4 Allowable Hold Loading for BC-A & BC-B Ships in Flooded Conditions

4.1 Evaluation of double bottom capacity and allowable hold loading

4.1.1 Shear capacity of the double bottom

The shear capacity of the double bottom is to be calculated as the sum of the shear strength at each end of:

• Floors connected to hopper tanks, less one half of the shear strength of the two floors adjacent to each stool, or transverse bulkhead if no stool is fitted as shown in Figure 7. The shear strength of floors is to be calculated according to [4.1.2].
• Double bottom girders connected to stools, or transverse bulkheads if no stool is fitted. The shear strength of girders is to be calculated according to [4.1.3].

The floors and girders to be considered when calculating the shear capacity of the double bottom are those inside the hold boundaries formed by the hopper tanks and stools or transverse bulkheads if no stool is fitted. Where both ends of girders or floors are not directly connected to the hold boundaries, their strength is to be evaluated for the connected end only.

The hopper tank side girders and the floors directly below the connection of the stools or transverse bulkheads if no stool is fitted to the inner bottom may not be included.

For special double bottom designs, the shear capacity of the double bottom is to be calculated by means of direct calculations carried out in accordance with requirements specified in Pt 1, Ch 7, as applicable.

4.1.2 Floor shear strength

The floor shear strength, in kN, is to be taken as given in the following formulae:

• In way of the floor panel adjacent to the hopper tank:

  

• In way of the openings in the outermost bay (i.e., that bay which is closer to the hopper tank):

  

where:

A_f : Net sectional area, in mm², of the floor panel adjacent to the hopper tank.

A_f,h : Net sectional area, in mm², of the floor panels in way of the openings in the outermost bay (i.e. the bay which is closer to the hopper tank).

τ_A : Allowable shear stress, in N/mm², to be taken as the lesser of:

and

For floors adjacent to the stools or transverse bulkheads, τ_A is taken as:

t : Floor web net thickness, in mm.

s : Spacing, in m, of stiffening members of the panel considered.

η₁ : Coefficient to be taken equal to 1.1.

η₂ : Coefficient to be taken equal to 1.2. It may be reduced to 1.1 where appropriate reinforcements are fitted in way of the openings in the outermost bay, to be examined by the Society on a case-by-case basis.

4.1.3 Girder shear strength

The girder shear strength, in kN, is to be taken as given in the following formulae:

• In way of the girder panel adjacent to the stool or transverse bulkhead, if no stool is fitted:

  

• In way of the largest opening in the outermost bay (i.e. that bay which is closer to the stool) or transverse bulk-head, if no stool is fitted:

  

A_g : Net sectional area, in mm², of the girder panel adjacent to the stool (or transverse bulkhead, if no

stool is fitted).

A_g,h : Net sectional area, in mm², of the girder panel in way of the largest opening in the outermost bay (i.e.that bay which is closer to the stool) or transverse bulkhead, if no stool is fitted.

τ_A : Allowable shear stress, in N/mm², as defined in [4.1.2] where t_N is the girder web net thickness.

η₁ : Coefficient to be taken equal to 1.1.

η₂ : Coefficient to be taken equal to 1.15. It may be reduced to 1.1 where appropriate reinforcements are fitted in way of the largest opening in the outermost bay, to be examined by the Society on a case-by-case basis.

4.1.4 Allowable hold loading

The allowable hold loading, in t, is to be taken as:

where:

ρ_C : Density of the dry bulk cargo, in t/m³, as defined Pt 1, Ch 4, Sec 6, [2.3.3].

ρ_st : Density of steel, in t/m³, to be taken as 7.8.

V : Volume, in m³, occupied by the cargo up to the level h_B.

h_B : Level of cargo, in m, to be taken as:

P : Pressure, in kN/m², to be taken as:

• For dry bulk cargoes, the lesser of:

  

  P = Z + ρg (z_F – 0.1 D₁ – h_F perm)

• For steel mill products:

  

D₁ : Distance, in m, from the baseline to the freeboard deck at side amidships.

h_F : Inner bottom flooded height, in m, measured vertically with the ship in the upright position, from the inner bottom to the flooded level z_F.

z_F : Flooded level, in m, as defined in Pt 1, Ch 4, Sec 6, [3.1.3].

perm : Permeability of cargo, which need not be taken greater than 0.3.

Z : Pressure, in kN/m², to be taken as the lesser of:

C_H : Shear capacity of the double bottom, in kN, to be calculated according to [4.1.1], considering, for each floor, the lesser of the shear strengths S_f1 and S_f2 as defined in [4.1.2] and, for each girder, the lesser of the shear strengths S_g1 and S_g2 as defined in [4.1.3].

A_DB,H : Area, in m², taken as:

C_E : Shear capacity of the double bottom, in kN, to be calculated according to [4.1.1], considering, for each floor, the shear strength S_f1 as defined in [4.1.2] and, for each girder, the lesser of the shear strengths S_g1 and S_g2 as defined in [4.1.3].

(B_DB-S)

n : Number of floors between stools or transverse bulkheads, if no stool is fitted.

S_i : Space of i-th floor, in m.

B_DB : Breadth, in m, of double bottom between the hopper tanks as shown in Figure 8.

B_DB,h : Distance, in m, between the two openings considered as shown in Figure 8.

s : Spacing, in m, of inner bottom longitudinal ordinary stiffeners adjacent to the hopper tanks.

Figure 7 : Double bottom structure

Figure 8 : Dimensions B_DB and B_DB,h