Section
7 Hull buckling strength
7.1 Application
7.1.1 These
requirements apply to plate panels and longitudinals subjected to
hull girder compression and shear stresses based on design values
for still water and wave bending moments and shear forces.
7.1.2 The
hull buckling strength requirements are applicable within 0,4L amidships
to ships of 90 m or greater in length.
7.1.3 Hull
buckling strength for ships less than 90 m in length will be specially
considered.
7.1.4 Hull
buckling strength outside 0,4L amidships of members contributing
to the longitudinal strength and subjected to compressive and shear
stresses is to be checked, in particular in regions where changes
in the framing system or significant changes in the hull cross-section
occur.
7.2 Symbols
7.2.1 The
symbols used in this Section are defined as follows:
|
s
|
= |
spacing
of secondary stiffeners, in mm. In the case of symmetrical corrugations, s is to be taken as b or c in Figure 3.3.1 Corrugation dimensions in Ch 3, whichever is
the greater
|
|
t
p
|
= |
as built thickness of plating less standard deduction d
t, in mm, (i.e. t
p =t — d
t)
|
|
E
|
= |
modulus of elasticity, in N/mm2
|
|
S
|
= |
spacing
of primary members, in metres |
|
σo
|
= |
specified minimum yield stress, in N/mm2
|
|
σA
|
= |
design longitudinal compressive stress in N/mm2
|
|
σ
CRB
|
= |
critical buckling stress in compression, in N/mm2
corrected for yielding effects |
|
σ
E
|
= |
elastic critical buckling stress in compression, in N/mm2
|
|
τA
|
= |
design shear stress in N/mm2
|
|
τCRB
|
= |
critical buckling stress in shear, N/mm2 corrected for
yielding effects |
|
τE
|
= |
elastic critical buckling stress in shear, in N/mm2 |
|
τo
|
= |
|
7.3 Elastic critical buckling stress
7.4 Design stress
7.4.1 Design
longitudinal compressive stress, σA, is to be determined
in accordance with Pt 3, Ch 4, 5 Hull bending strength:
minimum σA = 
for structural members above the neutral axis,
for structural members below the neutral axis,
σD based on sagging moment and σB based on hogging moment are determined in Pt 3, Ch 4, 5.8 Hull moment of inertia 5.8.1.
where
|
z
|
= |
vertical
distance from the hull transverse neutral axis to the position considered,
excluding deck camber, in metres |
|
z
D, z
B
|
= |
vertical distances from the hull transverse
neutral axis to the deck and keel respectively, in metres |
For initial design purposes, the hull transverse neutral axis
may be taken at a distance  above keel, where D is the depth of the ship,
in metres, as defined in Pt 3, Ch 1, 6 Definitions.
Table 4.7.1 Standard deduction for corrosion,
d
t
| Structure
|
d
t mm
|
d
t range mm
min. - max.
|
| (a) Compartments carrying
dry bulk cargoes
|
–
|
0,05t
|
0,5 - 1
|
| (b) One side exposure to
water ballast and/or liquid cargo.
|
Vertical surfaces and surfaces
sloped at an angle greater than 25° to the horizontal line.
|
| (c) One side exposure to
water ballast and/or liquid cargo.
|
Horizontal surfaces and surfaces
sloped at an angle less than 25° to the horizontal line.
|
0,10t
|
2 - 3
|
| (d) Two side exposure to
water ballast and/or liquid cargo.
|
Vertical surfaces and surfaces
sloped at an angle greater than 25° to the horizontal line.
|
| (e) Two side exposure to
water ballast and/or liquid cargo.
|
Horizontal surfaces and surfaces
sloped at an angle less than 25° to the horizontal line.
|
0,15t
|
2 - 4
|
Note
1. The standard deduction d
t is to be taken as appropriate and within the range given
above.
Note
2. For direct calculation
purposes, standard deductions will be specially considered.
|
Table 4.7.2 Elastic critical buckling strength
of plating
| Mode
|
Elastic critical
buckling stress, N/mm2
|
| (a) Compression of plating with
longitudinal stiffeners (parallel to compressive stress), see Note
|
|
| (b) Compression of plating with
transverse stiffeners (perpendicular to compressive stress), see Note
|
where
|
c
|
= |
1,3 when plating stiffened by floors or deep
girders |
| = |
1,21 when stiffeners are built up profiles or rolled
angles |
| = |
1,10 when stiffeners are bulb plates |
| = |
1,05 when stiffeners are flat bars |
|
| (c) Shear, see Note
|
|
Note Where the elastic critical buckling stress, as evaluated
from (a), (b) or (c), exceeds 50 per cent of specified minimum yield
stress of the material, the corrected critical buckling stresses in
compression (σCRB) and shear (τCRB) are given
by:
|
|
|
|
|
|
|
7.5 Scantling criteria
Table 4.7.3 Elastic critical buckling strength
of longitudinals
| Mode
|
Elastic critical
buckling stress, N/mm2
|
| (a) Column buckling (perpendicular to
plane of plating) without rotation of cross section, see Note 1
|
|
| (b) Torsional buckling, see Note 1
|
|
(c) Web buckling, see Notes 1 and
3
(flat bars are excluded)
|
|
| Symbols and Parameters
|
|
|
|
|
|
b
f
|
= |
flange width, in mm |
|
|
|
|
A
t
|
= |
cross-sectional area, in cm2, of
longitudinal, including attached plating, taking account of
standard deductions, see Note 4 |
|
 a
|
= |
moment of inertia, in cm4, of longitudinal,
including attached plating, taking account of standard deductions,
see Note 4 |
|
 t
|
= |
St.Venant's moment of inertia, in cm4, of
longitudinal (without attached plating) |
|
|
|
= |
 for flat bars |
|
|
|
= |
 for built up profiles, rolled angles and bulb
plates |
|
 p
|
= |
polar moment of inertia, in cm4, of
profile about connection of stiffener to plating |
|
|
|
= |
 for flat bars |
| = |
 for built up profiles, rolled angles and bulb
plates |
|
 w
|
= |
sectorial moment of inertia, in cm6, of
profile about connection of stiffener to plating |
| = |
 for flat bars |
| = |
 for `Tee' profiles |
|
|
|
= |
 for `L' profiles, rolled angles and bulb plates |
|
|
K
|
= |
|
|
| m is determined as follows:
|
| m
|
K range
|
| 1
|
0 < K ≤ 4
|
| 2
|
4 < K ≤ 36
|
| 3
|
36 < K ≤ 144
|
| 4
|
144 < K ≤ 400
|
| 5
|
400 < K ≤ 900
|
| 6
|
900 < K ≤ 1764
|
| m
|
(m -
1)2m2< K ≤ m2
(m + 1)2
|
|
C |
= |
spring stiffness exerted by supporting plate
panel |
| = |
 |
|
| kp = 1 - ηp, and
is not to be taken less than zero. For built up profiles, rolled angles and
bulb plates, kp need not be taken less than 0,1
|
 where σEP = elastic critical buckling stress
(σE) of supporting plate derived from Table 4.7.2 Elastic critical buckling strength
of plating
|
| All
other symbols as defined inPt 3, Ch 4, 7.2 Symbols 7.2.1 .
|
Note
1. Where the elastic critical buckling
stress, as evaluated from (a), (b) or (c), exceeds 50 per cent of
specified minimum yield stress of the material, the corrected critical
buckling stress in compression (σCRB) is given by:
|
|
|
Note
3. For flanges on angles and T-sections
of longitudinals, the following requirement is to be satisfied:
 for 'Tee' profiles,
where
|
t
|
= |
as built flange thicknesses, in mm |
|
Note
4. The area of attached plating is to be
calculated using actual spacing of secondary stiffeners.
|
|