Section 3 Stress control
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Special Service Craft, July 2022 - Part 7 Hull Construction in Aluminium - Chapter 7 Failure Modes Control - Section 3 Stress control

Section 3 Stress control

Parent topic: Chapter 7 Failure Modes Control

3.1 General

3.1.1 The nominal limiting stress requirements for plating and primary and secondary stiffening members subject to local loading conditions are given in terms of limiting stress coefficients, see Table 7.3.1 Limiting stress coefficients for local loading. The coefficients are expressed as a proportion of the 0,2 per cent proof stress of the material.

3.1.2 The limiting stress coefficients for structural elements subject to global loading conditions are given in Table 7.3.2 Limiting stress coefficients for global loading.

3.1.3 In the determination of the magnitude of the equivalent stress, σeq, it is assumed that the stresses are combined using the following formula:

where
σx = direct stress in the x direction
σy = direct stress in the y direction
τ = shear stress in the xy plane

Table 7.3.1 Limiting stress coefficients for local loading

Item Limiting stress coefficient
Bending Shear Equivalent
f σ f τ f e
Shell envelope:      
(a) Bottom shell plating:
  • slamming zone
 0,85 - -
 
  • elsewhere
 0,75 - -
(b) Side shell plating:
  • slamming zone
 0,85 - -
 
  • elsewhere
 0,75 - -
(c) Keel   0,75 - -
Bottom structure:      
(a) Secondary stiffening:
  • slamming zone
 0,75 0,75 -
 
  • elsewhere
 0,65 0,65 -
(b) Primary girders and web frames 0,65 0,65 0,75
(c) Engine girders 0,55 0,55 0,75
Side structure:      
(a) Secondary stiffening:
  • slamming zone
 0,75 0,75 -
 
  • elsewhere
 0,65 0,65 -
(b) Primary girders and web frames 0,65 0,65 0,75
Bow doors:      
(a) Plating 0,65 - -
(b) Secondary stiffening 0,51 0,433 -
(c) Primary stiffening 0,51 0,34 0,64
Main/strength deck plating and stiffeners:

(a) Plating

(b) Secondary stiffening

(c) Primary girders and web frame

(d) Hatch covers

0,75

0,65

0,65

0,55

-

0,65

0,65

0,55

-

-

0,75

0,64
Superstructures/deckhouses:      
(a) Deckhouse front, 1st tier:
  • plating
 0,65 - -
 
  • stiffening
 0,60 0,60 -
(b) Deckhouse front upper tiers:
  • plating
 0,75 - -
 
  • stiffening
 0,65 0,65 -
(c) Deckhouse aft and sides:
  • plating
 0,75 - -
 
  • stiffening
 0,75 0,75 -
(d) Coachroof:
  • plating
 0,65 - -
 
  • stiffening
 0,65 0,65 -
(e) House top:
  • plating
 0,75 - -
 
  • stiffening
 0,75 0,75 -
(f) Lower/inner decks and house top subject to personnel loading:
  • plating
 0,75 - -
 
  • stiffening
 0,60 0,60 -
Bulkheads:      
(a) Watertight bulkhead:
  • plating
 1,0 - -
 
  • secondary stiffening
 0,95 0,95 -
 
  • primary stiffening
 0,90 0,90 1,0
(b) Watertight bulkhead doors   0,825 0,825 0,825
(c) Structure supporting watertight doors   0,80 0,80 -
(d) Minor bulkheads:
  • plating
 0,65 - -
 
  • secondary stiffening
 0,65 0,65 -
 
  • primary stiffening
 0,65 0,65 0,75
(e) Deep tank bulkheads:
  • plating
 0,65 - -
 
  • secondary stiffening
 0,65 0,65 -
 
  • primary stiffening
 0,75 0,75 -
Multi-hull cross-deck structure:        
(a) Plating:
  • slamming zone
 0,85 - -
 
  • elsewhere
 0,75 - -
(b) Secondary stiffening:
  • slamming zone
 0,75 0,75 -
 
  • elsewhere
 0,65 0,65 -
(c) Primary stiffening   0,65 0,65 0,75
Vehicle deck:      
(a) Plating 0,60 - -
(b) Secondary stiffening 0,425 0,425 -
(c) Primary stiffening 0,525 0,525 0,75
Helicopter/flight decks:      
(a) Normal usage:
  • plating
 0,65 - -
   
  • secondary stiffening
 0,75 0,75 -
   
  • primary stiffening
 0,625 0,625 0,60
(b) Emergency landing:
  • plating
 0,75 - -
   
  • secondary stiffening
 1,0 1,0 -
   
  • primary stiffening
 0,825 0,825 0,9
(c) Crane pedestal/foundation structural elements 0,7 0,7 0,75
Definitions
The slamming zone is the region where the operational non-displacement mode pressures exceed the operational displacement mode pressures, see Pt 7, Ch 7, 1.3 Symbols and definitions 1.3.2.

Table 7.3.2 Limiting stress coefficients for global loading

Operational mode of craft Limiting stress coefficient
Hull girder Cross-deck
Bending

f σgH

 Shear

f τgH

 Equivalent

f σeg

 Bending

f σgV

Shear

f τgV

 Equivalent

f σeg
Γ ≥ 3,0 or 0,80 0,80 0,825 0,80 0,80 0,825
Δ ≤ 0,04(L R B)1,5
Γ < 3,0 and 0,72 0,72 0,75 0,72 0,72 0,75
Δ > 0,04(L R B)1,5
Symbols
f σgH = limiting hull bending stress coefficient.
f τgH = limiting hull shear stress coefficient.
f σgV = limiting cross-deck bending stress coefficient.
f τgV = limiting cross-deck shear stress coefficient.
f σeg = limiting equivalent stress coefficient.
L R and B = are as defined in Pt 3, Ch 1, 6.2 Principal particulars
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