Section 3 Scantling determination for NS2 and NS3 ships
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 5 Structural Design Factors - Section 3 Scantling determination for NS2 and NS3 ships

Section 3 Scantling determination for NS2 and NS3 ships

Parent topic: Chapter 5 Structural Design Factors

3.1 Design criteria

3.1.1 The allowable stress coefficients for plating and stiffening required by Vol 1, Pt 6, Ch 3, 2 Minimum structural requirements for use in plating and stiffening design equations in Vol 1, Pt 6, Ch 2, 2.7 Plating general and Vol 1, Pt 6, Ch 2, 2.8 Stiffening general are to be determined as follows:

f σ = f 1 f hts
f τ = f 1 f hts
f δ = f 1

where

f 1 is taken from Table 5.3.2 Allowable stress factors f 1 as specified by Table 5.3.1 Specification of design criteria value f 1

f hts is the correction factor for higher tensile steel given in Vol 1, Pt 6, Ch 5, 1.3 Higher tensile steel

3.1.2 The buckling factors of safety for plating and stiffeners are given in Table 5.3.2 Allowable stress factors f 1 and are to be used in conjunction with the buckling requirements specified in Vol 1, Pt 6, Ch 2, 3 Buckling

3.1.3 The assessment of scantling requirements to satisfy the impact or slamming pressure loads for plating and stiffening are given in Vol 1, Pt 6, Ch 3, 14 Strengthening for bottom slamming and Vol 1, Pt 6, Ch 3, 15 Strengthening for wave impact loads above waterline

Table 5.3.1 Specification of design criteria value f 1

Failure mode Stress factor Column for f 1 in Table 5.3.2 Allowable stress factors f 1
Plating requirements
Membrane stresses f σ Use σx or σy column (1)
Local plate bending f σ Use σbcolumn
Shear stresses f τ Use τxy column
Buckling, hull girder stresses λσ Use λσ column
Shear buckling, hull girder stresses λτ Use λτ column
Stiffener requirements    
Section modulus f σ Use σx or σy column (1)
Web area f τ Use τxy column
Inertia f δ Use f δ column
Buckling modes λσ Use λσ column

Note Use the σx or σy column as appropriate to the structure under consideration.

Table 5.3.2 Allowable stress factors f 1

Structural item Limiting stress and other criteria
Longitudinally effective structure Combined
Stress 		Longitudinal
stress or
stiffener
bending
stresses 		Shear stress
in Plating
and Stiffener
webs 		Local plate
bending 		Deflection
ratio for
primary
members and
secondary
stiffeners
(3) 		Buckling
factor (5)

Compressive
stresses 		Buckling
factor (7)

Shear
stresses
Normal stress descriptor σvm σx τxy σb f δ λσ λτ
Longitudinal plating
Bottom shell plating 0,90 0,75 - f 2 0,00125 (1) 1,0 -
Inner bottom plating 0,90 0,75f WT - f 2 f WT 0,00125 (1) 1,0 -
Upper deck, outboard the line of openings 0,90 0,75 - f 2 0,00100 (1) 1,0 -
Side shell plating 0,90 0,75 0,80 0,9f 2 0,00125 (1) 1,0 1,1
Longitudinal bulkhead plating 0,90 0,75 0,80 0,9f 2 0,00125 (1) 1,0 1,1
Inner skin plating 0,90 0,75 0,80 0,9f 2 0,00125 (1) 1,0 1,1
Intermediate decks - - - 0,65 - - -
Longitudinal primary members
Double bottom girders 0,90 0,75 0,80 - 0,00100 (2) 1,0 1,1
Longitudinal girders - 0,75 0,65 - 0,00100 (2) 1,0 1,1
Longitudinal stringer plating and diaphragms - 0,75 0,65 - 0,00100 (2) 1,0 1,1
Longitudinal secondary stiffeners 0,90 f 2 0,65 - see above plating 1,1 (4) -
Other longitudinal plating and secondary stiffeners
Superstructures/deckhouses
(partially longitudinally effective) 		0,90 0,75 0,65 - 0,00167 (1) 1,0 -
Watertight bulkheads and internal boundaries plating 0,90 0,75 0,80 f WT - 1,0 1,1
primary members - 0,90f WT 0,90f WT - 0,00100 f WT (2) 1,1 -
secondary stiffeners - 0,90f WT 0,95f WT - 0,00167 f WT(1) 1,1 (4) -
Deep tank bulkheads and internal boundaries plating 0,90 0,75 0,80 0,65f DT - 1,0 1,1
primary members - 0,75f DT 0,75f DT - 0,00080 f DT (1) 1,1 -
secondary stiffeners - 0,65f DT 0,65f DT - 0,00100 f DT(1) 1,1 (4) -
Normal stress descriptor σvm σy τxy σb f δ λσ λτ
Transverse plating
Watertight bulkheads and internal boundaries 1,00 1,00 0,80 1,00f WT 0,00167 f WT (1) 1,0 1,1
Deep tank bulkheads and boundaries 0,75 0,65 0,65 0,65f DT 0,00100 f DT(1) 1,2 1,2
Cross deck structure at ends of major openings 0,75 0,65 0,65 0,50 0,00100 (1) 1,1 1,1
Superstructures/deckhouses (local loads only) - 0,75 - 0,75 0,00167 (1) - -
Transverse primary members
Double bottom floors 0,75 0,65 0,65   0,00100 (2) 1,1 1,2
Web frames - 0,65 0,65 - 0,00100 (2) 1,1 -
Side frames - 0,65 0,65 - 0,00100 (2) 1,1 -
Transverse beams - 0,65 0,65 - 0,00100 (2) 1,1 -
Watertight bulkheads and internal boundaries - 0,90f WT 0,90f WT - 0,00100 f WT(2) 1,1 -
Deep tank bulkheads and internal boundaries - 0,75f DT 0,75f DT - 0,00080 f DT(2) 1,1 -
Transverse secondary stiffeners
Watertight bulkheads and internal boundaries - 0,95f WT 0,95f WT - see above plating 1,1 (4) -
Deep tank bulkheads and internal boundaries - 0,65f DT 0,65f DT -   1,1 (4) -
Other secondary stiffeners - 0,65 0,65 -   1,1 (4) -
Structure subjected to military or operational loads, e.g. gun blast, missile efflux, or for aircraft and vehicle operation (8)
(Additional requirements in accordance with Vol 1, Pt 4, Ch 2, 9 Military installation and operational loads, Vol 1, Pt 4, Ch 2, 10 Aircraft operations, and Vol 1, Pt 4, Ch 3, 2 Vehicle decks and fixed ramps) 		Com-
bined Stress 		Primary member and stiffener bending stress Shear stress in primary member and Stiffener webs Local plate bending Deflection ratio for primary members and secondary stiffeners (3) Buckling factor of safety (6) Buckling factor of safety (7)
Normal stress descriptor σvm σx or σy τxy σb f δ λσ λτ
Deck and superstructure areas exposed to gun blast or missile efflux secondary stiffeners - 0,75 (8) 0,75 0,9 - - -
primary members - 0,65 (8) 0,65 - - - -
Vehicles and aircraft parking areas secondary stiffeners - 0,75 (8) 0,75 - 0,00100 (1) - -
primary members - 0,60 (8) 0,60 - 0,00080 (2) - -
Aircraft normal landing, manoeuvring stowage and take-off areas secondary stiffeners - 0,75 (8) 0,75 - 0,00100 (1) - -
primary members 0,70 0,65 (8) 0,65 - 0,00080 (2) - -
Aircraft emergency landing areas secondary stiffeners - 1,00 (8) 1,00 - 0,00160 (1) - -
primary members - 1,00 (8) 1,00 - 0,00100 (2) - -
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:
for NS2 ships
f 2 = 0,9 (1,83–) but not greater than 0,95. Note for initial design assessment f 2 may be taken as 0,75.
for NS3 ships
f 2 = 0,75
where
σhg is the stress due to hull girder bending in the appropriate structural item, see Vol 1, Pt 6, Ch 4, 2 Hull girder strength
σa is the lower of
(1) allowable hull girder bending stress, σp, given in Vol 1, Pt 6, Ch 4, 2.2 Bending strength 2.2.3
(2)
λσ is the buckling factor for this item
σcr is the critical buckling stress, see Vol 1, Pt 6, Ch 2, 3 Buckling.
Additional design factors for deep tank and watertight bulkheads and boundaries
f DT = 0,90
f WT = 1,40 Note watertight plating is assessed using plastic design methods

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

Note 2. Deflection ratio for primary structure, expressed as a ratio of the primary member's span, i.e. δ ≤ f δ span.

Note 3. The deflection ratios are applicable to the primary members and secondary stiffeners attached to the specified plating areas. The ratios are not applicable to the plating.

Note 4. The buckling factor of safety for stiffeners attached to plating which is allowed to buckle in the elastic mode due to the applied loads is to be taken as 1,25 see also Vol 1, Pt 6, Ch 2, 4.5 Effect of submergence.

Note 5. Buckling factor of safety to be applied to the compressive stress due to global longitudinal stresses.

Note 6. Buckling factor of safety to be applied to the compressive stress due to local stresses, either vertical or transverse.

Note 7. Buckling factor of safety to be applied to the shear stress.

Note 8. For longitudinally effective primary structure and longitudinal stiffeners, the stress factor is to be reduced by:0% at 0,0L R,30% at 0,3L R,30% at 0,7L R,
0% at 1,0L R,
with intermediate values determined by interpolation.

Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.