土木工程毕业设计外文文献翻译.docx
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土木工程毕业设计外文文献翻译.docx
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土木工程毕业设计外文文献翻译
外文文献翻译
Reinforced Concrete
Concreteandreinforced concreteare usedas buildingmaterialsin everycountry.Inmany,includingthe UnitedStates andCanada,reinforced concrete is adominant structuralmaterialin engineeredconstruction.Theuniversalnatureofreinforcedconcreteconstructionstems fromthewideavailabilityofreinforcingbarsandthe constituents of concrete,gravel,sand,andcement,therelativelysimpleskills required inconcreteconstruction,andtheeconomyofreinforcedconcretecompared tootherforms ofconstruction.Concreteandreinforcedconcreteare usedinbridges,buildingsof allsorts undergroundstructures,watertanks,televisiontowers, offshoreoilexplorationandproductionstructures,dams,and evenin ships.
Reinforced concretestructuresmaybecast-in—placeconcrete, constructed intheirfinallocation,ortheymaybeprecastconcrete producedina factoryanderectedattheconstructionsite.Concrete structuresmaybesevere andfunctional indesign, orthe shapeandlayoutandbewhimsicalandartistic.Fewother buildingmaterialsoff thearchitectandengineersuchversatilityandscope.
Concreteisstrongincompressionbutweakin tension.Asaresult,cracksdevelopwhenever loads,orrestrainedshrinkageoftemperature changes,give risetotensilestressesinexcessofthe tensilestrengthoftheconcrete。
Inaplainconcrete beam, the momentsabout theneutralaxisdue to appliedloads are resistedbyaninternal tension-compressioncoupleinvolvingtension inthe concrete. Suchabeamfailsverysuddenlyandcompletely whenthe firstcrack forms.Inareinforcedconcretebeam, steelbarsareembeddedintheconcrete insucha waythatthe tensionforcesneededfor momentequilibriumafter theconcretecrackscanbedevelopedinthe bars。
Theconstructionof a reinforcedconcretememberinvolvesbuilding afrom ofmoldintheshapeofthememberbeingbuilt.Theform must bestrong enoughto supportboth the weightandhydrostaticpressureof thewetconcrete,andanyforcesappliedtoitbyworkers,concretebuggies,wind, andso on. Thereinforcementisplacedin thisformand held inplaceduringtheconcretingoperation。
Aftertheconcretehashardened, the forms areremoved.Asthe formsareremoved,propsofshoresareinstalled tosupporttheweightoftheconcreteuntilithasreachedsufficientstrengthtosupporttheloadsbyitself。
Thedesigner mustproportiona concretemember foradequate strengthtoresistthe loadsandadequatestiffness to preventexcessivedeflections.Inbeammust beproportionedsothatitcanbeconstructed.Forexample,the reinforcement must be detailedso thatit canbeassembledin thefield,andsincethe concreteis placedintheformafterthe reinforcementisinplace,theconcrete mustbe ableto flow around, between,andpastthereinforcementtofill allpartsoftheform completely.
Thechoice ofwhetherastructureshouldbebuiltofconcrete,steel,masonry,or timber dependsontheavailabilityof materialsand onanumberofvaluedecisions.Thechoice ofstructuralsystemis made bythearchitectofengineer early inthedesign,basedon thefollowing considerations:
1.Economy.Frequently,the foremostconsiderationistheoverall constofthestructure。
Thisis,of course, afunction ofthecosts ofthematerialsandthelabornecessary to erectthem.Frequently,however,theoverall costisaffected asmuchor morebytheoverallconstructiontime since thecontractor and ownermustborroworotherwiseallocatemoneytocarry outtheconstructionandwillnotreceiveareturnonthis investmentuntilthebuildingisreadyfor occupancy。
Ina typical largeapartmentofcommercialproject,the costofconstruction financingwillbea significantfractionofthetotalcost.Asaresult,financial savings duetorapidconstructionmaymore thanoffset increasedmaterialcosts。
Forthisreason, anymeasuresthedesigner cantaketostandardizethedesignandforming willgenerallypayoffinreducedoverall costs。
Inmany casesthelong-termeconomyof the structuremay bemoreimportant than thefirstcost。
Asa result,maintenance anddurability areimportant consideration.
2.Suitabilityofmaterialfor architecturalandstructural function。
A reinforcedconcretesystem frequentlyallows the designerto combinethearchitectural andstructuralfunctions.Concretehastheadvantagethatitisplacedina plastic conditionandisgiventhedesiredshapeandtextureby meansoftheforms andthefinishingtechniques.Thisallows suchelementsadflatplatesorother typesofslabstoserve asload—bearingelementswhileprovidingthefinishedfloor and/orceilingsurfaces。
Similarly, reinforcedconcretewalls canprovidearchitecturallyattractivesurfacesin addition tohaving theabilitytoresist gravity,wind, orseismicloads。
Finally,the choiceofsizeofshapeisgoverned by the designerandnotbythe availabilityofstandardmanufactured members。
3.Fireresistance.Thestructure inabuildingmustwithstand theeffectsof afire and remainstandingwhilethebuildingisevacuatedand thefire isextinguished. Aconcrete buildinginherentlyhasa 1— to3-hourfireratingwithoutspecialfireproofingorotherdetails。
Structuralsteelortimber buildingsmustbefireproofedtoattainsimilar fireratings.
4。
Lowmaintenance。
Concretemembersinherentlyrequireless maintenancethan dostructuralsteelortimber members. Thisisparticularlytrueifdense,air—entrainedconcretehasbeenusedforsurfacesexposed tothe atmosphere,and if carehas beentakeninthedesigntoprovideadequate drainage offand awayfromthestructure.Specialprecautionsmustbe takenforconcreteexposed tosaltssuchas deicingchemicals。
5.Availabilityof materials. Sand,gravel,cement,andconcretemixingfacilities areverywidelyavailable,and reinforcingsteelcan betransportedtomostjob sites moreeasilythancanstructural steel.Asa result,reinforcedconcreteisfrequentlyusedin remoteareas。
Ontheother hand,there area number of factorsthatmaycauseonetoselectamaterialotherthanreinforcedconcrete. Theseinclude:
1.Lowtensile strength.Thetensilestrengthconcrete ismuchlower thanitscompressivestrength(about1/10),andhenceconcreteissubjecttocracking。
Instructuralusesthisisovercomebyusingreinforcementtocarrytensile forces andlimit crackwidthstowithin acceptablevalues.Unlesscareis takenindesignandconstruction, however,thesecracksmaybeunsightlyormayallowpenetration ofwater.Whenthisoccurs,waterorchemicalssuchasroaddeicingsaltsmaycausedeteriorationor stainingoftheconcrete。
Specialdesigndetailsarerequiredinsuch cases.Inthe caseofwater-retainingstructures, special detailsand/ ofprestressingarerequiredtoprevent leakage。
2.Formsandshoring.Theconstructionof acast-in—placestructureinvolves threesteps notencounteredin theconstructionof steelortimberstructures. Theseare(a) theconstructionoftheforms,( b)theremovalof these forms,and(c)proppingorshoringthenewconcreteto support itsweightuntil itsstrengthis adequate。
Each ofthesestepsinvolveslabor and/ ormaterials,which arenotnecessarywith otherforms ofconstruction.
3.Relativelylowstrengthperunit ofweightforvolume. Thecompressivestrengthofconcreteisroughly5to10%thatof steel,whileitsunit density isroughly30%thatofsteel.Asaresult,aconcrete structure requiresa larger volumeanda greaterweightof materialthandoesacomparablesteelstructure.Asaresult,long-spanstructuresare oftenbuiltfromsteel.
4.Time-dependentvolumechanges.Bothconcreteand steel undergo—approximatelythe sameamountof thermalexpansionandcontraction.Becausethereisless massof steeltobeheatedorcooled,andbecausesteelisa betterconcrete,asteelstructure isgenerallyaffectedbytemperaturechangestoagreaterextent thanisaconcretestructure. Ontheotherhand, concrete undergoes fryingshrinkage,which,if restrained,maycausedeflectionsor cracking. Furthermore, deflectionswill tendtoincreasewithtime,possiblydoubling,duetocreepofthe concreteundersustainedloads.
In almosteverybranchofcivilengineeringandarchitectureextensiveuse is madeofreinforcedconcreteforstructuresandfoundations. Engineersandarchitectsrequiresbasic knowledgeofreinforcedconcretedesignthroughouttheirprofessionalcareers。
Muchofthistextisdirectly concernedwith thebehavior andproportioningofcomponents thatmakeup typical reinforced concretestructures-beams,columns,andslabs。
Oncethebehaviorof theseindividual elementsisunderstood,thedesignerwill havethebackgroundtoanalyzeanddesign awide range ofcomplexstructures,suchasfoundations,buildings, andbridges,composedoftheseelements。
Sincereinforcedconcrete isanohomogeneousmaterialthatcreeps,shrinks,andcracks,itsstressescannotbe accuratelypredictedbythetraditional equationsderived inacourseinstrengthofmaterialsforhomogeneouselastic materials。
Muchofreinforcedconcretedesigninthereforeempirical,i。
e.,designequationsanddesignmethodsare basedonexperimentalandtime—provedresultsinstead ofbeingderivedexclusivelyfromtheoretical formulations。
Athoroughunderstandingofthebehavior ofreinforcedconcrete will allowthedesignertoconvertanotherwisebrittlematerial intotoughductilestructuralelements and therebytakeadvantageofconcrete's desirablecharacteristics,itshighcompressive strength,its fire resistance,anditsdurability。
Concrete,astonelikematerial,ismadebymixingcement,water, fineaggregate(oftensand ), coarse aggregate,andfrequentlyotheradditives(thatmodi
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