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76 Pari I Smtctural Design Principles
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Figure 4.5 Design Corrosion Allowance for Tankers (ABS, 2002)
4.3 Initial Scantling Criteria for Longitudinal Strength
4.3.1 Introduction
In order to assess the structural strength of the ship, the minimum basic scantlings, which
depend on the expected loads, must be determined. The load effects acting on a ship may be
categorized as primary and secondary stresses. The primary stresses, also termed hull girder
stresses, refer to the global response induced by hull girder bending. In contrast, the secondary
stresses are termed local stresses and refer to the local response caused by local pressure or
concentrated loads. The design rules require that the combined effect of primary and
secondary stresses of structural members fall below the allowable strength limits of various
failure modes.
Basic scantling is an iterative procedure, as shown in Figure 4.6. The left part of the figure
represents the scantling based on hction requirements and engineering experience. The right
part shows that these basic scantlings have to be evaluated against applicable design rules.
Alternatively, the structural strength may be evaluated by means of rational analysis, such as
finite element methods, see Chapter 5.
