Section 11 Direct calculation procedures

11.1 General

11.1.1 This Section contains guidance for direct calculations, information concerning maximum permissible stresses and minimum requirements for structural members included in the hull midship section modulus and for other structural members which do not form part of the hull midship section modulus.

11.1.2 Where direct calculation is adopted as an alternative to scantlings derived by Rule formulae, or for the assessment of scantlings of structural members not covered by the Rules, all data in support of the calculation, i.e. support conditions and loads, are to be submitted for approval together with the calculation.

11.2 Permissible stresses

11.2.1 In addition to the permissible stresses given in Pt 3, Ch 4, 6 Hull bending strength the following stress criteria are to be applied:

For structural members included in the hull section modulus the maximum bending stresses, shear stresses and equivalent stresses are not to exceed the values given in Table 9.11.1 Maximum permissible stresses in longitudinal continuous members, in N/mm².
For structural members not included in the hull section modulus the maximum bending stresses, shear stresses and equivalent stresses are not to exceed the values given in Table 9.11.2 Maximum permissible stresses in local members, in N/mm².

Table 9.11.1 Maximum permissible stresses in longitudinal continuous members, in N/mm²

Item	Local bending stress, σ_b	Combined bending, σ_c See Note 1	Shear stress, τ	Equivalent stress, σ_e See Note 2
Bottom girders	0,46σ_L	0,75σ_L	0,35σ_L	0,80σ_L
Bottom longitudinals	0,58σ_L	0,75σ_L	0,35σ_L	0,80σ_L
Inner bottom longitudinals
Side shell longitudinals
Symbols
Where σ_L = 235/k_L Note 1. The combined stress σ_cis the sum of the stresses due to longitudinal bending and local loading. Note 2. The equivalent stress σ_e is to be calculated according to the formula

Table 9.11.2 Maximum permissible stresses in local members, in N/mm²

Item	Bending stress, σ_b	Shear stress, τ	Equivalent stress, σ_e See Note
Floors, non-continuous girders, bottom and deck, deck transverses, bottom transverses	0,53σ_o	0,35σ_o	0,75σ_o
Frames	0,48σ_o	0,35σ_o	0,73σ_o
Deck beams	0,58σ_o	0,35σ_o	0,79σ_o
Note The equivalent stress σ_e is to be calculated according to the formula

11.3 Structural requirements

11.3.1 As a first approximation the structural components may be determined according to the requirements of the preceding Sections of this Chapter.

11.3.2 In addition to the maximum permissible stresses given in Pt 4, Ch 9, 11.2 Permissible stresses the following minimum plating thickness requirements are to be complied with:

The thickness of bottom plating and side shell plating amidships is to be not less than the thickness of shell plating at ends, see Pt 3, Ch 5, 2 Hull envelope plating.
The thickness of the bilge plating amidships is to be 2 mm more than the bottom plating in way.
The minimum thickness of the deck plating is to be not less than required by Table 5.2.2 Deck plating forward and aft(1) in Pt 3, Ch 5.
Depending on the level of compressive stresses, additional buckling calculations may be required.