SECTION1GENERAL
1Introduction
Lashingbridgesareusedonboardcontainervesselstoraisethelashinglevelofcontainersstowedondeck
and,thus,toincreasethecargocapacityofthedeckstowagesystems.
Primaryoperationloadsonalashingbridgeoccurinlashedcondition,whencontainersarestowedinthe
adjacentbays.Insuchcondition,wind,gravityandinertialloadsactingoncontainersaretransmittedto
lashingbridgestructurevialashingrods.Thisresultsmainlyintheoveralllashingbridgeloadintransverse
shipdirection.Longitudinalbendingoflashingbridgescanalsobesignificantincaseofunsymmetrical
stowage,e.g.whencontainersarestowedonlyatonesideofthelashingbridge.
Besidesprimaryoperationloads,lashingbridgesarealsosubjectedtovibrationeffectscausede.g.bymain
engineandpropellerexcitation.Particularly,theglobalvibrationoflashingbridgescanbesignificantwith
respecttotheresultingstressese.g.inconnectionstotheship-sidestructure.
Calculatingthenaturalfrequenciesforcomparisonwiththerelevantexcitationfrequenciesmaynot
besufficientformitigatingtheriskoflashingbridgeresonancesandtherelatedfatigueissues.For
comprehensivedesignverificationoflashingbridgeswhereriskofresonancesisindicatede.g.bynatural
vibrationanalysis,forcedvibrationanalysisandsubsequentfatiguestrengthanalysisshouldbeperformed.
2Objective
Theobjectiveofthisdocumentistoprovidemethodsforassessingthevibrationeffectsonfatigueoflashing
bridgesonboardcontainervessels.
3Scope
Thisclassguidelinedescribestheprocedureforfatiguestrengthassessmentoflashingbridgesandtheir
ship-sidefoundationstakingintoaccounttheeffectofglobalvibrationoflashingbridgescausedbythemain
engineandpropellerexcitation.Thisprocedurecomprises:
— lashingbridgefreevibrationanalysis,seeSec.3[4]
— lashingbridgeforcedvibrationanalysisforrelevantexcitationordersofmainengineandpropellerforces,
seeSec.3[5]
— fatiguestrengthassessmentoflashingbridgeandship-sidefoundationstructureconsideringvibration-
inducedstresses,seeSec.4.
Theanalysisscopeshouldcoverfollowinglashingbridgesasaminimum:
— theaftmostlashingbridgewiththedesigntypicalfortheshipunderconsideration
— lashingbridgessignificantlydeviatingfromthetypicaldesignwithrespecttotheexpectedvibration
behaviour,e.g.thetwoaftmostlashingbridgesandthelashingbridgeimmediatelyaftofthefunnel.
LashingbridgesmaybeselectedforvibrationandfatigueanalysisuponagreementwiththeSociety.
Theassessmentoflocalvibrationsofsecondarystructuralmembersoflashingbridgeslikeplatforms,plate
fields,stiffenersandhandrailsisnotcoveredbythisguideline.
4Application
Thisdocumentappliestothedesignoflashingbridgesoncontainervessels.
5References
Table1andTable2listrespectivelyDNVGLandexternaldocuments.
Section1
Classguideline—DNVGL-CG-0447.EditionSeptember2020 Page5
Lashingbridgevibration
DNVGLAS