土木工程外文翻译外文框架.docx

土木工程外文翻译外文框架.docx

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土木工程外文翻译外文框架

4.1INVESTIGATIONOFSTRUCTURALBEHAVIOR

Investigatinghowstructuresbehaveisanimportantpartofstructuraldesign:

itprovidesabasisforensuringtheadequacyandsafetyofadesign,InthissectionIdiscussstructuralinvestigationingeneral.AsIdothroughoutthisbook.Ifocusonmaterialrelevanttostructuraldesigntasks.

PurposeofInvestigation

Moststructuresexistbecausetheyareneeded.Anyevaluationofastructurethusmustbeginwithananalysisofhoweffectivelythestructuremeetstheusagerequirements.

Designersmustconsiderthefollowingthreefactors:

●Functionality.orthegeneralphysicalrelationshipsofthestructure'sform.detail.durability.fireresistance.deformationresistance.andsoon.

●Feasibility.includingcost.availabilityofmaterialsandproducts.andpracticalityofconstruction.

●Safety.orcapacity10resistanticipatedloads.

Means

Aninvestigationofafullydefinedstructureinvolvesthefollowing:

1.Determinethestructure'sphysicalbeing-materials,form,scale.orientation.location.supportconditions,andinternalcharacteranddetail.

2.Determinethedemandsplacedonthestructure-thatis.loads.

3.Determinethestructure'sdeformationlimits.

4.Determinethestructure'sloadresponse-howithandlesinternalforcesandstressesandsignificantdeformations.

5.Evaluatewhetherthestructurecansafelyhandletherequiredstructuraltasks.

Investigationmaytakeseveralforms.Youcan

●Visualizegraphicallythestructure'sdeformationunderload.

●Manipulatemathematicalmodels.

●Testthestructureorascaledmodel,measuringitsresponsestoloads.

Whenprecisequantitativeevaluationsarerequired.usemathematicalmodelsbasedonreliabletheoriesordirectlymeasurephysicalresponses.Ordinarily.mathematicalmodelingprecedesanyactualconstruction-evenofatestmodel.Limitdirectmeasurementtoexperimentalstudiesortoverifyinguntestedtheoriesordesignmethods.

VisualAids

Inthisbook,Iemphasizegraphicalvisualization;sketchesarcinvaluablelearningandproblem-solvingaids.Threetypesofgraphicsaremostuseful:

thefree-bodydiagram.theexaggeratedprofileofaload-deformedstructure.andthescaledpial.

Afree-bodydiagrambinesapictureofanisolatedphysicalclemenIwithrepresentationsofallexternalforces.Theisolatedclementmaybeawholestructureorsomepartofit.

Forexample.Figure4.1ashowsanentirestructure-abeamand-eolumnrigidbent-andtheexternalforces（representedbyarrows）.whichincludegravity.wind.andthereactiveresistanceofthesupports（calledthereactions）.Note:

Suchaforcesystemholdsthestructureinstaticequilibrium.

Figure4.lbisafree-bodydiagramofasinglebeamfromthebent.Operatingonthebeamaretwoforces:

itsownweightandtheinteractionbetweenthebeamendsandthecolumns10whichthebeamisallached.TheseinteractionsarenotvisibleintheIreebodydiagramofthewholebent.soonepurposeofthediagramforthebeamistoillustratetheseinteractions.Forexample.notethatthecolumnstransmittotheendsofthebeamshorizontalandverticalforcesaswellasrotationalbendingactions.

Figure4.lcshowsanisolatedportionofthebeamlength.illustratingthebeam'sinternalforceactions.Operatingonthisfreebodyarcitsownweightandtheactionsofthebeamsegmentsontheoppositesidesoftheslicingplanes.sinceitistheseactionsthatholdtheremovedportioninplaceinthewholebeam.

Figure4.ld.atinysegment.orparticle.ofthebeammaterialisisolated,illustratingtheinteractionsbetweenthisparticleandthoseadjacenttoit.Thisdevicehelpsdesignersvisualizestress:

inthiscase.duetoitslocationinthebeam.theparticleissubjectedtoabinationofshearandlinearpressionstresses.

Anexaggeratedprofileofaload-deformedstructurehelpsestablishthequalitativenatureoftherelationshipsbetweenforceactionsandshapechanges.Indeed.youcaninfertheformdeformationfromthetypeofforceorstress.andviceversa.

FIGURE4.1Free-bodydiagrams.

Forexample.Figure4.lashows{heexaggerateddeformationofthebentinFigure4.1underwindloading.Notehowyoucandeterminethenatureofbendingactionineachmemberoftheframefromthisfigure.Figure4.2bshowsthenatureofdeformationofindividualparticlesundervarioustypesofstress.

FIGURE4.2Structuraldeformation

Thescaledplotisagraphofsomemathematicalrelationshiporrealdata.Forexample,thegraphinFigure4.3representstheformofadampedibrationofanelasticspring.Itconsistsoftheplotofthedisplacementsagainstelapsedtimet.andrepresentsthegraphoftheexpression.

FIGURE4.3Graphicalplotofadampedcyclicmotion.

Althoughtheequationistechnicallysufficienttodescribethephenomenon,thegraphillustratesmanyaspectsoftherelationship.suchastherateofdecayofthedisplacement.theintervalofthevibration.thespecificpositionatsomespecificelapsedtime.andsoon..

4.2METHODSOFINVESTIGATIONANDDESIGN

Traditionalstructuraldesigncenteredontheworkingstressmethod.amethodnowreferredtoasstressdesignorallowablestressdesign（ASD）.Thismethod.whichreliesontheclassictheoriesofelasticbehavior,measuresadesign'ssafetyagainsttwolimits:

anacceptablemaximumstress（calledallowableworkingstress）andatolerableextentofdeformation（deflection.stretch.erc.）.Theselimitsrefertoastructure'sresponsetoserviceloads-thatis.theloadscausedbynormalusageconditions.Thestrengthme/hod,meanwhile,measuresadesign'sadequacyagainstitsabsoluteloadlimit-thatis.whenthestructuremustfail.

Toconvincinglyestablishstress.strain.andfailurelimits,testswereperformedextensivelyinthefield（onrealstructures）andlaboratories（onspecimenprototypes.ormodels）.Note:

Real-worldstructuralfailuresarestudiedbothforresearchsakeandtoestablishliability.

Inessence.theworkingstressmethodconsistsofdesigningastructuretoworkatsomeestablishedpercentageofitstotalcapacity.Thestrengthmethodconsistsofdesigningastructuretofail.butataloadconditionwellbeyondwhatitshouldexperience.Clearlythestressandstrengthmethodsarcdifferent.butthedifferenceismostlyprocedural.

TheStressMethod（ASD）

Thestressmethodisasfollows:

1.Visualizeandquantifytheservice（working）loadconditionsasintelligentlyaspossible.Youcanmakeadjustmentsbydeterminingstatisticallylikelyloadbinations（i.e,deadloadplusliveloadpluswindload）.consideringloadduration.andsoon.

2.Establishstandardstress.stability,anddeformationlimitsforthevariousstructuralresponses-intension.bending,shear,buckling.deflection,andsoon.

3.Evaluatethestructure'sresponse.

Anadvantageofworkingwiththestressmethodisthatyoufocusontheusagecondition（realoranticipated）.Theprincipaldisadvantageesfromyourforceddetachmentfromrealfailureconditions-moststructuresdevelopmuchdifferentformsofstressandstrainastheyapproachtheirfailurelimits.

TheStrengthMethod（LRFD）

Thestrengthmethodisasfollows:

1.Quantifytheserviceloads.Thenmultiplythembyanadjustmentfactor'（essentiallyasafetyfactor）toproducethejaclOredload.

2.Visualizethevariousstructuralresponsesandquantifythestructure'sultimate（maximum,failure）resistanceinappropriateterms（resistancetopression,buckling.bending.etc.）.Sometimesthisresistanceissubjecttoanadjustmentfactor,calledtheresistancefacror.Whenyouemployloadandresistancefactors.thestrengthmethodisnowsometimescalledfoadandresistancefaaordesign（LRFD）（seeSection5.9）.

3.paretheusableresistanceofthestructuretotheultirnatcresistancerequired（aninvestigationprocedure）,orastructurewithanappropriateresistanceisproposed（adesignprocedure）.

Amajorreasondesignersfavorthestrengthmethodisthatstructuralfailureisrelativelyeasytotest.Whatisanappropriateworkingconditionisspeculation.Inanyevent,thestrengthmethodwhichwasfirstdevelopedforthedesignofreinforcedconcretestructures,isnowlargelypreferredinallprofessionaldesignwork.

Nevertheless,theclassictheoriesofclasticbehaviorstillserveasabasisforvisualizinghowstructureswork.Butultimateresponsesusuallyvaryfromtheclassicresponses,becauseofinelasticmaterials,secondaryeffects,multimoderesponses,andsoon.Inotherwords,theusualprocedureistofirstconsideraclassic,elasticresponse,andthentoobserve（orspeculateabout）whathappensasfailurelimitsareapproached.