ssc-367 - Ship Structure Committee

3.2 REVIEW OF FATIGUE ANALYSIS PARAMETERS
3.2.1 Fatique Analysis Criteria
Fatigue analysis criteria for marine structures are developed in
conjunctionwith the overall design criteria. The structure type,
environmentalconditionsand the scope of the overall design effort
all affect the fatigue analysis criteria. A fatigue life that is
twice as long as the structure’sdesign life is routinely specified
to ensure satisfactory fatigue performance. Larger safety factors
are often used for critical components where inspection and/or
repairs are difficult.
For many marine structures the use of a probabilistic fatigue
analysis, based on a probabilistic simulation of applied forces,
residual stresses, defects and imperfections, crack growth and
failure, appears to be desirable. This true probabilistic method
may be considered an emerging technology and the time and cost
constraints often require alternative methods to develop a design
that meets the fatigue criteria.
Although the following sections refer to both “deterministic”and
“probabilistic”fatigue methods, essentially the discussions cover
deterministicmethods. The probabilisticmethodsdefined only refer
to probabilistictreatment of the ocean environment.
3.2.2 Interacting Parameters
Fatiguedesign and analysis is carriedout in conjunctionwith other
activities that ensure proper design of the structure to meet all
pre-service and in-service loading conditions. The structure and
its component members must have sufficient strength to resist the
extreme loads for a range of conditions, and these conditions are
often interdependent.
The design is an iterative process in which the general
configuration gradually evolves. Thus, the fatigue design and
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