Page 293 - Marine Structural Design

Chapter 13 Collapse Analysis of Ship Hulls 269

The net area Ai(t) of the stiffened panel available to carry longitudinal stress is dependent on
the crack size q(t) and the corrosion depth di(t),

w=rb,, -2aio)m, -di(t)1+[h, -a,(t)tirb, -diwi (1 3.5 1)
where b, and hp are the width and thickness of the attached plating, and h, and b, are the
web height and thickness of the stiffener.
From an engineering viewpoint, a stiffened panel is considered ineffective when the crack size
exceeds the critical crack size determined by the Crack Tip Opening Displacement (CTOD)
method (Ghose, 1995) or when the corrosion induced thickness reduction exceeds 25% of the
original plate thickness.

13.5 Comparisons of Hull Girder Strength Equations and Smith Method

Many examples of progressive collapse analysis for box girders and ship primary hulls have
been calculated to verify the efficiency and accuracy of the present modified Smith method.
The examples used in the International Ship and Offshore Structures Congress (ISSC)
benchmark calculations by Yao et a1 (2000) are given in Table 13.1 together with the results of
the modified Smith method described in Section 13.4, and the equation described in Section
13.3.
.

Ship Type
-

Bulk Camel

Container Sagging 6.5 1 x 103 0.14 5.84~ O3 6.25~10~
1
Hogging 7.43~103 0.08 6.93~10~ 6.80~10~
Sagging 2.24~10~ 0.11 1.98~10~ 2.23~10~
DH VLCC
Hogging 2.91~10~ 0.04 2.76~10~ 2.68~ O4
1
Sagging I 1.72~10~ 0.02 1 .46x104** 1.70~10~
SH VLCC
Hogging 1 1.82~10~ 0.02 1 .79x104** 1.8 1 x 1 O4
Frigate sagging 10.39 0.07 9.61 9.73
Hogging I 12.38 0.08 12.10 12.26

Sagging 3.58~10~ 3.61~10~
FPSO
1
1
Hogging 5.14~ O3 4.90~ O3