河北聯(lián)合大學(xué)建筑工程學(xué)院學(xué)號：200804010305

HEBEIUNITEDUNIVERSITY畢業(yè)設(shè)計(jì)外文GRADUATEDESIGN設(shè)計(jì)題目：唐山市中山賓館建筑結(jié)構(gòu)設(shè)計(jì)學(xué)生姓名：史知廣專業(yè)班級：08土木3班學(xué)院：建筑工程學(xué)院指導(dǎo)教師：韓建強(qiáng)副教授2012年05月25日外文外文PrestressedConcreteConcreteisstrongincompression,butweakintension:itstensilestrengthvariesfrom8to14percentofitscompressivestrength.Duetosuchalovetensilecapacity,flexuralcracksdevelopatearlystagesofloading.Inordertoreduceorpreventsuchcracksfromdeveloping,aconcentricoreccentricforceisimposedinthelongitudinaldirectionofthestructuralelement.Thisforcepreventsthecracksfromdevelopingbyeliminatingorconsiderablyreducingthetensilestressesatthecriticalmidspanandsupportsectionsatserviceload,therebyraisingthebending,shear,andtorsionacapacityoftheconcreteincompressioncanbeefficientlyutilizedacrosstheentiredepthoftheconcretesectionswhenallloadsactonthestructure.Suchanimposedlongitudinalforceiscalledaprestressingforce,i.e.,acompressiveforcethatprestressesthesectionsalongthespanofthestructuralelementpriortotheapplicationofthetransversegravitydeadandliveloadsortransienthorizontalliveloads.Thetypeofprestressesingforceinvolved,togetherwithitsmagnitude,aredeterminedmainlyonthebasisofthetypeofsystemtobeconstructedandthespanlengthandslendernessdesired.Sincetheprestressingforceisappliedlongitudinallyalongorparalleltotheaxisofthemember,theprestressingprincipleinvolvediscommonlyknownaslinearprestressing.Circularprestressing,usedinliquidcontainmenttanks,pipes,andpressurereactorvessels,essentiallyfollowsthesamebasicprinciplesasdoeslinearprestressing,Thecircumferentialhoop,or”hugging”stressonthecylindricalorsphericalstructure,neutralizesthetensilestressesattheouterfibersofthecurvilinearsurfacebytheinternalcontainedpressure.Itisplainthatpermanentstressesintheprestressedstructuralmemberarecreatedbeforethefulldeadandliveloadsareappliedinordertoeliminateorconsiderablyreducethenettensilestressescausedbytheseloads.Withreinforcedconcrete,itisbecausethetensileforcesresultingfromthebendingmomentsareresistedbythebondcreatedinthereinforcementprocess.Crackinganddeflectionarethereforeessentiallyirrecoverableinreinforcedconcreteoncethememberhasreacheditslimitstateatserviceload.Thereinforcementinthereinforcedconcretememberdoesnotexertanyforceofitsownonthemember,contrarytotheactionofprestressingsteel.Thesteelrequiredtoproducetheprestressingforceintheprestressedmemberactivelypreloadsthemember,permittingarelativelyhighcontrolledrecoveryofcrackinganddeflection.Oncetheflexuraltensilestrengthoftheconcreteisexceeded,theprestressedmemberstartstoactlikeareinforcedconcreteelement.Prestressedmemberareshallowerindepththantheirreinforcedconcretecounterpartsforthesamespanandloadingconditions.Ingeneral,thedepthofaprestressedconcretememberisusuallyabout65to80percentofthedepthoftheequivalentreinforcedconcretemember.Hence,theprestressedmemberrequireslessconcrete,andabout20to35percentoftheamountofreinforement.Unfortunately,thissavinginmaterialweightisbalancedbythehighercostofthehigherqualitymaterialsneededinprestressing.Also,regardlessofthesystemused,prestressingoperationsthemselvesresultinanaddedcost:formworkismorecomplex,sincethegeometryofpresstressedsectionsisusuallycomposedofflangedsectionswiththinwebs.Inspiteofthetheseadditionalcosts,ifalargeenoughnumberofprecastunitsaremanufactured,thedifferencebetweenatleasttheinitialcostsofprestressedandreinforcedconcretesystemsisusuallynotverylarge.Andtheindirectlong-termsavingsarequitesubstantial,becauselessmaintenanceisneeded,alongerworkinglifeispossibleduetobetterqualitycontroloftheconcrete,andlighterfounationsareachievedduetothesmallercumulativeweightofthesuperstructure.Oncethebeamspanofreinforcedconcreteexceeds70to90feet(21.3to27.4m),thedeadweightofthebeambecomesexcessives,resultinginheaviermembersand,consequently,greaterlong-termshrinkageandcreeptheyundergo.Verylargespanssuchassegmentedbridgesorcable-stayedbridgescanonlybeconstructedthroughtheuseofprestressing.Prestressedconcreteisnotanewconcept,datingbackto1872,whenP.H.Jackson,anengineerfromCalifornia,patentedaprestressingsystemthatusedatierodtoconstructbeamsorarchesfromindividualblocks.Afteralonglapseoftimeduringwhichlittleprogresswasmadebecauseoftheunavailabilityofhigh-strengthsteeloftheshrinkageandcreep(transversematerialflow)ofconcreteonthelossofprestress.Hesubsequentlydevelopedtheprinciplesofcircularprestressing.Hehoop-stressedhoriaontalreinforcementaroundwallsofconcretetanksthroughtheuseofturnbucklestopreventcrackingduetointernalliquidpressure,therebyachieveingwatertightness.Thereafter,prestressingoftanksandpipesdevelopedatanacceleratedpaceintheUnitedStates,withthousandsoftanksforwater,liquid,andgasstoragebuiltandmuchmileageofprestressedpressurepipelaidinthetwotothreedecadesthatfollowed.LinearprestressingcontinuedtodevelopinEuropeandinFrance,inparticularthroughtheingenuityofEugeneFreyssined,whoproposedin1926~28methodstoovercomepretresslossesthroughtheuseofhigh-strengthandhigh-ductilitysteels.In1940,heintroducedthenowwell-knownandwell-acceptedFreyssinetsystem.P.W.AbelesofEnglandintroducedanddevelopedtheconceptofpartialprestressingbetweenthe1930sand1960s.F.LeonhardtofGermany,V.MikhailovofRussia,andT.Y.LinoftheUnitedStatesalsocontributedagreatdealtotheartandscienceofthedesignofprestressedconcrete.Lin’sload-balancingmethoddeservesparticularlmentioninthisregard,asitconsiderablysimplifiedthedesignprocess,particularlyincontinuousprestressingthroughouttheworld,andintheUnitedStatesinparticular.Today,prestressedconcreteisusedinbuildings,undergroudstructures,TVtowers,floatingstorageandoffshorestructures,powerstations,nuclearreactorvessels,andnumeroustypesofbridgesystemincludingsegmentalanditsall-encompassingapplication.Thesuccessinthedevelopmentandconstructionofallthesestructureshasbeendueinnosmallmeasurestotheadvancesinthetechnologyofmaterials,particularlyprestressingstelel,andtheaccumulatedknowledgeinestimatingtheshort-andlong-termlossesintheprestressingforces.StructureofBuildingsConstructionEngineeringandConstructionEngineeringAbuildingiscloselyboundupwithpeople,foritprovidespeoplewiththenecessaryspacetoworkandlivein.Asclassifiedbytheiruse,buildingsaremainlyoftwotypes:industrialbuildingsandcivilbuildings.Industrialbuildingsareusedbyvariousfactoriesorindustrialproductionwhilecivilbuildingsarethosethatareusedbypeoplefordwelling,employment,educationandothersocialactivities.Theconstructionofindustrialbuildingsisthesameasthatofcivilbuildings.However,industrialandcivilbuildingsdifferinthematerialsused,andinthestructuralformsorsystemstheyareused.Consideringonlytheengineeringessentials,thestructureofabuildingcanbedefinedastheassemblageofthosepartswhichexistforthepurposeofmaintainingshapeandstability.Itsprimarypurposeistoresistanyloadsappliedtothebuildingandtotransmitthosetotheground.Intermsofarchitecture,thestructureofabuildingisanddoesmuchmorethanthat.Itisaninseparablepartofthebuildingformandtovaryingdegreesisageneratorofthatform.Usedskillfully,thebuildingstructurecanestablishorreinforceordersandrhythmsamongthearchitecturalvolumesandplanes.Itcanbevisuallydominantorrecessive.Itcandevelopharmoniesorconflicts.Itcanbebothconfiningandemancipating.And,unfortunatelyinsomecases,itcannotbeignored.Itisphysical.Thestructuremustalsobeengineeredtomaintainthearchitecturalform.Theprinciplesandtoolsofphysicsandmathematicsprovidethebasisfordifferentiatingbetweenrationalandirrationalformsintermsofconstruction.Artistscansometimesgenerateshapesthatobviateanyconsiderationofscience,butarchitectscannot.Thereareatleastthreeitemsthatmustbepresentinthestructureofabuilding:stability,strengthandstiffness,economy.Takingthefirstofthethreerequirements,itisobviousthatstabilityISneededtomaintainshape.Anunstablebuildingstructureimpliesunbalancedforcesoralackofequilibriumandaconsequentaccelerationofthestructureoritspieces.Therequirementofstrengthmeansthatthematerialsselectedtoresistthestressesgeneratedbytheloadsandshapesofthestructure(s)mustbeadequate.Indeed,a"factorofsafety"isusuallyprovidedsothatundertheanticipatedloads,agivenmaterialisnotstressedtoalevelevenclosetoitsrupturepoint.Thematerialpropertycalledstiffnessisconsideredwiththerequirementofstrength.Stiffnessisdifferentfromstrengthinthatitdirectlyinvolveshowmuchastructurestrainsordeflectsunderload.Amaterialthatisverystrongbutlackinginstiffnesswilldeformtoomuchtobeofvalueinresistingtheforcesapplied.Economyofabuildingstructurereferstomorethanjustthecostofthematerialsused.Constructioneconomyisacomplicatedsubjectinvolvingrawmaterials,fabrication,erection,andmaintenance.Designandconstructionlaborcostsandthecostsofenergyconsumptionmustbeconsidered.Speedofconstructionandthecostofmoney(interest)arealsofactors.Inmostdesignsituations,morethanonestructuralmaterialrequiresconsideration.Completivealternativesalmostalwaysexist,andthechoiceisseldomobvious.Apartfromthesethreeprimaryrequirements,severalotherfactorsareworthyofemphasis.First,thestructureorstructuralsystemmustrelatetothebuilding'sfunction.Itshouldnotbeinconflictintermsofform.Forexample,alinearfunctiondemandsalinearstructure,andthereforeitwouldbeimpropertoroofabowlingalleywithadome.Similarly,atheatermusthavelarge,unobstructedspansbutafinerestaurantprobablyshouldnot.Statedsimply,thestructuremustbeappropriatetothefunctionitistoshelter.Second,thestructuremustbefire-resistant.Itisobviousthatthestructuralsystemmustbeabletomaintainitsintegrityatleastuntiltheoccupantsaresafelyout.Buildingcodesspecifythenumberofhoursforwhichcertainpartsofabuildingmustresisttheheatwithoutcollapse.Thestructuralmaterialsused'forthoseelementsmustbeinherentlyfire-resistantorbeadequatelyprotectedbyfireproofingmaterials.Thedegreeoffireresistancetobeprovidedwilldependuponanumberofitems,includingtheuseandoccupancyloadofthespace,itsdimensions,andthelocationofthebuilding.Third,thestructureshouldintegratewellwiththebuilding'scirculationsystems.Itshouldnotbeinconflictwiththepipingsystemsforwaterandwaste,theductingsystemsforair,orthemovementofpeople.Itisobviousthatthevariousbuildingsystemsmustbecoordinatedasthedesignprogresses.Onecandesigninasequentialstep-by-stepmannerwithinanyonesystem,butthedesignofallofthemshouldmoveinaparallelmannertowardcompletion.Spatially,allthevariouspartsofabuildingareinterdependent.Fourth,thestructuremustbepsychologicallysafeaswellasphysicallysafe.Ahigh-riseframethatswaysconsiderablyinthewindmightnotactuallybedangerousbutmaymakethebuildinguninhabitablejustthesame.Lightweightfloorsystemsthataretoo"bouncy"canmaketheusersveryuncomfortable.Largeglasswindows,uninterruptedbydividingmotions,canbequitesafebutwillappearveryinsecuretotheoccupantstandingnexttoon40floorsabovethestreet.Sometimesthearchitectmustmakedeliberateattemptstoincreasetheapparentstrengthorsolidnessofthestructure.Thisapparentsafetymaybemoreimportantthanhonestlyexpressingthebuilding'sstructure,becausetheuntrainedviewercannotdistinguishbetweenrealandperceivedsafety.Thebuildingdesignerneedstounderstandthebehaviorofphysicalstructuresunderload.Anabilitytointuitor"feel"structuralbehaviorispossessedbythosehavingmuchexperienceinvolvingstructuralanalysis,bothqualitativeandquantitative.Theconsequentknowledgeofhowforces,stresses,anddeformationsbuildupindifferentmaterialsandshapesisvitaltothedevelopmentofthis"sense".Structuralanalysisistheprocessofdeterminingtheforcesanddeformationsinstructuresduetospecifiedloadssothatthestructurecanbedesignedrationally,andsothatthestateofsafetyofexistingstructurescanbechecked.Inthedesignofstructures,itisnecessarytostartwithaconceptleadingtoaconfigurationwhichcanthenbeanalyzed.Thisisdonesomemberscanbesizedandtheneededreinforcingdetermined,inorderto:a)carrythedesignloadswithoutdistressorexcessivedeformations(serviceabilityorworkingcondition);andb)topreventcollapsebeforeaspecifiedoverloadhasbeenplacedonthestructure(safetyorultimatecondition).Sincenormallyelasticconditionswillprevailunderworkingloads,astructuraltheorybasedontheassumptionsofelasticbehaviorisappropriatefordeterminingserviceabilityconditions.Collapseofastructurewillusuallyoccuronlylongaftertheelasticrangeofthematerialshasbeenexceededatcriticalpoints,sothatanultimatestrengththeorybasedontheinelasticbehaviorofthematerialsisnecessaryforarationaldeterminationofthesafetyofastructureagainstcollapse.Nevertheless,anelastictheorycanbeusedtodetermineasafeapproximationtothestrengthofductilestructures(thelowerboundapproachofplasticity),andthisapproachiscustomarilyfollowedinreinforcedconcretepractice.Forthisreasononlytheelastictheoryofstructuresispursuedinthischapter.Lookedatcritically,allstructuresareassembliesofthree-dimensionalelements,theexactanalysisofwhichisaforbiddingtaskevenunderidealconditionsandimpossibletocontemplateunderconditionsofprofessionalpractice.Forthisreason,animportantpartoftheanalyst'sworkisthesimplificationoftheactualstructureandloadingconditionstoamodelwhichissusceptibletorationalanalysis.Thus,astructuralframingsystemisdecomposedintoaslabandfloorbeamswhichinturnframeintogirderscarriedbycolumnswhichtransmittheloadstothefoundations.Sincetraditionalstructuralanalysishasbeenunabletocopewiththeactionoftheslab,thishasoftenbeenidealizedintoasystemofstripsactingasbeams.Also,long-handmethodshavebeenunabletocopewiththree-dimensionalframingsystems,sothattheentirestructurehasbeenmodeledbyasystemofplanarsubassemblies,tobeanalyzedoneatatime.Themodemmatrix-computermethodshaverevolutionizedstructuralanalysisbymakingitpossibletoanalyzeentiresystems,thusleadingtomorereliablepredictionsaboutthebehaviorofstructuresunderloads.Actualloadingconditionsarealsobothdifficulttodetermineandtoexpressrealistically,andmustbesimplifiedforpurposesofanalysis.Thus,trafficloadsonabridgestructure,whichareessentiallybothofdynamicandrandomnature,areusuallyidealizedintostaticallymovingstandardtrucks,ordistributedloads,intendedtosimulatethemostsevereloadingconditionsoccurringinpractice.Similarly,continuousbeamsaresometimesreducedtosimplebeams,rigidjointstopin-joints,filler-wallsareneglected,shearwallsareconsideredasbeams;indecidinghowtomodelastructuresoastomakeitreasonablyrealisticbutatthesametimereasonablysimple,theanalystmustrememberthateachsuchidealizationwillmakethesolutionmoresuspect.Themorerealistictheanalysis,thegreaterwillbetheconfidencewhichitinspires,andthesmallermaybethesafetyfactor(orfactorofignorance).Thus,unlesscode'provisionscontrol,theengineermustevaluatetheextraexpenseofathoroughanalysisascomparedtopossiblesavingsinthestructure.Themostimportantuseofstructuralanalysisisasatoolinstructuraldesign.Asuch,itwillusuallybeapartofatrial-and-errorprocedure,inwhichanassumedconfigurationwithassumeddeadloadsisanalyzed,andthemembersdesignedinaccordancewiththeresultsoftheanalysis.Thisphaseiscalledthepreliminarydesign;sincethisdesignisstillsubjecttochange,usuallyacrude,fastanalysismethodisadequate.Atthisstage,thecostofthestructureisestimated,loadsandmemberpropertiesarerevised,andthedesignischeckedforpossibleimprovements,Thechangesarenowincorporatedin.thestructure,amorerefinedanalysisisperformed,andthememberdesignisrevised,Thisprojectiscarriedtoconvergence,therapidityofwhichwilldependonthecapabilityofthedesigner,Itisclearthatavarietyofanalysismethods,rangingfrom"quickanddirtytoexact",isneededfordesignpurposes.Anefficientanalystmustthusbeincommandoftherigorousmethodsofanalysis,mustbeabletoreducethesetoshortcutmethodsbyappropriateassumptions,andmustbeawareofavailabledesignandanalysisaids,aswellassimplificationspermittedbyapplicablebuildingcodes.Anup-to-dateanalystmustlikewisebeversedinthebasesofmatrixstructuralanalysisanditsuseindigitalcomputersaswellasintheuseofavailableanalysisprogramsorsoftware.ConstructionEngineeringConstructionengineeringisaspecializedbranchofcivilengineeringconcernedwiththeplanning,execution,andcontrolofconstructionoperationsforsuchprojectsashighways,buildings,dams,airports,andutilitylines.Planningconsistsofschedulingtheworktobedoneandselectingthemostsuitableconstructionmethodsandequipmentfortheproject.Executionrequiresthetimelymobilizationofalldrawings,layouts,andmaterialsonthejobtopreventdelaystothework.Controlconsistsofanalyzingprogressandcosttoensurethattheprojectwillbedoneonscheduleandwithintheestimatedcost.PlanningTheplanningphasestartswithadetailedstudyofconstructionplansandspecifications.Fromthisstudyalistofallitemsofworkisprepared,andrelateditemsarethengroupedtogetherforlistingonamasterschedule.Asequenceofconstructionandthetimetobeallottedforeachitemisthenindicated.Themethodofoperationandtheequipmenttobeusedfortheindividualworkitemsareselectedtosatisfythescheduleandthecharacteroftheprojectatthelowestpossiblecost.Theamountoftimeallottedforacertainoperationandtheselectionofmethodsofoperationandequipmentthatisreadilyavailabletothecontractor.Afterthemasterorgeneralconstructionschedulehasbeendrawnup,subsidiarydetailedschedulesorforecastsarepreparedfromthemasterschedule.Theseincludeindividualschedulesforprocurementofmaterial,equipment,andlabor,aswellasforecastsofcostandincome.ExecutionThespeedyexecutionoftheprojectrequiresthereadysupplyofallmaterials,equipment,andlaborwhenneeded.Theconstructionengineerisgenerallyresponsibleforinitiatingthepurchaseofmostconstructionmaterialsandexpeditingtheirdeliverytotheproject.Somematerials,suchasstructuralsteelandmechanicalequipment,requirepartialorcompletefabricationbyasupplier.Forthesefabricatedmaterialstheengineermustprepareorcheckallfabricationdrawingsforaccuracyandcaseofassemblyandofteninspectthesupplier'sfabrication.Otherconstructionengineeringdutiesarethelayoutoftheworkbysurveyingmethods,thepreparationofdetaildrawingstoclarifythedesignengineer'sdrawingsfortheconstructioncrews,andtheinspectionoftheworktoensurethatitcomplieswithplansandspecifications.Onmostlargeprojectsitisnecessarytodesignandprepareconstructiondrawingsfortemporaryconstructionfacilities,suchasdrainagestructures,accessroads,officeandstoragebuildings,formwork,andcofferdams.Otherproblemsaretheselectionofelectricalandmechanicalequipmentandthedesignofstructuralfeaturesforconcretematerialprocessingandmixingplantsandforcompressedair,water,andelectricaldistributionsystems.ControlProgresscontrolisobtainedbycomparingactualperformanceontheworkagainstthedesiredperformancesetuponthemasterordetailedschedules.Sincedelayononefeatureoftheprojectcouldeasilyaffecttheentirejob,itisoftennecessarytoaddequipmentorcrewstospeedupthework.Costcontrolisobtainedbycomparingactualunitcostsforindividualworkitemsagainstestimatedorbudgetedunitcosts,whicharesetupatthebeginningofthework.Aunitcostisobtainedbydividingthetotalcostofanoperationbythenumberofunitsinthatoperation.Typicalunitsarecubicyardsforexcavationorconcreteworkandtonsforstructuralsteel.Theactualunit,costforanyitematanytimeisobtainedbydividingtheaccumulatedcostschargedtothatitembytheaccumulatedunitsofworkperformed.Individualworkitemcostsareobtainedbyperiodicallydistributingjobcosts,suchaspayrollandinvoicestothevariousworkitemaccounts.Payrollandequipmentrentalchargesaredistributedwiththeaidoftimecardspreparedbycrewforemen.Thecardsindicatethetimespentbythejobcrewsandequipmentonthedifferentelementsofthework.TheallocationofmaterialcostsISbasedonthequantityofeachtypeofmaterialusedforeachspecificitem.Whenthecomparisonofactualandestimatedunitcostsindicatesanoverrun;ananalysisismadetopinpointthecause.Iftheoverrunisinequipmentcosts,itmaybethattheequipmenthasinsufficientcapacityorthatitisnotworkingproperly.Iftheoverrunisinlaborcosts,itmaybethatthecrewshavetoomanymen,lackofpropersupervision,orarebeingdelayedforlackofmaterialsorlayout.Insuchcasestimestudiesareinvaluableinanalyzingproductivity.Constructionoperationsaregenerallyclassifiedaccordingtospecializedfields.Theseincludepreparationoftheprojectsite,earthmoving,foundationtreatment,steelerection,concreteplacement,asphaltpaving,andelectricalandmechanicalinstallations.Proceduresforeachofthesefieldsaregenerallythesame,evenwhenappliedtodifferentprojects,suchasbuildings,dams,orairports.However,therelativeimportanceofeachfieldisnotthesameinallcases.PreparationofsiteThisconsistsoftheremovalandclearingofallsurfacestructuresandgrowthfromthesiteoftheproposedstructure.Abulldozerisusedforsmallstructuresandtrees.Largerstructuresmustbedismantled.EarthmovingThisincludesexcavationandtheplacementofearthfill.Excavationfollowspreparationofthesite,andisperformedwhentheexistinggrademustbebroughtdowntoanewelevation.Excavationgenerallystartswiththeseparatestrippingoftheorganictopsoil,whichislaterreusedforlandscapingaroundthenewstructure.Thisalsopreventscontaminationofthenonorganicmaterialwhichisbelowthetopsoilandwhichmayberequiredforfill.Excavationmaybedonebyanyofseveralexcavators,suchasshovels,draglines,clamshells,cranes,andscrapers.Efficientexcavationonlandrequiresadryexcavationarea,becausemanysoilsareunstablewhenwetandcannotsupportexcavatingandhaulingequipment.Dewateringbecomesamajoroperationwhentheexcavationliesbelowthenaturalwatertableandinterceptsthegroundwaterflow.Whenthisoccurs,dewateringandstabilizingofthesoilmaybeaccomplishedbytrenches,whichconductseepagetoasumpfromwhichthewaterispumpedout.Dewateringandstabilizingofthesoilmayinothercasesbeaccomplishedbywellpointsandelectroosmosis.Somematerials,suchasrock,cementedgravels,andhardclays,requireblastingtoloosen.Blastholesaredrilledinthematerialjexplosivesarethenplacedintheblastholesanddetonated.Thequantityofexplosivesandtheblast-holespacingaredependentuponthetypeandstructureoftherockandthediameteranddepthoftheblastholes.Afterplacementoftheearthfill,itisalmostalwayscompactedtopreventsubsequentsettlement.Compactionisgenerallydonewithsheepfoot,grid,pneumatic-tired,andvibratory-typerollers,whicharetowedbytractorsoverthefillasitisbeingplaced.Handheld,gasoline-drivenrammersareusedforcompactionclosetostructureswherethereisnoroomforrollerstooperate.FoundationtreatmentWhensubsurfaceinvestigationrevealsstructuraldefectsinthefoundationareatobeusedforastructure,thefoundationmustbestrengthened.Waterpassages,cavities,fissures,faults,andotherdefectsarefilledandstrengthenedbygrouting.Groutingconsistsofinjectionoffluidmixturesunderpressure.Thefluidssubsequentlysolidifyinthevoidsofthestrata.Mostgroutingisdonewithcementandwatermixtures,butothermixtureingredientsareasphalt,cementandclay,andprecipitatingchemicals.ConcreteconstructionConcreteconstructionconsistsofseveraloperations:forming,concreteproduction,placement,andcuring.Formingisrequiredtocontainandsupportthefluidconcretewithinitsdesiredfinaloutlineuntilitsolidifiesandcansupportitself.Theformismadeoftimberorsteelsectionsoracombinationofbothandisheldtogetherduringtheconcreteplacingbyexternalbracingorinternalties.Theformsandtiesaredesignedtowithstandthetemporaryfluidpressureoftheconcrete.Theusualpracticeforverticalwallsistoleavetheformsinpositionforatleastadayaftertheconcreteisplaced.Theyareremovedwhentheconcretehassolidifiedorset.Slipformingisamethodwheretheformisconstantlyinmotion,justaheadoftheleveloffreshconcrete.Theformisliftedupwardbymeansofjackswhicharemountedonverticalrodsembeddedintheconcreteandarespacedalongtheperimeterofthestructure.Slipformsareusedforhighstructuressuchassilos,tanks,orchimneys.Concretemay