Section 2 Minimum structural requirements
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules for the Classification of Trimarans, July 2022 - Volume 1 Regulations and Structural Arrangements - Part 6 Scantling Determination - Chapter 4 Local Scantling Requirements - Section 2 Minimum structural requirements

Section 2 Minimum structural requirements

Parent topic: Chapter 4 Local Scantling Requirements

2.1 General

2.1.1 This Section gives the basic principles to be adopted in determining the Rule structural requirements.

2.1.2 The equations given in this Section are to be used to determine the scantling requirements for shell envelope, wet-deck, weather deck and inner bottom, see Vol 1, Pt 6, Ch 4, 4 Wet-deck.

2.1.3 The remaining scantlings not listed in Vol 1, Pt 6, Ch 4, 2.1 General 2.1.2 and Vol 1, Pt 6, Ch 4, 2.1 General 2.1.3 are to be determined directly from the Complementary Rules as defined in Vol 1, Pt 6, Ch 4, 7 Internal decks.

2.2 Plate thickness

2.2.1 The requirements for the thickness of plating, t p, is in general to be in accordance with the following:

where
= f σ is defined in Table 4.2.3 Acceptance criteria
= s, f curv, f ar, P des and σyd are defined in Vol 1, Pt 6, Ch 1, 1.3 Symbols and definitions 1.3.1.

2.3 Stiffener properties

2.3.1  Primary stiffening members. The requirements for section modulus, inertia and web area of primary stiffening members subjected to pressure loads are, in general, to be in accordance with the following: Section Modulus:

Inertia:

Web area:

where
= f σ is a structural element type factor and is 0,5 in general, for primary stiffening members
= f σ factors are listed for specific structural items in Table 4.2.2 Stiffening type factors
= c A, c Z and c l are coefficients defined in Table 4.2.1 Section modulus, inertia and web area coefficients for different load models
= f σ, f τ, f δ are defined in Table 4.2.3 Acceptance criteria
= P des, S, l e, σyd, τyd and E are defined in Vol 1, Pt 6, Ch 1, 1.3 Symbols and definitions 1.3.1.

2.3.2  Secondary stiffening members. The requirements for section modulus, inertia and web area of secondary stiffening members subjected to pressure loads are, in general, to be in accordance with the following: Section Modulus:

Inertia:

Web area:

where
= δf is a structural element type factor and is 0,8 in general, for secondary stiffening members
= δf factors are listed for specific structural items in Table 4.2.2 Stiffening type factors
= c A, c Z and c l are coefficients defined in Table 4.2.1 Section modulus, inertia and web area coefficients for different load models
= f σ, f λ and f δ are defined in Table 4.2.3 Acceptance criteria
= P des, s, l e ,σyd, τo and E are defined in Vol 1, Pt 6, Ch 1, 1.3 Symbols and definitions 1.3.1.

Table 4.2.1 Section modulus, inertia and web area coefficients for different load models

 Load Model Position (i)   Web area coefficient C A Section modulus coefficient C Z Inertia coefficient C I Application
1 End 2 Midspan 3 End (i)
(A) 1 1/2 1/2 — Primary and other members where the end fixity is considered encastre and the pressure is uniformly distributed
2 — –1/24 1/384
3 1/2 1/12 —
(B) 1 1/2 1/10 — Local, secondary and other members where the end fixity is considered to be partial and the pressure is uniformly distributed
2 — –1/10 1/288
3 1/2 1/10 —
(C) 1 7/20 1/20 — Fully fixed and the pressure is a linearly varying distribution
2 — — 1/764
3 3/20 1/30 —
(D) 1 1 1/2 1/8 Cantilever and uniformly distributed pressure
2 — — —
3 — — —
(E) 1 1/2 — — Simply supported and uniformly distributed pressure
2 — –1/10 5/384
3 1/2 — —
(F) 1
— Fully fixed and a single point load anywhere on the span
2 —
3
—
(G) 1 1/2 1/8 — Fully fixed and a single point load at the centre of the span
2 — –1/8 1/192
3 1/2 1/8 —
(H) 1
— — Simply supported and a single point load anywhere on the span
2  
3
— —
(J) 1 1/2 — — Simply supported and a single point load at the centre of the span
2 — –1/4 1/48
3 1/2 — —

Table 4.2.2 Stiffening type factors

Structural element δf
Shell envelope  
  Main hull bottom and bilge longitudinals  
  Main hull side longitudinals  
  Side hull bottom and bilge longitudinals 0,8
  Side hull side longitudinals  
  Main hull bottom transverse frames  
  Main hull side frames  
  Side hull bottom transverse frames 0,8
  Side hull side frames  
  Bottom girders  
  Side stringers  
  Floors 0,5
  Bottom transverse web frames  
  Side transverse web frames  
  Wet deck  
  Wet-deck longitudinals 0,8
  Wet deck transverse frames
  Wet-deck transverse web frames 0,5
  Wet-deck girders
  Weather and exposed decks  
  Deck longitudinals 0,8
  Deck beams
  Deck girders 0,5
  Deck transverses
  Deck deep beams
  Inner bottom  
  Inner bottom longitudinals 0,8
  Inner bottom transverse frames 0,5

Table 4.2.3 Acceptance criteria

Structural item Limiting criteria
Longitudinally effective structure Bending stress Stiffener web shear stress Stiffener deflection ratio Buckling factor, Compressive stresses See Note 3
Stress descriptor f σ f τ f δ λσ
Plating See Note 5   See Note 1  
Main hull bottom shell f 2 — 0,00125 1,0
Main hull side shell f 2 — 0,00125 1,0
Side hull bottom shell 0,9f 2 — 0,00125 1,0
Side hull side shell 0,9f 2 — 0,00125 1,0
Wet-deck 0,9f 2 — 0,00125 1,0
Weather deck, outboard the line of openings f 2 — 0,00100 1,0
Inner bottom 1,4f 2 — 0,00125 1,0
Secondary stiffeners     See Note 1 1,1
Main hull bottom and bilge longitudinals f 2 0,65 0,00125 1,1
Main hull side longitudinals f 2 0,65 0,00125 1,1
Side hull bottom and bilge longitudinals f 2 0,65 0,00125 1,1
Side hull side longitudinals f 2 0,65 0,00125 1,1
Wet-deck longitudinals f 2 0,65 0,00125 1,1
Main hull bottom transverse frames 0,65 0,65 0,00125 1,1
Main hull side frames 0,65 0,65 0,00125 1,1
Side hull bottom transverse frames 0,65 0,65 0,00125 1,1
Side hull side frames 0,65 0,65 0,00125 1,1
Wet-deck transverse frames 0,65 0,65 0,00125 1,1
Weather deck longitudinals f 2 0,65 0,00100 1,1
Weather deck beams 0,65 0,65 0,00100 1,1
Inner bottom longitudinals f 2 0,65 0,00125 1,1
Primary stiffeners     See Note 2  
Single bottom girders 0,75 0,65 0,00100 1,0
Double bottom girders 0,75 0,80 0,00100 1,0
Side stringers 0,75 0,65 0,00100 1,0
Floors 0,75 0,65 0,00100 1,0
Bottom transverse web frames 0,65 0,65 0,00100 1,0
Side transverse web frames 0,65 0,65 0,00100 1,0
Wet-deck transverse web frames 0,65 0,65 0,00100 1,0
Wet-deck girders 0,75 0,65 0,00100 1,0
Deck transverses 0,75 0,65 0,00100 1,0
Deck deep beams 0,65 0,65 0,00100 1,0
Wet-deck transverse frames 0,65 0,65 0,00100 1,0
Weather deck girders 0,75 0,65 0,00100 1,0
Weather deck transverses 0,65 0,65 0,00100 1,0
Weather deck deep beams 0,65 0,65 0,00100 1,0
Symbols
f 2 is applicable to stiffeners and plating subjected to global hull girder bending stresses and local bending stresses and is to be taken as follows:
but not greater than 0,95. Note that for initial design assessment f 2 may be taken as 0,75.
where
σhg is the stress due to hull girder bending in the appropriate structural item, see Vol 1, Pt 6, Ch 3, 2.4 Longitudinal bending strength 2.4.4
σa is the lower of
λσ is the buckling factor for this item
σcr is the critical buckling stress, see Note 4.

Note 1. Deflection ratio for secondary stiffeners, expressed as a ratio of the stiffener's span, i.e. δ ≤ f δ x span where ∊ is the deflection

Note 2. Deflection ratio for secondary stiffeners, expressed as a ratio of the stiffener's span, i.e. δ ≤ f δ x span where ∊ is the deflection

Note 3. Buckling factor of safety to be applied to the compressive stress due to global longitudinal stresses

Note 4. If the Complementary Rules are the Rules and Regulations for the Classification of Naval Ships (hereinafter referred to as the Rules for Naval Ships) then see Vol 1, Pt 6, Ch 2, 4 Vibration control of the Rules for Naval Ships. If the Complementary Rules are the Rules and Regulations for the Classification of Ships (hereinafter referred to as the Rules for Ships) then see Pt 3, Ch 4, 7 Hull buckling strength of the Rules for Ships. If the Complementary Rules are the Rules and Regulations for the Classification of Special Service Craft (hereinafter referred to as the Rules for Special Service Craft) then see Pt 6, Ch 7, 4 Buckling control of the Rules for Special Service Craft.

Note 5. If the Complementary Rules are the Rules for Special Service Craft then for bottom, bow and wet-deck slamming f 2 is to be taken as 0,85.

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