Section
7 Transverse oiltight bulkheads
7.1 General
7.1.1 Transverse
oiltight bulkheads may be plane or with corrugations arranged horizontally
or vertically. Scantlings are to be in accordance with Table 9.7.1 Transverse oiltight bulkhead
scantlings, except as otherwise
provided for in this Section. The arrangement of stiffening is to
be such as will efficiently support loads transmitted by end connections
of inner hull, longitudinal bulkhead, shell and deck longitudinals.
The thickness of bulkhead plating is also to be confirmed by direct
calculation in respect of panel stability. The calculation is to take
account of the shear stresses and direct stresses derived from both
the transverse and longitudinal strength investigations.
7.1.2 Where
tanks are intended to be partially filled, the scantlings and structural
arrangements of the boundary bulkheads are to be capable of withstanding
the loads imposed by the movement of liquid in the tanks. The magnitude
of the predicted loadings, together with the scantling calculations,
may require to be submitted.
7.1.3 The
scantlings of water ballast tank and cofferdam bulkheads not forming
the boundary of a cargo tank are to be as required by Pt 4, Ch 1, 9 Bulkheads for deep tanks. Where the bulkheads
are boundaries of `U' shaped tanks, the scantlings are also to be
confirmed by the requirements of this Section.
Table 9.7.1 Transverse oiltight bulkhead
scantlings
| Item
|
Horizontally stiffened
|
Vertically stiffened
|
|
(1) Plating thickness (mm)
|
t =
0,0044sf
|
|
(a) Generally, including corrugations see also item 3
|
|
|
|
(b) But not less than:
|
|
For the upper 3/4 of the bulkhead
see Note 5
|
|
|
|
For the lower 1/4 of the bulkhead
see Note 5
|
|
|
|
(2) Stiffener modulus (cm3)
|
Z =
0,0067ksS
1
2
h
2
|
|
(3) Corrugation properties
|
|
|
(a) Modulus (cm3)
|
Z = 0,0085ph
2le
2
k
|
|
(b) Inertia (cm4) see Note 4
|
 = 0,032ph
2le
3
|
Note
1. The section modulus given by the
formula is that of the stiffeners and associated plating or of the
corrugation over pitch p.
Note
2. The ratio of web depth to web
thickness is not to exceed 60 for stiffeners with flanges or face plates and 18 for flat bars.
Note
4. The minimum moment of inertia required
by item 3(b) of the Table is not to be reduced on account of higher
tensile steel being incorporated.
|
7.1.4 Where
the pump-room acts as a cofferdam, a bulkhead which does not form
part of the boundary of a cargo tank or a fuel oil bunker may be of
watertight bulkhead scantlings in accordance with the requirements
of Pt 4, Ch 1, 9 Bulkheads provided that an inert
gas system is fitted in the cargo tanks, and the corresponding notation
provided for in Pt 1, Ch 2, 2 Character of classification and class notations is
assigned.
7.1.6 Where
bulkheads are penetrated by cargo or ballast piping, the structural
arrangements in way are to be capable of withstanding the loads imparted
to the bulkheads by the hydraulic forces in the pipes.
7.1.7 Special
consideration will be given to any proposals to fit permanent repair/maintenance
access openings with oiltight covers in cargo tank bulkheads. Attention
is drawn to the existence of National Authority Regulations concerning
load line and oil outflow aspects of such arrangements.
7.2 Symbols
7.2.1 The
symbols used in this Section are defined as follows:
|
a
|
= |
the
lesser dimension of an unstiffened plate panel, in mm |
|
b
|
= |
the
greater dimension of an unstiffened plate panel, in mm |
|
b
1
|
= |
the greater horizontal distance, in metres, from the centre
of the plate panel or mid-point of the stiffener span to the corners
at the top of the tank on either side. |
|
f
|
= |
 but not to be taken greater than 1,0 |
|
h
|
= |
load
height, in metres measured vertically as follows: |
- for bulkhead plating, the distance from a point one-third of the height of the plate
panel above its lower edge to the highest point of the tank, excluding hatchway
- for bulkhead stiffeners or corrugations, the distance from the mid-point of span of
the stiffener or corrugation to the highest point of the tank, excluding
hatchway
|
h
1
|
= |
 but not less than 0,72 (h + Rb
1) |
|
h
2
|
= |
 but not less than 0,55 (h + Rb
1) |
|
p
|
= |
pitch
of symmetrical corrugations, in mm |
|
s
|
= |
spacing,
in mm, of bulkhead stiffeners or the breadth, in mm, of flange or
web, whichever is the greater, of symmetrical corrugations |
|
D
1
|
= |
D, in metres, but is to be taken not less than
10 and need not be taken greater than 16
|
where θ is the roll angle, in degrees
and 
|
S
1
|
= |
spacing of primary members, in metres. For the span at top,
span may be reduced by the depth of deck longitudinal. |
Other symbols are defined in Pt 4, Ch 9, 1.5 General definitions and symbols
7.3 Corrugated bulkheads
7.3.2 Where
transverse bulkheads are vertically corrugated, adequate resistance
to transverse compressive forces is to be provided by horizontal stringers
or equivalent.
7.3.3 Where
transverse bulkheads are horizontally corrugated, the span of the
corrugations should not, in general, exceed 5,0 m. Consideration is
to be given to providing an efficient connection between the corrugations
and the inner hull and longitudinal bulkhead stiffeners including
local reinforcement where necessary.
7.3.4 Corrugations
are to be aligned and stiffening arrangements on plane members are
to be arranged to give adequate support in way of flanges of abutting
corrugations. Where both the longitudinal and transverse bulkheads
are horizontally corrugated, the arrangements at intersections are
to be designed to facilitate attachment and maintain continuity.
7.3.5 Where
asymmetrical girders or webs are fitted to corrugated bulkheads, the
angle of corrugation is not to exceed 60°.
7.3.6 Where
corrugated bulkheads on stools are adopted, attention is to be paid
to the design of end connection. The arrangements are to be in accordance
with the requirements of Pt 4, Ch 9, 7.4 Bulkheads supported by stools.
7.4 Bulkheads supported by stools
7.4.1 The
scantlings of vertically corrugated and double plate bulkheads supported
by stools are generally to be confirmed by direct calculations which
are to be submitted.
7.4.2 In addition
the scantlings are to be determined in accordance with the requirements
of Pt 4, Ch 1, 9.2 Watertight and deep tank bulkheads 9.2.1 for deep tank
bulkheads with the load head h
4, in metres,
measured to the highest point of the tank, excluding hatchway, but
is not to be taken less than 0,44 (h
4 + Rb
1).
7.4.4 The
stools are to be reinforced with plate diaphragms or deep webs, and
in bottom stools the diaphragms are to be aligned with double bottom
side girders. Continuity is also to be maintained between the diaphragms
and the webs of bulkhead corrugations as far as practicable.
7.4.5 Additional
double bottom girders are to be arranged extending at least to the
first plate floor adjacent to the bulkhead each side and, in general,
are to be spaced not more than 3,8 m apart.
7.4.6 The sloping plate of bottom stools is to be aligned with double bottom
floors. Particular attention is to be given to the through thickness properties of the
inner bottom plating and continuity at the connection to the inner bottom, and to the
through thickness properties of the bottom stool shelf plate. For requirements for
plates with specified through thickness properties see
Ch 3, 8 Plates with specified through thickness properties of the Rules for Materials.
7.4.7 An efficient
system of reinforcement is to be arranged in line with the tank transverse
bulkheads or bulkhead stools at the intersection with the sloped plating
of the double bottom hopper tanks and topside tanks. The reinforcement
fitted in the tanks is to consist of girders or intercostal bulb plate
or equivalent stiffeners fitted between and connected to the sloped
bulkhead longitudinals.
7.4.8 The
shelf plates of the bulkhead stools are to be arranged to align with
the longitudinals in the double bottom hopper tank and topside tanks.
Where sloping shelf plates are fitted to stools suitable scarfing
is to be arranged in way of the connections of the stools to the adjoining
structures.
7.4.9 The
arrangement of stools and adjacent structure common with the cargo
tank is to be designed to avoid pockets in which gas could collect.
7.5 Connections
7.5.2 Stiffeners
are to be bracketed or otherwise efficiently connected at their ends
to provide adequate fixity.
7.5.4 Horizontal
stiffener end brackets are generally to satisfy the requirements of Pt 3, Ch 10 Welding and Structural Details. However, the length of the
bracket arm at the side shell, inner hull and longitudinal bulkhead
longitudinals is, in general, not to exceed the depth of the longitudinal.
In order to provide the necessary weld connection, consideration may
require to be given to fitting brackets on both sides of the bulkhead
or to welding the stiffener to the longitudinal. The arrangements
are also to be such as to maintain transverse continuity at intersections.
Examples can be seen in the ShipRight FDA Procedure, Structural
Detail Design Guide, (SDDG), published by LR.
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