ssc-367 - Ship Structure Committee

stresses several times greater than the nominal stresses. The
fatigue test results for a wide variety of shiphull stiffener
geometries can be used directly with the nominal stresses.
At an intersectionof a tubular brace and chord, depending on the
interfacegeometry,the maximum hot-spotstressesoften occur either
on the weld toe of the incoming brace member or on the main chord.
The ratio of the hot-spot stress to the nominal stress is defined as
the stress concentrationfactor (SCF).
SCF =U.aX/Un
The SCF value is probably the most important single variable that
affects the fatigue life of a detail/joint,necessitating accurate
determination of SCFS.
There are several practical approaches for determining SCF values.
The first approach is to develop an analytical model of the
detail/joint and carry out a finite element analysis (FEA). When
modeled correctly, determination of SCFS by FEA is a very reliable
approach. The second approach is to test a physical model and
obtain the hot-spot stresses from measurements. Whether a straingauged
acrylicmodel or other alternativesare used, the accuracyof
hot-spotstresseslargelydependson the abilityto predict hot-spot
stress locations and obtain measurements in those areas.
Although reliable and recommended for obtaining SCFS, these two
methods are time consuming and expensive. Thus, a third approach,
based on applying empirical formulations to determine SCFS, has
been extensively accepted for fatigue analysis of marine
structures. A set of empirical formulae developed by Kuang
(Reference 3.4) were derived by evaluating extensive thin-shell
finite element analyses results. The formulae proposed by Smedley
(Reference 3.5) and Wordsworth (Reference3.6) of Lloyds Register
were derived from evaluating the results of strain-gauged acrylic
models.
3-14