Section 11 Direct calculation procedures

11.1 General

11.1.1 This Section contains guidance for direct calculations, information regarding 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 modulus.

11.1.2 Direct calculations are to be carried out as required by the Rules and may be used as an alternative to derrive scantlings instead of Rule formulae, or for the assessment of scantlings of structural members not covered by the Rules.

11.1.3 Where direct calculation is carried out, calculation results are to be submitted together with all data in support of the calculation e.g. support conditions and details of loads.

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 5.11.1 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 Pt 4, Ch 5, 11.2 Permissible stresses 11.2.1.

Table 5.11.1 Maximum permissible stresses in longitudinal continuous members, in N/mm²

Item	Local bending stress, σ_b, See Note 1	Combined bending stress, 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
Deck girders
Bottom longitudinals
Inner bottom longitudinals	0,58σ_L	0,75σ_L	0,35σ_L	0,80σ_L
Deck and trunk deck longitudinals
Side shell longitudinals
Where σ_L = 235/k_L Note 1. The combined stress, σ_c, is 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 5.11.2 Maximum permissible stresses in local members, in N/mm²

Item	Local bending stress, σb	Shear stress, τ	Equivalent stress, σe See Note 1
Non-continuous bottom girders, side stringers, see Note 2, deck beams, deck transverses and non-continuous deck girders	0,53σ_o	0,35σ_o	0,75σ_o
Floors, bottom transverses and bottom structure supporting tanks	0,50σ_o	0,35σ_o	0,73σ_o
Side frames	0,48σ_o	0,35σ_o	0,73σ_o
Webs supporting side stringers and side transverses, see Note 2	0,44σ_o	0,35σ_o	0,71σ_o
Note 1. The equivalent stress, σ_e, is to be calculated according to the formula: Note 2. The scantlings of stringers, or web frames fitted to comply with the requirements of Pt 4, Ch 5, 1.2 Ship arrangement 1.2.4 are not to be determined by direct calculation but are to be in accordance with Pt 4, Ch 5, 8.4 Reinforcement of single skin side shell.

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 5, 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, seePt 3, Ch 5, 2 Hull envelope plating.
The thickness of the bilge plating amidships is to be 2 mm greater than the bottom plating, in way.
The minimum thickness of the deck plating is to be not less than the thickness of deck plating at ends, seePt 3, Ch 5, 5.2 Deck stiffening.
Depending on the level of compressive stresses, additional buckling calculations may be required.