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:

Pt 10 SHIP UNITS for ship units; and
Pt 4, Ch 4, 4 Surface type units for other surface type units.

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.

7.1.4 The number and disposition of watertight bulkheads are to be in accordance with Pt 4, Ch 3, 5 Number and disposition of bulkheads and the requirements of Pt 4, Ch 7 Watertight and Weathertight Integrity and Load Lines regarding watertight integrity are to be complied with.

7.1.5 The buckling requirements of Pt 4, Ch 5, 4 Buckling strength of primary members are also to be satisfied.

7.1.6 The height of the air and overflow pipes are to be clearly indicated on the plans submitted for approval and the load heads for scantlings are to be not less than those defined in Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4.

7.2 Symbols

7.2.1 The following symbols are applicable to this Section:

higher tensile steel factor, see Pt 4, Ch 2, 1 Materials of construction

spacing of secondary stiffeners, in mm

inertia of stiffening member, in cm⁴, see Pt 4, Ch 3, 3 Structural idealisation

spacing or mean spacing of primary members, in metres

section modulus of stiffening member, in cm³, see Pt 3, Ch 3, 3 Hazardous areas and ventilation

relative density (specific gravity) of liquid carried in a tank, but is not to be taken less than 1,025.

7.3 Watertight and deep tank bulkheads

7.3.1 The scantlings of watertight and deep tank bulkheads are to comply with the requirements of Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4 to Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.10. Where tanks cannot be inspected at normal periodic surveys, the scantlings derived from this Section are to be suitably increased. All tanks are to be considered as deep tanks.

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 not less than 5,5 mm		t = 0,004s f +2,5 mm nor less than 7,5 mm
	In the case of symmetrical corrugations, s is to be taken as b or c in Pt 4, Ch 3, 3.2 Geometric properties of section 3.2.4 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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4
(5) Stringers or webs supporting vertical or horizontal stiffening
(a) Modulus	Z = 5,5k S cm³		Z = 11,7 ρk S 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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4
= load head, in metres measured vertically as follows:		p = spacing of corrugations as shown in Pt 4, Ch 3, 3.2 Geometric properties of section 3.2.4 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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.10, see also Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4
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 Pt 4, Ch 3, 3.2 Geometric properties of section 3.2.4 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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4			See also Note 4
= shear area, in cm₂, of webs of double plate bulkhead		d	––	To be not less than: 39mm
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: 39mm
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 at top, and	cm² at top, and
			cm²	cm²

7.3.5 In deep tanks, oil fuel or other liquids are to have a flash point of 60°C or above (closed-cup test). Where tanks are intended for liquids of a special nature, the scantlings and arrangements will be specially considered in relation to the properties of the liquid, see Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.6. For the scantlings of mud tanks, see Pt 4, Ch 6, 7.6 Mud tanks.

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:

Pt 10 SHIP UNITS for ship units.
Pt 4, Ch 4, 4 Surface type units for other surface-type units.
This Section for other unit types.

The minimum scantlings and arrangements on all units are also to comply with Pt 3, Ch 3 Production and Storage Units.

7.3.7 For cofferdams on units with oil storage tanks, as defined in Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.6, the separation of tanks and spaces are to comply with Pt 3, Ch 3 Production and Storage Units. Cofferdams are to be fitted between tanks as necessary, depending on the liquids stored. In general, cofferdams are to be fitted between tanks in accordance with the requirements of Pt 4, Ch 3, 5 Number and disposition of bulkheads.

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 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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4			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 unit’s 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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4			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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4			where μ > 1,0		α = 0,5 –
= but measured from the middle of the overall length l , p, as defined in Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4			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 Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads 7.3.4
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

7.4.1 The scantlings and arrangements of watertight flats, trunks and tunnels are to be equivalent to the requirements for watertight bulkheads or tanks as defined in Pt 4, Ch 6, 7.3 Watertight and deep tank bulkheads as appropriate. The scantlings of shaft tunnels will be specially considered. The scantlings at the crown or bottom of tanks are to comply with the requirements of Pt 4, Ch 6, 4.3 Deck stiffening 4.3.3.

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 7.3.4for 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

7.7.1 The scantlings of non-watertight bulkheads supporting decks are to be in accordance with Pt 4, Ch 6, 4.5 Deck openings 4.5.7.