Section 1 Bulkheads

1.1.1 The requirements of Ch 1,9 are to be applied, together with the requirements of this Section.

1.1.2 Where vertically corrugated transverse watertight bulkheads are fitted, the scantlings and arrangements are also to satisfy the requirements of Ch 4, 1.4 Corrugated transverse watertight bulkheads – application and definitions Other transverse watertight bulkhead types will be specially considered.

1.1.3 In way of ballast holds, the scantlings are to satisfy the requirements of Table 1.9.1 in Chapter 1 for deep tanks with the load head, h ₄, in metres, taken to the deck at centre. This includes the scantlings of vertically corrugated and double plate transverse bulkheads supported by stools. In addition, the thickness of corrugations is to be not less than given by Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.10 for watertight corrugated bulkheads. Alternatively, the scantlings may be based on direct calculations which are to be submitted.

1.1.4 All bulk carriers to be classed ‘100A1 Bulk carrier, strengthened for heavy cargoes, any hold may be empty, ESP’ are to be arranged with top and bottom stools. The requirements of Ch 4, 1.2 Bulkheads supported by stools are to be complied with as appropriate.

1.2.1 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 bulkhead corrugations for 90° corrugations.

1.2.2 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. (See Pt 2, Ch 3,8 regarding requirements for plates with specified through thickness properties).

1.2.3 An efficient system of reinforcement is to be arranged in line with the hold transverse bulkheads or bulkhead stools at the intersection with the sloped plating of the hopper 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.

1.2.4 The shelf plates of the bulkhead stools are to be arranged to align with the longitudinals in the hopper 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.

1.3.1 In dry cargo holds where transverse bulkheads are arranged without bottom stools, the stiffeners and brackets of plane bulkheads, and rectangular corrugations of corrugated bulkheads, are to be aligned with floors and inner bottom longitudinals. In the case of non-rectangular corrugations, the flanges are to be aligned with floors, but consideration will be given to the fitting of a substantial transverse girder in place of one of the floors.

1.3.2 Where transverse corrugated bulkheads are arranged without top stools, transverse beams are to be arranged under the deck in way.

1.4.1 Where corrugated transverse watertight bulkheads are fitted, the scantlings are to be determined in accordance with the following requirements. In no case are the scantlings to be taken less than given by Ch 1,9.

1.4.2 For ships of length, L, 190 m or above, the vertically corrugated transverse bulkheads are to be fitted with a bottom stool and, generally, with a top stool below the deck. The requirements of Ch 4, 1.6 Vertically corrugated transverse bulkheads – support structure at ends are to be complied with as appropriate.

1.4.3 The loads to be considered as acting on the bulkheads are those given by the combination of cargo loads with those induced by the flooding of one hold adjacent to the bulkhead under consideration. The most severe combinations of cargo induced loads and flooding loads are to be used for the determination of the scantlings of each bulkhead, depending on the specified design loading conditions:

1. homogeneous loading conditions,

2. non-homogeneous loading conditions,

3. packed cargo conditions (such as steel mill products).

   The individual flooding of loaded and empty holds is to be considered.

1.4.4 Unless the ship is designed to carry only iron ore or a cargo of a similar density, such that a hold will only be partially filled in non-homogeneous conditions, the maximum mass of cargo which may be carried in the hold is to be taken as filling that hold to the upper deck level at side. A permeability of 0,3 and angle of repose of 35° is to be assumed for this application.

1.4.5 An homogeneous load condition is defined as one where the ratio between the highest and the lowest filling levels, d₁, in adjacent holds (see Figure 4.1.1 Corrugated transverse watertight bulkdeads - Heights and Heads) does not exceed 1,20. For this purpose, where a loading condition includes cargoes of different densities, equivalent filling levels are to be calculated for all holds on the basis of a single reference value of cargo density, which can be the minimum to be carried.

Figure 4.1.1 Corrugated transverse watertight bulkdeads - Heights and Heads

1.4.6 The permeability, μ, of cargo may be taken as:

0,5 for light cargoes (bulk cargo density and angle of repose for grain may generally be taken as 0,8 tonne/m³ and 20°).

0,3 for ore and coal cargoes (bulk cargo density and angle of repose for iron ore may generally be taken as 3,0 tonne/m³ and 35°).

0,3 for cement (bulk cargo density and angle of repose for cement may generally be taken as 1,3 tonne/m³ and 25°).

1.4.7 The flooding head, h_f, is defined as the distance, in metres, measured vertically with the ship in the upright position, from the location under consideration to a level located at a distance, d _f, in metres, from the baseline equal to:

1. In general:

   1. Bulkheads bounding No. 1 hold d_f = D

   2. Other bulkheads d_f = 0,90D

2. For ships less than 50 000 tonnes deadweight with Type B freeboard:

   1. Bulkheads bounding No. 1 hold d_f = 0,95D

   2. Other bulkheads d_f = 0,85D

where

1.4.8 In considering a flooded hold, the total load is to be taken as that of the cargo and flood water at the appropriate permeability. Where there is empty volume above the top of the cargo, this is to be taken as flooded to the level of the flooding head.

1.4.9 Corrugations may be constructed of flanged plates or fabricated from separate flange and web plates, which may be of different thicknesses. The corrugation angle is to be not less than 55°. See Figure 4.1.2 Corrugated Bulkhead Construction.

Figure 4.1.2 Corrugated Bulkhead Construction

1.4.10 The term net plate thickness is used to describe the calculated minimum thickness of plating of the web, t_w, or flange, t_f. The required plate thickness to be fitted, t_req, is the net thickness plus a corrosion addition, t_c. The corrosion addition is generally to be taken as 20 per cent of the net thickness, but not less than 2,5 mm and need not exceed 4,0 mm. For the foremost and aftermost bulkheads of the cargo hold region, the corrosion addition is to be taken as 15 per cent, but not less than 1,5 mm and need not exceed 3,0 mm.

1.5.1 The design pressure on the bulkhead is to be calculated in accordance with Table Table 4.1.1 Bulkhead pressure

1.5.2 The bending moment in the bulkhead corrugations is given by:

where

M

=

kNm (tonne-f m)

where

1.5.3 The applied bending stresses, in N/mm² (kgf/mm²), are to be determined by dividing the bending moments derived from Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.2 by the section modulus of the corrugation. Alternatively, assessment by direct calculation in accordance with Section 11 is permitted. The resulting stresses are not to exceed the values given in Table 4.1.3 Permissible stresses except as indicated in Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.9

Table 4.1.3 Permissible stresses

Failure Mode	Permissible stress in
	N/mm2(kgf/mm2)
Bending	σp = 0.09σo
Shear	τp = 0,50σo
Compressive buckling	σcr = σo
Shear buckling	τcr =
Symbols
t w = web plate net thickness, in mm t f = flange plate net thickness, in mm b = width of the corrugation flange, in meters (see Figure 4.1.2 Corrugated Bulkhead Construction) c = width of the corrugation web, in meters (see Figure 4.1.2 Corrugated Bulkhead Construction) k = τE = E = modulus of elasticity = 206000 N/mm2 (21000 kgf/mm2) σo = specified minimum yield stress, N/mm2 (kgf/mm2) τo =

1.5.4 The shear force in the bulkhead corrugation is given by:

Other symbols are defined in Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.2.

1.5.5 The applied shear stresses, in N/mm² (kgf/mm²), are to be determined by dividing the shear forces derived from Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.4 by the shear area of the corrugation. Alternatively, assessment by direct calculation in accordance with Section 11 is permitted. The resulting stresses are not to exceed the values given in Table 4.1.3 Permissible stresses.

1.5.6 Buckling checks are to be performed for the corrugation flanges in all areas of high in-plane compressive stress and also for the web plates at the corrugation ends. For the purpose of compressive buckling checks at the lower end of the corrugation, the bending moment may be taken as 85 per cent of the value calculated in accordance with Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.2 for the lower part (see Table 4.1.2 Bending moment coefficient). The procedure to be used when stresses are determined by direct calculation is given in Section 11.

1.5.7 The section modulus of the corrugations is to be calculated at each position where stresses are to be checked, using the net plate thickness and actual flange width, b, and taking the following into consideration:

1. If corrugation webs are not supported by local brackets below the shelf plate (or below the inner bottom), the section modulus at the bottom of the corrugation span is to be calculated using the corrugation flanges only. The webs may, however, be included when calculating the section modulus for the buckling check.

2. When calculating the section modulus of the corrugations at the lower end, the net area of flange plates may be increased by 25 per cent provided effective shedder plates are fitted (see Figure 4.1.3 Symmetric shedder plates,Figure 4.1.4 Asymmetric shedder plates) and Figure 4.1.7 Shedder gusset plates with sloped shelf plate which:

   1. are not knuckled; and

   2. are welded to the corrugations and the top of the lower stool by full penetration welds; and

   3. have a minimum slope of 45° with the lower edge fitted in line with the stool side plating; and

   4. have thickness and material properties at least equal to those for the flanges.

However, no such increase is permitted when carrying out the buckling check.

1. When calculating the section modulus of the corrugations at the lower end, the net area of the flange plates may be increased by 35 per cent provided effective gusset plates are fitted (see Figure 4.1.6 Asymmetric gusset/shedder plates, Figure 4.1.6 Asymmetric gusset/shedder plates and Figure 4.1.7 Shedder gusset plates with sloped shelf plate) which:

   1. are in combination with shedder plates which have thickness, material properties and welded connections in accordance with the requirements in (b); and

   2. have a height not less than half the flange width; and

   3. are fitted in line with the stool side plating; and

   4. are welded to the corrugations to the top of the lower stool and the shedder plates by full penetration welds; and

   5. have thickness and material properties at least equal to those provided for the flanges.

For the buckling check, an increase of 35 per cent in section modulus is permitted for guessets with asymmetic shedder plates (see Figure 4.1.6 Asymmetric gusset/shedder plates and Figure 4.1.7 Shedder gusset plates with sloped shelf plate) and 25 per cent in section modulus is permitted for gussets with symmetric shedder plates (see Figure 4.1.5 Symmetric gusset/shedder plates and Figure 4.1.7 Shedder gusset plates with sloped shelf plate).

Figure 4.1.3 Symmetric shedder plates

Figure 4.1.4 Asymmetric shedder plates

Figure 4.1.5 Symmetric gusset/shedder plates

Figure 4.1.6 Asymmetric gusset/shedder plates

Figure 4.1.7 Shedder gusset plates with sloped shelf plate

1.5.8 For the derivation of the shear area the following are to be taken into consideration:

1. the net plate thickness is to be used,

2. the effective shear area is to take account or non perpendicularity between the corrugation webs and flanges. In general, this may be achieved by multiplying the web sectional area by (sinΦ), where Φ is the angle between the web and the flange (see Figure 4.1.2 Corrugated Bulkhead Construction).

1.5.9 Where the compressive buckling check given in Table 4.1.3 Permissible stresses is not satisfied, the scantlings will be acceptable if the applied stress, calculated using the effective modulus, does not exceed σp as given in Table 4.1.3 Permissible stresses. The width of the compression flange, in metres, to be used for calculating the effective modulus is:

where

Ce

=

for β > 1,25

β

=

Other symbols are defined in Table 4.1.3 Permissible stresses.

1.5.10 The corrugation flange and web local net plate thickness are not to be less than:

tnet

=

mm

1.5.11 For built-up corrugated bulkheads, where the thicknesses of the flange and of the web are different, the net thickness of the wider plating is to be not less than t_wp, in mm, given by:

t wp

=

mm

Other symbol are as defined in Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.10.

1.5.12 The required thickness of plating is the net thickness plus the standard allowance for corrosion. See Ch 4, 1.4 Corrugated transverse watertight bulkheads – application and definitions 1.4.10.

1.5.13 The required scantlings of corrugations at the lower end are to be maintained for a distance from the inner bottom, or, where the stools are fitted, the top of the lower stool, to a point not less than:

l _c is as defined in Ch 4, 1.5 Vertically corrugated transverse bulkheads – scantling assessment 1.5.2.

1.6.1 The requirements of Ch 4, 1.2 Bulkheads supported by stools are to be complied with as applicable, together with the following.

1.6.2  Lower stool:

1. The height of the lower stool is generally to be not less than three times the depth of the corrugations.

2. The thickness and steel grade of the stool shelf plate are to be not less than those required for the bulkhead plating above.

3. The thickness and steel grade of the upper portion of vertical or sloping stool side plating, within the depth equal to the corrugation flange width from the stool top, are to be not less than the flange plate thickness and steel grade needed to meet the bulkhead requirements at the lower end of the corrugation.

4. The thickness of the stool side plating and the section modulus of the stool side stiffeners are to be not less than those required for a plane transverse bulkhead and stiffeners with the corresponding ballast or cargo, flooded pressure.

5. The ends of stool side vertical stiffeners are to be attached to brackets at the upper and lower ends of the stool.

6. The width of the shelf plate is to be not less than the depth of the corrugation plus three times the thickness of the flange plate.

7. The stool bottom is to have a width not less than 2,5 times the width of the shelf plate.

8. Scallops in the brackets and diaphragms in way of the top and bottom connections to the shelf plate and the double bottom floors or girders are to be avoided.

9. Where corrugations are cut at the bottom stool, corrugations and stool side plating are to be connected to the stool shelf plate by full penetration welds.

1.6.3  Upper stool:

1. The upper stool, where fitted, is to have a height generally between two and three times the depth of corrugations.

2. Rectangular stools are to have a height generally equal to twice the depth of corrugations, measured from the deck level and at hatch side girder.

3. The upper stool is to be properly supported by girders or deep brackets between the adjacent hatch-end beams.

4. The width of the shelf plate is generally to be the same as that of the lower stool shelf plate.

5. The upper end of a non-rectangular stool is to have a width not less than twice the depth of corrugations.

6. The thickness and steel grade of the shelf plate are to be the same as those of the bulkhead plating below.

7. The thickness of the lower portion of stool side plating is to be not less than 80 per cent of that required for the upper part of the bulkhead plating and is to be of the same steel grade as that of the corrugated bulkhead plating.

8. The thickness of the stool side plating and the section modulus of the stool side stiffeners are to be not less than those required for plane transverse bulkheads and stiffeners with the corresponding ballast and cargo, flooded pressure.

9. Where vertical stiffening is fitted, the ends of stool side stiffeners are to be attached to brackets at the upper and lower end of the stool.

10. Diaphragms are to be fitted inside the stool, in line with, and effectively attached to, longitudinal deck girders extending to the hatch end coaming girders for effective support of the corrugated bulkhead.

11. Scallops in the brackets and diaphragms in way of the connection to the stool shelf plate are to be avoided.

1.6.4 If no bottom stool is fitted, corrugations and floors are to be connected to the inner bottom plating by full penetration welds. The thickness and steel grades of the supporting floors are to be at least equal to those provided for the corrugation flanges. The cut-outs for connections of the inner bottom longitudinals to double bottom floors are to be closed by collar plates. The supporting floors are to be connected to each other by suitably designed shear plates. Stool side plating is to align with the corrugation flanges. Stool side vertical stiffeners and their brackets in the lower stool are to align with the inner bottom longitudinals to provide appropriate load transmission between these stiffening members. The lower stool side plating is not to be knuckled.

1.6.5 The design of local details is to take into account the transfer of the bulkhead forces and moments to the boundary structures and particularly to the double bottom and cross-deck structures.