ssc-367 - Ship Structure Committee

2. Weibull AtIDroach
The Weibull shape factor is a stress range distribution
parameter. The Weibull shape factor used with the
characteristicstress range allows carrying out of a fatigue
analyses with a relatively
Since the Weibull approach
few structural analysis cases.
differs from detailed spectral
fatigueanalysisonly in how the stressrange is obtained,the
accuracyof fatigue lives obtainedwith this approach largely
depends on the validity of Weibull shape factor.
The Weibull shape factor may vary between 0.8 and 1.2. If
information on structure and route characteristics are not
available, a shape factor of 1.0 may be used. Shape factors
obtained by calibrating the characteristic stress range
against a spectral fatigue approach indicate that single most
important variable affecting the shape factor is the
environment. In severe North Atlantic and Pacific wave
loadings,the shape factoris higher;the shape factoris also
generally lower for those ship structures with longer hulls.
Although the shape factor may be somewhat different for
differentparts of the structure (i.e. bulkheads, bottom) and
itmay also depend on the number of cycles to failure, further
work is necessary to document those effects.
Fixed and Mobile Marine Structures
The structures referred to in this section are both floating and
bottom-supported steel structures. Most organizations that issue
recommendations, rules, regulations and codes distinguish between
floating and fixed structures because of the differences in their
configurations and the resulting differences in applied loads,
structureresponse,redundancyand accessibilityfor inspectionand
repairs. The requirements vary substantially in scope and detail
from one document to another, but efforts to provide consistent yet
flexible fatigue analysis requirements have been successful.
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