SSC-178

ASurveyofSomeRecentBritishWorkontheBehaviourofWarshipStructures

byL Clarkson

SHIPSTRUCTURECOMMITTEE

——-—....—— . —— .-

SHIP STRUCTURE COMMITTEE

MEMBER AGENCIES,

6“,s.” 0,5“,,s,D.P,.o, NAVY

M, I.,TARY SrA TRANSPORTATION SERVICE, 0.,7. 0, NAVY

UN IT,. STATES COAST G“,.., TR,ASURY Dir,,

MARITIME ADM, NIsmAT,.aN, D,,,, OF C.. ”,...

..,.,..?4 8“.,.” 0, s.,,,,..

November 1966

ADDRESS CORRESPONDENCE TO.

S...,,..”S.,Ps,.”.,..,co..,,,,,U.S.COASI GUARD Hmc..avAn7Kns

WA, V,.G’10., Q. c, 2022Q

Dear Sir:

“A Survey of Some Recent British Work on theBehaviour of Warship Structures” by J. W. Clark son(ssc- 178) reflects the excel lent remarks and data theabove author presented to the Ship Structure Subcom-mittee at its Annual New York Meeting held May 4, 1966.

The Ship Structure Committee appreciates the

close cooperat ion and information exchange that hasdeveloped through the many years of its existence with

overseas research establ ishments.

Rear Admiral, U. S. Coast GuardChairman, Ship Structure

Comnittee

SSC-178

SpecialReport

A SURVEYOFSOMERECENTBRITISHWORKONTHEBEHAVIOUR

OFWARSHIPSTRUCTURES

by

J.Clarkson,B.SC.A.M.R.I.N.A.SeniorPrincipalScientificOfficerattheNavalConstructionResearch

Establishment,Dunfermline,Scotland

Washington,D.C.U. S. CoastGuardNovember1966

CONTENTS

I!z$!s

Introduction. . . . . . . . . . . . . . . . . . . . .

MeasurementofServiceStresses. . . . . . . . . . .

ElasticAnalysis.. .. . . .. .. .. . . . . . . .

PlasticCollapse. . . . . . . .. . . . . . . . . .

StrengthofBottomStructures. . . . .. . . . . . .

ExperimentalTechniques. . . . .. .. . . . .. . .

ProtectionStructuresforMarineNuclearReactors. .

Conclusions. . . . . . . .. .. . . . . . . . . .

Acknowledgement. . .. . . . . .. . . . . . . . ..References. .. . .. . . . . . . . .. . . . , .

1

1

4

8

1012

1516

16

16

ThaSHIPSTRUCTUEEstructure ofshipsfabtieat-ion.

SllIPSTRUCTURECOIIVI1’1’EE

COLMYITYEE{s constituted to prosecutea ~esearchprogramto improvethe hullby an extensionofknow2edgepe~tain-ingto design, mater<a2sandmethodsof

RearAdmiralJohnB.Or@n,USCGChief,OfficeofEngineeringU.S.CoastGuardHeadquarters

CaptainW.M.Nicholson,USNAssistantChiefofBureauofDesign

ShipbuildingandFleetMaintenanceNavalShipEngineeringCenter

Mr.D.B.Bannerman,Jr.VicePresident- TechnicalAmericanBureauofShipping

Chairman

CaptainP.E.Shetenhelm,USNMaintenanceandRepairOfficerMilitarySeaTransportationService

HHPSTRUCTURESUBCOMMITTEE

TheSflIPSTRUCTURESUBCOMMITTEEacts for the Ship Structure Committeeon technicalmattersb.yprovid{ngtechnieaLcoo~dinationfor the determinationof goa2sandobjectives of the progmm,andby wakating andintap~et{ng tk resu2ts in termsof ship structural des{gn,constructionandoperation.

NAVALSHIPENGINEERINGCENTER OFFICEOFNAVALRESEARCHCaptainS.R.Hell@r,USN- Chairman Mr.J.M.Crowley- MemberMr.JohnVasta- ContractAdministrator Dr.G.R.Irwin- AlternateMr.GeorgeSorkin.MemberMr.T.J.Griffin- AlternateMr.IvoFioriti-Alternate

MARITIMEADMINISTRATIONMr.R.W.Black-MemberMr.AnatoleMaillar- MemberMr.R.Falls- AlternateMr.W.G.Frederick- Alternate

AMERICANBUREAUOFSHIPPINGMr.G.F.Casey- MemberMr.F.J.Crum- Member

DAVIDTAYLORMODELBASINMr.A.B.Stavovy- Alternate

NATIONALACADEMYOFSCIENCES-NATIONALRESEARCHCOUNCIL

Dr.Wm.G.Rauch-“Al~ernate

MILITARYSEATRANSPORTATIONSERVICELCDRDonaldB.Bosley,USN- MemberMr.R.R.Askren- Member

U.S.COASTGUARDCDRClaudeR.Thompson,USCG-MemberLCDRR.Nielsen,Jr.,USCG- MemberMr.J.B.Robertson,Jr.-MemberLCDRJ.F.Lobkovich,USCG- AlternateLCDRJamesL.Howard,USCG- Alternate

LIAISONREPRESENTATIVES

BRITISHNAVYSTAFFMr.A.C.Law

Mr.A.R.Lytle- Director,Shipl-lull ConstructionCDRT.R.Rumens,RCNCResearchCommittee

Mr.R.W.Rumke,ExecutiveSecretary,SHRC WELDINGRESEARCHCOUNCIL

AMERICANIRONANDSTEELINSTITUTE Mr.K.K.Koopman,DirectorMr.CharlesLarson,Asst.Director

Mr.J.R.LeCron

INTRODUCTION

Forsurfaceshipstructures,entirelyra-tionalelasticorplasticdesignprocedureshavenotyetbeenachieved,although,sinceWorldWar11,researchactivityhasbeencon-siderablyincreased.Theunderlyingreasonsforthepresentratherempiricalmethodsofdesignaretobefoundintheconsiderablecomplexityofthestructuresandthe~resentlackofknowledgeonloadingsatsea.Itisinterestingtoobservethatsurfaceshipstruc-turesareusuallyfarmorecomplexthanthesubmarineortheaircraft,andthiscomplexityresultsina requirementforappreciablein-genuitytoreducetheoreticalanalysestoman-ageableproportions.Ontheotherhand,thecomparat~velackofknowledgeonsurf-aceshipstructuresisnotparticularlycritical,sincethedesignofstructureshasevolvedquiteslowly,beingbasedmainlyonpreviousexperi-ence,andthesafetyoftheshipandpersonnelisseldomcalledintoquestion.Newdevelop-mentssuchastheintroductionofmorebrittleorfatiguesensitivematerials,includingthehigh-strengthsteels,aluminiumalloysorglass-reinforcedplastics,mayalterthissit-uationandleadtoa morepressingrequirementforrationaltreatment.

ThepresentauthorhasbeenworkingattheNavalConstructionResearchEstablishment(N.C.R.E.)Dunfermline,Scotland,duringthepast15years,mainlyinthefieldofsurfaceshipstructures.Thisperiodhasseen.con-siderableadvancesanddevelopmentbothintheunderstandingofthemechanicsofshipstruc-turesandintheapplicationofdigitalcomput-erstoshipproblems.A numberoflong-termprojectshavebeeninitiatedtomeasurethestrainsexperiencedatsea.Althoughtheworkfamiliartotheauthorhasbeenmainlycon-cernedwithwarshipstructures,muchofitispotentiallyapplicabletosurfaceshipstruc-turesgenerally.Thepresentreviewisanat-tempttohighlightsomeofthemoresignificantadvances.

MEASUREMENTOFSERVICESTRESSES

Thereisconsiderableagreementthatthepresentlackofknowledgeoftheloadingonsurfaceshipsconstitutesthelargestunknownaffectingthestructuraldesignofsurfaceships,andN.C.R.E.isnowdevotingquiteasignificantefforttowardsthemeasurementofloadsatsea,usingstatisticalstraingauges.Itiswidelyrecognizedthatloadingsmaybemostconvenientlymeasuredusingstra~ngaugesplacedontheship’sdeckorbottomstructureatpositionsunaffectedbystressconcentra-tions.TheworkatN.C.R.E.hasbeenreviewedina recentpaperbySmith.1

Itisconsideredthatthemeasurementofservicestressesshouldbedirectedtowardstwoobjectives.Thefirstrequirementistoobtaininformationontheextremevaluesofstressex-periencedatsea,whilethesecondistoobtainhistogramsofstressreversals.Itisbynomeansclearthatthesameinstrumentwouldbeequallysuitableforboththesepurposes.

Morerealisticinformationonextremesofstressisrequiredforplacingthelongitudinalstrengthcalculationona soundbasis,andYuille2firstproposedusinga verysimplemaximum-readingstraingaugewhichhassubse-quentlybeenadoptedforextensivemeasurementsbyN.C.R.E.(Fig.1). Theinstrumentispure-lymechanicalinactionandrequiresnopowersupply.Wheninoperationthegaugeisboltedinpositionbybearingagainstthesurfaceoftheteststructureontwopairsofhardenedconicalstudswhichgiveaneffectivebaselengthof10in. Anychangeintheseparationofthesebearingpointsismagnifiedbya sim-pleleversystemandismarkedbya recordingpenona stationaryreelofrecordingpaper.Themagnificationfactorisabout100,sothata line1 in.longontherecordingpapercor-respondstoa strainvariationofabout0,001ora stresschangeinsteelofabout13ton/in.2.Thereelofpaperismovedforwardman-uallyatfixedtimeintervalsleavinga seriesoflinesonthepapereachofwhichcorres-pondstothemaximumstrainvariationduringoneinterval.Thegaugeisdesignedsothatbysimplemodificationitsbaselengthcanbeincreasedtoanyrequiredspan.Theshort10-in.baselengthhashoweverprovedsufficient-lyaccurateandhasinanycaseprovedneces-sarybecauseoftherestrictedspaceavailableforfittingofthegaugesinwarships.

Twenty-fivemaximumreadinggaugeshavenowbeenoperatedforsometime,andrecordshavebeenobtainedfrommorethanfortyBritishwarshipsofvariousclassesincludingfrigates,destroyers,cruisersandanaircraftcarrier.Animprovedproductionversionofthegaugehasrecentlybeendeveloped,andafurtherfiftyoftheseinstrumentsarenowcomingintouse.Itisintended,ultimately,thateveryoperativeshipintheNavyshouldbefittedwithoneofthesegauges.Thegaugesarenormallypositionedonthewebofa longitudinalstiffenerunderthestrengthdeck,wellawayfrompositionsofstressconcentration.

Intheanalysisofresults,hoggingandsaggingstressesareseparated,Thisisac-complishedbymarkingstillwaterdat’umsim-mediatelybeforeandaftereachvoyage.Lowamplitude5trainvariationscorrespondingtoperiodsofcalmweatherarealsoused,tofixintermediatedatums,andtheseareconnected

.-L-REEL OF RECORDING

e . . . . . .

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PIVOT. \J

CROSSEDPIVOT.

l-.

SPRING

PA,ROF CONICAL/-’BEARING PoINTS.

TESTSTRUCTURE’(STIFFENERWEB)

T\PAIR OF CONICALBEARING POINTS,

t= EFFECTIVEBASELENGTH=IO”

FIG.1. N.C.R.E.MAXIMUMREADINGSTRAINGAUGESHOWINGLEVERSYSTEM.

RETURN PERIOD (DAYS)

1.001

20

10

Id

‘g,4:----12tJII‘1 1,

10LnVIwtin+ I‘/20SAG(* .—. .6 STRESS=

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.001.01 .10.23.30 .50 .70 .00 .90 .95 .97.VB ,99 .995.997.990 .999.9995 .9998.9999FREQUENCYF(x)

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REDuCEDVARIATE(y)

FIG.2. TYPICALEXTREMEVALUEPROBABILITYPAPER.

bya datumline.Mostofthemaximumstrainreadingssofarhavecorrespondedto24-hourperiodsatsea.Withtheobjectofrepresent-ingaccumulateddataina conciseform,allow-inginterpolationbetweentheresultsforshipsofdifferenttypesandpossiblyallowingex-trapolationbeyondtheobservedrangesofstrain,thedailymaximahavebeenanalysedandplottedusinganextreme-valuestatisticaltheorydescribedbyGumbel.3Inthisanalysis,thecumulativefrequencyoftheobservedex-

tremevaluesisrepresentedbya seriesofpointsplottedona specialprobabilitypaper.Anextreme-valueprobabilityfunction,whichappearsasa straightlineontheprobabilitypaper,isfittedtotheobserveddatabyaleastsquaresmethod,togetherwithcontrolcurveswhichdefinelimitswithinwhichaspecifiedproportionofthedatashouldlie.A typicalprobabilitypaper,showingthere-sultsfroma groupoffourshipsofthesameclass,isshowninFig.2. Itmaybeseen

-3-

TRUE DATUM(zERO WAVE-

~STRAIN INDUCEDSTRAIN) m h

TIMEjI II 1 111 1I I 11 I1

I 1 [11

( 1 !

ARBITRARYFIXEb DATUM—.—. -.Ililllllllll

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/ INDICATES

X INDICATES

FIG.3. SAMPLESTRAINRECORD.

m- Xxxx Xxxx xxx

1ISECONDINSIGNIFICANTSTRAINREVERSAL.NON-ZEROFREQUENCYDIGIT.

thatthemeasuredstressesbearlittlerelationtothosepredictedbythestandardL/20staticwavecalculation,andalsothatthesaggingstressesareappreciablyhigherthanthehog-gingstresses,possiblyduetotheeffectsofslamming.Ithasbeenfoundthatextrapola-tiontolongerperiodsusingtheGumbelplotproducesresultswhicharenotgenerallycon-firmedbysubsequentmeasurements.Oftentheextrapolationpredictsextremeswhicharetoohigh,andforthisreasonithasbeendecidedtomeasureextremesforverylongperiodsoftime,possiblyfortenyearsormoreoneachship.Untilmoredataareobtained,itwillnotbepossibletoestablishanystatisticalpatternoftheextremes.

Themainreasonforinvestigatingcyclicleadingasdistinctfrommaximumleadsistoprovideameansofensuringthatnewshipswillnotrununacceptablerisksoffatiguefailure.Inex~stlngships,theproblemoffatiguehasnotprovedcritical,andminorfatiguecrackshavebeentroublesomeratherthancatastrophic.Infuture,thepossibleuseoffatigue-sensitivematerialssuchashigh-yieldsteel,aluminiumandglass-reinforcedplastics,mayleadtomoreseverefatigueproblems.Inmild-steelships,anyincreaseintheacceptablegeneralstresslevelmustbeaccompaniedbyimprovedfatiguestrengthofstructuralcom-ponents.Itisalsopossiblethatmajorstruc-turaldiscontinuitiesofanunfamiliartypemayoccur,inevitablycausingstressconcen-trationsandrequiringanestimateoflocalfatiguestrength.

Itisconsideredthattheexistingtheo-riesofcumulativedamagesuchasMiner’sLawarenotfullysatisfactory,andfutureimprove-mentsmaybeexpected.Equally,itiscon-sidereddesirabletobeabletoseparatevibra-torystressesinordertoindentlfytheeffectsofslammingandbowflareimmersion.A sampleofa continuousstraincurveisshowninFig.3,anditisclearthata simplecountinggaugewouldberatherunsuitable,theresultinghis-togrambeingdependentontheparticularmethodofcounting.AtN.C.R.E.,a strain-recorderde-sign‘isbeingsponsored,whichwillsupplytheequivalentofa continuousstrainrecordinaformsuitableforinterpretationandanalysisbya digitalcomputer.Theinstrumentwillrecordtheamplitudesofmaximumandminimumpointsonthestraincurverelatlvetoanar-bitraryfixeddatumwhichwillsubsequentlybecorrectedtothestillwaterdatum.Specialprovisionwillbemadetoidentifyvibratorystrainswitha periodoflessthantwoseconds.Minorstrainvariationslessthana specifiedamount6willbesuppressed,and6maybead-justedintherange0.00002to0.0002(0.27to2.7tons/in.2forsteel).Thelengthofthedigitizedrecordwilldependquitecriticallyonthevalueof6.

Twopossiblesystemshavebeenconsidered,thefirstbasedona ship-borneslowmagnetic-taperecorderinconjunctionwitha shore-basedanaloguetodigitalconverteranddata-process-ingunit.Thesecondconsistsofa self-containedship-bornedigitalrecorderincorpor-atinganalogue-digitalconversionanda data

-4-

processingunitemployingmicro-logiccir-cuits.Ineachcasetheanaloguestrainsignalwouldbeobtainedusingelectricalresistancestraingauges.Atthepresenttime,thesecondtypeofsystemisfavoured,since~treducestheeffortindataprocess-ing,ismorecompact,andisthoughttobepotentiallymorereliable.A designhasbeenproducedbyPlesseyLimited,anditislikelythattwoprototypeunitswillbeorderedinthenearfuture.

ELASTICANALYSIS

MostoftherecentworkInthisfieldhasbeenconcernedwithtransversestrength,though,withthesecondgenerationofdigitalcomputersnowbecomingavailable,completestructuralanalysisincludinginteractionbe-tweenlongitudinalandtransverseload”ingsmayshortlybecomefeasible.Althoughtrans-versestrengthanalyslshasbeentraditionallybasedontreatmentofa singleringframe,thesubjectismorecorrectlyconcernedwiththeanalysisofflatorcurvedplatedgrillages.Untiltheadventofthedigitalcomputer,grillageanalysiswasrestrictedtoverysim-plecases,andmucheffortwasdevotedtofindingshortcutstotheveryheavyarithme-ticinvolved.Nowadays,straightforwardgrillageanalysisisquitecommonplace.Atextrev~ewlngelasticgrillageanalysisap-pliedtoshipstructureshasrecentlybeenpublishedbythepresentauthor.q

Ideally,eachplatepanelofa grillageshouldbeanalysedbythewell-knownlinearplatetheoryequations,

V4$= o (1)V4W= q/D (2)

where$ istheAirystressfunction,w isthebendingdeflectionq isthelateralpressureandD = Eh~/12(1-u2).Thebeamsmaybean-alysed”bytheusualEuler-Bernoullitheory,andtheboundaryconditionsforequations(1)and(2)areobtainedbyspecifyingequilibriumandcompatibilityateachbeamposition.Thisapproachwasadoptedbythepresentauthortoanalysea simplysupportedpanelstiffenedinonedirectiononly,undera singleconcentrat-edloads TheanalysishasbeengeneralisedmorerecentlybySmithGtoapplytoa verywidevarietyofinterconnectedsystemsofrectangularplatesandparallelbeamsinonedirection,simplysupportedattheends.Structureswhichcanbeanalysedincludeun-symmetricalorskewstiffeners,swedgedorcorrugatedplating,boxbeamsortheVee bot-tomregionofa frigatewitha riseoffloor,asshowninFig.4. A rathersimilarana-lysisfororthogonallyIntersectingbeamgril-lageswasattemptedabout10yearsagoby

Kendrick7whoassumedthattheorthogonalcom-ponentsofthein-planedisplacementcouldbeconsideredseparately,theonlyinteractionarisingfromtheverticalshearforcesatthestiffenerintersections.Kendrick’sworkin-dicatedthatveryaccurateresultscouldbeobtainedbytreatingthestiffenersaloneusingbeamtheoryandincludingtheplatingasanef-fectiveflangetothelongitudinalandtrans-versebars.Theeffectivebreadthofplatingwastakeninthisinstanceasthefullstiff-enerspacing.Inpractice,theplatepanelsofwarshipgrillagesareseldomperfectlyflat,andtheremaybepermanentsetuptoaboutaplatethicknessdeepcausedeitherbyweldingdistortionsorearlyloadingsonthestructure.Thishastheeffectofrenderingthesimplelinearplateequationsinvalid,and,inviewofthecomplexityoftheproblem,thepracticeatN.C.R.E.istoestablishmethodsofchoos~ngstructuralidealisationsbycomparisonwithexperiment.

Nowadays,transversestrengthandgrillageanalysisisbasedonfiniteelementidealisa-tionswiththeproblemsbeingsolvednumerical-lyona digitalcomputer.Untilrecently,acomparativelysmallfirstgenerationcomputer,theFerrantiPegasus,hasbeenusedatN.C.R.E.Initiallytherewasa 4096wordhigh-speedstorewhichhasnowbeenincreasedto7168words.Generalstructuralanalysisprogramshavebeendevelopedforthiscomputer,includ-inga planeframeprogram8suitableforthetraditionaltransversestrengthcalculation.Thisprogramwilltreatanyrigid-jointedmulti-connectedframeuptoabout20intersections.A facilityexistsfortreatingmoreintersec-tionsbypartitioning,andsheardeflectionscanbeincluded.Twoprogramshavebeenwrittenforflatgrillages.g-~oThefirstisverygen-eralandwilltreatanynetworkofstraightelements,notnecessarilyorthogonal,uptoabout20intersections,includingbothshearandtorsion.Thesecondislimitedtoortho-gonalgrillageswitha rectangularboundaryignoringtorsion,butitcantackleupto72intersections.AtthepresenttimeprogramsarebeingwrittenfortheEnglishElectricKDF9 computerwhichwilltreatgrillageswithuptoabout200intersections.Theplaneframeandgrillageprogramsconsidertheplatingtoberepresentedasaneffectiveflangetothebeamelements.A programhasalsobeenwrittentoanalysethetransversestrengthofa com-pletemidshipcompartmentofa ship’shull.11-12Thisprogramincludesshearpanelelements,inadditionto~hebeamelements,toallowfortransferofin-planeforcesbetweenadjacentframes.Duetothelargenumberofunknownsandthelimitedsizeofcomputer,theanalysisisrestrictedtocylindricalcompartmentsiden-t~calthoughnotnecessarilyevenlyspacedframes,andlongitudinaluniformalongtheir

-5-

IN”,..,.A“CLE

A-’’-”L

-r

FIG.4, TYPICALBEAM-PLATINGsTRUCTURESFORPLATETHEORYANALYSIS.

lengththoughnotequalinsize.

Throughoutthegrillageandtransversestrengthinvestigations,experimentalworkhasbeencarriedoutoftenatfullscaleontypi-calsteelstructures,toassistinformulatingstructuralidealisations,Inparticular,thechoiceofaneffectivebreadthofplatingandoneffectiverigidityofshearpanels.Theprocedurehasusuallybeentocarryoutcal-culationsfora wholerangeofassumedvaluesfortheseparameters,andchoosethevaluesgivingthebestagreement.Generally,forflatgrillages,theassumptionthateffectivebreadthisequaltohalfthebeamspacinggivesresultswhicharesufficientlyaccuratefordesignpurposes,andsometypicalresultsfora grillageunderuniformpressureareshowninFig.5. Thisgraphisparticularlyinterestingasitillustratesthepronouncedeffectoflocalbendingbetweentheintersec-tionsina gr~llagehavingwidelydifferentlongitudinalandtransversemembers.Thechoiceofidealisationfortransversestrengthcurvedgrillagecalculationshasbeensupportedbyexperimentsbothonsmall-scalemodelsinxylonite(aplasticmaterial)andona nearfull-scalesteelmodelofa frigatesection.~3Th~smodelisillustratedinFig.6,andtheresultsformsometrialcalculationsforaloadatthekeel,usingvariouseffectivebreadths(PLandPT)andshearrigidities(G),areshownirIFig.7. Itwasfoundthatcalcu-lation2,shownasthefull-linecurves,gavethebestoverallagreementwithexperiment.

GRILLAGEN..3-STRESSESON TABLESOFOUTERLONGITUDINALBEAMS.

Q FXPERIMmmL Pomm. roP GRILLAGELOAPED 0. PLhTlH6 s,m.= bOTTOM GmlLLAGE LOADED 0?46TIFFEMER SIDE.

_ TWORCTICAL =..”= FOliCFFCCTIVC BR!2?.DTH. HAIX BEAM GPAC!WG6.

)4,.SPAN rDGE

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i----HALT L.NG7H 0. GRILLAG.=100IN.—

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m (’)

L_,,FIG.5. STRESSMEASUREMENTSONGRILLAGEUNDERUNIFORMPRESSURE.

ThestructuralidealisationcloselyfollowedtheshapeoftheframeandincludedalltheIongitudinalsintheregionoftheappliedloadatthekeel,butamoreapproximateide-alisationwasadequateelsewhere.

Theverys~gnificantadvanceusinggril-Iageanalysis,overtheoldsingle-ringframecalculations,canbeseeninFig.8 fora con-centratedkeelloadandFig.9 fora hydrosta-ticwaterpressureloadingextendingto28ftabovethekeel.Theseresultsarefora com-parativelyshortcompartmentmeasuring13%ftlongby24-3/4ftwide.Thecurvedgrillagetransversestrengthanalysisagreesverywellwiththemeasurementsinbothcases,whereastheringframecalculationisout.byfactorsfrom5 to25,andbearslittleornorelationtotheactualbehaviour.Fora longercom-partmentora structureonlytransverselyframed,theagreementusingthesinglering

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,.,,;,r::yT~framecalculationwould,ofcourse,becloser.

t ‘,1!!:!!: ~-”.,

FIG.6. FRIGATEMODELINLARGETESTINGFRAME.

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—’”~”–--–- ~,~FLANGE 5TRE55

(PLOTTED NOUMALL7TO OUTLINEOF HULL)

L ,5

Nowthatconsiderablylargerandfastercomputersofthesecondgenerationai-ebecomingavailable,generalstructuralanalysisprogramsarebeingdevelopedforthree-dimensionalstruc-turescomposedofstiffenedplatepanelsorplatedgrillages.OnesuchprogramisbeingwrittenbytheEnglishElectricCompany,Ltd.atKidsgrove,England.Usingthistypeofpro-gram,itshouldbepossibletoexaminethein-teractionbetweenlongitudinalandtransverseloading,andalsoanyeffectduetotaperoftheshipsection.Equallywell, generalstruc-turalanalysisprogramsareapplicabletoprob-lemsmoreconcernedwithlongitudinalstrengthsuchasthebreakofforecastleindestroyersandfrigates,theeffectofsuperstructures,andtheanalysisinwayoflargehatchesandopeningssuchasthesidel~ftopeningsinair-craftcarriers.Atthepresenttime,theEnglishElectric(Kidsgrove)programisbeingevaluatedatN.C.R.E.forthetypeofproblemswhichariseinshipstructures.Asyet,itisnotclearthatthegeneralanalysisprogramre-ferredtoisIdeallysuitedtoallproblems,anditisquitepossiblethatprogramsforpar-ticulartypesofproblemwillstillbere-quired.Inviewoftheconsiderablerecentde-velopmentsinthecomputeranalyslsofshipstructures,particularlyinregardtotransversestrength,thecommitteeoftheInternationalShipStructuresCongressdealingwithstiffened

I

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FIG.7.THEORETICALANDEXPERIMENTALCOM-PARISONSFORLOADINGONKEELOFFRIGATEMODEL.

f COMPRE5510M

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FIG.8. COMPARISONBETWEENCURVEDGRILLAGEANALYSISANDRINGCALCULATIONFORKEELLOADINGONFRIGATEMODEL.

~“~–Ll~G.6

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FIG.9. COMPARISONBETWEENCURVEDGRILLAGEANALYSISANDRINGCALCULATIONFORHYDROSTATICLOADINGONFRIGATEMODEL.

-8-

platepanelsinthree-dimensionalstructuresissponsoringanenquiryregardingcomputerpro-gramsinvariouscountries.

Toconcludethissectiononelasticanaly-sis,Iwouldliketorefertotheanalysisofashipina floatingdockbyVaughan.15Inthisanalysis,theshipisrepresentedasa beamconsistingofa numberoffiniteelements,eachofwhichisreactedbya dockblockregardedasanelasticspringrestingonthedockfloor,itselfa grillage.Thecompletesystemisre-actedbybuoyancyforces,andinitiallackoffitbetweenthedockblocksandfloorisin-cluded.Thisisa veryusefulexampleofaparticularproblemwhichcouldnotbetackledusingoneofthestandardcomputerprograms.Nevertheless,realisticanalysiscouldnothavebeenaccomplishedat.allwithouta computer.Ina previousanalysls,AmerikianlGassumedthatthefloorofthedockwasrigidandthattheshiphaduniformrigidityandwassupportedbyuniformdockblocks,inordertobeabletocalculatethedockblockloads.Induecourse,itisintendedtocarryoutparametricnumeri-calstudiesusingtheN.C.R.E.computerprogramtoexaminemorewidelytheeffectoflackoffitandnon-uniformityofthedockblockswhichareimponderableaffectingthepracticalproblem.

PLASTICCOLLAPSE

Themostimportantpotentialapplicationof plasticcollapsetheoryto,ships’structuresisinlongitudinalstrength,wherethemomenttobreakthebackoftheshipisequaltothefullyplasticmomentoftheship’scross-section.This“strength”approachtolongitu-dinalbendinghasbeenproposedina recentpaperbyCaldwell.~7

Inalmostallothershipstructuralprob-lems,themethodsofbendingcollapseanalysisarenotsoobviouslyapplicable.Thisisbe-causea stiffenedpanelsupportedalongallitsedgescannotbelaterallydeformedwithoutde-flectionswhichhavecurvatureintwodirec-tions,andthisinturnleadstoa significantmembranestretchingaction,oncethedeflec-tionsbecome“large”.Fora singleplatepanelbetweenstiffeners,“large”deflectionsImplyamagnitudefromaboutoneplatethick-ness,sayhalfaninchinthecaseofa war-ship.Membranestretchingarisesevenifthesupportingstructureattheedgescannotpro-videanymembranerestraint,andtheactioninsidethegrillageisthenoneofmembranetensionaroundthecentreandtangentialcom-pressionattheedges.Theplatingofshipgrillagesaddsappreciablytothemembranestrengthofthesestructures.Longafterthestructurehasexhausteditsbendingstrength,thestructurewilldeformasamembrane,and

thefinalfailurewouldusuallybeexpectedatsomeweakpointinthedetailsoftheconnec-tions.Itwouldbedifficulttopredictwhe-thergrossplasticdeformationwouldoccurbe-foreanylocalfailures.

Althoughthesimplecollapsetheoryisnotconsideredtobeparticularlyrelevanttoshipstructures,thepresentlackofknowledgeonstrengthandcollapsebehav-iourmakesitalmostmandatorytoloadallexperimentalormodelstructurestocollapse,andthispolicyhasbeeninvariablyfollowedatN.C.R.E.

Threeflatgrillagesweretestedtocol-lapseunderconcentratedloads,thegrillagesbeingsupportedonlyatthecornersforexperi-mentalconvenience.18Twoofthegrillagesfailedina simplemechanisminvolvingonlybendingaction,generallyconfirmingthesimpleplastictheory,butthedeformationsoftheothergrillageinvolvedmembraneaction.Theload-deflectioncurveforthislattergrillageisshowninFig.10,anditcanbeseenthatthereisnoindicationofanycollapsearoundthetheoreticalbendingtheoryvalueof47.5tons.Finalfailureoccurredduetofractureofa weldatanintersectionjoint.Single-directionstiffenedpanelshavealsobeentestedtocollapseunderconcentratedloadinglgandfairlyconsiderablestrengthduetomem-braneactionwasindicated,whichwouldbeex-pectedintheabsenceofanyintersectionjoints.Someflatgrillageshavealsobeenloadedtocollapseunderuniformpressure.LOInonecase,collapsewasbyplasticlateralinstabilityoftheheavytransversebeams,asshowninFig.11,ata loadhigherthanthetheoreticalbendingcollapsepressure.

Morerecently,thelarge-scalesteelfri-gatemodelreferredtoearlierhasbeenloadedtocollapseundera uniformpressureappliedtothebottomstructure.~3 Thestressduetotheappliedloadfirstreachedyieldlocallyinthelongitudinalatabout20lb./in.2,buttherewasnosignoffailureuntil28lb./in.Zwasreached.Atthisstage,a numberoflocalbucklesandcracksoccurredinthemainlongi-tudinalandframes.Thestructurewasloadedseveraltimesfromzeroto28lb./in.2,andthefailuresbecamesuccessivelymoremarked.Eventually,itwasonlypossibletomaintaina pressureof22lb./in.2.A generalviewofthedamage,seenfromtheinsideofthemodel,inFig.12,showsmarkedshearbucklingof“theframewebsadjacenttothekeelinwayofscal-lopholestotakethe2-3/4in.deepsmalllongitudinalstiffeners.Thesewebsweresome-whatslenderbeing0.22in.thickand9%in.deep.Afterthefinalloading,thewebswereverybadlybuckledandfractured,asshowninFig.13. Inassessmentofthecollapsetest,itwasconcludedthatthesewebshadfailedby

-9-

$00 Io 20 30 40 50 60 70 HO 90DEFLECTION,INCHESFIG.10.LOAD-DEFLECTIONCURVEFORCOLLAPSEOFGRILLAGEUNDERCONCENTRATEDLOAD.

a combinationof”plasticinstabilityandfrac-turecausedbyhigh-stressconcentrationsatthescallopsandintermittentweldsbetweenthewebandflange.Otherpositionsofhighstresswereonthemainlongitudinalflangesadjacenttotheendbulkheads.Theseflangesbuckledplasticallyinwayofgapsinthein-termittentweldruns,asshowninFig.14.Similarbucklesoccurredinthetransverseframeflanaesat the bilae wherethere wasareduction. . ;nthesection:Inaddition,there

werea fairnumberofminorcracksandbucklesthroughoutthestructure.

Althoughthecollapseofthefrigatemodeltooktheformofa seriesoflocalfailures,allofwhichoccurredatapproximatelythesamepressure,itisofi[lteresttocomparethe28lb/in.2maximumpressureattained,withthetheoreticalmechanismcollapsepressure.Thetheoreticalcollapsepressure,inthisinstance,wasmodifiedtoinclude,veryapproximately,theeffectofin-planedisplacementsormem-braneaction.Thesecalculationsindicatedthatthetruecollapsepressureintheabsenceofanylocalinstabilityorfractures,orfailureofthesupportingsidestructureorbulkheads,wouldbesomethinglike45lb/in.~,andthatthemodeofcollapsewoulddiffersomewhatfromthatobserved.Thetheoreticalcollapsepressurefortheobservedmodewouldbe70lb/in.2withallmemberstakingthefullplasticmoment,andwithoutallowingforstrengthduetoa planeaction.Thisresultemphasisesthattheratherlowcollapsepres-sureofthemodelwasentirelycausedbyin-adequatedetaildesign.

Theimportanceofrationaldesignofde-tails,particularlyweldedconnections,hasbeenrecognizedatN.C.R.E.forsometimepast,andFaulkner2~haspresenteda reviewofworkonthestaticstrengthofsimpleweldedkneejoints,longitudinaltobulkheadconnections,

FIG.J1. PORTIONOFGRILLAGELOADEDTOCOLLAPSEUNDERUNIFORMPRESSURE.

-1o-

FIG.12. GENERALVIEWOFDAMAGETOFRIGATEMODELAFTERCOLLAPSETEST.

andgrillageintersections.Theobjectofthisworkwastoexaminethestrengthofa numberofsimplejointdesignsandplacethemintoanorderofmerit.Asa resultofthiswork,jointsofvariousdegreesofsophisticationarenowrecommendedforuseinshipdesign,accord-ingtothemagnitudeofloadinganticipated.Itisappreciatedthat“thefatiguestrengthofconnectionsisalsoanimportantissueaffect-ingsurfaceshipsandfatiguetestsona num-berofgrillageintersectionjointsareplannedforthenearfuture.

STRENGTHOFBOTTOMSTRUCTURES

A knowledgeoftheultimatestrengthofthestiffenedplatepanelsorgrillagesform-ingship’sbottomstructuresisrequiredtodeterminethefullv~lasticmomenttobreakaship’sback.Thisl~nconjunctionwithaknowledgeofthemaximumbendingmomenta-swillpermitthetruemarginofsafetyorfactoragainstcollapsetobedetermined.isalsonecessarytounderstandthebehavoftheindividualplatepanelsundersimu’taneouslyappliedlateralandendloadbe-thedesignofthemid-shipcross-sect~on(beoptimised.

sea,oadItour

orean

Withregardtotheplatingofwarships,fewquantitativeresultsapplicableinde-signhaveyetbeenobtained,despitea greatdealofworkatN.C.R.E.andelsewhere.Theprincipalachievementssofarhavebeenforthecaseoflateralpressurealone.A concept

FIG.13.DAMAGETOFRAMEWEBAFTERCOLLAPSETEST.

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FIG.14. BUCKLESINKEELANDLONGITUDINALADJACENTTOBULKHEAD.

FIG,15. TESTARRANGEMENTFORGRILLAGEUNDERCOMBINEDLATERALANDAXIALLOADING.

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FIG.16. FIRSTGRILLAGEAFTERCOLLAPSEUNDERAXIALLOAD.

hasbeenadvancedofdesigningtoa smallbutacceptablepermanentset,assumingthat.theedgesareclampedagainstrotationbutfreetoslideinwards.22Ithasrecentlybeenes-tablishedthattherearesomecaseswhereacompressivestressfieldintheplatingduetobendingofthestiffeningmembersmaysig-nificantlyaffectthepermanentset.20

ExperimentalworkIsnowinhandintheLargeTestingFrameatN.C.R.E.tostudythebehaviouroffull-scaleweldedgrillagesundersimultaneouslyappliedlateralpressureandendload.Fivepairsofmild-steelgrillagesarebeingtestedinitially,eachwithoveralldimensionsof20ftby10ft,coveringa rangeofwidthtothicknessratiosforplatepanelsbetweenstiffenersfrom40to100,anda rangeofspantoradiusofgyrationratiosforlongi-tudinalgirders(betweenframes)from20to60.Thefirst’grillageofeachpairisbeingtestedtocollapseunderendloadonly,whilethesecondwillbecollapsedundera combinationoflateralandendload.In-planeloadingisappliedthroughsix150-.tonhydraulicjacksactingthroughloadcellsandballcaps;later-alloadisappliedbya waterfilledrubberbag,asshowninFig.15. Approximatecondi-tionsofsimplesupportareprovidedbylight

flexureplatesattheendsofeachgrillageandbytie-barsatthesides.ThecompletetestassemblyisshowninFig.16,whichalsoillus-tratesthecollapseofthefirstgrillagebyelasto-plasticinstabilitybetweentwoadjacentframes.Inparallelwiththeexperimentalwork,numericalcomputerprogramshavebeendevelopedfortheelastlcanalysisofgrillagesundercom-binedlateraland~n-planeloading,andtocal-culatethebucklingloadsandmodes.ProgramsforPegasusarecomplete,andprogramsforthelargerKDF9 computerareinpreparation.

EXPERIMENTALTECHNIQUES

Evenwiththelargeandhigh-speeddigitalcomputersnowavailable,thecomplexityofshipstructuresissuchthatconsiderablesimpliflca-t.ionandapproximationareusuallyrequiredbe-foretheoreticalanalysisisfeasible.AtN.C.R.E.,allthestructuralinvestigationshaveincludedexperimentalworktoassistinformu-latingidealisationsandtocheckontheaccu-racyoftheresults.Ideally,large-scalemodelsusingfull-scalematerialsandfabrica-tiontechniquesaredesirablesothatthede-tailsatjointsandtheweldingdistortionsaretypicaloffull-scalepractice.Thesedistor-tionshaveanimportantbearingontheeffec-

_13-

F.IG.17. SMALL-SCALEGRILLAGEMODELAFTERCOLLAPSE.

ofthe~latinuasstiffenerflanaestivenessandundershear.Becafiseoflimitations&thesmallestsizeofstraingaugeavailable,large-scalemodelsarealsonecessarytocarryoutdetailedstrainsurveys.Informationoncollapsestrengthcanonlybeobtainedfromrealistic,preferablylarge-scalemodels.

N.C.R.E.isfortunateinhavinga largetestingframemeasuring69ftlongby33ftwideby39ftfthigh,capableofwithstandingloadsupto500tons(or2,000tonsaxially).!!3Thefrigatemodelmentionedearlierwastestedinthislargetestingframe.

Large-scaletestshavetheunfortunatedisadvantageofprovingextremelycostlyanddifficulttocarryoutduetotheverylargeloadsandtestrigsrequired.A largenumberofsmallmodelscanbeconstructedandtestedforthesameoutlayasonelargemodel,andsmallmodelsareusuallyadoptedbyN.C.R.E.wheneveritisdesiredtostudytheeffectsoffairlywidechangesofparameters.Ontheotherhand,small-scaleweldedsteelmodelshaveoftensufferedfromlargeandcompletelyunacceptableweldingdistortionswhichrenderstrainmeasurementsintheelasticrangeofverylimitedvalue.Small-scalesteelmodelsmayalsobefabricatedusingsilversoldertechniquesorbyintermittentorspotwelding,buttheseconstructionsareseldomsufficient-ly strong for tests in the plastic range, Inrecentyears,thediptransfergasshieldedelectrodemethodofweldinghasbeenadoptedforcomparativelysmall-scalesteelmodels.Thisprocessproducesverymuchsmallerweld-ingdistortionsthanthemanualprocesses,

owingtothesmallerheatinput.Partlyasatestonthediptransferprocedures,twosmallgrillageshaverecentlybeenconstructedatN.C.R.E.usingmaterialrangingfrom0.15to0.27in.thick,whichmightberegardedas1/3or1/4offullscale.zqThemodelsincorpor-atedfilletwelds,buttweldsintheplating,andcorrectlyscaleddetailsattheintersec-tions.Onlyverysmallweldingdistrotionswereobtainedwhichwerequitetypicalofgoodfull-scalepractice.Themodelswereloadedelasticallyandthenintotheplasticrange.Themaximumloadsappliedwereabovethetheoreticalplasticcollapseloadsbuttherewerenocracksorsignsoffailure.A viewofthefirstmodelaftertestingisshowninFig.17. Thepresenceofbuttweldsintheplatingdidnothaveanynoticeableeffectoneitherthebehaviourofa panelbetweenstiff-enersundera localizedloadingorontheover-allbehaviouruptothemaximumloadapplied.Asa resultofthesedevelopments,it~san-ticipatedthatfuturestructuraltestingmaytendtobecarriedoutmoreonsmall-scalesteelmodels.

Forpurelyelasticmeasurements,small-scalemodelsina plasticmaterialsuchasXy-lonite(cellulosenitrate),celastoid(celluloseacetate),perspex(polymethylmethacrylate),orvybak(rigidpolyvinylchloride)havemanyad-vantages.Despitetheirnomenclatureasplasticmaterials,themechanicalbehaviourofthesematerialsiselastic,obeyingHooke’sLawuptoverylargestrains,say0.6to0.8%,pro-videdthemeasurementsaretakenata constanttimeintervalafterapplicationoftheloadtoallowforcreep.Oftheseplasticmaterials,

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FIG.18. GRILLAGEMODELINVYBAK.

celastoidcanberuledoutsinceitisverysensitivetohumiditychanges,whileperspexisonlyavailablefora fairlylimitednumberofthicknesses.Xyloniteispossiblythemostcommonlyusedplasticmaterialformodelsus-ingstraingaugetechniques.Incommonwithmostplastics,xylonitehastheadvantagesofa veryuniformthicknesswithsmoothsurfacesreadyforcementingstraingauges,softnessmakingiteasytocutandwork,andeaseofformingbymouldingatabout120”C,somewhataboveitssofteningpoint.ThelowYoung’smodulus,roughly1/100ofthatofsteel,leadstoappreciablysmallertestloadsandsimpli-fiestheproblemofprov~dingstiffsupportingstructures.Unfortunately,Xylonitehaspoordimensionalstability,andthematerialisfrequentlyfoundtowarp,distortandcontractoverperiodsofmonths.Itselasticconstantsatanyonetimeareaffectedbytemperatureandhumiditychanges,andtheyalsovarywiththelifeofthesheet.Also,thebondsatconnectionswhicharemadebywettingwiththesolventacetoneora mixtureofacetoneandamylacetatearenotfullyreliableandmay“give”orevenfailatquitelowstresses.AnotherdisadvantageofXyloniteisitsin-flammablenature.

AtN.C.R.E.,a rigidpolyvinylchloridematerialmanufacturedbyBakelite,Ltd.underthetradename“Vybak~’,hasbeenadoptedasasuperiorreplacementtoXylonite.Vybakhascompletedimensionalstability;itisnotin-flammable;it’sYoung’smodulusismoreuni-formthanXylonite;anditisnotaffectedbyatmospherichumidity.Therigidityofthematerialisaffectedbytemperature,rathermorethanXylonite,sothattemperaturecon-trolofthelaboratoryisrequired.VybakcanbebondedveryeasilyusingthecementsTensolNo.6 andTensolNo.7,manufacturedbythePlasticsDivisionofImperialChemicalIndus-tries,Ltd.forusewithperspex.Boththesecementsarecoldsetting,TensolNo.6 issuitableforshearconnectionsbutshrinksoncuring,whilecementNo.7 canbeusedtofillgapsandwilldevelopalmostthefulltensilestrengthofthevybak.Vybakhasbeensuccess-fullyusedatN.C.R.E.fora numberofgrillageandtransversestrengthexperiments,(suchastheaircraftcarrierflightdeckstructureshowninFig.18)andmodelstoinvestigatestressconcentrationsathatchopenings.

A reviewofmodelproceduresfornavalstructureswaspublishedbythepresentauthor

-15-

in1962,25butthispaperwaswrittenbeforethediptransferweldingwasintroducedforsmall-scalesteelmodels.Anothermodeltechnique,currentlyunderdevelopment,Istousevybakmodelsforelasticinstabilityex-periments.Duetotheverylargeelasticrangeofstrainforvybak,bucklinganalyslscanbecheckedforrealisticfull-scalegeo-metriesofdesignswhichwouldfailbyyieldwhenconstructedinsteel.Inthisway,thetruemarginofsafetyagainstbucklingmaybedetermined.Vybakisalsoverysuitableforinstabilityexperimentsbecauseitcanbebondedtogetherwithonlyminordistortions,evenwhenverysmallthicknessesareused.Thismakesitpossibletoapproachthebuck-lingloadmore closelywithoutlargeeffectscausedbymagnificationofinitialimperfec-tions.

PROTECTIONSTRUCTURESFORMARINENUCLEARREACTORS

N.C.R.E.hasmadeanimportantcontribu-tiontothedesignofcollisionbarrierstoprotectthereactorofa proposednuclearpoweredship.TheworkhasbeensponsoredbytheMinistryofTransportTechnicalCommitteeontheStructuralProtectionofMarineNuclearReactorsandthereportofthiscommitteeisnowbeingdrafted.Fourpossiblemethodsofprovidingstructuralprotectionhavebeenconsidered;namely,a decksystem,grillagesystem,membranetensionbarrierandmembranecompressionbarrier.Ofthese,thedecksys-temwasfavouredsince,bystiffeningtopre-ventinstability,thestrikingshipwouldberesistedbyforcesneartoyieldstressthroughoutthedeckmaterial,andthespacerequirementswouldnotbetoosevere.TheprincipleofthedeckresistingstructureisillustratedinFig.19,thestrikingwedgebe-ingresistedbya directcripplingstressinthedeck,normaltothewedge,anda frictionalforcetangentialtothewedge.Thedeckre-sistanceattheleadingedgeofthebow,andthebendingrigldltyandfrictionfromtheoutershellplatingwereconsideredtobesecondaryterms.Withtheseassumptions,someverysimpleexpressionswerederivedforthepenetratingforceandworkdone,andtheseweresubsequentlyconfirmedbystatictestsona seriesofmodels.Inordertoachieveashighaspossiblea valueforo,thecripplingstressnormaltothewedge,thebreadthtothicknessratioforeachplatepanelbetweenstiffenerswaslimitedto50,andtheeffec-tivespantoradiusofgyrationratioforthestiffenerswaslimitedto40.

Thepossibilityofcarryingoutdynamictestswasconsidered,butwasruledoutduetodifficultiesincorrectlyscalingboththevelocityofloadapplication,andinertiaef-

\/ Hedge

l-#\Crippling Stressi \.Frictional Stress= uainDeck= o

(Takena. 90%of 0.3%ProofStress)

PenetratingForce= 2oA(sin~ + UCOE~) foreachdeck

= 2kut(tml; + U)X

where A = effectiTemea of contactoneachBideofwedge

k = (effectiveareaofCOntact)i(areaofplating)= A/APt - thicknessof plating

Workdone .I

Fdx . kmt(tan; + “)X2

ResultB~or54in.penetrationonModel2:

k“+ u IF tons workEme tonsin. I1.0 0.2 105 284o1.0 0.3 128 34401,85 0.2 ‘- 5250

Experimental\ 126.5I 3200-l

FIG.19. PRINCIPLEOFDECKPROTECTIONSTRUCTUREFORNUCLEARREACTOR.

fects.Itwasthoughtthatdynamiceffectswouldbesmallina practicalprobleminvol-vinggrossplasticdeformationofmanysquarefeetofmaterial.Thetestswerethereforecarriedoutonsmall-scalemodelsloadedstaticallyina 500-tontestingmachine.Statictestsalsoprovideda continuousrecordoftherelationbetweenloadanddepthofpenetrationwhichwouldrequirea largenumberofmodelsifdeterminedbydynamictests.Thepossibil-ityofa finaldynamictestatfullscalewasconsidered,buthasnotbeenfollowedupduetotheprohibitivecostsinvolved.

Themodelswerebasedona full-scalebarrierdepthof20ftanddeep-framespacingof10ft. Twodesignswereconsidered,onehavinga deckplatingthicknessof1/2in.andthesecond1 in. Thefirstmodelwasa 1/8scalemodelofl/2-in,thickdeckstructure,constructedinmildsteelusinga silversol-dertechnique.Itwasloadedbya rigidwedgewitha 30°includedangleand3/4in.radiusnose.Thistestwasnotfullysuccessful,duetoinsufficientendconstraintinthetest

-16-

ring,andfailureofsomeofthesolderedjoints.Thesecondmodelwas1/4scaleofweldedconstruction,andthismodelfailedprogressivelybylocalcripplingofthestif-feneddeckstructureinwayofthepenetratingwedge.Theresultsarecomparedwithpredic-.tionsfromthesimpletheory,fora 54-in.penetrationinFig.19.

Thethirdmodelwassimilartothesecondbutrepresenteda l-in.thickdeckatfullscale,andthemodelscalewas1/8.Thismodelwasfabricatedbyweldingusingthediptransferweldingprocedure.Themodelwasloadedbya rigidwedgewitha 20°rakeandanincludedangleof30°.Inthismodeltherewasmorepronouncedcurlingofthedeckasitwaspushedbackbythesidesofthewedge,andtheenergyabsorbedwasabout70%ofthevalueestimatedfora verticalwedge,basedonthetestofModel2. Thefourthmodelwasidenti-caltothethird,andwasloadedbya bowrepre-sentativeoftheactualstructureIna fastcarcargoship.Inthiscase,thebowwassevere-lycrumpledwithlittlepenetrationofthebar-rierdecks.ThisIndicatesthatthetypesofdeckstructurebarrierinvestigatedwouldbemosteffectiveinfull-scalecollisions,andthattheenergyabsorbedwouldbesignificant-lygreaterthanthatderivedfromcripplingofthecollisionprotectionstructurealone.Theexperimentswiththerakedrigidbowhavein-dicatedthat,atfullscale,theenergywhichcouldbeabsorbedbytheprotectionstructurewouldbe32,000tonsft(or360,000tons- knot2)foreachdeck,anditiscon-sideredthatthiswouldbeincreasedbyatleast1/3foranysimulatedactualbowstruc-ture.Bearinginmindthatpartoftheenergyofanycollisionwillremainaskineticenergy,itisfeltthata satisfactoryprotectionstructurecanbebasedintheN.C.R.E.designusingsaysixdecks,andthatthiswillbeadequateagainstalmostallpossiblecolli-sionsatsea.

CONCLUSIONS

Itmaybeseenthatsignificantprogresshasbeenmadeintheunderstandingofshipstructures,particularlybydeveloping.methodsofelasticanalysisusingelectroniccomputers.Furthermore,researchisinprogresstoobtaininformationonloadingsatsea,withregardtobothextremesandrepeatedcyclicloading.Itis consideredthatthemostimportantoutstand-ingproblemaffectingsurfaceshipstructuresistoformulaterationaldesigncriteria.Withmoreinformationontheloadingbecomingavailable,thechoiceofmaximumallowablede-signstressmustbere-examined,forboththemeanfieldstress,andlocallyatstresscon-centrations.Atthepresenttimethereap-pearstobesomeinconsistencyindesigners’

attitudestostressconcentrations.Whilemajorstructuraldiscontinuitiessuchasthebreakofforecastleormajorhatchopeningsreceivecarefulattention,itisquitecommonforsmallerdiscontinuitiessuchasscallopholes,jointsandconnectionseithertobede-signedbyeyeorhardlytobeconsideredatall.Ourshipdesignersmustalsoassesswhetherminimumweightdesign,possiblyac-companiedbyincreasulmanufacturingcosts,isofinterest.Minimumweightandcostingstudiesarenowquitefeasibleusingelectron-iccomputers,thoughdifficultiesmaybeex-periencedinobtainingdataonthebreakdownofmanufacturingcosts.

ACKNOWLEDGEMENT

ThispaperispublishedbypermissionoftheMinistryofDefence(NavyDepartment).

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Clarkson,J.,“ElasticAnalysisofa Beam-PlatingStructureundera SingleConcen-trated-Load.”Proc.IXInt.Congr.Appl.Mech.Bruxelles1956.pp.176-186.

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tions- ElasticAnalysisofOrthogonal 24.Clarkson,J.,“SmallScaleGrillageTests,”GrillagesExcludingTorsionalEffects.” ReportNo.N.C.R.E./R5l7,February1966.ReportNo.N.C.R.E./R52O.Tobeissuedshortly. 25.Clarkson,J.,“SteelorPlastic?TheChoice

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16.Amerikian,A.,“AnalysisandDesignofFloatingDryDocks,”Trans.S.N.A.M.E.,Vol.65,1957,pp.307-361.

17.Caldwell,J.B.,“UltimateLongitudinalStrength.”Trans.R.I.N.A.Vol.107,No.3,July1965,pp.411-430.

18.Clarkson,J.,“TestsofFlatPlatedGrillagesunderConcentratedLoads.”Trans.I.N.A.,Vol.101,No.2,1959,pp.129-142.

19.Clarkson,J.,“TheBehaviourofDeckStiffeningunderConcentratedLoads.”Trans.R.I.N.A., Vol.104,No. 1, 1962,pp.57-65.

20.Clarkson,J.,“TestsofFlatPlatedGrillagesunderUniformPressure.”Trans.R.I.N.A.Vol.105,No.4,1963,pp.467-484.

21.Faulkner,D.,“WeldedConnectionsusedinWarshipStructures.”Trans.R.I.N.A.,Vol.106,No,1,January1964,pp.39-70.

22.Clarkson,J.,“UniformPressureTestsonPlateswithEdaesFreetoSlideInwards.”Trans.R.I.N.A~,Vol.104,No.”1,1962:-pp.67-80.

23.“TestingFrameforShips’Structures.”

Hi5-!7:: ’76’‘0’456”‘“’y24’

C..,...,i... r-’l,.””:c:-n.:--ticLLIL,Ly L,,az,F, LLILe LA”,L

DOCUMENTCONTROLDATA- R&D(Securityclaaai{icationof title,bodyofabatractand,r!dexingartmfat?ofirnuatbcenteredwhentheoverallreporris classified)

1 ORIGINATINGACTIVITY(Corporateauthor) 2a. REPORT SECURITY CLASSIFICATION

NoneShip Structure Committee 2b GROUP

3.REPORTTITLE

A SURVEYOFSOMERECENTBRITISHWORKONTHEBEHAVIOUROFWARSHIPSTRUCTURES

4.DESCRIPTIvE NOTES(Typeofreportand)nclusivodates)

Special Reportj AUTHORI’S)(Laxtriruna,firstn.am~,inlficd)

Clarkson, J.

;.REPORTDATE 7a. TOTALNo. OF PAGES 7b. NO.OFREFSNovember1966 25Ja.CONTRACTORGRANT NO. 9a. ORIGINATOR-S REPORT NUMBER(S)

Noneb. PROJECT No. SSC-178c, gb. OTHEW REPORT NO(S) (Anyothernumbersfhafmayboaaaignod

fhisreport)

d.10.AVAILABILITY/LIMITATIONNOTICES

Distribution of this documentis unlimited.

Il. SUPPLEMENTARYNOTES 12.SPONSORINGMILITARYACTIVITY

None

13,ABSTRACT

Entirely rational elastic or plastic design procedures for surfaceship structures have not beenachieved. During the past 15 years, considerableadvancesand developmentboth in the understandingof the mechanicsof shipstructures and in the application of digital computersto ship problemshavebeenmade. This is a report orI research in progress to obtain information onloadings at sea, with regard to both extreme and repeated cyclic loading.

. - . ..., . . - ArUKM1JAN64 14/3

SecurityClassification

.. -,. .. ..securl~y~lasslncatlon4- LINKA LINK~ LINKC

KEYWORDS ROLE WT ROLE WT ROLE ‘#T

Ship Hull Structures

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SecurityClassification

NATIONALACADEMYOFSCIENCES-NATIONALRESEARCHCOUNCILDIVISIONOFENGINEERING

TheShipHullResearchCommitteeundertakesresearchserviceactivitiesinthegeneralfieldsofmaterials,design,andfabrication,as.relatingtoimprovedshiphullstructure,whensuchactivitiesareacceptedbytheAcademyaspartofitsfunctions.TheConnnitteerecommendsresearchobjectivesandprojects;providesliaisonandtechnicalguidancetosuchstudies;re-viewsprojectreports;andstimulatesproductiveavenuesofresearch.

S!+IPHULLRESEARCHCOMMITTEEChairman:

ViceChaimnan:

Mr.MauriceL.SellersNewportNewsShipbuildingandDryDockCompany

Dr.H.NormanAbramsonDirector,Dept.ofMechanicalSciences

SouthwestResearchInstituteMr.HaroldG.AckerShipbuildingDivisionBethlehemSteelCorporation

Mr.W.H.BuckleyChief,AirframeCriteriaStructuralSystemsDepartmentBellAerosystemsCompanyMr.A.E.CoxAssistantNavalArchitectNewportNewsShipbuildingandDryDockCompany

Dr.N.H.JasperTechnicalDirectorU.S.NavyMineDefenseLaboratory

Mr.F.J.JoyceManager,MarineDesignNationalBulkCarriers,Inc.

ArthurR.LytleDirector

Mr.T.M.BuermannGibbs&Cox,Inc.

ViceChairman:

Dr.J.M.FranklandRetiredNationalBureauofStandards

Members

Mr.WilliamR.JensenStructuralMethodsEngineerGrummanAircraftEngineeringCorporation

Mr.J.A.KiesHead,BallisticsBranchMechanicsDivisionNavalResearchLaboratoryDr.WilliamR.OsgoodProfessorofMechanicsCatholicUniversityofAmerica

Dr.G.M.SinclairResearchProfessorofTheoreticalandAppliedMechanics

UniversityofIllinoisMr.MervilleWillisNavalArchitectNewYorkShipbuildingCorporation

ProfessorRaymondA.YagleDept.ofNavalArchitectureandMarineEngineering

UniversityofMichigan

R.W.RumkeExecutiveSecretary

SHIP STRUCTURE COMMITTEE PUBLICATIONS

Theseat%umentsare distributedby the Clearinghouse,Sptingfie2d,Vu. 22151. Thesedoctunentshavebeen announcedin the TechnicalAbstractBu22etin(TAB)of the DefenseDocumentationCenter(DDC),CameronStation,ALexandria,Vu. 22314,underthe indicatedADnwnbers. Thereis no chargefor doetenentsfor registeredusersofthe DDC services. Otherusersmustpay the prescribedrateset bythe Clearinghouse.

Indexof Ship StructureCommitteePublications(1946 - Apri 1 1965 )

SSC- 165, LocalYZeZdingand Extensionof a CraokUnderPlaneStressby

G. T. Hahn and A. R, Rosenfield. December 1964. AD 610039.

SSC-166, Reversed-BendTestsof ABS-CSteelwithAs-Rolledand MachinedSurfacesby K. Satoh and C. Mylonas. April 1965. AD 460575.

SSC-167, Restorationof Ductilityof Hot or ColdStrainedABS-BSteelbyTpeatmentat 700 to 1150F by C. Mylonas and R. J. Beaul ieu.

April 1965. AO 461705.

SSC-168, RollingHisto~ in Re.Zationto the Toughnessof ShipPlate byB. M. Kapadia and W. A. Backofen. May 1965. AO 465025.

SSC-169, InterpretativeReporton Weid-MetalToughnessby K. Masubuchi ,R. E. Monroe and D. C. Martin. July 1965. AO 466805.

SSC-170, Studiesof SomeBrittleFractureConceptsby R. N.Hall, S. W. Terry, W. J. Nordell and G. R. Erhard.AD 476684.

SSC-171, Micro-and MacrocraokFormationby B. L. Averbach.AD 473496.

SSC-172, CrackExtensionand PropagationUnderPlaneStressRosenfield, P. K. Dai and G. T. Hahn. March 1966.

Wright, W. J.September 1965.

October 1965.

by A. R.AD 480619.

SSC-173, Exhaustionof DuctilityunderNotchConstraintFolZ.owingUniformPrestraZningby C. Mylonas, S. Kobayashi and A. Armenakas.August 1966. AD 637143.

SSC-174, Investigationof ResidualStressesin SteelWeZdmentsby K.Masubuchi and D. C. Martin. September 1966.

SSC-175, MechanicalPropertiesof a High-Manganese,Low-CarbonSteelforWeZdedHeavy-SectionS7zipPlate by R. O. Stout and C. R. Roper, Jr.August 1966. AD 637211.

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