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Chapter 10

Structural Design

10.1 FACTORS INFLUENCING STRUCTURAL DESIGN

Structural design decisions have as their primary objective the evolution of a
structure that will withstand all the forces acting on it. The most important of these
forces are the bending moments and shear forces which stem from the waves
which the ship encounters and the loading applied by the cargo carried. As the
structure must continue to meet these forces throughout the ship’s life, the
scantlings must include allowances for the corrosion and wear which can be
expected.
Theoretical approaches to strength calculations are described in textbooks on
naval architecture, whilst up-to-date practical methods which should be used are
given in the rules of the classification societies and there seems no point in
repeating them here.
Regrettably, classification rules are so complicated nowadays that they provide
little guidance to designers towards the best structural configuration, however
excellent they may be for checking a design once this has been completed.
Fortunately, computer programs such as LRPASS take much of the work out of
determining the scantlings for a new design, but the optimising tricks that a good
designer used to learn in the course of his work no longer come so easily.
Classification societies verify the scantlings required by a proposed structural
design, but unless the design has serious shortcomings they do not usually suggest
changes in the main features of the structural design, although such changes might
improve the reliability of the structure, reduce the steelweight andor improve the
ease of construction.
It is on such features of structural design that this chapter’s attention is focused.