《船舶与海洋工程结构风险评估》课程教学课件（讲稿）Lecture 10 & 11 Stiffened Shells I &II

asranetCriteria for good strength modellingStatistical RequirementsConsistencySufficiencyLow BiasLowSamplingVarianceEngineering ReguirementsRobustnessRepeatabilityAppropriateEquationsAvoidUnsafeFeatures16

Criteria for good strength modelling 16 • Consistency • Sufficiency • Low Bias • Low Sampling Variance Statistical Requirements Engineering Requirements • Robustness • Repeatability • Appropriate Equations • Avoid Unsafe Features

asranetModified Strength Model of Ring StiffenedShellsUnderAxialCompressionThe limit state approach estimate the elastic buckling strength of a ring stiffenedcylinder subjected to axial compression as,o,=Bp,Coerwhere1EtEt0.605Classical elastic axial buckling stress (Timoshenko &a.RR/3(1-v2)Gere, 1961)17

Modified Strength Model of Ring Stiffened Shells Under Axial Compression 17 The limit state approach estimate the elastic buckling strength of a ring stiffened cylinder subjected to axial compression as,    e n cr  B C where 2 1 0.605 3(1 ) cr Et Et R R      , Classical elastic axial buckling stress (Timoshenko & Gere, 1961)

asranet1.2RtOp,Co.C is a Length dependent coefficient,[1,for Z,≥2.85C =31.425, for Z, <2.85+0.175Z,R, for 1≤Z, <200.75-0.142(Z,-1)0.4 +0.003Z300tPn:R, for Z, ≥200.35-0.0003t18

2 2 1 l L Z Rt   y n n cr C      C is a Length dependent coefficient, 1 1.425 0.175 l C Z        0.4 0.75 0.142( 1) 0.003 1 300 0.35 0.0003 l l n R Z Z t R t                    , for 1 20   Zl , for 20 Zl  , for 2.85 Zl  , for 2.85 Zl  18

asRanet,for ,≥11.3K,for ,<11+0.3元,A quadratic interaction of Ao,and , can be used to predict the inelastic collapsestress.g.=owhere10NowtheModeluncertaintyfactorfortheaxial load,Xa19

1.3 1 0.3 n B       A quadratic interaction of  y and  e can be used to predict the inelastic collapse stress.   c y  where 4 1 (1 ) e     y e e     Now the Model uncertainty factor for the axial load, m c X    , for 1 n  , for 1 n  19

asranetUnderHydrostaticpressureFor hydrostatic pressure,theproposed formulation (Faulkner D,Chen YNandDeOliveiraJG,1983)is identical withthe approach inBS5500.The inelastic hydrostaticcollapsepressureisestimatedas,,for P,≥Pm[0.5PhmP,for P,<PmDVon Mises, 1929 propose the solution for elastic hydrostatic buckling pressure of anunsupported cylinderis asfollows.Et1RPhr元Rn12LTR20

Under Hydrostatic pressure 20 For hydrostatic pressure, the proposed formulation (Faulkner D, Chen YN and De Oliveira JG, 1983) is identical with the approach in BS5500. The inelastic hydrostatic collapse pressure is estimated as, 0.5 1 0.5 hm hc y y hm p p p p p              Von Mises, 1929 propose the solution for elastic hydrostatic buckling pressure of an unsupported cylinder is as follows.   2 2 2 2 2 2 2 2 2 2 2 1 1 1 12 1 1 1 2 hm Et R t R p n R R L L n n L R                                                             , for y hm p p  , for y hm p p 