Page 186 - Practical Design Ships and Floating Structures

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loading, the conclusions are likely to be different. (Specimen no 2 was subjected to the loaded
condition and the fatigue capacity is not presented in the same figure as for ballast loading).
2.3 Finite Element Analyses of Details

Different typical ship details were analysed that earlier were missing in design guidance documents to
provide stress concentration factors. As mentioned in the introduction the procedure for derivation of
stress concentration factors are linked to the hot spot S-N curve used. Thus the presented stress
concentration factors are linked to the hot spot stress derivation method.
2.3. I Cut outs and man holes

Different cut out geometries were analysed by Umoe:
Circular cut-out with diameter = 600 mm
Rectangular cut-out 600 x 800 mm with rounded corner R = 300 mm
Rectangular cut-out 600 x 1200 mm with rounded comer R = 300 mm
A number of different stiffener arrangements around the cut out were analysed, see Figure 4. The
analysis procedure and some selected results are presented by Chen and Landet (2001). The following
main conclusions were drawn:
> To insert a plate at the cutout edge is an efficient measure to reduce the stress concentration at the
plate edge.
k A single side reinforcement may not reduce the stress concentration in the plate around cutout edge
due to extra local bending deformation.
> A double side reinforcement will reduce the stress concentration in the plate around cutout edge.
2.3.2 Longitudinal to web9ame connections

Five different geometries of longitudinal to web frame co~~ti~tls similar to that of specimen 4
shown in Figure 2 were analysed by Aker MaritimeMmitime Trosvig. The analysis results are
presented by Ulleland et al. (2001). It is shown that the local design of the lug plates is important for
the calculated fatigue life.
2.3.3 Scallops

Different scallop geometries were analysed by Germanischer Lloyd (Siibel et al., 2000). A number of
stress concentration factors were presented.

2.3.4 Topside supports
A number of different geometries (R and $) of topside supports were analysed by Bluewater (2000),
see Figure 5. The results were presented in terms of stress concentration factors. It is demonstrated that
the radius and the angle are important parameters with respect to fatigue when considering the force
range from the topside. However, it is of small influence considering the fatigue life due to the stress
range in the deck plate.

2.3.5 Doublingplates
A number of different geometries of doubling plates on deck plates were analysed by Bluewater
(2000). Stress concentration factors and stress intensity factor for some fatigue cracks at hot spots were
derived. For a well defined stress direction a radius of the doubling plates in the order of the plate
thickness is sufficient. A circular doubling plate leads to a larger stress concentration factor than a