10 Bulkhead Structure

10.1 Application

10.1.1 The requirements of this article apply to longitudinal and transverse bulkheads, which may be plane or corrugated.

10.2 General

10.2.1 The web height of vertical PSMs on bulkheads may be gradually tapered from bottom to deck.

10.2.2 Bulkheads are to be stiffened in way of deck girders.

10.2.3 Bulkheads that support girders, or pillars and longitudinal bulkheads which are fitted in lieu of girders, are to be stiffened to provide supports not less effective than required for stanchions or pillars that would be located at the same position.

10.2.4 Where bulkheads are penetrated by cargo or ballast piping, the structural arrangements in way of the connection are to be adequate for the loads imparted to the bulkheads by the hydraulic forces in the pipes.

10.3 Plane bulkheads

10.3.1 General

Plane bulkheads may be horizontally or vertically stiffened.

Horizontally framed bulkheads are made of horizontal stiffeners supported by vertical primary supporting members.

Vertically framed bulkheads are made of vertical stiffeners supported by horizontal stringers, if needed.

The bulkhead stiffener webs of hopper and topside tank watertight bulkheads are to be aligned with the webs of longitudinal stiffeners of sloping plates of inner hull.

Floors are to be fitted in the double bottom in line with the plane transverse bulkhead.

10.3.2 End connection of stiffeners

The crossing of stiffeners through a watertight bulkhead is to be watertight.

End connections of stiffeners are to be bracketed. For isolated areas of the ship where bracketed end connections cannot be applied due to hull lines, other arrangements including sniped ends are acceptable.

10.3.3 Sniped end of stiffener

Sniped ends may be used on bulkheads subject to hydrostatic pressure provided they comply with [3.4].

10.4 Corrugated bulkheads

10.4.1 General

For ships of 18 m moulded depth and above, the transverse vertically corrugated watertight bulkheads are to be fitted with a lower stool, and generally with an upper stool below deck. For ships of 16 m moulded depth and above, the transverse vertically corrugated watertight bulkheads subject to liquid pressure, e.g. tank bulkheads and ballast hold bulkheads, are to be fitted with a lower stool, and generally with an upper stool below deck. Otherwise corrugations may extend from inner bottom to deck.

10.4.2 Construction

The main dimensions b_f-cg, R, b_w-cg, d_cg, t_f, t_w, S_cg of corrugated bulkheads are defined in Figure 21.

The corrugation angle ϕ is not to be less than 55°.

When welds in a direction parallel to the bend axis are provided in the zone of the bend, the welding procedures are to be submitted to the Society for approval.

Figure 21 : Dimensions of a corrugated bulkhead

10.4.3 Corrugated bulkhead depth

The depth of the corrugation, d_cg, in mm, is not to be less than:

where:

: Mean span of considered corrugation, in m, as defined in [10.4.5].

10.4.4 Actual section modulus of corrugations

The net section modulus of a corrugation may be obtained, in cm³, from the following formula:

where:

t_f, t_w : Net thickness of the plating of the corrugation, in mm, shown in Figure 21.

d_cg, b_f-cg, b_w-cg : Dimensions of the corrugation, in mm, shown in Figure 21.

Where the web continuity is not ensured at ends of the bulkhead, the net section modulus of a corrugation is to be obtained, in cm³, from the following formula:

Z = 0.5 b_f-cg t_f d_cg 10^–3

10.4.5 Span of corrugations

The span _C of the corrugations is to be taken as the distance shown in Figure 22.

For the definition of _C, the bottom of the upper stool is not to be taken more than a distance from the deck at the centre line equal to:

• 3 times the depth of corrugation, for non rectangular stool.
• 2 times the depth of corrugation, for rectangular stool.

Figure 22 : Span of the corrugations

10.4.6 Structural arrangements

Where corrugated bulkheads are cut in way of primary supporting members, corrugations on each side of the primary member are to be aligned with each other.

10.4.7 Bulkhead end supports

The strength continuity of corrugated bulkheads is to be maintained at the ends of corrugations.

Where a bulkhead is provided with a lower stool, floors or girders are to be fitted in line with both sides of the lower stool. Where a bulkhead is not provided with a lower stool, floors or girders are to be fitted in line with both flanges of the vertically corrugated transverse bulkhead.

The supporting floors or girders are to be connected to each other by suitably designed shear plates.

At deck, if no upper stool is fitted, transverse or longitudinal stiffeners are to be fitted in line with the corrugation flanges.

When the corrugation flange connected to the adjoining boundary structures (i.e. inner hull, side shell, longitudinal bulkhead, trunk, etc) is smaller than 50% of the width of the typical corrugation flange, an advanced analysis of the connection is required.

10.4.8 Bulkhead stools

Stool side plating is to be aligned with the corrugation flanges.

10.4.9 Lower stool

The lower stool, when fitted, is to have a height in general not less than:

• 3 corrugation depths, for bulk carriers.
• One corrugation depth, for oil tankers.

The ends of stool side ordinary stiffeners, when fitted in a vertical plane, are to be attached to brackets at the upper and lower ends of the stool. Lower stool side vertical stiffeners and their brackets in the stool are to be aligned with the inner bottom structures such as longitudinals or similar. Lower stool side plating is not to be knuckled anywhere between the inner bottom plating and the stool top plate.

The distance d from the edge of the stool top plate to the surface of the corrugation flange is to be in accordance with Figure 23.

The lower part of the stool side plates is to be in line with double bottom floors or girders as the case may be, and the stool bottom is to have a width not less than:

• 2.5 corrugation depths, for bulk carriers.
• One corrugation depth, for oil tankers.

The stool is to be fitted with diaphragms in line with the longitudinal double bottom girders or floors. Scallops in the brackets and diaphragms in way of the connections to the stool top plate are to be avoided.

Figure 23 : Permitted distance, d, from the edge of the stool top plate to the surface of the corrugation flange

The stool side plating is to be connected to the stool top plate and the inner bottom plating by either full penetration or partial penetration welds. The supporting floors are to be connected to the inner bottom by either full penetration or partial penetration welds.

10.4.10 Upper stool

The upper stool, when fitted, is to have a height:

• Not less than two times the corrugation depth, for bulk carriers.
• At least one corrugation depth, for oil tankers.

Rectangular stools are to have a height in general equal to twice the depth of corrugations, measured from the deck level and at the hatch side girder or at the inner hull as applicable. Brackets or deep webs are to be fitted to connect the upper stool to the deck transverse or hatch end beams.

The upper stool of a transverse bulkhead is to be properly supported by deck girders or deep brackets between the adjacent hatch end beams. The width of the upper stool bottom plate is generally to be the same as that of the lower stool top plate. The stool top of non-rectangular stools of bulk carriers is to have a width not less than twice the depth of corrugations. The ends of stool side ordinary stiffeners when fitted in a vertical plane, are to be attached to brackets at the upper and lower end of the stool.

The stool is to be fitted with diaphragms in line with and effectively attached to longitudinal deck girders extending to the hatch end coaming girders or transverse deck primary supporting members. Scallops in the brackets and diaphragms in way of the connection to the stool bottom plate are to be avoided.

10.5 Non-tight bulkheads

10.5.1 General

In general, openings in wash bulkheads are to have generous radii and their aggregate area is not to be less than 10% of the area of the bulkhead. The area of non-tight bulkhead is the whole cross sectional area in one plane that covers the tank boundaries.

10.5.2 Non-tight bulkheads not acting as pillars

In general, the maximum spacing of stiffeners fitted on non-tight bulkheads not acting as pillars is to be:

• 0.9 m, for transverse bulkheads.
• Two frame spacings, with a maximum of 1.5 m, for longitudinal bulkheads.

The net thickness of bulkhead stiffener, in mm, is not to be less than:

t = 3 + 0.015 L₂

The depth of bulkhead stiffener of flat bar type is in general not to be less than 1/12 of stiffener length.

A smaller depth of stiffener may be accepted based on calculations showing compliance with Ch 6, Sec 5 and Ch 8.

10.5.3 Non-tight bulkheads acting as pillars

Non-tight bulkheads acting as pillars are to be provided with bulkhead stiffeners with a maximum spacing equal to:

• Two frame spacings, when the frame spacing does not exceed 0.75 m.
• One frame spacing, when the frame spacing is greater than 0.75 m.

Where non-tight bulkheads are corrugated, the depth of the corrugation is not to be less than 100 mm.

Each vertical stiffener, in association with a width of plating equal to 35 times the plating net thickness, 1/12 of stiffener length or the stiffener spacing, whichever is the smaller, is to comply with the applicable requirements in Ch 6, for the load being supported.

10.6 Watertight bulkheads of trunks and tunnels

10.6.1 Watertight trunks, tunnels, duct keels and ventilators are to be of the same strength as watertight bulkheads at corresponding levels. The means used for making them watertight, and the arrangements adopted for closing openings in them, are to be to the satisfaction of the Society.