Section
7 Bulkheads
7.1 General
7.1.1 This Section is applicable to watertight and deep tank transverse and
longitudinal bulkheads, watertight flats, trunks and tunnels of all units except
ship units and other surface type units. Requirements are also given for
non-watertight bulkheads.
7.1.2 The scantlings of bulkhead structures are to comply with:
7.1.3 The requirements of this Section apply to a vertical system of
stiffening on bulkheads. They may also be applied to a horizontal system of
stiffening provided that equivalent end support and alignment are provided.
7.2 Symbols
7.2.1 The following symbols are applicable to this Section:
s |
= |
spacing of secondary stiffeners, in mm |
S |
= |
spacing or mean spacing of primary members, in metres |
ρ |
= |
relative density (specific gravity) of liquid carried in a
tank, but is not to be taken less than 1,025. |
l |
= |
overall length, in metres, of the primary support member' |
7.3 Watertight and deep tank bulkheads
7.3.2 Where bulkhead stiffeners support deck girders, transverses or pillars
over, the scantlings are to satisfy the requirements of Pt 4, Ch 6, 4 Decks.
7.3.3 The strength of bulkheads and flats which support the ends of bracings or
columns will be specially considered.
7.3.4 In way of partially filled tanks, the scantlings and structural
arrangements of the boundary bulkheads are to be capable of withstanding the loads
imposed by the movement of the liquid in those tanks. The magnitude of the predicted
loadings, together with the scantling calculations, may require to be submitted,
see also
Pt 4, Ch 3, 4.18 Other loads.
Table 6.7.1 Watertight and deep tank
bulkhead scantlings
Item and
requirement
|
Watertight bulkheads
|
Deep tank
bulkheads
|
(1) Plating thickness for plane,
symmetrically corrugated and double
plate bulkheads
|
t = 0,004sf
mm
but t + tc not less
than 5,5 mm
|
t = 0,004s f
mm
but t + tc not less than
7,5 mm
|
In the
case of symmetrical corrugations, s is to be taken as
b or c in Figure 3.3.1 Corrugation geometry in Pt 4, Ch 3 Structural Design, whichever is the greater
|
(2) Modulus of rolled and built stiffeners,
swedges, double plate bulkheads and
symmetrical corrugations
|
Z = cm3
|
Z = cm3
|
In the case of symmetrical corrugations, s
is to be taken as p, see also Note 2
|
(3) Inertia of rolled and built stiffeners
and swedges
|
|
I = cm4
|
(4) Symmetrical corrugations and
double plate bulkheads
|
Additional requirements to be complied with as
detailed in Table 6.7.2 Symmetrical corrugations and
double plate bulkheads (additional requirements)
|
(5) Stringers or webs supporting
vertical or horizontal stiffening
|
|
|
(a) Modulus
|
Z = 4,5k
S
le2 cm3
|
Z = 6,3 ρk
S
le2 cm3
|
(b) Inertia
|
|
I = cm4
|
Symbols
|
s, S, I, k,ρ as defined in Pt 4, Ch 6, 7.2 Symbols 7.2.1
|
(c) For watertight bulkhead stiffeners
or girders, the distance from the middle of the effective length
to a point 0,91 m above the bulkhead deck at side or to the
worst damage waterline, whichever is the greater
|
= web depth of stiffening member, in mm
|
(d) For tank bulkhead stiffeners or
girders, the distance from the middle of the effective length to
the top of the tank, or half the distance to the top of the
overflow, whichever is the greater
|
f = 1,1 but not to be taken greater than 1,0
|
= effective length of stiffening member, in
metres, and for bulkhead stiffeners, to be taken as l , see also
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
|
= load head, in metres measured vertically as
follows:
|
p = spacing of corrugations as shown in Figure 3.3.1 Corrugation geometry in Pt 4, Ch 3 Structural Design
|
(a) For watertight bulkhead plating, the distance
from a point one-third of the height of the plate above its
lower edge to a point 0,91 m above the bulkhead deck at side or
to the worst damage waterline, whichever is the greater
|
γ = 1,4 for rolled or built sections and double
plate bulkheads
= 1,6 for flat bars
= 1,1 for symmetrical corrugations of deep tank
bulkheads
= 1,0 for symmetrical corrugations of watertight
bulkheads
|
(b) For
tank bulkhead plating, the distance from a point one-third of
the height of the plate above its lower edge to the top of the
tank, or half the distance to the top of the overflow, whichever
is the greater
|
ω, e = as defined in Table 6.7.3 Bulkhead end constraint
factors, see
also
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
|
NOTES
|
1. In no
case are the scantlings of deep tank bulkheads to be less than
the requirements for watertight bulkheads where the boundary
bulkheads of the tanks form part of the watertight sub-division
of the unit to meet damage stability requirements, see
Pt 4, Ch 3, 5 Number and disposition of bulkheads.
|
4. The
scantlings of all void compartments adjacent to the sea are also
to comply with Pt 4, Ch 6, 7.5 Watertight void compartments 7.5.1.
|
2. For
self-elevating units, the bulkhead deck is to be taken as the
freeboard deck.
|
5. In
calculating the actual modulus of symmetrical corrugations the
panel width b is not to be taken greater than that given
by Pt 4, Ch 3, 3.2 Geometric properties of section.
|
3. For
column-stabilised units, the bulkhead deck is, in general, to be
taken as the uppermost continuous strength deck unless agreed
otherwise with LR.
|
6. For rolled or built stiffeners with flanges
or face plates, the web
thickness is to be not less than whilst for flat bar
stiffeners the web thickness is to be not less
than
|
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
Table 6.7.2 Symmetrical corrugations and
double plate bulkheads (additional requirements)
Symbols
|
Type of bulkhead
|
Parameter
|
Watertight
bulkheads
|
Deep tank
bulkheads
|
s, k as defined in Pt 4, Ch 6, 7.2 Symbols 7.2.1
|
Symmetrically corrugated,
see also Notes 1 and 2
|
|
Not to exceed:
|
Not to exceed:
|
b = panel width as shown in Figure 3.3.1 Corrugation geometry in Pt 4, Ch 3 Structural Design
|
85 at top, and
|
70 at top and
|
d = depth, in mm, of symmetrical corrugation or double plate
bulkhead
|
70 at bottom
|
bottom
|
as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
See also Note 4
|
= shear area, in cm2, of webs of double
plate bulkhead
|
d
|
|
To be not less than:
39 mm
|
θ = angle of web corrugation to plane of
bulkhead
|
θ
|
To be not less than 40°
|
NOTES
|
Double plate,
see also Note 3
|
|
Not to exceed:
|
75 at top and
|
1. The plating thickness at the
middle of span of corrugated or double plate bulkheads is to
extend not less than 0,2 m above mid-span.
|
|
65 at bottom
|
|
|
Not to
exceed:
|
85 at top and
|
2. Where the span of corrugations exceeds
15 m, a diaphragm plate is to be arranged at about mid-span.
|
|
75 at bottom
|
|
d
|
|
To be not less than:
39 mm
|
3. See also
Pt 4, Ch 8 Welding and Structural Details.
|
|
To be not
less than:
|
|
|
cm2 at top, and
|
cm2 at top, and
|
4. In calculating the actual
modulus of symmetrical corrugations, the panel width b is not
to be taken greater than that given by Pt 4, Ch 3, 3.2 Geometric properties of section.
|
|
cm2
|
cm2
|
7.3.6 Where tanks are intended for the storage of oil with a flash point less
than 60°C (closed-cup test) the scantlings of bulkheads are to comply with:
The minimum scantlings and arrangements on all units are also to comply
with Pt 3, Ch 3 Production and Storage Units.
7.3.8 Where watertight bulkhead stiffeners are cut in way of watertight doors
in the lower part of a bulkhead, the opening is to be suitably framed and
reinforced. Where stiffeners are not cut but the spacing between the stiffeners is
increased on account of watertight doors, the stiffeners at the sides of the
doorways are to be increased in depth and strength so that the efficiency is at
least equal to that of the unpierced bulkhead, without taking the stiffness of the
door frame into consideration. Watertight recesses in bulkheads are generally to be
so framed and stiffened as to provide strength and stiffness equivalent to the
requirements for watertight bulkheads.
7.3.9 Wash bulkheads or divisions are to be fitted to deep tanks as required by
Pt 4, Ch 7, 4 Watertight integrity. The division bulkhead may be
intact or perforated as desired. If intact, the scantlings are to be as required for
boundary bulkheads. If perforated, the gross plating thickness is not to be less
than 7,5 mm and the modulus of the stiffeners may be 50 per cent of that required
for boundary bulkheads, using measured to the crown of the tank. The stiffeners are to be
bracketed at top and bottom. The area of perforation is to be not less than five per
cent nor more than 10 per cent of the total area of the bulkhead. Where brackets
from horizontal girders on the boundary bulkheads terminate at the centreline
bulkhead, adequate support and continuity are to be maintained.
7.3.10 The scantlings of end brackets fitted to bulkhead stiffeners are, in
general, to comply with Pt 4, Ch 8 Welding and Structural Details.
Table 6.7.3 Bulkhead end constraint
factors
Type
|
End connection, see
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
|
ω
|
e
|
μ
|
Rolled or built stiffeners and swedges
|
1
|
End of
stiffeners unattached or attached to plating only
|
0
|
0
|
|
2
|
Members with webs and flanges (or bulbs) in line
and attached at deck or horizontal girder See also Note 1
|
Adjacent member of B of smaller modulus
|
The lesser of
or 1,0
|
0
|
|
3
|
Adjacent member B of same or larger
modulus
|
1,0
|
0
|
|
4
|
Bracketless connection
to longitudinal member
|
Member A within length l
|
1,0
|
|
|
5
|
Member A within length l
|
1,0
|
0
|
|
6
|
Bracketed connection
|
To
transverse member
|
Bracket extends to floor
|
1,0
|
The lesser of
βa or 0,1l
|
|
7
|
Otherwise
|
1,0
|
0
|
|
8
|
To longitudinal member
|
1,0
|
The lesser of
βa or 0,1l
|
|
Symmetrical corrugations or double plate
bulkheads
|
9
|
Welded directly to deck
no bulkhead in line
|
No longitudinal brackets
|
0
|
0
|
|
10
|
With longitudinal brackets and transverse
stiffeners supporting corrugated bulkhead
|
The lesser of
or 1,0
|
0
|
|
11
|
Welded directly to deck or girder
|
Bulkhead B, having same section, in line
|
The least of
or or 1,0
|
0
|
|
12
|
Welded directly to tank top and
effectively supported by floors in line with each bulkhead
flange, see also Note 2
|
Thickness at bottom same as that at
mid-span
|
The least of
or or 1,0
|
0
|
|
13
|
Thickness at bottom greater than that at
mid-span
|
The least of
or or 1,0
|
The lesser of
αl or a
|
The lesser of
or
|
14
|
Welded to stool efficiently
supported by the units structure
|
For deep tank bulkheads
1,0 For watertight bulkheads
the least of
or or 1,0
|
The lesser of
αl or a
|
|
Symbols
|
s, l, ρ, k, as defined in Pt 4, Ch 6, 7.2 Symbols 7.2.1
|
= section modulus, in cm3, of
adjacent member B
|
a = height, in metres, of bracket or end stool or lowest
strake of plating of symmetrically corrugated or double plate
bulkheads, see
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
|
α = a factor depending
on μ and determined as follows:
|
= web overall depth, in mm, of adjacent member
A
|
where μ ≤ 1,0
|
α = 0
|
e = effective length, in metres, of bracket or end stool,
see
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
|
where μ >
1,0
|
α = 0,5
|
= but measured from the middle of the overall
length l
, p, as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
β = a factor depending
on the end bracket stiffening and to be taken as:
|
= thickness of supporting floor, in mm
|
1,0 for brackets with face bars directly
connected to stiffener face bars
0,7 for flanged brackets
0,5 for unflanged brackets
|
, = thickness, in mm, of flange plating of
corrugation or double plate bulkhead at mid-span or end,
respectively
|
δ = 1,0
generally
|
= thickness, in mm, of stool adjacent to
bulkhead
|
δ = for corrugated watertight bulkheads
|
= thickness, in mm, of flange plating of
member B
|
η = lesser of 1,0 and for welded sections
|
Subscripts 1 and 2,
when applied to ω, e and a, refer to the top and
bottom ends of stiffener respectively
|
η = lesser of 1,0 and for cold formed sections
|
= for watertight bulkheads
|
μ = a factor
representing end constraint for symmetrical corrugation and
double plate bulkheads
|
= for deep tank bulkheads
|
ξ = 1,0 where full
continuity of corrugation webs is provided at the ends
|
= for watertight bulkheads
|
ξ = greater of 1,0 and
(η + 0,333) where full continuity is not provided
|
= for deep tank bulkheads
|
ω = an end constraint
factor relating to the different types of end connection,
see
Figure 6.7.1 Effective length and end
constraint definitions for bulkheads
|
In the case of
symmetrical corrugations s = p
|
|
= section modulus, in cm3, of
horizontal section of stool adjacent to deck or tank top
over breadth s or p (as applicable)
All material which is continuous from top to
bottom of stool may be included in the calculation
|
|
NOTES
|
1. Where the end connection is
similar to type 2 or 3, but member flanges (or bulbs) are not
aligned and brackets are not fitted, ω = 0.
|
2. Where the end connection is
similar to type 12 or 13, but a transverse girder is arranged in
place of one of the supporting floors, special consideration
will be required.
|
7.4 Watertight flats, trunks and
tunnels
7.4.2 Additional strengthening is to be fitted to tunnels under the heels of
pillars, as necessary.
7.5 Watertight void compartments
7.5.1 In all units where watertight void compartments are adjacent to the sea,
the scantlings of the boundary bulkheads are to be determined from Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4 for watertight bulkheads but
the scantlings are not to be less than required for tank bulkheads using the load
head , measured to the maximum operating draught of the unit.
7.6 Mud tanks
7.6.1 The scantlings of mud tanks are to be not less than those required for
tanks using the design density of mud. However, in no case is the relative density
of wet mud to be taken as less than 2,2 unless agreed otherwise with LR.
7.7 Non-watertight bulkheads
|