外文翻译结构设计.docx

外文翻译结构设计.docx

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外文翻译结构设计

2011届毕业设计外文翻译

结构设计

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结构设计

AugustineJ.Fredrich

摘要：

结构设计是选择材料和构件类型，大小和形状以安全有用的样式承担荷载。

一般说来，结构设计暗指结构物如建筑物和桥或是可移动但有刚性外壳如船体和飞机框架的工厂稳定性。

设计的移动时彼此相连的设备（连接件），一般被安排在机械设计领域。

关键词：

结构设计；结构分析；结构方案；工程要求

Abstract:

Structuredesignistheselectionofmaterialsandmembertype,size,andconfigurationtocarryloadsinasafeandserviceablefashion.Ingeneral,structuraldesignimpliestheengineeringofstationaryobjectssuchasbuildingsandbridges,orobjectsthatmaybemobilebuthavearigidshapesuchasshiphullsandaircraftframes.Deviceswithpartsplannedtomovewithrelationtoeachother（linkages）aregenerallyassignedtotheareaofmechanical.

Keywords:

StructureDesign；Structuralanalysis；structuralscheme；Projectrequirements

StructureDesign

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,butmaybelimitedifthecompressionsideofthebeamisnotwellbracedagainstbuc