Section 1 Bulkhead

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 5, 1.4 Vertically 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 5, 1.5 Vertically corrugated transverse watertight bulkheads – scantling assessment 1.5.8 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 5, 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.

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 5, 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 (excluding part loading conditions associated with multi-port loading and unloading),

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

The individual flooding of loaded and empty holds is to be considered, but the pressure used in the assessment is not to be less than that obtained for flood water alone. Holds containing packed cargo are to be treated as empty holds.

1.4.4 The cargo surface is to be taken as horizontal and at a distance d ₁, in metres, from the base line, see Figure 5.1.1 Vertically corrugated transverse watertight bulkheads - Heights and Heads, where d ₁ is calculated taking into account the cargo properties and the hold dimensions. Unless the ship is designed to carry only cargo of bulk density greater than or equal to 1,78 tonne/m³ in non-homogeneous loading 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 centreline. A permeability, μ, of 0,3 and angle of repose, ψ, of 35° is to be assumed for this application.

Figure 5.1.1 Vertically corrugated transverse watertight bulkheads - Heights and Heads

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 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.

1.4.6 The permeability, μ, may be taken as 0,3 for ore, coal and cement cargoes. The bulk density and angle of repose,ψ, may generally be taken as 3,0 tonne/m³ and 35°respectively for iron ore and 1,3 tonne/m³ and 25° respectively for cement.

1.4.7 The flooding head, h_f, see Figure 5.1.1 Vertically corrugated transverse watertight bulkheads - Heights and Heads, is the distance, in metres, measured vertically with the ship in the upright position, from the location P, under consideration, to a position d_f, in metres, from the baseline as given in Table 5.1.1 Flooding head.

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 5.1.2 Corrugated Bulkhead Construction.

Figure 5.1.2 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 plate thickness to be fitted is the net plate thickness plus a corrosion addition of 3,5 mm.

1.5.1 The bending moment M, in kNm (tonne-f m), for the bulkhead corrugations is given by:

M

=

Figure 5.1.3 Scantling assessment

1.5.2 The shear force, Q, in kN (tonne-f) at the lower end of the bulkhead corrugation is given by:

1.5.3 The section modulus of the corrugations is to be calculated using net plate thicknesses. At the lower end, the following requirements apply:

1. An effective width of compression flange, b _ef, not greater than given in Ch 5, 1.5 Vertically corrugated transverse watertight bulkheads – scantling assessment 1.5.7, is to be used.

2. Where corrugation webs are not supported by local brackets below the shelf plate (or below the inner bottom if no lower stool is fitted), they are to be assumed 30 per cent effective in bending. Otherwise, the full area of web plates may be used, see also (e).

3. Where effective shedder plates are fitted, see Figure 5.1.4 Symmetric shedder plates and Figure 5.1.5 Asymmetric shedder plates, the net area of the corrugation flange plates, in cm², may be increased by the lesser of:

   =

   and 2,5b t f

   where

   b	=	width of corrugation flange, in metres, see Figure 5.1.2 Corrugated Bulkhead Construction
   t f	=	net flange plate thickness, in mm
   t sh	=	net shedder plate thickness, in mm

   A shedder plate is considered effective when it:

   • is not knuckled; and
   • is welded to the corrugations and the lower stool shelf plate by one-side penetration welds or equivalent; and
   • has a minimum slope of 45° and lower edges in line with the stool side plating; and
   • has a thickness not less than 0,75 times the thickness of the corrugation flanges; and
   • has material properties at least equal to those of the corrugation flanges.

4. Where effective gusset plates are fitted, see Figure 5.1.6 Symmetric gusset/shedder plates and Figure 5.1.7 Asymmetric gusset/shedder plates the net area of the corrugation flange plates, in cm², may be increased by:

   =

   7h g t f

   where

   h g	=	height of the gusset plate, in metres, but is not to be taken greater than
   t f	=	net flange plate thickness, in mm
   s gu	=	width of the gusset plate, in metres

   A gusset plate is considered effective when it:

   • is fitted in combination with an effective shedder plate as defined in (c); and
   • has height not less than half the flange plate width; and
   • is fitted in line with the stool side plating; and
   • has thickness and material properties at least equal to those of the flanges; and
   • is welded to the top of the lower stool by full penetration welds and to the corrugations and shedder plates by one-side penetration welds or equivalent.

5. Where the corrugation is welded to a sloping stool shelf plate, set at an angle of not less than 45° to the horizontal, the corrugation webs may be taken as fully effective in bending. Where the slope is less than 45°, the effectiveness is to be assessed by linear interpolation between fully effective at 45° and the appropriate value from (b) at 0°. Where effective gusset plates are also fitted, the area of the flange plates may be increased in accordance with (d). No increase is permitted in the case where shedder plates are fitted without gussets.

Figure 5.1.4 Symmetric shedder plates

Figure 5.1.5 Asymmetric shedder plates

Figure 5.1.6 Symmetric gusset/shedder plates

Figure 5.1.7 Asymmetric gusset/shedder plates

1.5.4 The section modulus of corrugations at crosssections other than the lower end is to be calculated with fully effective webs and an effective compression flange width, b _ef not greater than given in Ch 5, 1.5 Vertically corrugated transverse watertight bulkheads – scantling assessment 1.5.7.

1.5.5 The bending capacity of the bulkhead corrugations is to comply with the following relationship:

=

In the above expression Z _le, in cm³, is not to be taken greater than Z’ _le where

Z'le

=

and Z _m is not to exceed the lesser of 1,15Z _le and 1,15Z’_le

1.5.6 The applied shear stress, in N/mm² (kgf/mm²), is determined by dividing the shear force derived from Ch 5, 1.5 Vertically corrugated transverse watertight bulkheads – scantling assessment 1.5.2 by the shear area of the corrugation, calculated using the net plate thickness. The shear area is to be reduced to account for non-perpendicularity between the corrugation webs and flanges. In general, the reduced area may be obtained by multiplying the web sectional area by sin φ, where φ is the angle between the web and the flange, see Figure 5.1.2 Corrugated Bulkhead Construction. The applied shear stress is not to exceed the permissible shear stress or the shear buckling stress given in Table 5.1.4 Permissible shear and buckling stresses.

Table 5.1.4 Permissible shear and buckling stresses

Bending,	Shear,	Shear buckling,
N/mm2 (kgf/mm2)	N/mm2 (kgf/mm2)	N/mm2 (kgf/mm2)
σp = σ0	τp = 0,5σ0	τcr= τ0
Symbols
b = width of corrugation flange, in metres, see Figure 5.1.2 Corrugated Bulkhead Construction c = width of corrugation web, in metres, see Figure 5.1.2 Corrugated Bulkhead Construction t f = net flange plate thickness, in mm t w = web plate net thickness, in mm E = modulus of elasticity = 206 000 N/mm2 (21000 kgf/mm2) σ 0 = specified minimum yield stress, in N/mm2 (kgf/mm2) τ E = 5,706E(t w/1000c)2 N/mm2 (kgf/mm2) τ0 = N/mm2 (kgf/mm2)

1.5.7 The width of the compression flange, in metres, to be used for calculating the effective modulus is:

where

Cef	=	for β>1,25
Cef	=	for β ≤ 1,25
β	=

Other symbols are as defined in Table 5.1.4 Permissible shear and buckling stresses.

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

t

=

1.5.9 For built-up corrugations, where the thickness of the flange and of the web are different, the net thickness of the narrower plating is to be not less than:

tn

=

where

sn	=	width of the narrower plating, in metres. The net thickness, in mm, of the wider plating is not to be taken less than the greater of:
t wp	=	or
t wp	=

where

t np	=	actual net thickness of the narrower plating but not greater than:
	=

1.5.10 The required thickness of plating is the net thickness plus the corrosion addition given in Ch 5, 1.4 Vertically corrugated transverse watertight bulkheads – application and definitions 1.4.10.

1.5.11 Scantlings required to meet the bending and shear strength requirements at the lower end of the bulkhead corrugation are to be maintained for a distance of 0,15l from the lower end, where l is as defined in Ch 5, 1.5 Vertically corrugated transverse watertight bulkheads – scantling assessment 1.5.1. Scantlings required to meet the bending requirements at mid-height are to be maintained to a location no greater than 0,3l from the top of the corrugation. The section modulus of the remaining upper part of the corrugation is to be not less than 0,75 times that required for the middle part, corrected for differences in yield stress.

1.6.1 The requirements of Ch 5, 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 by Ch 1,9 for a plane transverse bulkhead and stiffeners using the greater of the pressures determined from the head, h ₄, in Table 1.9.1 and the expressions given in Table 5.1.2 Bulkhead pressure and force.

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 1.5 times the thickness of the flange plate on each side.

7. The stool bottom is to have a width not less than 2,5 times the mean depth of the corrugation.

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

9. Where corrugations are terminated on the bottom stool, the corrugations and stool plating are to be connected to the stool top plate by full penetration welds. The plating of the stool and the supporting floors are also to be connected to the inner bottom 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 where the same materials is used.

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 by Ch 1,9 for plane transverse bulkheads and stiffeners using the greater of the pressures determined from the head, h ₄, in Table 1.9.1 and the expressions given in Table 5.1.2 Bulkhead pressure and force.

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, the 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.