Section 12 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 6 Tankers of Types C and N - Section 12 Direct calculation procedures

Section 12 Direct calculation procedures

Parent topic: Chapter 6 Tankers of Types C and N

12.1 General

12.1.1 This Section contains guidance for direct calculation, 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.

12.1.2 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, calculation results are to be submitted for approval together with all data in support of the calculation, i.e. support conditions and applied loads.

12.2 Loads

12.2.1 Load heads to be used in direct calculations to determine the required section moduli of structural members listed in Table 6.12.1 Maximum permissible stresses in longitudinal continuous members, in N/mm² and Table 6.12.2 Maximum permissible stresses in local members, in N/mm2, are to be in accordance with Pt 4, Ch 6, 4 Hull envelope framing – Transversely framed ships to Pt 4, Ch 6, 8 Construction of tankers with cargo tanks independent from the ship’s structure, as applicable.

Table 6.12.1 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 and deck girders in transversely framed ships

0,46σL

 0,75σL 0,35σL 0,80σL
Bottom, deck and side longitudinals 0,58σL 0,75σL 0,35σL 0,80σL
Symbols

Where σL = 235/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 6.12.2 Maximum permissible stresses in local members, in N/mm2

Item Bending stress,
σb
Shear stress,
τ 		Equivalent stress,
σe
See Note
Floors, bottom transverses, non-continuous bottom girders, side stringers, deck beams, deck transverses and non-continuous deck girders 0,53σo 0,35σo 0,75σo
Side frames 0,48σo 0,35σo 0,73σo
Webs supporting side stringers, side transverses 0,43σo 0,35σo 0,71σo

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

12.3 Permissible stresses

12.3.1 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 6.12.1 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 6.12.2 Maximum permissible stresses in local members, in N/mm2.

12.3.2 Where finite plate element calculations are carried out, local peak stresses in excess to those given in Pt 4, Ch 6, 12.3 Permissible stresses 12.3.1will be specially considered.

12.4 Structural requirements

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

12.4.2 In addition to the maximum permissible stresses given in Pt 4, Ch 6, 12.3 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 the bilge plating amidships is to be 2 mm more than the bottom plating in way.

  3. The 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, nor less than the minimum compartment thickness, see Pt 4, Ch 6, 1.10 Compartment minimum thickness. Depending on the level of compressive stresses and panel dimensions, additional buckling calculations may be required.

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