2 Hull Girder Bending Assessment

2.1 General

2.1.1 Scantlings of all continuous longitudinal members of the hull girder based on moment of inertia and section modulus requirement in [2.3] are to be maintained within 0.4 L amidships.

2.1.2 The k material factors are to be defined with respect to the materials used for the bottom and deck members contributing to the longitudinal strength according to [1]. When material factors for higher strength steels are used, the requirements in [2.4] apply.

2.2 Normal stresses

2.2.1 The normal stress, σ_L induced by vertical bending moments, is to be assessed for both hogging and sagging conditions, along the full length of the hull girder, from AE to FE.

The normal stress, σ_L at any point of the hull transverse section located below z_VD is to comply with the following formula:

σ_L ≤ σ_perm

where:

σ_L : Normal stress, in N/mm², as defined in [2.2.2].

σ_perm : Permissible hull girder bending stress, in N/mm², as given in Table 1.

2.2.2 The normal stresses, σ_L in N/mm², induced by vertical bending moments are given in Table 2:

2.2.3 The normal stresses in a member made in material other than steel with a Young’s modulus, E equal to 2.06 × 10⁵ N/mm², included in the hull girder transverse sections as specified in [1.2.8], are obtained from the following formula:

where:

σ_LS : Normal stress, in N/mm², in the member under consideration, calculated according to [2.2.2] considering this member as having the steel equivalent sectional area A_SE defined in [1.2.8].

2.3 Minimum net moment of inertia and net section modulus at midship section

2.3.1 At the transverse section in the midship part, the net moment of inertia about the horizontal axis, I_y-n50 is to be not less than the value obtained, in m⁴, from the following formula:

I_yR = 2.7 C_w L³ B (C_B + 0.7) 10^–8

2.3.2 At the transverse section in the midship part, the vertical hull girder net section modulus at the deck and the bottom, Z_D-n50 and Z_B-n50, are not to be less than the value obtained, in m³, from the following formula:

Z_R = 0.9k C_w L² B (C_B + 0.7) 10^–6

2.4 Extent of high tensile steel

2.4.1 Vertical extent

The vertical extent of higher strength steel, z_hts,i, in m, used in the deck zone or bottom zone and measured respectively from the moulded deck line at side or baseline is not to be taken less the value obtained from the following formula, see Figure 3:

where:

z₁ : Distance from horizontal neutral axis to moulded deck line or baseline respectively, in m.

σ_perm,i : Permissible hull girder bending stress of the considered steel, in N/mm², as given in Table 1 and Figure 3.

σ_L : Hull girder bending stress, σ_dk at moulded deck line or σ_bl at baseline respectively, in N/mm² given in Table 3.

Figure 3 : Vertical extent of higher strength steel

2.4.2 Longitudinal extent

Where used, the application of higher strength steel is to be continuous over the length of the ship to the location where the longitudinal stress levels are within the allowable range for mild steel structure, as shown in Figure 4.

Figure 4 : Longitudinal extent of higher strength steel