Section 1 General
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Naval Ships, January 2023 - Volume 1 Ship Structures - Part 6 Hull Construction in Steel - Chapter 2 Design Tools - Section 1 General

Section 1 General

Parent topic: Chapter 2 Design Tools

1.1 General

1.1.1 The guidance notes, information and formulae contained within this chapter are to be used in the scantling determination (Vol 1, Pt 6, Ch 3 Scantling Determination) and total load assessment.

1.2 Equivalents

1.2.1 Clasifications Register (hereinafter referred to as 'LR') will consider direct calculations for the derivation of scantlings as an alternative and equivalent to those derived by Rule requirements in accordance with Vol 1, Pt 3, Ch 1, 3 Equivalents

1.3 Symbols and definitions

1.3.1 The symbols used in this Chapter are defined below and in the appropriate Section:

Z = section modulus of stiffening member, in cm3
= moment of inertia, in cm4
A w = shear area of stiffener web, in cm2
= overall length of stiffener or primary member, in metres
e = effective span length, in metres, as defined in Vol 1, Pt 6, Ch 2, 2.6 Determination of span length
p = design pressure, in kN/m2
s = secondary stiffener spacing, in mm
S = primary stiffener spacing, in metres
t p = plating thickness, in mm
β = panel aspect ratio correction factor as defined in Vol 1, Pt 6, Ch 2, 2.5 Aspect ratio correction
γ = convex curvature correction factor as defined in Vol 1, Pt 6, Ch 2, 2.4 Convex curvature correction
k s = higher tensile steel factor for local loads, see Vol 1, Pt 6, Ch 5, 2.1 Design criteria 2.1.1
k L = higher tensile steel factor for global loads, see Vol 1, Pt 6, Ch 5, 2.1 Design criteria 2.1.2
σ o = guaranteed minimum yield strength of the material, in N/mm2
τ o = shear strength of the material in N/mm2
=
E = modulus of elasticity, in N/mm2.

1.4 Rounding policy for Rule plating thickness

1.4.1 Where plating thicknesses as determined by the Rules require to be rounded then this should be carried out to the nearest full or half millimetre, with thicknesses 0,75 and 0,25 being rounded up.

1.5 Material properties

1.5.1 The basic grade of steel used in the determination of the Rule scantling requirements is taken as mild steel with the following mechanical properties:

  1. Yield strength (minimum) σ o = 235 N/mm2

  2. Tensile strength = 400–490 N/mm2

  3. Modulus of elasticity, E = 200 x 103 N/mm2.

1.6 Higher tensile steel

1.6.1 Steels having a yield stress not less than 265 N/mm2 are regarded as higher tensile steels.

1.6.2 Where higher tensile steels are to be used, due allowance is given in the determination of the Rule requirement for plating thickness, stiffener section modulus, inertia and cross-sectional area by the use of higher tensile steel correction factors k s and k L or f hts. Normally, this allowance is included in the appropriate scantling requirements. Where this is not the case, the following correction factors may be applied:

(a) Plating thickness factor = for local loads

= for global loads

(b) Section modulus and cross sectional area factor = k s

where k s and k L are defined in Vol 1, Pt 6, Ch 2, 1.3 Symbols and definitions 1.3.1

f hts is defined in Vol 1, Pt 6, Ch 5, 1.3 Higher tensile steel

1.6.3 Higher tensile steel may be used for both deck and bottom structures or deck structure only. Where fitted for global strength purposes, it is to be used for the whole of the longitudinal continuous material for the following vertical distances:

  1. z htd below the line of deck at side

  2. z htb above the top of keel

In the above formulae F D and F B are to be taken not less than k L

where

  1. F D and F B are defined in Ch 3,3.6. Note the F D and F B factors derived inVol 1, Pt 6, Ch 3, 3.6 Local reduction factors for NS1 ships may also be applied to ship types NS2 and NS3.

  2. z D and z B are the vertical distances, in m, from the transverse neutral axis of the hull cross-section to the uppermost continuous longitudinally effective material and to the top of the keel respectively.

k L is defined in Vol 1, Pt 6, Ch 2, 1.3 Symbols and definitions 1.3.1.

1.6.4 The designer should note that there is no increase in fatigue performance with the use of higher tensile steels.

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