Section 7 Direct calculation procedures
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Inland Waterways Ships, July 2022 - Part 4 Ship Structures (Ship Types) - Chapter 2 Ferries and Roll on-Roll off Ships - Section 7 Direct calculation procedures

Section 7 Direct calculation procedures

Parent topic: Chapter 2 Ferries and Roll on-Roll off Ships

7.1 General

7.1.1 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 section modulus.

7.1.2 Where direct calculation is adopted as an alternative to scantlings derived by Rule formulæ, 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.

7.2 Permissible stresses

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

  1. 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 2.7.1 Maximum permissible stresses in longitudinal continuous members, in N/mm2 .

  2. 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 2.7.2 Maximum permissible stresses in local members, in N/mm2 .

Table 2.7.1 Maximum permissible stresses in longitudinal continuous members, in N/mm2

Item Local bending stress
,

σb

Combined bending stress, σc,
see Note 1 		Shear stress,
τ 		Equivalent stress, σe,
see Note 2
Bottom girders 0,46σL 0,75σL 0,35σL 0,80σL
Deck girders
Bottom longitudinals 0,58σL 0,75σL 0,35σL 0,80σL
Inner bottom longitudinals
Deck longitudinals
Side shell longitudinals

where σL = kL

Note 1. The combined stress σc is the sum of the stresses due to longitudinal bending and local loading.

Note 2. The equivalent stress σe is to be calculated according to the formula

Table 2.7.2 Maximum permissible stresses in local members, in N/mm2

Item Bending stress, σb Shear stress,τ Equivalent stress, σe, see Note
Floors, non-continuous bottom girders, non-continuous deck girders, deck transverses, 0,53σO 0,35σO 0,75σO
Web frames 0,42σO 0,35σO 0,69σO
Frames, bottom transverse 0,48σO 0,35σO 0,73σO
Deck beams 0,58σO 0,35σO 0,79σO

Note The equivalent stress σe is to be calculated according to the formula

7.3 Structural requirements

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

7.3.2 In addition to the maximum permissible stresses given in Pt 4, Ch 2, 7.2 Permissible stresses, the following minimum plating thickness requirements are to be complied with:

  1. 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.

  2. The thickness of bilge plating amidships is to be 2 mm more than the bottom plating in way.

  3. The minimum thickness of the deck plating is to be not less than the thickness of deck plating at ends, see Pt 3, Ch 5, 2 Hull envelope plating.

  4. Depending on the level of compressive stresses, additional buckling calculations may be required.

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