ssc-367 - Ship Structure Committee

The stressmodel parametersdiscussedabove are summarizedon Figure
3-5. A summary of empirical equations, parametric study results
obtained by using applicable empirical equations for T, K and X
joints, and an illustrative finite element analyses results for a
complex joint are presented in Appendix C.
3.2.4 Stress History Model Parameters
The wave scatterdiagram and wave directionalitydata are necessary
whether a deterministic or a spectral analysis technique is used.
In a deterministicanalysiswave exceedance curves are generated in
each wave direction and used with the hot-spot stresses to obtain
the stress exceedance curves.
For a spectral fatigue analysis, a scatter diagram and the
directional probability is used with wave or wind spectrato obtain
the stress spectrum from hot-spot stresses. These parameters are
summarized on Figure 3-6. Stress History Models are discussed
further in Section 6.
3.2.5 FaticiueDamaqe Comtmtation Parameters
Many parameters affect the fatigue life computation. Some, such as
stress sequence, maintenance and repairs, lapses in corrosion
protection, etc., are not accounted for in fatigue damage
computation. Fatiguedamage is characterizedby an accumulationof
damage due to cyclic loading, with fatigue failure occurring when
the accumulateddamage reaches the critical level. To evaluate the
damage, the stress-time history is broken into cycles from which a
distribution of stress ranges is obtained. The variable-amplitude
stress range distribution is divided into constant-amplitudestress
range blocks, Sri, to allow the use of constant-amplitude S-N
curves.
3-15