Section
7 Hull buckling strength
7.1 Application
7.1.1 These requirements apply to plate panels and longitudinals subjected to
hull girder compression based on design values for still water and wave bending
moments.
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 , whichever is the
greater |
|
tp |
= |
as built thickness of plating less standard addition dt, in mm
(i.e. tp = t − dt) |
|
E |
= |
modulus of elasticity, in N/mm2 |
| = |
206000 N/mm2 for steel |
| = |
69000 N/mm2 for aluminium alloys |
|
S |
= |
spacing of primary members, in metres |
|
σo |
= |
specified minimum yield stress, in N/mm2 |
|
σA |
= |
design longitudinal compressive stress in N/mm2 |
|
σCRB |
= |
critical buckling stress in compression, in N/mm2, corrected
for yielding effects |
|
σE |
= |
elastic critical buckling stress in compression, in
N/mm2 |
7.3 Corrosion additions
7.3.3 or plating with a net thickness greater than 8 mm, the total corrosion addition
td, in mm, for both sides of the structural member is obtained by the
following formula:
td = td1 + td2
7.3.4 For plating with a net thickness less than or equal to 8 mm, the smaller of the
following values is to be applied for the total corrosion addition
td:
- 20 per cent of the gross thickness of the plating, or
- td = td1 + td2.
7.3.5 For an internal member within a given compartment, the total corrosion addition
td is obtained from the following formula:
td = 2td1
7.3.6 When a structural element is affected by more than one value of corrosion addition
(e.g. plate in a dry bulk cargo hold extending into the double bottom), the
scantling criteria are generally to be applied considering the severest value of
corrosion addition applicable to the member.
7.3.7 For structural members made of stainless steel or aluminium alloys, the corrosion
addition is to be taken equal to 0,25 mm, for one side exposure
(td1 = td2 = 0,25 mm).
7.4 Elastic critical buckling stress
7.4.3 Alternatively, the elastic critical buckling stress of plating and longitudinals may
be assessed in accordance with Chapter 3 of the ShipRight Procedure Additional
Calculation Procedures for Longitudinal Strength.
7.5 Design stress
7.5.1 Design longitudinal compressive stress, sA, is to be determined in
accordance with Pt 3, Ch 4, 6.5 Permissible hull vertical bending stresses:
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 by the hull moment of inertia.
where
|
z |
= |
vertical distance from the hull transverse neutral axis to the
position considered, excluding deck camber, in metres |
|
zD, zB |
= |
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 Corrosion additions for one side exposure, dt1 or dt2
| Compartment type
|
General Note 1d
|
| Ballast tank
|
|
1,00
|
| Cargo tank and fuel oil tank
|
Plating of horizontal surfaces
|
0,75
|
| Plating of non-horizontal surfaces
|
0,50
|
| Ordinary stiffeners and primary supporting members
|
0,50
|
| Dry bulk cargo hold
|
General
|
1,00
|
| Inner bottom plating
Side plating for single hull
vessel
Inner side plating for double hull
vessel
Transverse bulkhead plating
|
1,25
|
| Frames, ordinary stiffeners and primary supporting
members
|
0,50
|
| Hopper well of dredging vessels
|
1,75
|
| Accommodation space
|
0,00
|
| Compartments and areas other than those
mentioned above
|
0,50
|
|
Note 1. Corrosion
additions are applicable to all members of the considered
item.
|
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
t compressive stress), see Note
|
|
| (b) Compression of plating with transverse stiffeners
(perpendicular to compressive stress), see Note
|
|
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 |
|
Note Where the elastic critical buckling stress, as evaluated from
(a) or (b), exceeds 50% of the specified minimum yield stress of
the material, the corrected critical buckling stresses in
compression (σ CRB) are given by:
|
σCRB |
= |
σE when  N/mm2 |
| = |
σo
 when  N/mm2 |
|
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) Web buckling, see Notes 1 and 3 (flat bars are
excluded)
|
|
| Symbols and
parameters
|
|
ts |
= |
as built web thickness less standard
addition dt as specified in Table 4.7.1 Corrosion additions for one side exposure, dt1 or dt2, in mm, (i.e.
tw = t −
dt). For webs in which the
thickness varies, a mean thickness is to be used |
|
At |
= |
cross-sectional area, in cm2, of
longitudinal, including attached plating, taking account
of standard additions, see Note 4 |
|
Ia |
= |
moment of inertia, in cm4, of
longitudinal, including attached plating, taking account
of standard additions, see Note 4 |
All other symbols as defined in Pt 3, Ch 4, 7.2 Symbols 7.2.1.
|
Note 1. Where the
elastic critical buckling stress, as evaluated from (a) or (b),
exceeds 50% of the specified minimum yield stress of the
material, the corrected critical buckling stress in compression
(σ CRB) is given by:
2
2. For flanges
on angles and T-sections of longitudinals, the following
requirement is to be satisfied:
Note  for angles,
 30 for 'Tee' profiles
where
|
t |
= |
as built flange thicknesses, in mm |
Note 3. The area of attached plating is to be calculated using
actual spacing of secondary stiffeners.
|
7.6 Scantling criteria
|