconcretetoproduceastrongersystemthanplainconcrete.Concreteisstrongincompressionbutweakintension.Tensileforcescauseconcretetocrackandeventuallyfailinabrittlemanneratstressessignificantlylowerthanthecompressionstrengthofconcrete.Steel,oranothertypeofreinforcementmaterial,canbeusedtocompensatefortheweaktensilestrengthofconcrete.Thissystemisreferredtoasreinforcedconcrete.Asreinforcedconcreteages,avarietyofdetrimentaleffectscanoccur.Theseincludespalling,flaking,orcrackingoftheconcrete,andsubsequentcorrosionofthereinforcingsteel.Theseoccurrencescansignificantlyaffectthestrengthofstructuralmembers.Membersdisplayingtheseadverseaffectsmayberehabilitatedusinganappropriateretrofitmethod.Retrofittingistypicallydonefortworeasons:rehabilitationorstrengthening.Aspreviouslydiscussed,rehabilitationisfixingthestructuraldeficienciesofadamagedstructureorstructuralmember.Thismaybenecessaryforagingmembersthatnolongerdisplaythestrengthoftheoriginaldesign.Strengtheningincreasestheload-carryingcapacityofastructuralmember(Ersoyetal.1993).Thismaybenecessaryifthesupportedloadisalteredthroughthelifeofthestructuralmember,orifcurrentdesignstandardshavemorestringentreinforcementrequirements.Additionally,structuralmembersinseismicregionsmayneedtobeupgradedtocurrentseismicrequirements.Retrofittingcanbeappliedtoanystructuralmembers,includingbeamsandcolumns.Severalmethodsaretraditionallyutilizedforretrofitting.Theseincludeconcretejacketing,steeljacketing,andFRPstrengthening(Wipfetal.1997).Reinforcementforconcretejacketscanbeprovidedbyrebarreinforcementorweldedwirefabric(WWF).Additionally,arelativelynewproduct,PrefabricatedCageSystemreinforcement(PCS),issuggestedasapossiblereinforcementalternativeforconcretejacketretrofits.品2珍.組2策撿湖P滅r峽e傍f巾a優(yōu)b歐r立i桿c蠅a暮t脖e側(cè)d沙導(dǎo)C驗a黎g扮e敞匙S柴y廳s旅t趙e物m疾仆(零P書C湯S膜)輔異R荷e勾i便n茂f們o曠r討c瞎e蠢m(xù)弱e汪n延t蹤P回C厭S閣顧r純e儉i格n廳f迅o豐r狼c巖e鹿m宋e典n透t剝,摩勿a尚s矛閃s敞h畝o縫w缺n黨依i棕n立秤F勤i靈g讓u拳r稼e并志2俊.薦1艘,歪英i賭s說漠e誤s淋s肌e壇n席t芒i呼a慰l未l晶y叢距a堡稅c蕉o晝n鑰t前i腔n衣u伶o閑u日s炮然s努t瓜e瀉e勢l充滿s舅e鞠c欲t肅i墾o管n卵脆w珍i手t繞h魚捧h牲o勺l炮e致s幕沉a部p蘇p萌l測i艦e潛d牢外a峽s佛統(tǒng)a凈剃s南e趴c格o敏n轟d沿a智r慨y協(xié)隨p餃r銀o簡c吼e拌s頌s縱.捎浸鋒T擺h席e憑是P雀C右S普易r搭e沫i腫n槽f驚o擠r站c小e刑m拐e市n帳t祥光p療r圓o華v束i救d跌e燭s概遙l澇o蝕n嶼g籃i句t哈u瞇d牛i挪n宴a胃l壁泥a幟n桑d增桐t風(fēng)r默a適n好s殼v創(chuàng)e踩r曾s毫e勤沖r粘e親i牲n渴f慚o箏r悼c頌e襲m匹e菜n澡t敵親s勢i刷m艦u器l么t厚a枕n贈e孝o憂u哪s秩l懸y券塵a緩n口d確面c表a綁n裁叼b市e蝴居u裝s已e賺d喉畫i欄n討辟c徐i紐r鋤c惰u音l拆a香r靈良o(jì)熱r精距r還e熱c畜t徒a焰n比g赴u做l妹a增r竟組s筑e洗c惠t焰i島o狠n碎s詢.拍騾膨T惑h顯i愧s懲障m少o霞n偏o番l濁i搜t踏h積i嫂c防環(huán)c弄o罪n姑n騙e哭c務(wù)t冷i預(yù)o棗n蘆迷r弟e尸d放u背c蟻e盡s宅適t禽h團(tuán)e還頂n嚇e畝e眉d溉嶄f看o照r己固s繞e前p役a像r蛛a劃t殺e庫識l鞠o孔n芳g交i皂t角u悅d里i傭n港a翁l弄隱a窗n眨d超芬t糟r插a往n挽s賓v鬧e柏r野s既e溝丑r銅e粗i太n集f聾o惡r穗c崇e代m版e坐n頂t壩.泛肉言P顯C擊S記答c勢a晃n宣舟b霜e雕遣u醒s插e擔(dān)d除灑a較s歇灑r怕e議i立n猶f雷o(hù)漲r喇c刮e堤m傳e敢n明t胡衰i朵n散體c叮o鍵l遮u里m丟n灰s磁,薪薦s羞h(yuǎn)胞e柿a師r弦歸w捆a獸l廚l挪s吹,拘講f副o私u謙n梅d陸a群t蔬i撥o傾n療s葛械o踢r陷揮b條e她a勇m虎s斃.隊果火P扯C砍S欄窄r雞e森i針n帶f姻o醉r牛c賀e舍m亮e味n菠t狂匪c脈a露n駱陵b賊e辭粗c錯o美n片c源e鏈n言t芳r告i癥c巖a丹l耀l莊y跡慌l傾a窩y草e尾r寒e怪d擇踐i呈f棟乓l睬a溝r缺g菜e換餅r柄e慨i然n候f睛o究r小c財e遣m燕e累n現(xiàn)t桌歲r參a城t喊i缺o針s員吉a臥r莫e晚吐r境e論q稀u爛i討r卻e轟d繡烤(同F(xiàn)錢i囑g漿u芬r甩e盛建2產(chǎn).蹲2岡)熊.舌煩懂F炒o京r滑氣a釘仰c喚o擠l棍u亂m務(wù)n股,晚娛v巴e膛r漸t何i慣c跑a盲l裙許s拾t窮e俊e悶l騾廳s牲t閘r么i蓮p跡s級血p軍r仔o熔v刻i趣d上e喘裝l劇o肥n紅g眼i地t井u類d碼i舟n芳a鐘l鉆綁r支e協(xié)i許n駱f既o茶r樣c電e搜m欺e墻n彼t羊瞧w龜h哭i酷l太e毀帶t惕h豎e刷夢h粥o秋r蟻i舊z響o椒n昆t姓a橋l斬亦s幟t舉e揀e醒l腿崗s恐t塵r稅i滿p陡s倒俗p唉r饞o橫v株i模d論e嫁級t科r館a錯n閥s廁v慨e悅r聚s哥e短疑r喘e鈔i跨n始f霧o乘r喉c競e悟m娘e遭n降t腳.衛(wèi)釋榜T貞e救s凳t辰s彎回h扇a殲v懂e忙桃s械h意o束w堡n獵垃t畝h衰a擁t音糊P烘C首S朱啄p引r雹o麻v雪i去d必e毛s廊新h餡i拔g百h戒e毒r毯劑c底o(hù)度n邪f影i非n笛e扁m澇e芒n最t地蒸c澇a內(nèi)p始a傭c委i斜t哥i星e席s圖懸t盒h煙a圍n櫻帖t金r茶a右d績i并t旬i下o業(yè)n殖a養(yǎng)l組拳r奇e稈b撲a攪r港職r辨e強(qiáng)i叢n爽f格o辛r收c警e載m閘e較n魄t雖棒s岸y愈s王t尋e捕m踩s既貍(錘S聞h黎a踢m萬s棕a戰(zhàn)i巡搭a遲n消d臣不S紐e別z單e拳n剖做2癢0黑0簽5鴨)悼.熄2佳.果2恩.捕1險渾閘乘P奮C勞S凡肚P臂r漂o早d暑u孟c活t餃i侵o懇n沃P伯C夜S汗短r獲e傳i忌n饅f腦o皺r茂c拘e誕m錘e薦n靜t昏忽i宅s販清p堂r呼o旨d狼u餃c盲e字d辱逃f假r用o訂m亮囑s遙t頃e紫e戰(zhàn)l雀有t協(xié)u菊b犧e喪s刺銜o矮r帖見p喜l宋a霉t供e鑄s均.汪洗晌S勿t藍(lán)a奏n書d勢a里r剝d扇塵s堪t等e撒e件l排光t竟u誤b嗽e粉s晚杏o耕r兵般p消l糞a熟t款e售s害盒a常r良e飄豈p強(qiáng)u輸n驗c秘h秀e兇d都汽o此r穗勒c鴨u私t偶斥t面o凳辮p就r院o好v睜i妙d粗e漫信h第o來l始e嫌s喝衰w績i漏t想h普夕t礙h漿e活惠d斑e箱s疑i飼r提e殃d咱靠d丘i貍m待e膜n鏟s們i略o襲n勒s品.騰荷鳴I烏n汁釀l由i刮e船u媽文o院f撿香t敢u役b宋e怖s萬,線話s備t診e曉e雖l凡您p袋l過a案t示e錦s泰政c芝a完n勾計b僑e歉脾b湯e藍(lán)n蔥t繞栽i競n塊t兼o裕密t裁h框e我嗽r馬e齡q治u讓i蝦r攜e障d盈框s糖h積a托p扮e第炎a必n父d州哥t掏h事e潑n合廣w索e缸l逝d艙e接d呀.介竿控C害a屬s夢t任i市n繪g差脈o煉f腸撤P捆C偉S壓遺r角e煉i露n堡f舊o蜜r真c概e班m捐e進(jìn)n長t爬定h叫a搏s膜汗a況l非s哀o預(yù)脊b父e才e襪n爹蠟s言u廊g核g量e煉s題t仆e煮d鳥餐a域s膝勺a呢佳m景e團(tuán)t耕h字o灰d繭誤o排f優(yōu)橡p宵r密o環(huán)d尾u冬c輩t婚i障o破n劫.段C量u萌t避t母i敗n霞g論幅o秤f尖壟h告o摘l活e省s蹈滋i勸n嚼斯t乞h歸e石族P蒼C困S盆霧c勇a懷n殼宗b帝e鮮活p罰e非r恒f矮o時r辦m棕e預(yù)d暑擱w地i值t申h控赤a喬扎v手a溉r降i其e壯t莖y浪困o嚴(yán)f別速m沈e漆t(yī)刑h彼o剃d透s乓纖i覆n另c岡l敵u經(jīng)d泊i員n可g稠便l盜a考s蟲e挨r任洽(溜a咸s嗎部s姥h剃o懂w畝n劇墳i兄n爪謠F億i召g牌u銳r帖e痕燈2捆.旋3鼠)蝦,儲傻p污l抓a逃s蜘m短a版,澡僵f脅l旅a駛m熟e蠶,彩龜a鐵n非d頂毀a去b墨r本a甜s時i父v題e櫻塵w保a快t漢e晉r鉛吉j禿e步t簽開c突u燕t奴t賭i目n蠻g孔.搏抹掏A披d可d歷i覆t隊i姐o川n趙a柏l備撕s齒u奔g用g越e戰(zhàn)s削t牲e街d矮波m曬e理t往h環(huán)o趣d倆s糊怨i雜n槳c燥l妖u社d辰e近婚m撿i厲l姓l大i祥n慨g珠,閘塘e榜l氧e搜c套t霸r菠o謠c躬h燃e珠m析i廈c匪a厭l塘亡m永a詞c蹤h歐i進(jìn)n傭i睜n恒g予,豎燈e請l逃e飾c自t已r行i錘c帥a賢l糕射d臨i破s析c蝕h怠a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ittedunderloadorafterunloading,respectively.SandRrepresentstrengtheningorrepairretrofits,respectively.Fromtheresultsitisobviousthatthestrengthenedspecimensperformadequatelyandcarryaxialloadscomparabletothemonolithicreferencespecimen.RodriguezandPark(1994)conductedfurthertestingonrectangularcolumnsrepairedandstrengthenedbyconcretejacketsundercompressiveaxialloadingaswellaslateralloading.Rebarhoopsareprovidedastheretrofitreinforcementfortheconcretejackets.Concretejacketsincreasethestrengthandstiffnessoftheas-built(unretrofittedorbase)columnsbyuptothreetimes.Itisalsoshownthatdamagebeforetheretrofithasnosignificantinfluenceontheperformanceofthejacketedcolumns.Overall,concretejacketswithrebarreinforcementsignificantlyimprovestiffness,strength,andductilityoftypicalreinforcedconcretecolumns,butconstructionisverylabor-intensive.SimilarresultsarereportedbyBettetal.(1988)forsimilarlyretrofittedcolumns.Threesquarecolumntestspecimensareconstructed,retrofittedwithaconcretejacket,andthentested.Oneofthespecimensistested,repaired,andthenretested.Theothertwospecimensarestrengthenedbeforetesting.Specimensaretestedunderaxialandlateralloadssimultaneouslytosimulateearthquakeloading.Again,theexperimentdeterminesthatadamagedretrofittedcolumnhasnearlythesamestrengthandstiffnessasanundamagedretrofittedcolumnwithasimilarconcretejacket.Lehman,etal.(2001)useconcretejacketstorepairseverelydamagedcolumns.Threerepairmethodsareconsideredandimplementedforthedamagedcolumns,whichwerebuilttomodernseismicspecifications.Initialdamagetothecolumnsincludescrushingofconcrete,bucklingandfractureoflongitudinalreinforcement,andfractureofthespiralreinforcement,whichwastheresultofaxialandlateralloading.Theconcretejacketretrofittedcolumndisplaysincreasedstiffnessandstrength,comparabletotheoriginalcolumnbeforedamage.2.3.1.2AdditionalReinforcementOptionsAdditionalreinforcementoptionsforconcretejacketinghavebeenintroduced.Weldedwirefabricisanothercommonmaterialthatcouldbeusedtoreinforceaconcretejacketretrofit.MorshedandKazemi(2005)proposeasimilarsystemproducedfromexpandedsteelmesh,showninFigure2.9.Theresearchdeterminesthatretrofittingmemberswiththeexpandedsteelmeshandmortarsignificantlyincreasestheshearstrengthandductilityoftheretrofittedmembers.2.3.2SteelJacketingSteeljacketspreventconcretefromexpandinglaterallyasaresultofhighaxialcompressionstrains.Thesteeljacketisequivalenttocontinuoushoopreinforcementandcanbeusedforcircularcolumnsorrectangularcolumnswithslightmodifications,asshowninFigure2.10.Steeljacketingofrectangularcolumnsisnotrecommendedbecausewhileshearstrengthisenhanced,flexuralductilityisonlyprovidedatthecorners.Anellipticalsteeljacketwithconcreteinfillshouldbeprovidedforrectangularmemberstofullyconfinealltheconcrete(Priestleyetal.1996).Acomprehensivetwo-partstudywasperformedbyPriestleyetal.(1994a,b)todeterminetheenhancedshearstrengthprovidedbysteeljacketretrofitting.Thefirstpartoftheresearchfocusesontheoreticalconsiderationsandtestdesign.ItisdeterminedthatACIdesignequationsareoverlyconservativeandnewdesignequationsarepresentedforcircularorrectangularcolumnsinneedofshearenhancement.Thesecondpartoftheresearchfocusesontheactualtestingofthecolumnsdesignedaccordingtotheproposedequations.Itisconcludedthatsteeljacketssignificantlyincreasetheshearstrengthandflexuralductilityofsheardeficientcolumns,whichisshowninTable2.1.SpecimenswithanAareas-builtcolumnsandanRrepresentsretrofittedcolumns.FurtherresearchperformedbyShamsandSaadeghvaziri(1997)determinesseveralneedsforresearchintoconcrete-filledsteeltubes(CFT).ItisconcludedthattheultimatestrengthofCFT’sisnotaccuratelypredictedandtheconfinementbenefitsneedtobeaccountedfor.Additionally,theresearchincludesaxialcompressiontestsperformedoncircularandrectangularCFTspecimens,showninFigure2.11.Itissuggestedthatfurtherresearchisneededtoaccuratelyunderstandthebondbetweenthesteelandconcrete,ductilityenhancement,andtoprovideanewdesignmethod.Aboutahaetal.(1999)usesvarioustypesofrectangularsteeljacketstostrengthenconcretecolumns.Thinsteelplatesarealsousedtomeasuretheconfinementandstrengtheningofthinplatesusedwithlargecolumns.Theresearchshowsthateventhinsteeljacketsareeffectiveforstrengtheningreinforcedconcretecolumns.Thesteeljacketsappliedincludefullandpartialsteeljackets,whichdonotfullyencompasstheentireretrofittedmember.Bothjacketsenhancetheductilityandstrengthofthemembers.Additionally,partiallystiffenedsteeljacketsareproposedbyXiaoandWu(2003a)toenhancestrengthandductilityforsquareorrectangularcolumns.Zhangetal.(1999)appliessteeljacketretrofitmeasurestypicallyusedforsinglecolumns,tomulticolumnbridgeapplications.Theretrofittedbridgestructureiscomparedtoanunretrofittedbridgestructureunderasimulatedseismicloadusingadynamicbridgeanalysisprogram.2.3.3FRPJacketingFiberreinforcedpolymer(FRP)confinementcanbeprovidedusingseveralcompositematerialsincludingfiberglass,carbonfiber,andKevlarbondedtotheconfinedconcretesurfaceusingepoxy(Priestleyetal.1996).Weightandcross-sectionoftheretrofittedmemberarenotsignificantlyaffectedwithFRPjackets.FRPjacketsaremostapplicableforcircularcolumns,asstressconcentrationscandevelopintheFRPwraparoundthecornersofsquareorrectangularcross-sections.FRPjacketscanbeusedforrectangularorothershapedmembers,ifshapemodificationisperformedtopreventstressconcentrationsfromdeveloping.TwotypesofFRPretrofits,wrapsandprefabricatedcompositejackets,aretypicallyutilized.2.3.3.1FRPWrapsFRPwrapshaveseveralbenefitsincludinghighstrength,lightweight,resistancetocorrosion,lowcost,andversatility(Saadatmaneshetal.1997).FRPwrappingisperformedbyfirstcleaningthesurfaceofthemembertoberetrofitted.EpoxyorresinisthenusedtoattachtheflexibleFRPfabrictothesurfaceofthemembertoberetrofitted.Thefabriccanbeapplieddry,butthepreferredmethodistosoakthefabricinepoxybeforeapplicationtoallowforbettercohesionwiththesurfaceofthemembertoberetrofitted.Thefabricisthensmoothedouttoensurenoairpocketsexistandextraepoxyissqueezedoutthesides.Anewlayerofepoxyshouldbeappliedbetweeneachlayeroffabricandafinallayerofepoxyontheoutermostsurfaceofthefabric.Thewrapshouldthenbeallowedtocureatambienttemperatures.Saadatmaneshetal.(1997)appliesFRPwrapstorepairseverelydamagedreinforcedconcretecolumns.CriticallystressedregionsnearthecolumnfootingjointarerepairedwithFRPwrap.ItisevidentfromtheresultsthatFRPcompositewrapseffectivelyrestoreflexuralstrengthandductilityindamagedcolumns.Similarly,Gergelyetal.(1998)usescarbonFRPwraptotesttheperformanceenhancementofreinforcedconcretecapbeamsandcapbeam-columnjoints.TheresearchshowsthatFRPwrapscansignificantlyincreasetheshearcapacityandductilityofcapbeamsandcapbeam-columnjoints.Hadi(2003)performssimilartestsonconcretebeamsandconcludesthatFRPwrapscontributetotheloadcarryingcapacity,aswellasflexuralstrength,ofreinforcedconcretebeams.AdditionallayersofFRPresultinincreasedflexuralstrength.XiaoandWu(2003b)performacomprehensiveresearchprogramtostudythebehaviorofconcreteconfinedbyvarioustypesofFRPwraps.CarbonfiberaswellasE-glasswrapsareinvestigated.Themethodsofapplicationvarybetweeninsitu(handlayup)andmachine-woundapplication.Again,itisdeterminedthatFRPcompositejacketssignificantlyincreasethestrengthandductilityofconcrete.2.3.3.2PrefabricatedFRPCompositePlatesFRPcompositeplatesaretypicallyshellsthatareprefabricatedinaquality-controlledenvironmentpriortofieldapplication.PrefabricatedFRPplatesareusedtoavoidthespecialattentionneededtoassurethaton-sitequalitycontrolandcuringconditionsarestrictlyenforced(XiaoandMa1997).Fiberreinforcementiscombinedwithresinandallowedtocureinthedesireddimensions,whichcreatesashell.Shellsareeitherfabricatedcontinuouslytoformamultilayerrollorcutintoindividualsingle-layercylindricalshellswithalongitudinalslitforeachlayer.Aftercuring,theshellsareopenedandclampedaroundthecolumntoberetrofitted.Adhesive,orepoxy,isthenappliedtobondtheshellstothecolumnsurface.Additionaladhesiveisappliedbetweeneachshelllayeralso.Slitsoftheindividuallayersarestaggeredtoavoidaconcentratedweakness(Xiaoetal.1999).XiaoandMa(1997)useprefabricatedglassfibershellstorepairfull-size,damaged,“asbuilt”columns.The“asbuilt”columnsareinitiallyfailedandthenretestedaftertheretrofitisapplied.Figure2.12displaysthetestset-upusedtoloadtheretrofittedcolumns.Theprefabricatedjacketsystemdelayscolumnfailurebyimprovingthehystereticresponseandincreasingtheductilityoftheretrofittedspecimens.Xiaoetal.(1999)continuethisresearchofprefabricatedFRPplatesbytestingplatesindividuallycuredandplatescuredtogetherasacontinuoussystem.Shearandductilityimprovementareverifiedforbothmethods,andlittleappreciabledifferenceisnoticedbetweenthetwosystems.AdditionalresearchisperformedbyShahroozandBoy(2004)tostrengthenbridgespanswithFRPplates.TheprefabricatedplatesarecomparedwithFRPfabric,asshowninFigure2.13.Testsareperformedtodeterminetheeffectivenessofthesystemsshortlyafterinstallationandagainayearlater.EffectivenessoftheFRPdidnotchangeintheoneyeartimeperiod.BothFRPretrofitsaresuccessfulinincreasingtheloadcarryingcapacityofthebridgeandthestiffness.Allretrofitmethodsdiscussedareshowntoincreasememberstrengthandconfinement.Thediscussedmethodshavebeenpreviouslytestedasretrofitsforreinforcedconcretecolumns.TheuseofPCSasreinforcementforconcretejacketshasnotpreviouslybeentested.Severalaspectsconsideredinevaluatingretrofitoptionsincludeapplication,confinement,cost,typeoffailure,bond,andconstructiontime.2.4.1ApplicationApplicationvariablesarefurtherdividedintoseveralfactorsthatcouldassistindeterminingthetypeofretrofittouse.Thesefactorsincludeconstructiontime,constructiondifficulty,andcuring.2.4.1.1ConstructionTimeTimerequiredforconcretejacketingisdependentuponthetypeofreinforcementused.Settingupformwork,creatingorsettingupreinforcement,pouringconcrete,andcuringoftheconcreteallcontributetothetimerequiredforthisretrofitting.PCSandweldedwirefabric(WWF)reduceconstructiontimebecausebothareproducedoff-site.ThetimerequiredtoproducePCSreinforcementisdependentonthemethodusedtocreatetheholes.WWFismassproducedandreadilyavailableonthemarket.SomeweldingmayberequiredforbothPCSandWWFtoenclosethemembertoberetrofitted.Rebarcageproductionisverytime-consumingwhetherproducedoff-siteorinthefield.Placementofthetransversereinforcementaroundthemembertoberetrofittedisalengthyprocessifmechanicalmeansarenecessarytoproperlypositionthereinforcement.Steeljacketsrequirelittleset-uptime.Noformworkisneededbecausethetubeservesasformwork.Littlefabricationandfieldtimeareneededfortheretrofit.Somefieldweldingmayberequiredtoenclosethemembertoberetrofitted.Pouringoftheconcrete,orgrout,doesnotrequiresignificanttime.FRPjacketsrequirepreparationofthesurfacetoberetrofitted.Forcircularsections,thistimeisminimal.Thesurfaceofthememberisthoroughlycleaned,andinsomecases,roughenedwithadiskgrinder.Forrectangularsections,allcornersorprotrudingedgesmustbesmoothedwhichcouldrequireadditionaltime.Iftherectangularcross-sectionistobealteredtoanellipticalshape,significanttimecouldberequiredforformworkset-up,concretepouring,andcuring.Actualapplicationofthematerialdoesnottakelong,asthematerialisapplieddirectlytothepreparedsurface.Closesupervisionisrequiredthroughoutcuringtoensurethatslidingorslippingofthematerialdoesnotoccur.Ifprefabricatedcompositeplatesareused,additionaltimeisrequiredforproductionandcuringoftheplates.2.4.1.2ConstructionDifficultyTheconstructionsequenceforconcretejacketconstructioncanbedividedintothreeparts:formwork,reinforcementapplication,andconcretecasting.Formworkissimilarforallconcretejacketingregardlessofthetypeofreinforcement.Difficultyinconcretecastingisafunctionofthetypeofmemberbeingretrofittedandspacingofthereinforcement.Closelyspacedreinforcementrestrictstheflowofconcreteandcreatesadditionalworktoensuretheconcreteisproperlydistributedthroughoutthemember.ProperclearancesallowconcretetoflowfreelythroughrebarcagesandWWFreinforcement.PCSrestrictsconcreteflowmorebecausethereinforcementprovidedisplanar,sothesurfaceareaconfiningtheconcreteisgreater.Ifproperclearancesareprovided,concreteflowisnotaproblem.Shotcrete,orthesprayingoflow-slumpconcrete,isanapplicationthatcouldpossiblyreducetheneedforformwork.Reinforcementapplicationisafactorsignificantlyaffectedbythetypeofreinforcementusedintheconcretejacket.WWFcaneasilybeplacedaroundthemembertoberetrofittedandthenweldedortiedtocreatethedesiredcage.Smallgaugewiresareeasilymanipulatedtothedesiredshape.Iflargeamountsofreinforcementareneeded,WWFwouldbespeciallyproduced,ormaynotbeaviableoptionatall.CircularPCScanbeplacedintwoC-sectionsandthenweldedtosurroundthemember.Placementofhooporspiralrebarreinforcementaroundanexistingmemberisadifficultandtimeconsumingprocessasmechanicalmeansmaybenecessarytobendthereinforcementintoplace.HoopreinforcementcanbelapsplicedorweldedastwoC-shapes,butthisisalsoatime-consumingprocess.Steeljacketsrequirethetwohalvesofthetubetobeweldedtogethertoencompassthemember.Noformworkisrequiredandtherearenoclearanceissuesbecausetheconcreteiscontainedwithinthetube.NoformworkorextraconcreteisrequiredforFRPretrofittingtypically.SurfacepreparationisveryimportantasFRPwrappingisverysensitivetostressconcentrationsandnecessarymeasuresmustbetakentoensuretheretrofitsurfaceisclean,butroughenoughtoprovideabondforthematerial.Itiscriticallyimportanttopreventanywrinklingorpocketingofthematerialduringapplication.Useofcompositeplatesreducethesesensitivities.Awetlay-uprequiresthefabrictobefullysaturatedbeforeapplication,whichmayrequiretheuseofamachine,tosoakandapplythewrap,tosignificantlyincreaseeaseofconstructionforlarge-scaleprojects.2.4.1.3CuringConcreteusedinsteeljacketsandconcretejacketsshould,preferably,beallowedtocureatmoderatetemperature.Freezingofconcreteduring