Page 103 - Marine Structural Design

Chapter 4 Scantling of Ship's Hulls by Rules 79

4.4 Initial Scantling Criteria for Transverse Strength

4.4.1 Introduction
Ship hull is subjected to static and dynamic hydrostatic pressure in its bottom and two sides,
and under loads due to weight of the cargo inside the hull, see Figure 4.7. The transverse loads
may cause cross-sectional deformation as shown in dotted lines, and stresses in transverse
bulkheads, floors, side frames and deck beams. In general, hulls of the cargo ships are based
on transverse system where the transverse strength may be modeled as two-dimensional
frames. The two-dimensional frame is subjected to the hydrostatic pressure and loads due to
cargo weight as shown in Figure 4.7, as well as the shear forces transferred from the
longitudinal members.
_*------- ___ __----- -_
--
I I
I I
- I I -

Hydrostatic pressure
Figure 4.7 Transverse Loads on Ship Hulls

4.4.2 Transverse Strength
Two-dimensional (2D) frame analysis may be applied to calculate transverse strength. The
frame analysis may be conducted using analytical equations that are available from typical
books on structural analysis, or by the finite element methods.
In some cases, the frame analysis may be based on 2D plane stress analysis. The allowable
stress for transverse strength is defined in classification rules with the methods for stress
analysis. Typical arrangements for transverse frame may be found in classification rules.

4.5 Initial Scantling Criteria for Local Strength

4.5.1 Local Bending of Beams
The local strength of primary and secondary structural members is evaluated by means of
stresses due to local loads, such as lateral pressure or concentrated loads etc. Again, the
elementary Bernoulli-Euler beam theory is utilized when computing the stresses or deflections
for stiffeners and girders. Plate theory is used for plates. The derivation of the equations for
stress and deflection, using the same assumptions as for elementary beam theory or plate
theory, may be found in textbooks on material strength, for instance, Timoshenko (1956).
Scantlings of individual structural members, as shown in Figwe 4.7, with respect to local
bending moments and shear strength are presented in this section.