Page 289 - Marine Structural Design

Chapter 13 Collapse Analysis of Ship Hulls 265

This Section presents a modified Smith method (Smith, 1975, 1977 and Yao, 1991, 1992
Rahman and Chow, 1996) in which the effect of corrosion defects, fatigue crack and lateral
pressure are accounted for.
As demonstrated by previous researchers, the advantages of the modified Smith method
include (1) efficiency, (2) flexibility to account for the effects of corrosion defects, fatigue
cracks, and other factors and (3) accuracy.
The stress-strain relationships for the elements are given below.
13.4.1 Tensile and Corner Elements
The stress-strain relationship for tensile and comer elements is assumed linear elastic and
elastic-perfectly plastic:

&<Ey
(13.40)
0, =EYE &>Ey

where E, D~, and E, are the elastic modulus, yield stress and, yield strain of the material,
respectively.

13.4.2 Compressive Stiffened Panels
A stiffened panel is composed of a longitudinal stiffener with its attached plating. Following
the approach of Rahman and Chowdhury (1996), three distinct zones in the whole range of the
loading-shortening behavior are considered: stable zone, no-load-shedding zone and load-
shedding zone, as shown in Fig 13.7. The stable zone is in the pre-ultimate strength region.
The no-load-shedding zone does not require any load-shedding to maintain equilibrium.
When the strain increases, the final zone is characterized by a drop-off.
More information on compressive stiffened panels may be found from Smith (1975).

-$ / j Shedding ~ ~ ~ Shedding
No-load I
load
load
No-load
s blei Shedding
Shedding

Figure 13.7 Typical Stress-Strain Relation of a Stiffened Panel
A stiffened panel is composed of a longitudinal stiffener with its attached plating. Following
the approach of Rahman and Chowdhury (1996), three distinct zones in the whole range of the
stiffened panel's loading-shortening behavior are considered. The ultimate strength of a
stiffened panel is given by