Section 2 Re-assessment of vertically corrugated transverse watertight bulkheads

2.1.1 Requirements for application of this procedure are given in Ch 2, 1.1 Application.

2.1.2 In the context of this Section, a homogeneous loading condition is defined as one where the ratio between the highest and the lowest filling levels, d ₁, in adjacent holds (see Figure 2.2.1 Loading) 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 2.2.1 Loading

2.1.3 The term net plate thickness is used to describe the required minimum thickness of the web plating, t _w, and flange plating, t _f, to which corrosion additions (see Ch 2, 2.4 Retrospective action) are added.

2.2.1 The most severe combinations of cargo induced loads and flooding loads are to be used to re-assess the scantlings of the transverse watertight bulkhead between cargo holds 1 and 2 or, where selected by the Shipowner, all cargo hold transverse watertight bulkheads. Both homogeneous and non-homogeneous conditions are to be included but part-loading conditions associated with multiport loading are not required to be considered.

2.2.2 The flooding head, h _f, (see Ch 2, 2.2 Loading 2.2.1) is the distance, in metres, measured vertically with the ship in the upright position, from the location under consideration to a position, d _f, in metres, from the baseline given by:

1. In general:

   1. d f

      =

      D for the bulkhead between holds 1 and 2

   2. d f

      =

      0,9D for the other bulkheads

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

   1. d f

      =

      0,95D for the bulkhead between holds 1 and 2

   2. d f

      =

      0,85D for the other bulkheads

For ships having an assigned maximum draught, T _r, less than the permissible load line draught, T, the flooding heads in (a) and (b) above may be reduced by T - T _r.

2.2.3 The cargo surface is assumed to be horizontal and at a distance, d ₁, in metres, from the baseline (see Figure 2.2.1 Loading) given by:

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

Figure 2.2.2 Scantling assessment

Figure 2.2.3 Scantling assessment

Table 2.2.1 Bulkhead pressure and force

Pressure, kN/m2 (tonne-f/m2)		Force, kN (tonne-f)
(1) In non-flooded bulk cargo holds
(2) In flooded bulk cargo holds,when df ≥ d1
(a) For positions between d1 and df from baseline
(b) For positions at a distance lower than d1 from baseline
(3) In flooded bulk cargo holds, when df < d1
(a) For positions between d1 and df from baseline
(b) For positions at a distance lower than df from baseline
(4) In flooded empty holds
Symbols
g = gravitational constant, 9,81 m/sec2 h f = flooding head, see Ch 2, 2.2 Loading 2.2.2 h LS = height of lower stool, in metres h 1 = vertical distance, in metres, from the calculation point to the top of the cargo, see Figure 2.2.1 Loading p c, p cf, p f = pressure on the bulkhead at the point under consideration, in kN/m2 (tonne-f/m2) p le = pressure at bottom of the corrugation, in kN/m2 (tonne-f/m2) s 1 = spacing of the corrugations, in metres, see Figure 2.2.2 Scantling assessment ρ = density of sea water = 1,025 tonne/m3 ρc = bulk cargo density, in tonne/m3 θ = 45° - (ψ/2) ψ = angle of repose of the cargo, in degrees, see Note μ = permeability of cargo, see Note
Note The permeability of ore and coal may be taken as 0,3 and the corresponding angle of repose as 35°.

Table 2.2.2 Resultant pressure and force

Loading conditions	Resultant pressure kN/m2 (tonne-f/m2)	Resultant force kN (tonne-f)
Homogeneous
Non-homogeneous See Note 1
Note 1. Where loading in a non-homogeneous condition is not permitted, the resultant pressure and force are to be obtained from p r = p f and F = F f Note 2. For symbols, see Table 2.2.1 Bulkhead pressure and force.

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

where F is defined in Ch 2, 2.3 Scantling assessment 2.3.1.

2.3.3 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 2, 2.3 Scantling assessment 2.3.7, 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 Ch 2, 2.3 Scantling assessment 2.3.3).

3. Where effective shedder plates are fitted (see Figure 2.2.4 Symmetric shedder plates and Figure 2.2.5 Asymmetric shedder plates), the net area of the corrugation flange plates, in cm², may be increased by the lesser of:

   
   where

   b	=	width of corrugation flange, in metres (see Figure 2.2.2 Scantling assessment)
   t f	=	net flange plate thickness, in mm
   t sh	=	net shedder plate thickness, in mm
   σ0fl	=	specified minimum yield stress of flange material, in N/mm2
   σ0sh	=	specified minimum yield stress of shedder material, in N/mm2

   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.

4. Where effective gusset plates are fitted (see Figure 2.2.6 Symmetric gusset/shedder plates and Figure 2.2.7 Asymmetric gusset/shedder plates) the net area of the corrugation flange plates, in cm², may be increased by:

   
   where

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

   A gusset plate is considered effective when it:

   • is fitted in line with the stool side plating; and
   • has material properties at least equal to those of the flanges.

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, (see Figure 2.2.7 Asymmetric gusset/shedder plates). Where the slope is less than 45°, the effectiveness is to be assessed by interpolating linearly 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 2.2.4 Symmetric shedder plates

Figure 2.2.5 Asymmetric shedder plates

Figure 2.2.6 Symmetric gusset/shedder plates

Figure 2.2.7 Asymmetric gusset/shedder plates

2.3.4 The section modulus of corrugations at cross-sections 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 2, 2.3 Scantling assessment 2.3.7.

2.3.5 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'_l1e where

and Z _m is not to exceed the lesser of 1,15Z _l1e and 1,15Z'_l1e

2.3.6 The applied shear stress, in N/mm² (kgf/mm²), is determined by dividing the shear force derived from Ch 2, 2.3 Scantling assessment 2.3.2 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 2.2.2 Scantling assessment). The applied shear stress is not to exceed the permissible shear stress or the shear buckling stress given in Table 2.2.3 Permissible shear and buckling stresses.

Table 2.2.3 Permissible shear and buckling stresses

Bending, N/mm2 (kgf/mm2)	Shear, N/mm2 (kgf/mm2)	Shear buckling, N/mm2 (kgf/mm2)
Symbols
b = width of corrugation flange, in metres, see Figure 2.2.2 Scantling assessment c = width of corrugation web, in metres, see Figure 2.2.2 Scantling assessment 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) σ0 = specified minimum yield stress, in N/mm2 (kgf/mm2) τE = 5,706 E (t w/1000c)2 N/mm2 (kgf/mm2) τ0 = N/mm2 (kgf/mm2)

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

where

	=
	=
	=
	=	Other symbols are as defined in Table 2.2.3 Permissible shear and buckling stresses

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

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

The net thickness, in mm, of the wider plating is not to be taken less than the greater of:

where

• t _np ≤ actual net thickness of the narrower plating but not greater than:
• 

2.4.1 Steel renewal will generally be required when the gauged thickness is less than:

where t _net is the minimum net thickness required to satisfy the bending, shear and local pressure checks given in Ch 2, 2.3 Scantling assessment. Alternatively, reinforcing doubling strips may be used, provided that the net thickness is not governed by shear strength requirements for web plates or by local pressure requirements for web or flange plates.

2.4.2 Where the gauged thickness is within the range (t _net + 0,5 mm) to (t _net + 1,0 mm), coating or annual gauging is acceptable as an alternative to steel renewal.

2.4.3 Where steel renewal is undertaken, a minimum renewed thickness of (t _net + 2,5 mm) is to be provided.

2.4.4 Scantlings required to meet the bending and shear strength requirements of Ch 2, 2.3 Scantling assessment at the lower end of the bulkhead are to be maintained for a distance of 0,15l from the lower end, where l is as defined in Ch 2, 2.3 Scantling assessment 2.3.1. Scantlings required to meet the bending requirements of Ch 2, 2.3 Scantling assessment at mid-height are to be maintained to a location no greater than 0,3l from the top of the corrugation.

2.4.5 Where the corrugation angle φ (see Figure 2.2.2 Scantling assessment) is less than 50°, a row of staggered shedder plates is to be fitted at approximately mid-span to preserve dimensional stability. The shedder plates are to be connected to the corrugations by double continuous welding. No connection is to be provided to the side shell.

2.4.6 Gussets with shedder plates, extending from the lower end of the corrugations to 0,1⋉ 1above the lower end, or reinforcing doubling strips fitted to the bulkhead corrugations and stool side plating are to be provided, if:

2.4.7 Gusset plates are to be of the same material as the corrugation flanges and are to be connected to the corrugations and lower stool shelf plate (or inner bottom if no lower stool is fitted) by deep penetration welds, see Figure 2.2.8 Welding.

Figure 2.2.8 Welding

2.4.8 The connection between renewed plating and the lower stool shelf plate (or inner bottom if no lower stool is fitted) is also to be deep penetration welded.

2.4.9 As an alternative to steel renewal or reinforcement, deadweight restrictions may be adopted in order to achieve compliance with Ch 2, 2.3 Scantling assessment. Where deadweight restrictions are introduced, the Loading Manual will require modification and approval. In addition, and in accordance with SOLAS Chapter XII, Regulation 8 - Information on compliance with requirements for bulk carriers, the sideshell amidships is to be permanently marked, both port and starboard, with a solid equilateral triangle having sides of 500 mm and its apex 300 mm below the deck line. The triangle is to be painted in a colour contrasting to that of the hull.