Page 120 - Marine Structural Design

96 Part I Struchrral Design Principles

level, analysis for structural notches, cutouts, bracket toes, and abrupt changes of structural
sections need to be performed.
Stress types commonly used in fatigue analysis based on S-N curves include nominal stress,
hot-spot stress, and notch stress. Each of these methods has specific applicable conditions.
Although only the nominal stress is used in the examples, the analysis approach is not limited
to any stress type.
Spectral Fatigue Analysis (SFA) based on the S-N curve and Palmgren-Miner’s cumulative
damage hypothesis has been widely applied in the fatigue damage assessment of marine
structures, see Part I11 of this book. Figure 5.4 shows the procedure for spectral fatigue
assessment.

Structural modeling
wave environment

Short-term wave
spectrum (Hs,T)(i,j;k,l) Stress FRF
I
(iJ;k,f)-th short-term

fatigue damge D(iJ;k,l)
1
I
I
Weighting & summing
density
probability
function
1
Long-term annudied

Fatigue Life (strength)

Figure 5.4 Procedure of Spectral Fatigue Analysis (Zhao, Bai & Shin,
2001)