ssc-367 - Ship Structure Committee

alternative, the accuracy of hot-spot stresses depends largely on
the ability to predict hot-spot stress locations in advance and
obtain measurements in those areas.
Since the use of both FEA and the physical model requires
substantial investmentof time and cost, they can be used only on a
selective basis. Thus, most structure hot-spot stresses must be
defined based on the applicationof empirical formulations.
Joint Geometry
The primary variables affecting the magnitude of stress
concentrationare weld profile and joint geometry. The weld profile
is accounted for in the S-N curve. The joint geometric
characteristics determine the magnitude of stress concentration.
For most simple structuraldetails, typically awide range of plate
and stiffener joints, the nominal stresses can be used directly to
compute fatigue lives as the effect of SCFS are incorporatedin the
S-N curves.
The joint geometriesof tubularmembers are quite complex andthe S-
N curves are used with the hot spot stresses, requiring definition
of SCFS for each joint geometry and loading. The SCFS are
determined for axial load, in-planemoment and out-of-planemoment.
Typically, a peak SCF is determined and conservatively applied to
eight points around the intersection. For the crown and saddle
points shown on Figure 5-7 separate SCFS can be determined. At
other locations, the SCFS are then interpolated between the crown
and saddle positions.
Joint Definition
When tubular members frame into one another, they form a tubular
joint, with the largest diameter or thickest member being the
through member or chord and all other members being braces.
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