Page 98 - Marine Structural Design

74 Part I Structural Design Principles

(a) Rectangular barge - unloaded (c) Barge - halfloaded

Weight and buoyancy curves 2
Buoyancy
Base line -, Base line 3

@) Weight and buoyancy curves of (d) Weight and buoyancy curves of loaded barge
unloaded barge

(e) Still water shear force
and bending moment curves of loaded barge
Figure 4.3 Bending Moment Development of a Rectangular Barge in
Stillwater

T
Water
line
(a) Ship in still water

(b) Ship in sagging condition
B

(c) Ship in hogging condition
Figure 4.4 Wave Bending Moment in a Regular Wave
In order to compute the primary stress or deflection due to vertical and horizontal bending
moments, the elementary Bernoulli-Euler beam theory is used. When assessing the
applicability of this beam theory to ship structures, it is useful to restate the following
assumptions:
The beam is prismatic, i.e. all cross sections are uniform.
Plane cross sections remain plane and merely rotate as the beam deflects.
Transverse (Poisson) effects on the strain are neglected.