ssc-367 - Ship Structure Committee

many design rules implement this approach, the recommended S-N
curves are often different from each other.
Assessment of defects detected during fabrication, or cracks
discovered while the structure is in service, is best accomplished
using fracturemechanicsand crackgrowth laws. Fitness-for-purpose
considerations will then directly affect repair programs and
inspection schedule.
The reconunendations,rules, regulations and codes that apply to
fatiguedesign have evolvedover the past 20 years, and severalhave
been revised or reissued in the last five years. These documents
are discussed briefly below as they apply to vessels and other
marine structures.
The American Welding Society (AWS) and American Institutefor Steel
Construction (AISC) fatigue design specifications (Reference4.15)
provide the basis for approximate fatigue design based on S-N
curves. However, unless the method developed accounts for the most
likely loads and other uncertainties, various critical and noncritical
fatigue cracks are.likely to occur.
Most documents on fatigue provide substantial flexibility in
carrying out comprehensivefatigue design and analysis, while also
incorporating extensive guidelines. Various DnV documents on
specific types of structures such as Steel Ships (Reference4.16),
Tension Leg Platforms (Reference4.17, Part 3, Chapter 6) and Fixed
Steel Platforms (Reference4.17, Part3, Chapter 4) provide general
guidelines and referto acomprehensive documenton fatigue’analysis
(Reference 1.7). The UEG Recommendations (Reference 1.8) are
similar to U.K. DEn Guidance Notes (Reference 1.6), differences
largely limited to the revisions introduced in the latest (fourth)
edition of Guidance Notes.
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