2 Vertically Corrugated Bulkheads

2.1 Application

2.1.1 In addition to the requirements of Pt 1, Ch 6, Sec 4, [1], vertically corrugated bulkheads of oil tankers are also to comply with the requirements of [2.2].

2.2 Scantling requirements

2.2.1 Net plate thickness over the height

The net plate thicknesses as required by [2.2.3] and [2.2.4] are to be maintained for two thirds of the corrugation length, ℓ_cg from the lower end. Above that, the net plate thickness may be reduced by 20% from the net thickness required in [2.2.3] for the mid part of the corrugation provided that the net section modulus of the upper end of the corrugation complies with [2.2.4].

2.2.2 Net web plating thickness over the height

The net web plating thickness of the lower 15% of the corrugation, t_w in mm, is to be taken as the greatest value calculated for all applicable design load sets, as given in Pt 1, Ch 6, Sec 2, [2], and given by the following. This requirement is not applicable to corrugated bulkheads without a lower stool.

where:

P_l : Design pressure given in Pt 1, Ch 6, Sec 2, Table 1 for the design load set being considered, calculated at the lower end of the corrugation, in kN/m².

P_u : Design pressures given in Pt 1, Ch 6, Sec 2, Table 1 for the design load set being considered, calculated at the upper end of the corrugation, in kN/m².

d_cg : Depth of corrugation, in mm, see Figure 4.

2.2.3 Net thicknesses of the flanges over the height

The net thicknesses of the flanges of corrugated bulkheads, t_f in mm, for two thirds of the corrugation length from the lower end are to be taken as the greatest value calculated for all applicable design load sets, as given in Pt 1, Ch 6, Sec 2, [2], and given by the following. This requirement is not applicable to corrugated bulkheads without a lower stool.

where:

σ_bdg-max : Maximum value of the vertical bending stresses in N/mm² in the flange. The bending stress is to be calculated at the lower end and at the mid span of the corrugation length.

M_cg : Vertical bending moment, in kNm, as defined in [2.2.4].

Z_cg-act : Actual net section modulus at the lower end and at the mid length of the corrugation, in cm³.

b_f-cg : Breadth of flange plating, in mm. See Figure 4.

b_w-cg : Breadth of web plating, in mm. See Figure 4.

2.2.4 Net section modulus over the height

The net section modulus at the lower and upper ends and at the mid length of the corrugation (ℓ_cg / 2) of a unit corrugation, Z_cg are to be taken as the greatest value calculated for all applicable design load sets, as given in Pt 1, Ch 6, Sec 2, [2] and given by the following.

where:

M_cg : Vertical bending moment in kNm.

P : Averaged pressure in kN/m².

P_l, P_u : Design pressure given in Pt 1, Ch 6, Sec 2, Table 1 for the design load set being considered, calculated at the lower and upper ends of the corrugation, respectively, in kN/m²:

• For transverse corrugated bulkheads, the pressures are to be calculated at a section located at b_tk / 2 from the longitudinal bulkheads of each tank.
• For longitudinal corrugated bulkheads, the pressures are to be calculated at the ends of the tank, i.e. the intersection of the forward and aft transverse bulkheads and the longitudinal bulkhead.

b_tk : Maximum breadth of tank under consideration measured at the bulkhead, in m.

ℓ_o : Effective bending span of the corrugation, in m, measured from the mid depth of the lower stool to the mid depth of the upper stool. Where no lower or upper stool is fitted, ℓ_o is to be measured to lower or upper end. See Figure 4.

C_i : Bending moment coefficient given in Table 7.

C_s-cg = c_e but not to be taken as greater than 0.90 for acceptance criteria set AC-SD.

At the lower and upper ends of the corrugation length, ℓ_cg:

C_s-cg = 0.75 for acceptance criteria set AC-S.

C_s-cg = 0.90 for acceptance criteria set AC-SD.

c_e : Coefficient taken as:

for β ≥ 1.25

c_e = 1.0 for β < 1.25

β : Coefficient taken as:

b_f-cg : Breadth of flange plating, in mm, see Figure 4.

t_f : Net thickness of the corrugation flange, in mm.

where:

A_bt : Cross sectional area enclosed by the moulded lines of the transverse bulkhead lower stool, in m².

A_bl : Cross sectional area enclosed by the moulded lines of the longitudinal bulkhead lower stool, in m².

b_av-t : Average width of transverse bulkhead lower stool, in m. See Figure 4.

b_av-l : Average width of longitudinal bulkhead lower stool, in m. See Figure 4.

h_st : Height of transverse bulkhead lower stool, in m. See Figure 4.

h_sl : Height of longitudinal bulkhead lower stool, in m. See Figure 4.

b_ib : Breadth of cargo tank at the inner bottom level between hopper tanks, or between the hopper tank and centreline lower stool, in m. See Figure 4.

b_dk : Breadth of cargo tank at the deck level between upper wing tanks, or between the upper wing tank and centreline deck box or between the corrugation flanges if no upper stool is fitted, in m. See Figure 4.

ℓ_ib : Length of cargo tank at the inner bottom level between transverse lower stools, in m. See Figure 4.

ℓ_dk : Length of cargo tank at the deck level between transverse upper stools or between the corrugation flanges if no upper stool is fitted, in m. See Figure 4.

Figure 4 : Definition of parameters for corrugated bulkhead (Tankers with longitudinal bulkhead at centreline)