ssc - 419 supplemental commercial design guidance for fatigue ship ...

Fatigue Analysis of Existing ShipsLocal LoadRangef RGf RLf Rc fc mFatigue ClassLong TermDistributionFactorPerm. StressRatio f R /PSThe difference in equivalent hydrostatic head between the two load cases forthe stiffener.The alternating stress range from global hull girder bending loads.The alternating stress range from local loads.The combined stress range, computed by the equationf R = c f c m (f RG + f RL )Coefficient equal to 0.95 to reduce stress from the fully wasted condition.SafeHull reduces scantlings by an average corrosion factor of (NDCVapplied with the approximate impact to the hull girder strength) 0.90 timesoriginal scantlings to analyze the strength of the structure at the end of thelifetime of the ship. This factor adjusts the stress level to approximate themid-life level.Factor of 0.85 applied to connections of longitudinals to transverse webs orfloors in the bottom.The assigned fatigue classification for the intersection of the longitudinalwith the transverse frame. (These were discussed in Chapter 5.)The Weibull distribution factor defining the shape of lifetime fatigue loadingspectrum.The permissible stress range for the fatigue classification and the Weibulldistribution factor.The ratio of the computed stress range to the permissible stress range. Avalue of 1.0 or less represents an acceptable fatigue life.The following additional definitions apply for the fatigue analysis of flat bars in Table 9.2and in Appendices A through J:ForceSupport Area A sA cSFCf sf Lf Ric wThe range in shear force at the end of the longitudinal.Sectional area of the flat barSectional area of the collar platesStress Concentration Factor for the detailNominal stress range in the flat bar stiffenerStress range in the longitudinal as computed for the fatigue analysis of thelongitudinal as shown in Table 9.6Stress range for assessing fatigue life of the flat bar stiffenerf Ri = [(SFC f s ) 2 + f 2 L ] 1/2coefficient for the weighted effect of two paired loading conditions9-7