工程结构中英文对照外文翻译文献.docx
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工程结构中英文对照外文翻译文献
中英文对照外文翻译文献
(文档含英文原文和中文翻译)
原文:
StructureDesign
Abstract:
Structuredesignistheselectionofmaterialsandmembertype,size,andconfigurationtocarryloadsinasafeandserviceablefashion.Ingeneral,structuraldesignimpliestheengineeringofstationaryobjectssuchasbuildingsandbridges,orobjectsthatmaybemobilebuthavearigidshapesuchasshiphullsandaircraftframes.Deviceswithpartsplannedtomovewithrelationtoeachother(linkages)aregenerallyassignedtotheareaofmechanical.
Keywords:
StructureDesign;Structuralanalysis;structuralscheme;Projectrequirements
Structuraldesigninvolvedatleastfivedistinctphasesofwork:
projectrequirements,materials,structuralscheme,analysis,anddesign.Forunusualstructuresormaterialsasixphase,testing,shouldbeincluded.Thesephasesdonotproceedinarigidprogression,sincedifferentmaterialscanbemosteffectiveindifferentschemes,testingcanresultinchangetoadesign,andafinaldesignisoftenreachedbystartingwitharoughestimateddesign,thenloopingthroughseveralcyclesofanalysisandredesign.Often,severalalternativedesignswillprovequitecloseincost,strength,andserviceability.Thestructuralengineer,owner,orenduserwouldthenmakeaselectionbasedonotherconsiderations.
Projectrequirements.Beforestartingdesign,thestructuralengineermustdeterminethecriteriaforacceptableperformance.Theloadsorforcestoberesistedmustbeprovided.Forspecializedstructures,thismaybegivendirectly,aswhensupportingaknownpieceofmachinery,oracraneofknowncapacity.Forconventionalbuildings,buildingscodesadoptedonamunicipal,county,or,statelevelprovideminimumdesignrequirementsforliveloads(occupantsandfurnishings,snowonroofs,andsoon).Theengineerwillcalculatedeadloads(structuralandknown,permanentinstallations)duringthedesignprocess.
Forthestructuraltobeserviceableoruseful,deflectionsmustalsobekeptwithinlimits,sinceitispossibleforsafestructuraltobeuncomfortable“bounce”Verytightdeflectionlimitsaresetonsupportsformachinery,sincebeamsagcancausedriveshaftstobend,bearingtoburnout,partstomisalign,andoverheadcranestostall.Limitationsofsaglessthanspan/1000(1/1000ofthebeamlength)arenotuncommon.Inconventionalbuildings,beamssupportingceilingsoftenhavesaglimitsofspan/360toavoidplastercracking,orspan/240toavoidoccupantconcern(keepvisualperceptionlimited).Beamstiffnessalsoaffectsfloor“bounciness,”whichcanbeannoyingifnotcontrolled.Inaddition,lateraldeflection,sway,ordriftoftallbuildingsisoftenheldwithinapproximatelyheight/500(1/500ofthebuildingheight)tominimizethelikelihoodofmotiondiscomfortinoccupantsofupperfloorsonwindydays.
Membersizelimitationsoftenhaveamajoreffectonthestructuraldesign.Forexample,acertaintypeofbridgemaybeunacceptablebecauseofinsufficientunderclearanceforrivertraffic,orexcessiveheightendangeringaircraft.Inbuildingdesign,ceilingheightsandfloor-to-floorheightsaffectthechoiceoffloorframing.Wallthicknessesandcolumnsizesandspacingmayalsoaffecttheserviceabilityofvariousframingschemes.
Materialsselection.Technologicaladvanceshavecreatedmanynovelmaterialssuchascarbonfiberandboronfiber-reinforcedcomposites,whichhaveexcellentstrength,stiffness,andstrength-to-weightproperties.However,becauseofthehighcostanddifficultorunusualfabricationtechniquesrequired,theyareusedonlyinverylimitedandspecializedapplications.Glass-reinforcedcompositessuchasfiberglassaremorecommon,butarelimitedtolightlyloadedapplications.Themainmaterialsusedinstructuraldesignaremoreprosaicandincludesteel,aluminum,reinforcedconcrete,wood,andmasonry.
Structuralschemes.Inanactualstructural,variousforcesareexperiencedbystructuralmembers,includingtension,compression,flexure(bending),shear,andtorsion(twist).However,thestructuralschemeselectedwillinfluencewhichoftheseforcesoccursmostfrequently,andthiswillinfluencetheprocessofmaterialsselection.
Tensionisthemostefficientwaytoresistappliedloads,sincetheentiremembercrosssectionisactingtofullcapacityandbuckingisnotaconcern.Anytensionschememustalsoincludedanchoragesforthetensionmembers.Inasuspensionbridge,forexample,theanchoragesareusuallymassivedeadweightsattheendsofthemaincables.Toavoidundesirablechangesingeometryundermovingorvaryingloads,tensionschemesalsogenerallyrequirestiffeningbeamsortrusses.
Compressionisthenextmostefficientmethodforcarryingloads.Thefullmembercrosssectionisused,butmustbedesignedtoavoidbucking,eitherbymakingthememberstockyorbyaddingsupplementarybracing.Domedandarchedbuildings,archbridgesandcolumnsinbuildingsframesarecommonschemes.Archescreatelateraloutwardthrustswhichmustberesisted.Thiscanbedonebydesigningappropriatefoundationsor,wherethearchoccursabovetheroadwayorfloorline,byusingtensionmembersalongtheroadwaytotiethearchendstogether,keepingthemfromspreading.Compressionmembersweakendrasticallywhenloadsarenotappliedalongthememberaxis,somoving,variable,andunbalancedloadsmustbecarefullyconsidered.
Schemesbasedonflexurearelessefficientthantensionandcompression,sincetheflexureorbendingisresistedbyonesideofthememberactingintensionwhiletheothersideactsincompression.Flexuralschemessuchasbeams,girders,rigidframes,andmoment(bending)connectedframeshaveadvantagesinrequiringnoexternalanchoragesorthrustrestrainsotherthannormalfoundations,andinherentstiffnessandresistancetomoving,variable,andunbalancedloads.
Trussesareaninterestinghybridoftheaboveschemes.Theyaredesignedtoresistloadsbyspanninginthemannerofaflexuralmember,butacttobreakuptheloadintoaseriesoftensionandcompressionforceswhichareresistedbyindividuallydesignedtensionandhaveexcellentstiffnessandresistancetomovingandvariableloads.Numerousmember-to-memberconnections,supplementarycompressionbraces,andasomewhatclutteredappearancearetrussdisadvantages.
Platesandshellsincludedomes,archedvaults,sawtoothroofs,hyperbolicparaboloids,andsaddleshapes.Suchschemesattempttodirectallforcealongtheplaneofthesurface,andactlargelyinshear.Whilepotentiallyveryefficient,suchschemeshaveverystrictlimitationsongeometryandarepoorinresistingpoint,moving,andunbalancedloadsperpendiculartothesurface.
Stressed-skinandmonologueconstructionusestheskinbetweenstiffeningribs,spars,orcolumnstoresistshearoraxialforces.Suchdesigniscommoninairframesforplanesandrockets,andinshiphulls.ithasalsobeenusedtoadvantageinbuildings.Suchadesignispracticalonlywhentheskinisalogicalpartofthedesignandisnevertobealteredorremoved.
Forbridges,shortspansarecommonlygirdersinflexure.Asspansincreaseandgirderdepthbecomesunwieldy,trussesareoftenused,aswellascablestayedschemes.Longerspansmayusearcheswherefoundationconditions,underclearance,orheadroomrequirementsarefavorable.Thelongestspansarehandledexclusivelybysuspensionschemes,sincetheseminimizethecrucialdeadweightandcanbeerectedwirebywire.
Forbuildings,shortspansarehandledbyslabsinflexure.Asspansincrease,beamsandgirdersinflexureareused.Longerspansrequiretrusses,especiallyinindustrialbuildingswithpossiblehungloads.Domes,arches,andcable-suspendedandair–supportedroofscanbeusedoverconventionhallsandarenastoachieveclearareas.
Structuralanalysis.Analysisofstructuresisrequiredtoensurestability(staticequilibrium),findthememberforcestoberesisted,anddeterminedeflections.Itrequiresthatmemberconfiguration,approximatemembersizes,andelasticmodulus;linearity;andcurvatureandplanesections.Variousmethodsareusedtocompletetheanalysis.
Finaldesign.onceastructuralhasbeenanalyzed(byusinggeometryaloneiftheanalysisisdeterminate,orgeometryplusassumedmembersizesandmaterialsifindeterminate),finaldesigncanproceed.Deflectionsandallowablestressesorultimatestrengthmustbecheckedagainstcriteriaprovidedeitherbytheownerorbythegoverningbuildingcodes.Safetyatworkingloadsmustbecalculated.Severalmethodsareavailable,andthechoicedependsonthetypesofmaterialsthatwillbeused.
Puretensionmembersarecheckedbydividingloadbycross-sectionarea.Localstressesatconnections,suchasboltholesorwelds,requirespecialattention.Whereaxialtensioniscombinedwithbendingmoment,thesumofstressesiscomparedtoallowancelevels.Allowable:
stressesincompressionmembersaredependentonthestrengthofmaterial,elasticmodulus,memberslenderness,andlengthbetweenbracingpoints.Stockymembersarelimitedbymaterialsstrength,whileslendermembersarelimitedbyelasticbucking.
Designofbeamscanbecheckedbycomparingamaximumbendingstresstoanallowablestress,whichisgenerallycontrolledbythestrengthofthematerial,butmaybelimitedifthecompressionsideofthebeamisnotwellbracedagainstbucking.
Designofbeam-columns,orcompressionmemberswithbendingmoment,mustconsidertwoitems.First,whenamemberisbowedduetoanappliedmoment,addingaxialcompressionwillcausethebowtoincrease.Ineffe