hull structural design, aluminium alloy · a 200 aluminium alloys 201 the alloy grades are listed...

RULES FORCLASSIFICATION OF

HIGH SPEED, LIGHT CRAFT AND NAVALSURFACE CRAFT

STRUCTURES, EQUIPMENT

PART 3 CHAPTER 3

HULL STRUCTURAL DESIGN, ALUMINIUM ALLOYJANUARY 2011

CONTENTS PAGE

Sec. 1 Structural Principles............................................................................................................. 7Sec. 2 Materials and Material Protection...................................................................................... 14Sec. 3 Manufacturing.................................................................................................................... 19Sec. 4 Hull Girder Strength .......................................................................................................... 21Sec. 5 Plating and Stiffeners......................................................................................................... 25Sec. 6 Web Frames and Girder Systems....................................................................................... 29Sec. 7 Pillars and Pillar Bulkheads ............................................................................................... 34Sec. 8 Weld Connections.............................................................................................................. 37Sec. 9 Direct Strength Calculations .............................................................................................. 42Sec. 10 Buckling Control................................................................................................................ 45

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CHANGES IN THE RULES

GeneralAs of October 2010 all DNV service documents are primarily published electronically.In order to ensure a practical transition from the “print” scheme to the “electronic” scheme, all rule chapters havingincorporated amendments and corrections more recent than the date of the latest printed issue, have been given the dateJanuary 2011. An overview of DNV service documents, their update status and historical “amendments and corrections” may be foundthrough http://www.dnv.com/resources/rules_standards/.

Main changesSince the previous edition (July 2000), this chapter has been amended, most recently in January 2006. All changespreviously found in Pt.0 Ch.1 Sec.3 have been incorporated and a new date (January 2011) has been given as explainedunder “General”.In addition, the layout has been changed to one column in order to improve electronic readability.

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Rules for High Speed, Light Craft and Naval Surface Craft, January 2011 Pt.3 Ch.3 Contents –

CONTENTS

Sec. 1 Structural Principles .......................................................................................................................... 7

A. General ........................................................................................................................................................................... 7A 100 The scantling reduction......................................................................................................................................... 7A 200 Aluminium alloys ................................................................................................................................................. 7

B. Bottom Structures ......................................................................................................................................................... 7B 100 Longitudinal stiffeners .......................................................................................................................................... 7B 200 Web frames ........................................................................................................................................................... 7B 300 Longitudinal girders.............................................................................................................................................. 7B 400 Engine girders ....................................................................................................................................................... 7B 500 Double bottom, if fitted ........................................................................................................................................ 8

C. Side Structure ................................................................................................................................................................ 8C 100 Stiffeners ............................................................................................................................................................... 8

D. Deck Structure............................................................................................................................................................... 8D 100 Longitudinal stiffeners .......................................................................................................................................... 8D 200 Bulwarks ............................................................................................................................................................... 8

E. Flat Cross Structure...................................................................................................................................................... 8E 100 Definition .............................................................................................................................................................. 8E 200 Longitudinal stiffeners .......................................................................................................................................... 8

F. Bulkhead Structures ..................................................................................................................................................... 9F 100 Transverse bulkheads............................................................................................................................................ 9F 200 Corrugated bulkheads ........................................................................................................................................... 9

G. Superstructures and Deckhouses................................................................................................................................. 9G 100 Definitions ............................................................................................................................................................ 9G 200 Structural continuity ............................................................................................................................................. 9

H. Structural Design in General ..................................................................................................................................... 10H 100 Craft arrangement ............................................................................................................................................... 10H 200 Soft local transitions ........................................................................................................................................... 10H 300 Impact strength ................................................................................................................................................... 10

I. Some Common Local Design Rules ........................................................................................................................... 10I 100 Definition of span ............................................................................................................................................... 10I 200 Effective girder flange ........................................................................................................................................ 11I 300 Sniped stiffeners ................................................................................................................................................. 12

J. Support of Equipment and Outfitting Details .......................................................................................................... 12J 100 Heavy equipment, appendages etc. ..................................................................................................................... 12J 200 Minor outfitting details ....................................................................................................................................... 12

K. Structural Aspects not Covered by Rules ................................................................................................................. 12K 100 Deflections .......................................................................................................................................................... 12K 200 Local vibrations .................................................................................................................................................. 13

Sec. 2 Materials and Material Protection ................................................................................................. 14

A. General ......................................................................................................................................................................... 14A 100 Application.......................................................................................................................................................... 14A 200 Material certificates ............................................................................................................................................ 14

B. Structural Aluminium Alloy ...................................................................................................................................... 14B 100 General................................................................................................................................................................ 14B 200 Aluminium grades............................................................................................................................................... 14B 300 Chemical composition ........................................................................................................................................ 14B 400 Mechanical properties......................................................................................................................................... 14

C. Corrosion Protection................................................................................................................................................... 16C 100 General................................................................................................................................................................ 16C 200 For information and approval ............................................................................................................................. 16C 300 Coating................................................................................................................................................................ 16C 400 Cathodic protection............................................................................................................................................. 17C 500 Other materials in contact with aluminium......................................................................................................... 18

D. Other Materials ........................................................................................................................................................... 18D 100 Steel .................................................................................................................................................................... 18D 200 Connections between steel and aluminium......................................................................................................... 18

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D 300 Fibre Reinforced Plastic (FRP)........................................................................................................................... 18

Sec. 3 Manufacturing.................................................................................................................................. 19

A. General ......................................................................................................................................................................... 19A 100 Basic requirements.............................................................................................................................................. 19

B. Inspection..................................................................................................................................................................... 19B 100 General................................................................................................................................................................ 19B 200 Penetrant testing.................................................................................................................................................. 19B 300 Radiographic testing ........................................................................................................................................... 19B 400 Ultrasonic examination ....................................................................................................................................... 19

C. Extent of Examination ................................................................................................................................................ 19C 100 General................................................................................................................................................................ 19

D. Acceptance Criteria for NDT..................................................................................................................................... 19D 100 Acceptance criteria.............................................................................................................................................. 19

E. Testing .......................................................................................................................................................................... 20E 100 Tanks................................................................................................................................................................... 20E 200 Closing appliances .............................................................................................................................................. 20

Sec. 4 Hull Girder Strength........................................................................................................................ 21

A. General ......................................................................................................................................................................... 21A 100 Introduction......................................................................................................................................................... 21A 200 Definitions .......................................................................................................................................................... 21

B. Vertical Bending Strength.......................................................................................................................................... 21B 100 Hull section modulus requirement ...................................................................................................................... 21B 200 Effective section modulus................................................................................................................................... 21B 300 Hydrofoil on foils................................................................................................................................................ 22B 400 Longitudinal structural continuity ...................................................................................................................... 22B 500 Openings ............................................................................................................................................................. 22

C. Shear Strength............................................................................................................................................................. 23C 100 Cases to be investigated ...................................................................................................................................... 23

D. Cases to be Investigated.............................................................................................................................................. 23D 100 Inertia induced loads ........................................................................................................................................... 23

E. Transverse Strength of Twin Hull Craft................................................................................................................... 23E 100 Transverse strength ............................................................................................................................................. 23E 200 Allowable stresses .............................................................................................................................................. 24

Sec. 5 Plating and Stiffeners....................................................................................................................... 25

A. General ......................................................................................................................................................................... 25A 100 Introduction......................................................................................................................................................... 25A 200 Definitions .......................................................................................................................................................... 25A 300 Allowable stresses............................................................................................................................................... 25

B. Plating .......................................................................................................................................................................... 25B 100 Minimum thicknesses ......................................................................................................................................... 25B 200 Bending............................................................................................................................................................... 26B 300 Slamming ............................................................................................................................................................ 26

C. Stiffeners ...................................................................................................................................................................... 27C 100 Bending............................................................................................................................................................... 27C 200 Slamming ............................................................................................................................................................ 28

Sec. 6 Web Frames and Girder Systems ................................................................................................... 29

A. General ......................................................................................................................................................................... 29A 100 Introduction......................................................................................................................................................... 29A 200 Definitions .......................................................................................................................................................... 29A 300 Minimum thicknesses ......................................................................................................................................... 29A 400 Allowable stresses............................................................................................................................................... 30A 500 Continuity of strength members ......................................................................................................................... 30

B. Web Frames and Girders ........................................................................................................................................... 30B 100 General................................................................................................................................................................ 30B 200 Effective flange................................................................................................................................................... 30B 300 Effective web ...................................................................................................................................................... 31B 400 Strength requirements ......................................................................................................................................... 31

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B 500 Girder tripping brackets ...................................................................................................................................... 32B 600 Girder web stiffeners........................................................................................................................................... 33

Sec. 7 Pillars and Pillar Bulkheads............................................................................................................ 34

A. General ......................................................................................................................................................................... 34A 100 Introduction......................................................................................................................................................... 34A 200 Definitions .......................................................................................................................................................... 34

B. Pillars............................................................................................................................................................................ 34B 100 Arrangement of pillars ........................................................................................................................................ 34B 200 Cross-section particulars..................................................................................................................................... 34B 300 Pillar scantlings................................................................................................................................................... 34B 400 Pillars in tanks..................................................................................................................................................... 35

C. Supporting Bulkheads ................................................................................................................................................ 36C 100 General................................................................................................................................................................ 36

Sec. 8 Weld Connections............................................................................................................................. 37

A. General ......................................................................................................................................................................... 37A 100 Introduction......................................................................................................................................................... 37A 200 Welding particulars............................................................................................................................................. 37

B. Types of Welded Joints............................................................................................................................................... 37B 100 Butt joints............................................................................................................................................................ 37B 200 Tee or cross joints ............................................................................................................................................... 37

C. Size of Connections ..................................................................................................................................................... 38C 100 Fillet welds, general ............................................................................................................................................ 38C 200 Fillet welds and penetration welds subject to high tensile stresses .................................................................... 38C 300 End connections of girders, pillars and cross ties ............................................................................................... 39C 400 End connections of stiffeners.............................................................................................................................. 39

Sec. 9 Direct Strength Calculations ........................................................................................................... 42

A. General ......................................................................................................................................................................... 42A 100 Introduction......................................................................................................................................................... 42A 200 Application.......................................................................................................................................................... 42

B. Plating .......................................................................................................................................................................... 42B 100 General................................................................................................................................................................ 42B 200 Calculation procedure ......................................................................................................................................... 42B 300 Allowable stresses............................................................................................................................................... 42

C. Stiffeners ...................................................................................................................................................................... 42C 100 General................................................................................................................................................................ 42C 200 Calculation procedure ......................................................................................................................................... 43C 300 Loads................................................................................................................................................................... 43C 400 Allowable stresses............................................................................................................................................... 43

D. Girders ......................................................................................................................................................................... 43D 100 General................................................................................................................................................................ 43D 200 Calculation methods ........................................................................................................................................... 43D 300 Design load conditions........................................................................................................................................ 43D 400 Allowable stresses............................................................................................................................................... 44

Sec. 10 Buckling Control .............................................................................................................................. 45

A. General ......................................................................................................................................................................... 45A 100 Definitions .......................................................................................................................................................... 45

B. Longitudinal Buckling Load ...................................................................................................................................... 46B 100 Longitudinal stresses........................................................................................................................................... 46

C. Transverse Buckling Load ......................................................................................................................................... 46C 100 Transverse stresses.............................................................................................................................................. 46

D. Plating .......................................................................................................................................................................... 46D 100 Plate panel in uni-axial compression .................................................................................................................. 46D 200 Plate panel in shear ............................................................................................................................................. 48D 300 Plate panel in bi-axial compression and shear .................................................................................................... 48

E. Stiffeners in Direction of Compression ..................................................................................................................... 49E 100 Lateral buckling mode ........................................................................................................................................ 49E 200 Torsional buckling mode .................................................................................................................................... 50

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E 300 Web and flange buckling .................................................................................................................................... 51

F. Stiffeners Perpendicular to Direction of Compression............................................................................................ 51F 100 Moment of inertia of stiffeners ........................................................................................................................... 51

G. Elastic Buckling of Stiffened Panels .......................................................................................................................... 52G 100 Elastic buckling as a design basis ....................................................................................................................... 52G 200 Allowable compression....................................................................................................................................... 52

H. Girders ......................................................................................................................................................................... 53H 100 Axial load buckling............................................................................................................................................. 53H 200 Girders perpendicular to direction of compression............................................................................................. 53H 300 Buckling of effective flange................................................................................................................................ 53H 400 Shear buckling of web ........................................................................................................................................ 54

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Rules for High Speed, Light Craft and Naval Surface Craft, January 2011 Pt.3 Ch.3 Sec.1 –

SECTION 1 STRUCTURAL PRINCIPLES

A. General

A 100 The scantling reduction101 The scantling reductions for high speed and light craft structures compared with Rules for Classificationof Ships are based on:

— longitudinal framing in bottom and strength deck— extended longitudinal and local buckling control— a sea and weather service restriction.

A 200 Aluminium alloys201 The alloy grades are listed in Sec.2 Tables B1 to B4.202 The various formulae and expressions involving the factor f1 may be applied when:

σf = yield stress is not to be taken greater than 70% of the ultimate tensile strength.

The material factor f1 included in the various formulae and expressions is given in Sec.2 Tables B1 to B3 forthe un-welded condition and in Table B4 for the welded condition.

B. Bottom Structures

B 100 Longitudinal stiffeners101 Single bottoms as well as double bottoms are normally to be longitudinally stiffened.102 The longitudinals should preferably be continuous through transverse members. If they are to be cut attransverse members, i.e. watertight bulkheads, continuous brackets connecting the ends of the longitudinals areto be fitted or welds are to be dimensioned accordingly.103 Longitudinal stiffeners are to be supported by bulkheads and web frames.104 Longitudinal stiffeners in slamming areas should have a shear connection to transverse members.

B 200 Web frames201 Web frames are to be continuous around the cross section i.e. floors side webs and deck beams are to beconnected. Intermediate floors may be used.202 In the engine room plate floors are to be fitted at every frame. In way of thrust bearings additionalstrengthening is to be provided.

B 300 Longitudinal girders301 Web plates of longitudinal girders are to be continuous in way of transverse bulkheads.302 A centre girder is normally to be fitted for docking purposes.303 Manholes or other openings should not be positioned at ends of girders without due consideration beingtaken of shear loadings.

B 400 Engine girders401 Under the main engine, girders extending from the bottom to the top plate of the engine seating are to befitted.

—

s = chosen spacing in m

sr =

a certain stiffener spacing reduction ratio ssr----

basic spacing =2 100 L+( )1000

--------------------------- m in general

f1σf

240---------=

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402 Engine holdingdown bolts are to be arranged as near as practicable to floors and longitudinal girders.403 In way of thrust bearing and below pillars additional strengthening is to be provided.

B 500 Double bottom, if fitted501 Manholes are to be cut in the inner bottom, floors and longitudinal girders to provide access to all partsof the double bottom. The vertical extension of lightening holes is not to exceed one half of the girder height.The edges of the manholes are to be smooth. Manholes in the inner bottom plating are to have reinforcementrings. Manholes are not to be cut in the floors or girders in way of pillars.502 In double bottoms with transverse stiffening, longitudinal girders are to be stiffened at every transverseframe.503 The longitudinal girders are to be satisfactorily stiffened against buckling.

C. Side StructureC 100 Stiffeners101 The craft's sides may be longitudinally or vertically stiffened.

Guidance note:It is advised that longitudinal stiffeners are used near bottom and strength deck.

---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

102 The continuity of the longitudinals is to be as required for bottom and deck longitudinals respectively.

D. Deck StructureD 100 Longitudinal stiffeners101 Decks are normally to be longitudinally stiffened.102 The longitudinals should preferably be continuous through transverse members. If they are to be cut attransverse members, i.e. watertight bulkheads, continuous brackets connecting the ends of the longitudinals areto be fitted.103 The plate thickness is to be such that the necessary transverse buckling strength is achieved, or transversebuckling stiffeners may have to be fitted intercostally.

D 200 Bulwarks201 The thickness of bulwark plates is not to be less than required for side plating in a superstructure in thesame position.202 A strong bulb section or similar is to be continuously welded to the upper edge of the bulwark. Bulwarkstays are to be in line with transverse beams or local transverse stiffening. The stays are to have sufficient widthat deck level. The deck beam is to be continuously welded to the deck in way of the stay. Bulwarks on forecastledecks are to have stays fitted at every frame.Stays of increased strength are to be fitted at ends of bulwark openings. Openings in bulwarks should not besituated near the ends of superstructures.203 Where bulwarks on exposed decks form wells, ample provision is to be made to freeing the decks forwater.

E. Flat Cross StructureE 100 Definition101 Flat cross structure is horizontal structure above waterline like bridge connecting structure between twinhulls, etc.

E 200 Longitudinal stiffeners201 Flat cross structures are normally to be longitudinally stiffened.202 The longitudinals should preferably be continuous through transverse members. If they are to be cut attransverse members, i.e. watertight bulkheads, continuous brackets connecting the ends of the longitudinals are

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to be fitted or welds are to be dimensioned accordingly.203 Longitudinal stiffeners are to be supported by bulkheads and web frames.

F. Bulkhead Structures

F 100 Transverse bulkheads101 Number and location of transverse watertight bulkheads are to be in accordance with the requirementsgiven in Ch.1 Sec.1 B200.102 The stiffening of the upper part of a plane transverse bulkhead is to be such that the necessary transversebuckling strength is achieved.

F 200 Corrugated bulkheads201 Longitudinal and transverse bulkheads may be corrugated.202 For corrugated bulkheads the following definition of spacing applies (see Fig. 1):

s = s1 for section modulus calculations = 1.05 s2 or 1.05 s3 for plate thickness calculations.

Fig. 1Corrugated bulkhead

G. Superstructures and Deckhouses

G 100 Definitions101 Superstructure is defined as a decked structure on the freeboard deck, extending from side to side of theship or with the side plating not inboard of the shell plating more than 4% of the breadth (B).102 Deckhouse is defined as a decked structure above the strength deck with the side plating being inboardof the shell plating more than 4% of the breadth (B).Long deckhouse - deckhouse having more than 0.2 L of its length within 0.4 L amidships.Short deckhouse - deckhouse not defined as a long deckhouse.

G 200 Structural continuity201 In superstructures and deckhouses, the front bulkhead is to be in line with a transverse bulkhead in thehull below or be supported by a combination of girders and pillars. The after end bulkhead is also to beeffectively supported. As far as practicable, exposed sides and internal longitudinal and transverse bulkheadsare to be located above girders and frames in the hull structure and are to be in line in the various tiers ofaccommodation. Where such structural arrangement in line is not possible, there is to be other effective support.202 Sufficient transverse strength is to be provided by means of transverse bulkheads or girder structures.203 At the break of superstructures, which have no set-in from the ship's side, the side plating is to extendbeyond the ends of the superstructure, and is to be gradually reduced in height down to the deck or bulwark.The transition is to be smooth and without local discontinuities. A substantial stiffener is to be fitted at the upperedge of plating. The plating is also to be additionally stiffened.204 In long deckhouses, openings in the sides are to have well rounded corners. Horizontal stiffeners are tobe fitted at the upper and lower edge of large openings for windows.Openings for doors in the sides are to be substantially stiffened along the edges. The connection area betweendeckhouse corners and deck plating is to be increased locally.Deck girders are to be fitted below long deckhouses in line with deckhouse sides.

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205 Deck beams under front and aft ends of deckhouses are not to be scalloped for a distance of 0.5 m fromeach side of the deckhouse corners.206 For deckhouse side stiffeners the scantlings need not be greater than required for tween deck frames withequivalent end connections.207 Casings supporting one or more decks above are to be adequately strengthened.

H. Structural Design in GeneralH 100 Craft arrangement101 Attention is drawn to the importance of structural continuity in general.102 The craft arrangement is to take into account:

— continuity of longitudinal strength, including horizontal shear area to carry a strength deck along— transverse bulkheads or strongwebs— web or pillar rings in engine room— twin hull connections— access for inspection— superstructures and deckhouses:

— direct support— transitions

— deck equipment support— multi-deck pillars in line, as practicable— external attachments, inboard connections.

103 Structural details in spaces that will be coated are to be designed in such way that a sound layer of coatingcan be achieved everywhere.

H 200 Soft local transitions201 Gradual taper or soft transition is specially important in high speed aluminium vessels, to avoid:

— stress corrosion and fatigue in heavy stressed members— impact fatigue in impact loaded members.

202 End brackets, tripping brackets etc. are not to terminate on unsupported plating.Brackets are to extend to the nearest stiffener, or local plating reinforcement is to be provided at the toe of thebracket.

H 300 Impact strength301 The slamming pressure in Ch.1 is (contrary to the Rules for Classification of Ships) expressed as anequivalent static load, and is to be compared with ordinary allowable stresses.

I. Some Common Local Design RulesI 100 Definition of span101 The effective span of a stiffener (l) or girder (S) depends on the design of the end connections in relationto adjacent structures. Unless otherwise stated the span points at each end of the member, between which thespan is measured, is to be determined as shown on Fig.1. It is assumed that brackets are effectively supportedby the adjacent structure. For stiffeners, see also Fig. 2 or Sec.5.

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Fig. 2Span points

I 200 Effective girder flange201 For girders with curved face plate, e.g. web frames, the effective area of the flange is given by:

Ae= k tf bf (mm2)

b = 0.5 (bf – tw) for symmetrical free flanges

bf = total face plate breadth in mmk = flange efficiency coefficient, see also Fig. 3

=

= 1.0 maximum

k1 =

for symmetrical and unsymmetrical free flange

=

for girder flange with two webs

=

for box girder flange with multiple webs

β =

l

l

23

b

l

b

STIFFENERS GIRDERS

R S

23 R

23 b

S

b

k1rtfb

----------

0.643 βsinh βcosh βsin βcos+( )

h β2sin β2sin+-------------------------------------------------------------------------------

0.78 βsinh βsin+( ) βcosh βcos–( )

h β2sin β2sin+---------------------------------------------------------------------------------------

1.56 βcosh βcos–( )βsinh βsin+

-------------------------------------------------

1.285brtf

----------------- (rad)

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= bf for unsymmetrical free flanges

= s – tw for box girder flangess = spacing of supporting webs for box girder (nun)tf = face plate thickness in general (mm) = tw (maximum) for unsymmetrical free flangestw = web plate thickness (mm)r = radius of curved face plate (mm)

Fig. 3Effective width of curved face plates for alternative boundary conditions

202 The effective width of curved plate flanges, or effective width of plate at knuckles, is to be speciallyconsidered.

I 300 Sniped stiffeners301 Stiffeners with sniped ends may be allowed where dynamic loads are small and vibrations considered tobe of small importance.

J. Support of Equipment and Outfitting DetailsJ 100 Heavy equipment, appendages etc.101 Whether the unit to be supported is covered by classification or not, the forces and moments at points ofattachment have to be estimated and followed through hull reinforcements in line, through craft girder andpillar system (taking into account hull stresses already existing) until forces are safely carried to craft's side orbulkheads.102 Doublers should be avoided normal to a tensile force.

J 200 Minor outfitting details201 Generally connections of outfitting details to the hull are to be such that stress-concentrations areminimized and welding to high stressed parts are avoided wherever possible.Connections are to be designed with smooth transitions and proper alignment with the hull structure elements.Terminations are to be supported.202 Connections to topflange of girders and stiffeners are to be avoided if not well smoothened. Preferablysupporting of outfittings are to be welded to the stiffener web.

K. Structural Aspects not Covered by RulesK 100 Deflections101 Requirements for minimum moment of inertia or maximum deflection under load are limited to structurein way of hatches and doors and some other special cases.102 Deflection problems in general are left to designer's consideration.

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K 200 Local vibrations201 The evaluation of structural response to vibrations caused by impulses from engine and propeller bladesand jet units are not covered by the classification, but the builder is to provide relevant documentation.

Guidance note:HSC Code 3.4:Cyclic loads, including those from vibrations which can occur on the craft should not:

a) impair the integrity of structure during the anticipated service life of the craft or the service life agreedwith the Administration;

b) hinder normal functioning of machinery and equipment; andc) impair the ability of the crew to carry out its duties.


Upon request such evaluation may be undertaken by the Society.

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SECTION 2 MATERIALS AND MATERIAL PROTECTION

A. GeneralA 100 Application101 The rules in this chapter apply to wrought aluminium alloys for objects classified or intended forclassification with the Society.

A 200 Material certificates201 Rolled and extruded wrought aluminium alloys, glass reinforced plastic and core materials for hullstructures and rolled steel are normally to be supplied with DNV material certificates.202 For class certificate requirement for chemical composition, mechanical properties, heat treatment andrepair of defects, see Pt.2 Ch.2.203 Particular attention is to be given to aluminium hull materials specification in Pt.2 Ch.2.204 Requirements for material certificates for forgings, castings and other materials for special parts andequipment are stated in connection with the rule requirements for each individual part.

B. Structural Aluminium AlloyB 100 General101 Aluminium alloy for marine use may be applied in hulls, superstructures, deckhouses, hatch covers andsundry items.

B 200 Aluminium grades201 Aluminium alloys are to have a satisfactory resistance to corrosion in marine environments. Grades forwelded structures are to be weldable, applying one of the welding methods approved by the Society.202 For major hull structural components, alloys with temper H116/H321 for rolled products, and alloys withtemper T5/T6 for extruded products, are normally to be used. The use of 0- or F temper must be agreed withthe Society.203 The use of 6000 series aluminium alloys in direct contact with sea water may be restricted depending onapplication and corrosion protection system. The use of these alloys are to be agreed with the Society.204 In weld zones (HAZ) of rolled or extruded products, the factor f1 given in Table B4 may in general beused as basis for the scantling requirements.205 Welding consumables are to be chosen according to Table C2 in Pt.2 Ch.3 Sec.2. The consumable chosenare to have minimum mechanical properties not less than specified for the parent alloy in the welded condition.

B 300 Chemical composition301 The chemical composition is to satisfy the requirements in Pt.2 Ch.2. Other alloys or alloys which do notfully comply with Pt.2 Ch.2, may be accepted by the Society after consideration in each particular case. Specialtests and/or other relevant information, e.g. which confirm a satisfactory corrosion resistance and weldability,may be required.

B 400 Mechanical properties401 Requirements to mechanical properties for different delivery conditions are given in Tables B1 and B2for wrought products, extruded products and rivet bars/-rivets, respectively. Other delivery conditions withrelated mechanical properties may be accepted by the Society after consideration in each particular case.

Table B1 Factor f1 for wrought aluminium alloy sheets, strips and plates, t: 2 mm ≤ t ≤ 40 mmDNV Designation Temper f1

NV-5052 H32 H34

0.61 0.69

NV-5154A 0, H111 0.35NV-5754 H24 0.69NV-5454 H32

H340.73 0.79

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V-5086 H116, H32 H34

0.80 0.88

NV-5083 H116, H321 0.89NV-5383 H116, H34 0.89

Note: For tempers 0 and H111, the factor f1 is to be taken from Table B4.

Table B2 Factor f1 for extruded aluminium alloy profiles, rods and tubes, t: 2 mm ≤ t ≤ 25 mmDNV

DesignationTemper f1

NV-6060 T5 0.55NV-6061 T4

T5/T60.46 0.76

NV-6063 T5 T6

0.44 0.60

NV-6005A T5/T6 0.76NV-6082 T4

T5/T60.46 0.90

Note: Table B2 only applies when the main loading direction is logitudinal to the extrusion, see also Table B3.

Table B3 Factor f1 for extruded aluminium alloy profiles, rods and tubes, t: 2 mm ≤ t ≤ 25 mm, transverse to extruding direction

DNVDesignation

Temper f1

NV-6060 T5 0.51NV-6061 T4

T5/T60.46 0.71

NV-6005A T5/T66 < t < 1010 < t < 25

0.760.67

NV-6082 T5 / T6 0.85Note: Table B2 only applies when the main loading direction is logitudinal to the extrusion

Table B4 Factor f1 in the welded conditionDNV

DesignationTemper Filler f1

NV-5052 0, H111, H32, H34 5356 0.27NV-5154A 0, H111 5356-5183 0.35NV 5754 0, H111, H24 5356-5183 0.33NV 5454 0, H111, H32, H34 5356-5183 0.35NV-5086 0, H111, H116, H32, H34 5356-5183 0.42NV-5083 H116, H321

H116, H3215356 5183

0.531) 0.601)

NV-5383 H116, H34 5183 0.642)

NV-6060 T5 5356-5183 0.27NV-6061 T4

T5/T65356-5183 0.48

0.48NV-6063 T5

T65356-5183 0.27

NV-6005A T5/T6 5356-5183 0.48NV-6082 T4

T5/T65356-5183 0.46

0.481) The utilisation of the material is higher than given by the f1 factor as given in Sec. 1 A. This is due to extended

utilisation in Rules for HS, LC and NSC, f1=(σ1/240) x 1.102) The utilisation of the material is higher than given by the f1 factor as given in Sec. 1 A. This is due to extended

utilisation in Rules for HS, LC and NSC, f1=(σ1/240) x 1.10

Table B1 Factor f1 for wrought aluminium alloy sheets, strips and plates, t: 2 mm ≤ t ≤ 40 mm (Continued)DNV Designation Temper f1

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C. Corrosion ProtectionC 100 General101 Loss of structural strength due to corrosion is not acceptable.102 All surfaces that are not recognised as inherently resistant to the actual marine environment are to beadequately protected against corrosion.

Guidance note:In these rules, corrosion is defined as degradation of material due to environmental influence.


C 200 For information and approval201 Specifications for corrosion protection, i.e. for coating, if applied, see 301, and for cathodic protection(including calculations), see 403, are to be submitted for information. The specifications are basis for approvalof drawings of the cathodic protection system.202 Drawings of cathodic protection system, e.g. fastening, numbers and distribution of anodes and referenceelectrodes (if impressed current), are subject to approval.203 Selection and combination of materials for exposure to sea water and/or marine atmosphere are subjectto approval.

C 300 Coating301 If coating is applied, the specification is to be submitted for information.

Guidance note:Coating of aluminium hulls is normally not required (see B200). However, hulls normally need to be coated for anti-fouling purposes. When coating is applied, it will influence the corrosion resistance of the hull, and constitute a basisfor cathodic protection design. The coating system including surface preparation before coating should therefore besubmitted for information.The following is normally included in a specification for coating:

— metal surface cleaning and preparation before application of the primer coat, including treatment of edges andwelds

— build-up and application of coating system with individual coats— curing times and over-coating intervals— acceptable temperatures of air and metal surface and dryness or humidity conditions during the above mentioned

operations (normally, the metal surface is minimum 3 °C above the dew point and the relative humidity is below85%)

— thickness of individual coats and final coating system— resistance to cathodic disbonding (for coatings to be used in connection with impressed current).


302 A sound anti-corrosion coating should always be combined with the anti-fouling coating on the externalhull.303 Anti-corrosion coating is not to contain copper or other constituents that may cause galvanic corrosionon the aluminium hull.304 Hull integrated water ballast tanks and other tanks holding corrosive liquids are to be coated. Allstiffeners and frames in these tanks are to be welded to plating with double continuous welding, see Sec.8 B202.305 In other internal compartments of the hull where corrosive water is likely to occur, the lower 0.5 m ofthe internal bottom surface, measured along the plate on each side of the keel, and the corresponding sectionof the bulkheads, is normally to be coated. The preparation of surfaces including welds and edges shall be suchthat the coating can be properly applied.

Guidance note:The use of 6000 alloys containing more than 0.15% Cu in internal compartments without coating may be restricted.Stagnant, chloride-containing water in internal compartments, e.g. condensation water, may cause corrosion onaluminium alloy plates and structures. Corrosion attacks will usually be of localised type, e.g. in the form of pitting.Corrosion attacks of galvanic type may also occur, see also 500, e.g. if equipment made of other metal alloy remainsin electrical contact with aluminium alloy material.Corrosion attacks of the above mentioned types can be reduced by means of e.g.:

— coating applied as described above— regular cleaning, drying and inspection of the actual compartment— electrical isolation of any other metallic part from aluminium alloy plates and structures— use of dehumidifying equipment in a closed compartment

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— ventilation holes (minimum 2)— drainage holes— hot air fans.


C 400 Cathodic protection401 Cathodic protection of aluminium hulls can be obtained with aluminium or zinc sacrificial anodes orimpressed current. Magnesium based sacrificial anodes are not to be used, and impressed current is not to beused in internal hull compartments.402 Cathodic protection is normally to be applied to aluminium hull craft due to electrical connection of thealuminium with another metals (in propeller, water jet, etc.), which may initiate galvanic corrosion, and toprotect the hull against local corrosion and damage that normally will occur in protective coatings.403 The following is normally to be included in a cathodic protection specification:

— areas to be protected (m2) for hull and attached metallic components such as water jet unit and water jet duct— stipulated protective current density demand (mA/m2) for coated and not coated surfaces of hull and

attached components, respectively— total current demand (A)— target design life of cathodic protection system— anode material and manufacturer— for sacrificial anodes; calculation of anode mass, distribution, total number— for impressed current systems; current capacity of rectifiers and anodes— for impressed current systems; reference electrodes, system control and monitoring arrangement, cabling

and procedures for exchange or renewal of components— target protective potential difference to be obtained— drawings of cathodic protection systems, showing anode types, mass, distribution, location and attachment

details (for sacrificial anodes or impressed current anodes with reference electrodes)— cathodic protection system drawings shall be in compliance with the specification and calculations for the

same.

Guidance note:The current density demand will vary dependent upon the speed of hull, the speed of propeller, and the type of metallicmaterial to be protected (aluminium, stainless steel, etc.).The target protective potential difference for aluminium alloy surfaces may be minus 950 mV versus the Ag/AgCl/seawater reference electrode, with an acceptable potential difference range of minus 800 mV to minus 1150 mV, i.e.approximately as for carbon steel and stainless steel. Due concern must be given to the possibility of detrimentaloverprotection of aluminium.Stainless steel surfaces in water jet units of high speed craft may need a current density of up to about 300 mA/m2 tobe protected, while values as high as 500 mA/m2 may give overprotection problems.


404 For documentation of instrumentation and automation, including computer based control andmonitoring, see Pt.4 Ch.9 Sec.1.405 The designed (target) service life of a cathodic protection system is normally to be at least as long as theexpected time interval between dockings.406 With impressed current cathodic protection systems, precautions are to be taken to avoid:

1) overprotection or excessive negative potential differences locally, especially on aluminium surfaces(implying transpassive corrosion) as well as

2) loss of protection,

by means of anode screens, automatic voltage control, overprotection alarm, or similar. The protective potentialdifference is to be kept within a specified and agreed range, see Guidance note to 403.407 Direct voltage stray currents may impose rapid electrolytic corrosion damage to hulls and is to beavoided.

Guidance note:Stray D.C. sources may be shore connections (e.g. ramps, cranes, cables, etc.), not properly grounded weldingmachines, etc. Special precautions should be taken if welding is carried out with the craft afloat, or if the craft isconnected to electrical power in port.


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C 500 Other materials in contact with aluminium501 If other metallic materials are used in propellers or impellers, piping, pumps, valves, etc. and are incontact with the aluminium hull, provisions are to be made to avoid galvanic corrosion. Acceptable provisionsare either one of or a combination of:

— coating of water or moisture exposed surfaces— electrical isolation of different materials from each other— cathodic protection.

Guidance note:Full electrical isolation of e.g. propeller or impeller from hull is usually difficult. Contact will be established when thepropeller is idle.Wooden material, cloth, debris, non-adherent coating or other organic material remaining in durable contact withaluminium may cause under-deposit corrosion on aluminium due to local oxygen deficiency at the surface.


D. Other MaterialsD 100 Steel101 Structural steel may be used in sundry items such as rudders, foils, propeller shaft brackets, etc.102 For requirements for chemical composition, mechanical properties, heat treatment, testing and repair ofdefects, see Pt.2.103 The material factor f1 = 1 for ordinary ship quality steel.104 All steel surfaces are to be protected against corrosion by paint of suitable composition or other effectivecoating.105 Shop primers applied over areas which will subsequently be welded, are to be of a quality accepted bythe Society as having no detrimental effect on the finished weld.See “Register of Approved Manufacturers” and “Register of Type Approved Products”.106 Coating systems are to be suitable for use on any previously applied shop primer.The coating and the assumed application conditions must have been approved by the Society. Such approvalwill normally be given as a «Type approval».The shipbuilders are to present a written declaration stating that the coating has been applied as specified.

Guidance note:Upon request approval programs for coating systems may be obtained from the Society.


D 200 Connections between steel and aluminium201 If there is risk of galvanic corrosion, provisions are to be made, see C500.202 Aluminium plating connected to a steel boundary bar is wherever possible to be arranged on the sideexposed to moisture.203 Direct contact between exposed wooden materials, e.g. deck planking, and aluminium is to be avoided.204 Bolts with nuts and washers are either to be of stainless steel or hot galvanized steel. The bolts are ingeneral to be fitted with sleeves of insulating material.

D 300 Fibre Reinforced Plastic (FRP)301 FRP materials, core materials and fillers are to be approved according to Sec. 3.302 Other reinforcement and plastic materials may be approved on the basis of relevant documentation andtesting in each individual case.

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SECTION 3 MANUFACTURING

A. General

A 100 Basic requirements

101 Welding of hull structures, machinery installations and equipment are to be carried out by approvedwelders, with approved welding consumables and at welding shops recognised by the Society. See Sec.2.

102 Shot blasting, priming and coating are to be carried out under indoor conditions. For coatingspecification and documentation, see Sec.2.

103 For vessels longer than 50 m, a plan for non-destructive testing (NDT) is to be submitted for approval.

B. Inspection

B 100 General

101 Welds are to be subject to visual survey and inspection as fabrication proceed. NDT is to be performedaccording to established procedures and if required, qualified for the work.

102 All examinations are to be carried out by competent personnel. The NDT operators are to be qualifiedaccording to a recognised certification scheme accepted by the Society. The certificate is clearly to state thequalifications as to which examination method and within which category the operator is qualified.

B 200 Penetrant testing

201 Penetrant testing is to be carried out as specified in the approved procedures.

B 300 Radiographic testing

301 Radiographic testing is to be carried out as specified in the approved procedures.

302 Processing and storage are to be such that the films maintain their quality throughout the agreed storagetime. The radiographs are to be free from imperfections due to development processing.

B 400 Ultrasonic examination

401 Ultrasonic testing is to be carried out as specified in the approved procedures. Ultrasonic examinationprocedures are to contain sketches for each type of joint and dimensional range of joints which clearly showscanning pattern and probes to be used.

402 The examination record is to include the imperfection position, the echo height, the dimensions (length),the depth below the surface and, if possible, the defect type.

C. Extent of Examination

C 100 General

101 All welds are to be subject to visual examination. In addition to the visual examination, at least 2 to 5%of total welded length are to be examined by penetrant examination and/or radiographic examination. Forhighly stressed areas the extent of examination may be increased.

102 If defects are detected, the extent of examination is to be increased to the surveyor’s satisfaction.

D. Acceptance Criteria for NDT

D 100 Acceptance criteria

101 All welds are to show evidence of good workmanship. The quality is normally to comply with ISO 10042quality level C, intermediate. For highly stressed areas more stringent requirements, such as ISO level B, maybe applied.

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E. TestingE 100 Tanks101 Protective coating systems may be applied before water testing.All pipe connections to tanks are to be fitted before testing. If engine bed plates are bolted directly on the innerbottom plating, the testing of the double bottom tank is to be carried out with the engine installed.102 Unless otherwise agreed, all tanks are to be tested with a water head equal to the maximum pressure towhich the compartment may be exposed. The water is in no case to be less than to the top of the air pipe or toa level h0 above the top of the tank except where partial filling alone is prescribed.

h0 = 0.03 L - 0.5 (m), minimum 1, generally = pressure valve opening pressure when exceeding the general value.

E 200 Closing appliances201 Inner and outer doors below the waterline are to be hydraulically tested.202 Weathertight and watertight closing appliances not subjected to pressure testing are to be hose tested.The nozzle inside diameter is to be 12.5 mm and the pressure at least 250 kN/m2. The nozzle should be held ata distance of maximum 1.5 m from the item during the test.Alternative methods of tightness testing may be considered.203 All weathertight or watertight doors and hatches are to be function tested.

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SECTION 4 HULL GIRDER STRENGTH

A. GeneralA 100 Introduction101 In this section requirements for longitudinal and transverse hull girder strength is given. In addition,buckling control according to Sec. 10 may be required.102 Longitudinal strength has generally to be checked for the craft types and sizes mentioned in theintroduction to Ch.1 Sec.3.103 For new designs (prototypes) of large and structurally complicated craft (e.g. multi-hull types) acomplete 3-dimensional global analysis of the transverse strength, in combination with longitudinal stresses, isto be carried out.104 Buckling strength in bottom and deck may, however, have to be checked also for the other craft.

A 200 Definitions201 Moulded deck line, Rounded sheer strake, Sheer strake and Stringer plate are as defined in Fig.1.

Fig. 1Deck corners

B. Vertical Bending StrengthB 100 Hull section modulus requirement101

M = the longitudinal midship bending moment in kNm from Ch.1 Sec. 3 = sagging or hogging bending moment = hollow landing or crest landing bending moment = maximum still water + wave bending moment for high speed displacement craft and semi-planing craft

in the displacement mode = maximum total moment for hydrofoil on foils σ = 175 f1 N/mm2 in general.

Guidance note:Simultaneous end impacts over a hollow are considered less frequent and giving lower moments than the crestlanding.Need not be investigated if deck buckling resistance force is comparable to that of the bottom.


B 200 Effective section modulus201 Where calculating the moment of inertia and section modulus of the midship section, the effectivesectional area of continuous longitudinal strength members is in general the net area after deduction ofopenings.

Z Mσ----- 103×= cm3( )

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Superstructures which do not form a strength deck are not to be included in the net section. This applies alsoto deckhouses and bulwarks.202 The effect of openings are assumed to have longitudinal extensions as shown by the shaded areas inFig.2, i.e. inside tangents at an angle of 30° to each other. Example for transverse section III:

bIII = b' + b’’ + b’’’203 For twin hull vessels the effective breadth of wide decks without longitudinal bulkhead support will beconsidered separately.

B 300 Hydrofoil on foils301 For hydrofoils in addition to the calculation for the midship section, the sections in way of the foils arerequired to be checked.

B 400 Longitudinal structural continuity401 The scantling distribution of structures participating in the hull girder strength in the various zones of thehull is to be carefully worked out so as to avoid structural discontinuities resulting in abrupt variations ofstresses.402 At ends of effective continuous longitudinal strength members in deck and bottom region large transitionbrackets are to be fitted.

Fig. 2Effect of openings

B 500 Openings501 A keel plate for docking is normally not to have openings. In the bilge plate, within 0.5 L amidships,openings are to be avoided wherever practicable. Any necessary openings in the bilge plate are to be kept clearof a bilge keel.502 Openings in strength deck are wherever practicable to be located well clear of the craft’s side and hatchcorners.503 Openings in strength members should generally have an elliptical form. Larger openings in deck may beaccepted with well rounded corners and are to be situated as near to the craft's centreline as practicable.504 For corners with rounded shape the radius is not to be less than:

r = 0.025 Bdk (m)

Bdk = breadth of strength deck.

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r need not be taken greater than 0.1 b (m) where b = breadth of opening in m. For local reinforcement of deckplating at circular corners, see Sec. 5 B.505 Edges of openings are to be smooth. Machine flame cut openings with smooth edges may be accepted.Small holes are to be drilled.506 Studs for securing small hatch covers are to be fastened to the top of a coaming or a ring of suitablethickness welded to the deck. The studs are not to penetrate the deck plating.

C. Shear StrengthC 100 Cases to be investigated101 If doors are arranged in the craft's side, the required sectional area of the remaining side plating will bespecially considered.102 If rows of windows are arranged below strength deck, sufficient horizontal shear area must be arrangedto carry down the midship tension and compression.103 In these and other locations with doubtful shear areas, allowable shear stress may be taken as:

D. Cases to be InvestigatedD 100 Inertia induced loads101 Transversely framed parts of forebody are to be checked for the axial inertia force given in Ch.1 Sec.3A700:

FL= Δal (kN)

al = maximum surge acceleration, not to be taken less than:

The distribution of stresses will depend on instantaneous forward immersion and on location of cargo.102 Bottom structure in way of thrust bearings may need a check for the increased thrust when vessel isretarded by a crest in front.103 Allowable axial stress and associated shear stresses will be related to the stresses already existing in theregion.104 For passenger craft, a separate analysis is to be performed to investigate the structural consequence whensubject to the collision load as given in the International Code of Safety for High-Speed Craft, paragraph 4.3.3(see Ch.7 Sec.1 B300).

Guidance note:Inertia forces from the collision deceleration should be considered for shear and buckling in the foreship area, and forthe forces acting on the supporting structure for cargo.


E. Transverse Strength of Twin Hull CraftE 100 Transverse strength101 The twin hull connecting structure is to have adequate transverse strength related to the design loads andmoments given in Ch.1.102 When calculating the moment of inertia, and section modulus of the longitudinal section of the

τ allowable bending stress3

-----------------------------------------------------------=

0.4 g for VL

------- 5≥

0.2 g for VL

------- 3≤

linear interpolaton of al for 3 Vl

----- 5< <

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connecting structure, the effective sectional area of transverse strength members is in general to be taken as thenet area with effective flange after deduction of openings.The effective shear area of transverse strength members is in general to be taken as the net web area afterdeduction of openings.

E 200 Allowable stresses 201 The equivalent stress is defined as:

σx = total normal stress in x-directionσy = total normal stress in y-directionτ = total shear stress in the xy-plane.

By total stress is meant the arithmetic sum of stresses from hull girder and local forces and moments.202 The following total stresses are normally acceptable:

— normal stress:σ = 160 f1 (N/mm2)

— mean shear stress:τ = 90 f1 (N/mm2)

— equivalent stress:σe = 180 f1 (N/mm2).

σc σx2 σy

2 σxσy 3τ2+–+=

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SECTION 5 PLATING AND STIFFENERS

A. GeneralA 100 Introduction101 In this section the general requirements for plate thicknesses and local strength of panels of aluminiumalloy are given.102 Buckling strength requirements are related to longitudinal hull girder stresses. Panels subjected to othercompressive, shear or biaxial stresses will be specially considered.

A 200 Definitions201 Symbols:

t = rule thickness of plating in mmZ = rule section modulus of stiffener in cm3

s = stiffener spacing in m, measured along the platingl = stiffener span in m, measured along the top flange of the member.

The depth of stiffener on crossing panel may be deducted when deciding the span.For curved stiffeners l may be taken as the chord length

p = design pressure in kN/m2 as given in Ch.1 Sec.2σ = nominal allowable bending stress in N/mm2 due to lateral pressure (see Table A1)f1 = see Sec.l A202τ = nominal allowable shear stress in N/mm2.

A 300 Allowable stresses301 Maximum allowable bending stresses in plates and stiffeners are to be according to Table A1.

B. PlatingB 100 Minimum thicknesses101 The thickness of structures is in general not to be less than:

Table A1 Allowable bending stressesItem Plate Stiffener

(N/mm2)Bottom, slamming load 200 f1 180 f1Bottom, sea load 180 f1 160 f1Side 180 f1 160 f1Deck 180 f1 160 f1Flat cross structure, slamming load 200 f1 180 f1Flat cross structure, sea load 180 f1 160 f1Bulkhead, collision 180 f1 160 f1Superstructure/deckhouse front 160 f1 140 f1Superstructure/deckhouse side/deck 180 f1 160 f1Bulkhead, watertight 220 f1 200 f1Tank bulkhead 180 f1 160 f1

f =

σf = yield stress in N/mm2 at 0.2% offset for unwelded alloy.σf is not to be taken greater than 70% of the ultimate tensile strength

tt0 kL+

f----------------- s

sR----- (mm)=

σf240---------

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t0 and k according to Table B1.

B 200 Bending201 The general requirement for thickness of plating subject to lateral pressure is given by:

C = correction factor for aspect ratio (= s/l) of plate field and degree of fixation of plate edges given in TableB2.

202 The thickness requirement for a plate field clamped along all edges and with an aspect ratio ≤ 0.5:

B 300 Slamming301 The bottom plating is to be strengthened according to the requirements given in 302 to 303.

302 The thickness of the bottom plating is not to be less than:

s = actual stiffener spacing (m)sR = basic stiffener spacing (m)

=

is not to be taken less than 0.5 or greater than 1.0.

Table B1 Values of t0 and kItem t0 k

Shell platingBottom, bilge and side to loaded water line 4.0 0.03Side above loaded water line 3.5 0.02Bottom aft in way of rudder, shaft brackets etc. 10.0 0.10

Deck and inner bottom plating

Strength deck weather part forward of amidships 3.0 0.03Strength deck weather part aft of amidships 2.5 0.02Inner bottom 3.0 0.03Car deck 4.0 0.03Accommodation deck 2.0 0.02Deck for cargo 4.0 0.03Superstructure and deckhouse decks 1.0 0.01

Bulkhead plating

Collision bulkhead 3.0 0.03Tank bulkhead 3.0 0.03Other watertight bulkheads 3.0 0.02Superstructure and deckhouse front 3.0 0.01Superstructure and deckhouse sides and aft 2.5 0.01

Other structures Foundations 3.0 0.08Structures not mentioned above 3.0 0

kr = correction factor for curved plates

=

r = radius of curvature in mPsl = as given in Ch.1 Sec.2

2 100 L+( )1000

---------------------------

ssR------

t s Cpσ

-------------- (mm)=

t 22.4s pσ

--------------------- (mm).=

t22.4krs Psl

σsl------------------------------ (mm)=

1 0.5sr--–⎝ ⎠

⎛ ⎞

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303 Above the slamming area the thickness may be gradually reduced to the ordinary requirement at side.For craft with rise of floor, however, reduction will not be accepted below the bilge curvature or chine.

C. Stiffeners

C 100 Bending101 The section modulus of longitudinals, beams, frames and other stiffeners subjected to lateral pressure isnot to be less than:

m = bending moment factor depending on degree of end constraints and type of loading, see also Sec. 6Table B2.

The m-values are normally to be as given in Table C 1.The m-values may have to be increased after special consideration of rotation/deflection at supports or variationin lateral pressure.The m-values may be reduced, provided acceptable stress levels are demonstrated by direct calculations.102 The requirement in 101 is to be regarded as a requirement about an axis parallel to the plating. As anapproximation, the requirement for standard section modulus for stiffeners at an oblique angle with the platingmay be obtained if the formula in 101 is multiplied by the factor:

α = angle between the stiffener web plane and the plane perpendicular to the plating.

For α-values less than 12° corrections are normally not necessary.103 When several members are equal, the section modulus requirement may be taken as the averagerequirement for each individual member in the group. However, the requirement for the group is not to be takenless than 90% of the largest individual requirement.104 Front stiffeners of superstructures and deckhouses are to be connected to deck at both ends with aconnection area not less than:

Side and after end stiffeners in the lowest tier of erections are to have end connections.

σsl = 200 f1 (N/mm2).

Table B2 Values of CDegree of fixation of plate edges Aspect ratio < 0.5 Aspect ratio = 1.0

σl σs σx σy σl σs σx σyClamped along all edges 500 342 75 250 310 310 130 130Longest edge clamped, shortest edge simply supported

500 0 75 250 425 0 140 200

σl = stress at midpoint of longest edge.σs = stress at midpoint of shortest edge.σx = maximum field stress parallel to longest edge.σy = maximum field stress parallel to shortest edge.

Table C1 Values of mItem mContinuous longitudinal members 85Non-continuous longitudinal members 100Transverse members 100Vertical members, ends fixed 100Vertical members, simply supported 135Bottom longitudinal members 85

Z m l2spσ

---------------- cm3( )=

1αcos

------------

a 0.07f1

-----------lsp= cm2( )

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C 200 Slamming201 The section modulus of longitudinals or transverse stiffeners supporting the bottom plating is not to beless than:

m = 85 for continuous longitudinals = 100 for transverse stiffenerspsl = slamming pressure as given in Ch.1 Sec. 2σsl = 180 f1 (N/mm2).

The shear area is not to be less than:

τsl = 90 f1 (N/mm2).

Bottom transverse members 100Side longitudinal members 85Side vertical members 100Deck longitudinal members 85Deck transverse members 100Watertight bulkhead stiffeners, fixed ends 65Watertight bulkhead stiffeners, fixed one end (lower) 85Watertight bulkhead stiffeners, simply supported ends 125Watertight bulkhead horizontal stiffeners, fixed ends 85Watertight bulkhead stiffeners, fixed one end (upper) 75Watertight bulkhead horizontal stiffeners, simply supported 125Tank cargo bulkhead, fixed ends 100Tank cargo bulkhead, simply supported 135Deckhouse stiffeners 100Casing stiffeners 100

Table C1 Values of m (Continued)Item m

Zm l2s psl

σsl---------------------- cm3( )=

AS6.7 l s–( )s psl

τsl----------------------------------- cm2( )=

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SECTION 6 WEB FRAMES AND GIRDER SYSTEMS

A. General

A 100 Introduction101 In this section the general requirements for simple girders and procedures for the calculations of complexgirder systems are given.

A 200 Definitions201 Symbols:

s = girder span in m. The web height of in-plane girders may be deductedb = breadth of load area in m (plate flange) b may be determined from Table A1p = design pressure in kN/m2 according to Ch. 1 Sec.2P = design axial force in kNσ = nominal allowable bending stress in N/mm2 due to lateral pressureτ = nominal allowable shear stress in N/mm2

σc = critical buckling stress in N/mm2

σel = ideal elastic buckling stress in N/mm2

Z = rule section modulus in cm3

AW = rule web area in cm2

A = rule cross-sectional area in cm2

tw = web thickness in mmhw = web height in mmbf = flange breadth in mm.

A 300 Minimum thicknesses301 The thickness of structures are in general not to be less than:

t0 and k according to Table A2.

f =

σf = yield stress in N/mm2 at 0.2% offset for unwelded alloy. σf is not to be taken greater than 70% of the ultimate tensile strength. For unwelded material, f may be taken as f1 in Sec.2 Tables B1 to B3.

s = actual stiffener spacing in msR = basic stiffener spacing in m

=

is not to be taken less than 0.5 or greater than 1.0.

Table A1 Breadth of load areaFor ordinary girders b = 0.5 (l1 + l2 (m)

l1 and l2 are the spans in m of the supported stiffenersFor hatch side coamings b = 0.2 (B1 - b2) (m)

B1 = breadth of craft in m measured at the middle of the hatchwayb2 = breadth of hatch in m measured at the middle of the hatchway

For hatch end beams b = 0.4 b3 (m)b3 = distance in m between hatch end beam and nearest deep transverse girder or transverse bulkhead

tt0 kL+

f----------------- s

sR----- mm( )=

σf240---------

2 100 L+( )1000

---------------------------

ssR------

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A 400 Allowable stresses

401 Maximum allowable bending stresses and shear stresses in web frames and girders are to be accordingto Table A3.

For watertight bulkheads (excluding the collision bulkhead), allowable stresses may be increased to 200 f1, 100f1 and 220 f1 for bending, shear and equivalent stresses, respectively.

A 500 Continuity of strength members

501 Structural continuity is to be maintained at the junction of primary supporting members of unequalstiffness by fitting well rounded brackets.Brackets are to extend to the nearest stiffener, or local plating reinforcement is to be provided at the toe of thebracket.

502 Where practicable, deck pillars are to be located in line with pillars above or below.

503 Below decks and platforms, strong transverses are to be fitted between verticals and pillars, so that rigidcontinuous frame structures are formed.

B. Web Frames and Girders

B 100 General

101 The requirements for section modulus and web area given in 400 are applicable to simple girderssupporting stiffeners or other girders exposed to linearly distributed lateral pressure. It is assumed that thegirder satisfies the basic assumptions of simple beam theory and that the supported members are approximatelyevenly spaced and similarly supported at both ends. Other loads will have to be specially considered.

102 When boundary conditions for individual girders are not predictable due to dependence of adjacentstructures, direct calculations according to the procedures given in Sec. 9 D will be required.

103 The section modulus and web area of the girder are to be taken in accordance with requirements as givenin the following. Structural modelling in connection with direct stress analysis is to be based on the samerequirements when applicable. Note that such structural modelling will not reflect the stress distribution at localflange cutouts or at supports with variable stiffness over the flange width. The local effective flange which maybe applied in stress analysis is indicated for construction details in various Classification Notes on «strengthanalysis of hull structures)».

B 200 Effective flange

201 The effective plate flange area is defined as the cross-sectional area of plating within the effective flangewidth. Continuous stiffeners may be included with 50% of their cross-sectional area. The effective flange widthbe is determined by the following formula:

be = C b (m)

C = as given in Table B1 for various numbers of evenly spaced point loads (r) on the span.

Table A2 Values of t0 and kItem t0 k

Girders and stiffeners

Bottom centre girder 3.0 0.05Bottom side girders, floors, brackets and stiffeners 3.0 0.03Side, deck and bulkhead longitudinals girders and stiffeners outside the peaks 3.0 0.02Peak girders and stiffeners 3.0 0.03Longitudinals 3.0 0.03Double bottom floors and girders 3.0 0.02

Other structuresFoundations 3.0 0.08Structures not mentioned above 3.0 0

Table A3 Allowable stressesItem Web frames and girders

Bending stress(N/mm2)

Shear stress(N/mm2)

Equivalent stress(N/mm2)

Dynamic load 180 f1 90 f1 200 f1Sea/static load 160 f1 90 f1 180 f1

DET NORSKE VERITAS


If the above method of calculation is used for strength members which support corrugations perpendicular tothe span of the strength member, C is to be reduced by 90%.

a = distance between points of zero bending moments = S for simply supported girders = 0.6 S for girders fixed at both ends.

202 The effective plate area is not to be less than the effective area of the free flange within the followingregions:

— ordinary girders: total span— continuous hatch side coamings and hatch end beams: length and breadth of the hatch, respectively, and an

additional length of 1 m at each end of the hatch corners.

B 300 Effective web301 Holes in girders will generally be accepted, provided the shear stress level is acceptable and the bucklingstrength is sufficient. Holes are to be kept well clear of end of brackets and locations where shear stresses arehigh.

B 400 Strength requirements401 The section modulus for girders subjected to lateral pressure is not to be less than:

σ = 160 f1 (maximum)m = bending moment factor, m-values in accordance with 403 may be applied.

402 The effective web area of girders subjected to lateral pressure is not to be less than:

ks = shear force factor.ks-values in accordance with 403 may be applied

a = number of stiffeners between considered section and nearest supportr = average point load in kN from stiffeners between considered section and nearest supportτ = 90 f1 (maximum).

n = number of supported stiffeners on the girder span. The web area at the middle of the span is not to beless than 0.5 AW.

403 The m- and ks-values referred to in 401 and 402 may be calculated according to general beam theory. InTable B2 m- and ks-values are given for some defined load and boundary conditions. Note that the greatest m-value is to be applied to simple girders. For girders where brackets are fitted or the flange area has been partlyincreased due to large bending moment, a smaller m-value may be accepted outside the strengthened region.

Table B1 Values of Ca/b 0 1 2 3 4 5 6 ≥ 7C (r ≥ 6) 0.00 0.38 0.67 0.84 0.93 0.97 0.99 1.00C (r = 5) 0.00 0.33 0.58 0.73 0.84 0.89 0.92 0.93C (r = 4) 0.00 0.27 0.49 0.63 0.74 0.81 0.85 0.87C (r ≤ 3) 0.00 0.22 0.40 0.52 0.65 0.73 0.78 0.80

Z mS2bpσ

----------------- cm3( )=

AW10 ksSbp ar–( )

τ------------------------------------- cm2( )=

The a-value is in no case to be taken greater than n 1+4

------------

DET NORSKE VERITAS


404 The m- and ks-values referred to in 401 and 402 are normally to be as given in Table B3 for the variousstructural items.

405 The equivalent stress is not to exceed 180 f1 N/mm2.

B 500 Girder tripping brackets501 The spacing ST of tripping brackets is normally not to exceed the values given in Table B4 valid forgirders with symmetrical face plates. For others the spacing will be specially considered.Tripping brackets are further to be fitted near the toe of bracket, near rounded corner of girder frames and inline with any cross ties.502 The tripping brackets are to be fitted in line with longitudinals or stiffeners, and are to extend the wholeheight of the web plate. The arm length of the brackets along the longitudinals or stiffeners, is not to be lessthan 40% of the depth of the web plate, the depth of the longitudinal or stiffener deducted. The requirementmay be modified for deep transverses.503 Tripping brackets on girders are to be stiffened by a flange or stiffener along the free edge if the length

Table B2 Values of m and ksLoad and boundary conditions Bending moment and shear force factors

Positions 1m1ks1

2m2—

3m3ks3

1Support

2Field

3Support

850.50 42 85

0.50

0.38 70 1.250.63

0.50 125 0.50

650.30 43 100

0.70

0.20 60 1350.80

0.33 130 0.67

Table B3 Values of m and ks for various structural itemsItem m ks

Bottom:Web frames 100 0.63Floors 100 0.63Longitudinal girders 100 0.63

Side:

Longitudinal girders 100 0.54Web frames, upper end 100 0.54Web frames, lower end 100 0.72Deck girders 100 0.63

Bulkhead:Horizontal girders 100 0.54Vertical girders, upper end 100 0.54Vertical girders, lower end 100 0.72

DET NORSKE VERITAS


of the edge exceeds:0.06 tt (m)

tt = thickness in mm of tripping bracket.

The area of the stiffening is not to be less than:10 lt (cm2)

lt = length in m of free edge.

The tripping brackets are to have a smooth transition to adjoining longitudinals or stiffeners exposed to largelongitudinal stresses.

B 600 Girder web stiffeners601 The web plate of transverse and vertical girders are to be stiffened where:

hw > 75 tw (mm)

tw = web thickness in mm,

with stiffeners of maximum spacing:s = 60 tw (mm)

within 20% of the span from each end of the girder and where high shear stresses.Elsewhere stiffeners are required when:

hw > 90 tw (mm)with stiffeners of maximum spacing:

s = 90 tw (mm)For girders supporting other girders, the end requirements may have to be applied all over the span.602 Stiffeners are to be fitted along free edges of the openings parallel to the vertical and horizontal axis ofthe opening. Stiffeners may be omitted in one direction if the shortest axis is less than 400 mm and in bothdirections if length of both axes is less than 300 mm. Edge reinforcement may be used as an alternative tostiffeners.

Table B4 Spacing between tripping bracketsGirder type ST (m)Bottom and deck transverses

0.02 bf maximum 6Stringers and vertical webs in general

Longitudinal girders in generalLongitudinal girders in bottom and strength deck for L > 50m within 0.5 L amidships

0.014 bf maximum 4Stringers and vertical webs in tanks and machinery spaces

Vertical webs supporting single bottom girders and transversesIf the web of a strength member forms an angle with the perpendicular to the ship’s side of more than 10°, ST is not to exceed 0.007 bf.

bf = flange breadth in mmS = distance between transverse girders in m.

DET NORSKE VERITAS


SECTION 7 PILLARS AND PILLAR BULKHEADS

A. GeneralA 100 Introduction101 In this section requirements for pillars and for bulkhead stiffeners substituting pillars are given.

A 200 Definitions201 Symbols:L, B, D, T, CB, see Ch.1.

t = thickness of plating in mms = stiffener spacing in m, measured along platel = length of pillars, cross ties, bulkhead stiffeners etc. between effective supports normal to their axis in mI = smallest moment of inertia in cm4, including 40 x plate thickness as flange for bulkhead stiffenerA = cross-sectional area in cm2, including 40 x plate thickness for bulkhead stiffenerp = design pressure as given in Ch.1.

B. PillarsB 100 Arrangement of pillars101 Where practicable, deck pillars are to be located in line with pillars above or below.If arrangement with pillars in line is not possible, deck beams or girders will have to be reinforced.102 Pillars or equivalent supports are to be arranged below deckhouses, windlasses, winches and other heavyweights.103 The engine room casing is to be supported.104 Doubters are to be fitted on deck and inner bottom, except in tanks where doublers are not allowed.Brackets may be used instead of doublers. Where pillar tension may occur, brackets are required.105 Structural reinforcement below pillars will be considered in the individual cases.

B 200 Cross-section particulars201 The radius of gyration of a member is to be taken as:

Ia = moment of inertia as built in cm4 about the axis perpendicular to the expected direction of bucklingAa = cross-sectional area as built in cm2.

If the end conditions are different with respect to the principle axes of the member, the i-value may have to bechecked for both axes.

B 300 Pillar scantlings301 The cross-sectional area of members subjected to compressive loads is not to be less than:

η =

P = axial load in kN as given for various strength members in 302 and 303. Alternatively, P may beobtained from direct stress analysis. See Sec.9 D

l = length of member in mi = radius of gyration in cmk = 0.7 in general

iIaAa------ cm( )=

A 10 Pησc----------- cm2( )=

k

1 li-+⎝ ⎠

⎛ ⎞---------------- minimum 0,3

DET NORSKE VERITAS


= 0.6 when design loads are primarily dynamic

The formula given for σE is based on hinged ends and axial force only.If, in special cases, it is verified that one end can be regarded as fixed, the value of σE may be multiplied by 2.If it is verified that both ends can be regarded as fixed, the value of σE may be multiplied by 4.In case of eccentric force additional end moments or additional lateral pressure, the strength member is to bereinforced to withstand bending stresses.302 The nominal axial force in pillars is normally to be taken as:

P = n F

n = number of decks above pillar. In case of a large number of decks (n > 3), a reduction in P will beconsidered based upon a special evaluation of load redistribution

F = the force contribution in kN from each deck above and supported by the pillar in question given by:

F = p AD (kN)

p = design pressure on deck as given in Ch.1 Sec.2AD = deck area in m2 supported by the pillar, normally taken as half the sum of span of girders supported,

multiplied by their loading breadth.For centre line pillars supporting hatch end beams (see Fig.1 and Fig.2):

b1 = distance from hatch side to craft's side.

303 The nominal axial force in cross ties and panting beams is normally to be taken as:P = e b p (kN)

e = mean value of spans in m on both sides of the cross tieb = load breadth in mp = the larger of the pressures in kN/m2 on either side of the cross tie (e.g. for a side tank cross tie, the

pressure head on the craft's side may be different from that on the longitudinal bulkhead).

B 400 Pillars in tanks401 Hollow pillars are not accepted.402 Where the hydrostatic pressure may give tensile stresses in the pillars and cross members, their sectionalarea is not to be less than:

A = 0.07 Adkpt (cm2)

Adk = deck or side area in m2 supported by the pillar or cross memberpt = design pressure, p in kN/m2 giving tensile stress in the pillar.

The formula may be used also tension control of panting beams and cross ties in tanks.Doubling plates at ends are not allowed.

σc =

=

σE =

σF = minimum upper yield stress of material in N/mm2

E = modulus of elasticity for aluminium = 69 000 N/mm2.

AD =

=

σE when σEσF2

------<

σF 1σF

4σE----------–⎝ ⎠

⎛ ⎞ when σEσF2

------>

π2E i100 l------------⎝ ⎠

⎛ ⎞ 2(N mm⁄ 2 )

4 A1 A2+( )b1B----- when transverse beams

4 A3 A4 A5+ +( )b1B----- when longitudinals

DET NORSKE VERITAS


C. Supporting BulkheadsC 100 General101 Bulkheads supporting decks are to be regarded as pillars. Compressive loads are to be calculated basedon supported deck area and deck design loading.102 Buckling strength of stiffeners are to be calculated as indicated in Sec.10 E101, assuming a plate flangeequal to 40 x the plate thickness when calculating IA, A and i.Local buckling strength of adjoining plate and torsional buckling strength of stiffeners are to be checked.

Fig. 1Deck with transverse beams

Fig. 2Deck with longitudinals

DET NORSKE VERITAS


SECTION 8 WELD CONNECTIONS

A. General

A 100 Introduction

101 In this section requirements for welding of aluminium alloys and various connection details are given.

102 For general requirements for approval of welding of wrought aluminium alloys, see Pt.2 Ch.3 Sec.2.

A 200 Welding particulars

201 Welding at ambient air temperature of – 5°C or below is only to take place after special agreement.

202 The welding sequence is to be such that the parts may as far as possible contract freely in order to avoidcracks in already deposited runs of weld. Where a butt meets a seam, the welding of the seam is to beinterrupted well clear of the junction and not be continued until the butt is completed. Welding of butt is tocontinue past the open seam and the weld be chipped out for the seam to be welded straight through.

203 Welding procedures and welding consumables approved for the type of connection and parent materialin question, are to be used. See “Register of Approved Manufac-turers” and “Register of Type ApprovedProducts”.

B. Types of Welded Joints

B 100 Butt joints

101 For panels with plates of equal thickness, the joints are normally to be butt welded with prepared edges.

102 For butt welded joints of plates with thickness difference exceeding 2 mm, the thicker plate is normallyto be tapered. The taper is generally not to exceed 1:3.

103 Welding against permanent or temporary backing is to be specially considered with respect to fatigue,non-destructive examination and any risk of crevice corrosion.

B 200 Tee or cross joints

201 The connection of girder and stiffener webs to plate panels, including plating abutting to other platepanels, is normally to be made by fillet welds as indicated in Fig.1.

Fig. 1Tee or cross joints

Where the connection is highly stressed, the edge of the abutting plate may have to be bevelled to give deep orfull penetration welding. Where the connection is moderately stressed, intermittent welds may be used. Withreference to Fig.2, the various types of intermittent welds are as follows:

— chain weld— staggered weld— scallop weld (closed).

DET NORSKE VERITAS


Fig. 2Intermittent welds

202 Double continuous welds are required in the following connections irrespective of the stress level:

— oiltight and watertight connections— connections in foundations and supporting structures for machinery— all connections in way of the steering gear arrangement— connections in rudders, except where access difficulties necessitate slot welds— all connections in a region above the propeller extending a radius of minimum 1.5 x the propeller diameter— connections at supports and ends of stiffeners, pillars, cross ties and girders— centreline girder to keel plate— all structures in ballast tanks and other tanks holding corrosive liquids.

C. Size of ConnectionsC 100 Fillet welds, general101 Unless otherwise stated, the requirements for throat thicknesses are given for double continuous filletwelds. It is assumed that the welding consumables used will give weld de posits with yield strength accordingto Pt.2 Ch.3 Sec.2 Table C2.102 The throat thickness of double continuous fillet weld is not to be less than:

t = 0.42 t0(mm)

t0 = thickness in mm of thinner of the plates.

The throat thickness is not to be less than 2 mm.The throat thickness may have to be increased when considered necessary due to a high stress level.103 The throat thickness of intermittent welds is to be as required in 102 for double continuous weldsprovided the welded length is not less than:

— 80% of total length in the slamming area forward of amidships— 60% of total length for connections in tanks and bottom aft of amidships— 45% of total length for connections elsewhere.

t0 = as given in 102.

Total length means total length of double continuous welds.104 Double continuous welds may be required in:

— slamming area— engine room area— adjacent to tanks.

C 200 Fillet welds and penetration welds subject to high tensile stresses201 In structural parts where high tensile stresses (> 50 N/mm2) act through an intermediate plate (see Fig.1)

DET NORSKE VERITAS


increased fillet welds or penetration welds are to be used. Examples of such structures are:

— transverse bulkhead connection to the double bottom— structural elements in double bottoms below bulkheads— transverse girders to longitudinal bulkheads.

202 The throat thickness of double continuous weld is not to be less than:

σ = calculated maximum tensile stress in abutting plate in N/mm2 = minimum 50 N/mm2 r = root face in mmt0 = thickness in mm of thinner of the plates.

C 300 End connections of girders, pillars and cross ties301 The weld connection area of bracket to adjoining girders or other structural parts is to be based on thecalculated normal and shear stresses. Double continuous welding is to be used. Where high tensile stresses areexpected, welding according to 200 is to be applied.302 The end connections of simple girders are to satisfy the requirements for section modulus given for thegirder in question.Where shear stresses in web plates exceed 35 fw N/mm2, double continuous boundary fillet welds are to havethroat thickness not less than:

τ = calculated shear stress in N/mm2

t0 = thickness of abutting plate.fw = material factor for weld deposit = σ fw/240σfw = yield strength in N/mm2 of weld deposit.

303 End connections of pillars and cross ties are to have a weld area not less than:

A = load area in m2 for pillar or cross tiep = design pressure in kN/m2 as given in Ch.1fw = as given in 302.

C 400 End connections of stiffeners401 Stiffeners may be connected to the web plate of girders in the following ways:

— welded directly to the web plate on one or both sides of the frame— connected by single- or double-sided lugs— with stiffener or bracket welded on top of frame— a combination of the above mentioned connections.

In locations with great shear stresses in the web plate, a double-sided connection or a stiffening of theunconnected web plate edge is normally required. A double-sided connection may be taken into account whencalculating the effective web area.402 The connection area at supports of stiffeners is normally not to be less than:

c = factor as given in Table C 1k = 0.125 for pressure acting on stiffener side = 0.1 for pressure acting on opposite sidel = span of stiffener in m

t 0.35 σ55------ r

t0---- 1–+⎝ ⎠

⎛ ⎞ t0 (mm)=

tτ t0

80 fw------------- (mm)=

a 0.14Apfw

------------------- (cm2 )=

a0c k l 0.5s–( ) s p

fw--------------------------------------- (cm2 )=

DET NORSKE VERITAS


s = spacing between stiffeners in mp = design pressure in kN/m2 as given in Ch.1fw = as given in 302.

403 Various standard types of connections are shown in Fig.3.Other types of connection will be considered in each case.

Fig. 3End connections

404 Connection lugs are to have a thickness not less than the web plate thickness.405 Lower ends of peak frames are to be connected to the floors by a weld area not less than:

l, s p and fw = as given in 402.406 Bracketed end connections as mentioned in 407 and 408 are to have a weld area not less than:

Z = section modulus of stiffener in cm3

h = stiffener height in mmk = 24 for connections between supporting plates in double bottoms and transverse bottom frames or

reversed frames = 25 for connections between the lower end of main frames and brackets = 15 for brackets fitted at lower end of tween deck frames, and for brackets on stiffeners = 10 for brackets on tween deck frames carried through the deck and overlapping the underlying bracketfw = as given in 302.

Table C1 c-factorsType of connection(see Fig. 3)

Stiffener or bracket on top of stiffener

None Single-sided Double-sideda 1.00 1.25 1.00b 0.90 1.15 0.90c 0.80 1.00 0.80

STIFFNER ORBRACKET

THIS DISTANCE SHOULD BEAS SHORT AS POSSIBLE

a

b

STIFFNER ORBRACKET

c

STIFFNER ORBRACKET

LUG

a 0.105 l s pfw

------------------------- (cm2 )=

a kZfwh--------- (cm2 )=

DET NORSKE VERITAS


407 Brackets between transverse deck beams and frames or bulkhead stiffeners are to have a weld area notless than:

tb = thickness in mm of bracketZ = as defined in 406.

408 The weld area of brackets to longitudinals is not to be less than the sectional area of the longitudinal.Brackets are to be connected to bulkhead by a double continuous weld.

a 0.41 Z tb (cm2 )=

DET NORSKE VERITAS


SECTION 9 DIRECT STRENGTH CALCULATIONS

A. General

A 100 Introduction101 In the preceding sections the scantlings of the various primary and secondary hull structures (girdersystems, stiffeners, plating) have been given explicitly, based on the design principles outlined in Ch.1 Sec.l.In some cases direct strength or stress calculations have been referred to in the text. The background andassumptions for carrying out such calculations in addition to or as a substitute to the specific requirements aregiven in this section. Load conditions, allowable stresses and applicable calculation methods are specified.

A 200 Application201 The application of direct stress analysis is governed by:

a) Required as part of rule scantling determination. In such cases where simplified formulations are not ableto take into account special stress distributions, boundary conditions or structural arrangements withsufficient accuracy, direct stress analysis has been required in the rules.

b) As alternative basis for the scantlings. In some cases direct stress calculations may give reduced scantlings,especially when optimisation routines are incorporated.

B. Plating

B 100 General101 Normally direct strength analysis of laterally loaded plating is not required as part of rule scantlingestimation.102 Buckling control of plating subjected to large in-plane compressive stresses is specified in Sec. 4.

B 200 Calculation procedure201 Laterally loaded local plate fields may be subject to direct stress analysis applying general 3-dimensionalplate theory or finite element calculations. The calculations should take into account the boundary conditionsof the plate field as well as membrane stresses developed during deflection of the plate.

B 300 Allowable stresses301 When combining the calculated local bending stress with in-plane stresses the equivalent stress σe in themiddle of a local plate field is not to exceed 240 f1 N/mm2. The local bending stress in the same point is in nocase to exceed 160 f1 N/mm2.

σx = aritmetic sum of local bending stress and in-plane stresses in the x-directionσy = aritmetic sum of local bending stress and in-plane stresses in the y-directionτ = shear stress in the xy-plane.

302 The final thickness is not, however, to be less than the minimum thickness given in Sec.1 for the structurein question.

C. Stiffeners

C 100 General101 Direct strength analysis of stiffeners may be requested in the following cases:

— stiffeners on supports with different deflection characteristics— stiffeners subjected to large bending moments transferred from adjacent structures at supports.

102 Buckling control of stiffeners subjected to large axial, compressive stresses is specified in Sec.4.

σe = σx2 σy

2 σxσy 3τ2+–+

DET NORSKE VERITAS


C 200 Calculation procedure201 The calculations are to reflect the structural response of the 2- or 3-dimensional structure considered.Calculations based on elastic beam theory may normally be applied, with due attention to:

— boundary conditions— shear area and moment of inertia variations— effective flange— effects of bending, shear and axial deformations— influence of end brackets.

C 300 Loads301 The local lateral loads are to be taken as specified in Ch.1 for the structure in question.

C 400 Allowable stresses401 The allowable stress level is given in Table C1.

D. GirdersD 100 General101 For girders which are parts of a complex 2- or 3-dimensional structural system, a complete structuralanalysis may have to be carried out to demonstrate that the stresses are acceptable when the structure is loadedas described in 300.102 Calculations as mentioned in 101 may be requested to be carried out for:

— bottom structures— side structures— deck structures— bulkhead structures— transverse frame structures— other structures when deemed necessary by the Society.

103 In addition to the complex structures indicated above, direct strength calculations may also be performedon more simple girders in order to optimise scantlings.

D 200 Calculation methods201 Calculation methods or computer programs applied are to take into account the effects of bending, shear,axial and torsional deformations.The calculations are to reflect the structural response of the 2- or 3-dimensional structure considered, with dueattention to boundary conditions.For systems consisting of slender girders, calculations based on beam theory (frame work analysis) may beapplied, with due attention to:

— shear area variation— moment of inertia variation— effective flange.

202 For deep girders, bulkhead panels, etc. where results obtained by applying the beam theory areunreliable, finite element analysis or equivalent methods are to be applied.

D 300 Design load conditions301 The calculations are to be based on loads at design level as given in Ch.1. For sea-going conditionsrealistic combinations of external and internal dynamic loads are to be considered.The mass of deck structures may be neglected when less than 5% of the applied loads.302 For transverse web frame beam element analysis, the following combinations of load apply:

— sea pressure on all elements

Table C1 Allowable stress levelsNominal local bending stress σ = 160 f1 N/mm2

Combined local bending stress or girder stress or longitudinal stress σ = 220 f1 N/mm2

Nominal shear stress τ = 90 f1 N/mm2

DET NORSKE VERITAS


— slamming pressure on bottom.

If twin hull, the following three conditions are to be added:

— slamming pressure on bottom from outside and sea pressure on hull outer side— slamming pressure on bottom from inside and sea pressure on tunnel side and tunnel top— slamming pressure on tunnel top and sea pressure on tunnel side and bottom from inside

For all load cases, deck load pressure from cargo, passengers etc. is to be added.

D 400 Allowable stresses401 The equivalent stress is defined as:

σx = normal stress in x-directionσy = normal stress in y-directionτ = shear stress in the xy-plane.

402 The longitudinal combined stress taken as the sum of hull girder and longitudinal bottom, side or deckgirder bending stresses, is normally not to exceed 190 f1 N/mm2.403 For girders in general, the following stresses are normally acceptable:Normal stress:

σ = 160 f1 N/mm2.

Mean shear stress:

τ = 90 f1 N/mm2 for girders with one plate flangeτ = 100 f1 N/mm2 for girders with two plate flanges.

Equivalent stress:

σe = 180 f1 N/mm2.

σe = σx2 σy

2 σxσy 3τ2+–+

DET NORSKE VERITAS


SECTION 10 BUCKLING CONTROL

A. General

A 100 Definitions

101 Symbols:

t = thickness in mm of platings = shortest side of plate panel in ml = longest side of plate panel in m = length in m of stiffener, pillar etc.E = modulus of elasticity of the material = 0.69 · 105 N/mm2 for aluminiumσel = the ideal elastic (Euler) compressive buckling stress in N/mm2

σf = minimum upper yield stress of material in N/mm2. Usually base material properties are used, but criticalor extensive weld zones may have to be taken into account

τel = the ideal elastic (Euler) shear buckling stress in N/mm2

τf = minimum shear yield stress of material in N/mm2

=

σc = the critical compressive buckling stress in N/mm2

τc = the critical shear stress in N/mm2

σa = calculated actual compressive stress in N/mm2

τa = calculated actual shear stress in N/mm2

102 Relationships:

Guidance note:When the required σc or τc is known, the necessary σel or τel will from the above expressions of the Johnson-Ostenfeldrelationship be

η =

Zn = vertical distance in m from the baseline or deckline to the neutral axis of the hull girder, whichever is relevant

Za = vertical distance in m from the baseline or deckline to the point in question below or above the neutral axis, respectively.

σc =

=

τc =

=

σf

3-------

stability (usage) factor = σaσc-----

τaτc----=

σel when σelσf2-----<

σf 1σf

4σel-----------–⎝ ⎠

⎛ ⎞ when σelσf2----->

τel when τelτf2----<

τf 1τf

4τel----------–⎝ ⎠

⎛ ⎞ when τelτf2---->

σelσc

KJ 0–------------- and τel

τcKJ 0–-------------= =

DET NORSKE VERITAS


KJ − 0 from Fig.1 or from formula

Fig. 1


B. Longitudinal Buckling Load

B 100 Longitudinal stresses101 See Ch.l Sec.3 A700.

C. Transverse Buckling Load

C 100 Transverse stresses101 Transverse hull stresses in compression may occur from:

— transverse loads and moments in twin hull craft, see Sec. 4 E— supports of craft's side structure, see Sec. 6.

D. Plating

D 100 Plate panel in uni-axial compression101 The ideal elastic buckling stress may be taken as:

For plating with longitudinal stiffeners (in direction of compressive stress):

For plating with transverse stiffeners (perpendicular to compressive stress):

KJ− 0 = 1σcor τc

0.5 σf or τf( )-------------------------------- 1–⎝ ⎠

⎛ ⎞ 2–

For σcσf----- 0.5, KJ 1–< 1=

σel 0.9 k E t1000s--------------⎝ ⎠

⎛ ⎞ 2 (N/mm2 )=

k kl8.4

ψ 1.1+------------------ for (0 ψ≤ 1)≤= =

k ks c 1 sl--⎝ ⎠

⎛ ⎞ 2+

2 2.1

ψ 1.1+------------------ for (0 ψ 1)≤ ≤= =

DET NORSKE VERITAS


c = 2.50 when stiffeners are hollow profiles with s/l <0.5 and the enclosed area of the hollow profile is largerthan 20 s t

= 1.21 when stiffeners are angles or T-sections = 1.10 when stiffeners are bulb flats = 1.05 when stiffeners are flat bars.

For double bottom panels the c-values may be multiplied by 1.1.ψ is the ratio between the smaller and the larger compressive stress assuming linear variation, see Fig. 2.The above correction factors are not valid for negative values of ψ.The critical buckling stress is found from A102.

Fig. 2Buckling stress correction factor

102 The critical buckling stress is to be related to the actual compressive stresses as follows:

σa = calculated compressive stress in plate panels. With linearly varying stress across the plate panel, σa isto be taken as the largest stress

η = 1.0 for deck, side, single bottom and longitudinal bulkhead plating = 0.9 for bottom and inner bottom plating in double bottoms = 1.0 for locally loaded plate panels where an extreme load level is applied = ηG for locally loaded plate panels where a normal load level is applied (e.g. plating acting as effective

flange for girders)

ηG =

ps and pd = static and dynamic parts of p.103 Guidance note:

The resulting thickness requirement (before elastic buckling) will be:

— with stiffeners in direction of compressive stress:

σc according to 102KJ - 0 from Fig. l

— with stiffeners perpendicular to compressive stress:

c according to 101.


104 For elastic buckling, see G.

σcσaη-----≥

ps 0.5pd+

ps pd+-------------------------

t 2sσc

KJ 0–------------- (mm)=

t 4=s

1 sl--⎝ ⎠

⎛ ⎞ 2+

--------------------σc

cKJ 0–---------------- (mm)

DET NORSKE VERITAS


D 200 Plate panel in shear

201 The ideal elastic buckling stress may be taken as:

The critical shear buckling stress is found from A102.

202 The critical shear stress is to be related to the actual shear stresses as follows:

η = 0.90 for craft's side and longitudinal bulkhead subject to hull girder shear forces = 0.95 ηG for local panels in girder webs when nominal shear stresses are calculated (τa = Q/A) = ηG for local panels in girder webs when shear stresses are determined by finite element calculations or

similarηG = according to 102.

Guidance note:The resulting thickness requirement will be:

τc according to 202KJ - 0 from Fig.1.


D 300 Plate panel in bi-axial compression and shear

301 For plate panels subject to bi-axial compression the interaction between the longitudinal and transversebuckling strength ratios is given by:

σax = compressive stress in longitudinal direction (perpendicular to stiffener spacing s)σay = compressive stress in transverse direction (perpendicular to the longer side l of the plate panel)σcx = critical buckling stress in longitudinal direction as calculated in 100σcy = critical buckling stress in transverse direction as calculated in 100τa and τc are as given in 200

ηx, ηy= 1.0 for plate panels where the longitudinal stress σa (as given in Ch.1 Sec.3 A700) or other extremestress is incorporated and constitutes a major part in σax or σay

= 0.95 ηG other casesηG = according to 102K = c β a

c and a are factors given in Table B1

τel 0.9ktEt

1000s--------------⎝ ⎠

⎛ ⎞ 2 (N/mm2 )=

kt 5.34 4 sl--⎝ ⎠

⎛ ⎞ 2+=

τcτaη----≥

t 4sτc

ktKJ 0–

------------------ (mm)=

σaxηxσcxq------------------ K

σaxσayηxηyσcxσcyq----------------------------------

σayηyσcyq------------------⎝ ⎠

⎛ ⎞n

1≤+–

β 1000 st--

σfE-----=

DET NORSKE VERITAS


n = factor given in Table B1

ητ = η as given in 200.

Only stress components acting simultaneously are to be inserted in the formula.For plate panels in structures subject to longitudinal stresses, such stresses are to be directly combined withlocal stresses to the extent they are acting simultaneously and for relevant load conditions. Otherwisecombinations based on statistics may be applied.

Guidance note:For shear in combination with:

— uni-axial compression:

may be written:

and with:

— bi-axial compression, approximately:

For bi-axial compression alone q = 1.---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

E. Stiffeners in Direction of Compression

E 100 Lateral buckling mode101 The ideal elastic lateral buckling stress may be taken as:

IA = moment of inertia in cm4 about the axis perpendicular to the expected direction of bucklingA = cross-sectional area in cm2.

When calculating IA and A, a plate flange equal to 0.8 times the spacing is included for stiffeners.The critical buckling stress is found from A102.The formula given for σel is based on hinged ends and axial force only.Continuous stiffeners supported by equally spaced girders are regarded as having hinged ends when consideredfor buckling.In case of eccentric force, additional end moments or additional lateral pressure, the strength member is to bereinforced to withstand bending stresses.

Table B1 Factors for buckling strengthc a n

1.0 < l/s < 1.5 0.78 – 0.12 1.01.5 ≤ l/s < 8 0.80 0.04 1.2

q 1τa

ηττc-----------⎝ ⎠

⎛ ⎞2

–=

σaxσcx-------- or

σayσcy-------- ηxor ηy( )q≤

σaxηxσcx--------------- 1.1

σayηyσcy--------------- 0 8,

ηxηy------------

σaxσcx--------

σayσcy-------- q≤–+

σel 10 E

100 li-⎝ ⎠

⎛ ⎞ 2--------------------- (N/mm2 )=

iIAA-----=

DET NORSKE VERITAS


102 For longitudinals and other stiffeners in the direction of compressive stresses, the critical buckling stresscalculated in 101 is to be related to the actual compressive stress as follows:

σa = calculated extreme compressive stress, or ordinary local load stress divided by ηG from D100η = 0.85 for continuous stiffeners. = 1– ηb, maximum 0.85 for single-span stiffeners

Guidance note:The resulting maximum allowable slenderness will be:

KJ-0 from Fig. 1.---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e---

E 200 Torsional buckling mode201 For longitudinals and other stiffeners in the direction of compressive stresses, the ideal elastic bucklingstress for the torsional mode may in general be calculated from formulae in Rules for Classification of ShipsPt.3 Ch.1 Sec.14.202 The critical buckling stress as found from 201 and A102 is not to be less than:

σa = calculated extreme compressive stress, or ordinary local load stress divided by ηG from D100η = 0.85 in general = 0.8 when the adjacent plating is allowed to buckle in the elastic mode, according to G.

Guidance note:To avoid torsional buckling the height of flats should not exceed:

tw = thickness of web in mm

KJ - 0 from Fig.1.

Minimum flange breadth may be taken as:For symmetrical flanges:

For unsymmetrical flanges:

σcσaη-----≥

ηbsimultaneous bending moment at midspan

bending moment capacity-----------------------------------------------------------------------------------------------------=

100 li- 830

KJ 0–

σc-------------=

σcσaη-----=

σcσaη-----≥

hw tw140

σcKJ 0–-------------

------------------ (mm)=

σcσaη-----=

For flanged profiles, 1hwbf------ 3:< <

bf 5lσc

KJ 0–------------- (mm)=

DET NORSKE VERITAS


KJ − 0 = according to Fig.1hw = height of web in mm.


E 300 Web and flange buckling301 The σel -value required for the web buckling mode may be taken as:

tw, hw = web thickness and height in mm.302 The ideal elastic buckling stress of flange of angle and tee stiffeners may be calculated from thefollowing formula:

tf = flange thickness in mmbf = flange width in mm for angles, half the flange width for T-sections.

303 The critical buckling stress σc found from A102 is not to be less than as given in 202.Guidance note:

— Web thickness, see plating with stiffener in direction of compression stress, D103.— Flange width from web:

σc = according to 202KJ − 0 = according to Fig.1


F. Stiffeners Perpendicular to Direction of Compression

F 100 Moment of inertia of stiffeners101 For stiffeners supporting plating subject to compressive stresses perpendicular to the stiffener directionthe moment of inertia of the stiffener section (including effective plate flange) is not to be less than:

l = span in m of stiffeners = spacing in m of stiffenerst = plate thickness in mm

σel=

bf 3.5 lσc

KJ 0–------------- (mm)=

σcσaη-----=

σel 3.8 Etwhw------⎝ ⎠

⎛ ⎞2

N mm2⁄( )=

σel 0.38 Etfbf----⎝ ⎠

⎛ ⎞2

N mm2⁄( )=

bf tf140

σcKJ 0–-------------

------------------ (mm)<

I0.81σaσell

4st

--------------------------------- cm4( )=

σcKJ 0–-------------

DET NORSKE VERITAS


σc =

σa = calculated extreme compressive stress, or ordinary local load stress divided by ηG from D100KJ − 0=according to Fig.1.

G. Elastic Buckling of Stiffened PanelsG 100 Elastic buckling as a design basis101 Elastic buckling may be accepted for plating between stiffeners when:

— ησc of stiffener in direction of compression > ησel of plating.ησc from E and A102. To be multiplied by ηG for ordinary local load.ησel from D and A102

— there are no functional requirements prohibiting the deflections— extreme loads are used in the calculations.

Guidance note:For the torsional buckling mode of flats may be taken


G 200 Allowable compression201 The allowable compressive force in the panel may be increased from:

PA = 0.l ηp σel (Ap + As) (kN)to:

PA = 0.l ηp σel (Ap + As) +

ηp, ηs = η for plating and stiffener from D and E. ηs to be multiplied by ηG for ordinary local loadσel, σc= for plating and stiffener, respectively, from D and E. Ordinary effective flange is to be used for

stiffenersAp, As= area of plating and stiffener in cm2

=

σu = ultimate average stress of plating

=

202 For transversely stiffened plating (compressive stress perpendicular to longest side l of plate panel) is

— plating

= fraction of Ap participating in the post-buckling stress increase

σa0.85-----------

σelσf2-----, i.e. σel< σc=

σel 0.385Etwhw------⎝ ⎠

⎛ ⎞2

N mm2⁄( )=

0.1 ηsσc ηpσel–( )beb-----Ap As+⎝ ⎠

⎛ ⎞ (kN)

beb-----

σu σel–

σf σel–-------------------

σel 1 0.375σfσel------- 2–⎝ ⎠

⎛ ⎞+

σu σel 1 cσfσel------- 2–⎝ ⎠

⎛ ⎞+=

DET NORSKE VERITAS


c =

As = 0resulting in:

PA = 0.l ηp σu Ap (kN).203 σu may be substituted for σel when calculating uniaxial compression and shear in D300.

H. GirdersH 100 Axial load buckling101 For lateral, torsional, web and flange buckling, see E, Stiffeners in direction of compression.

H 200 Girders perpendicular to direction of compression201 For transverse girders supporting longitudinals or stiffeners subject to axial compression stresses, theideal elastic buckling stress may be taken as:

S = span of girder in ml = distance between girders in ms = spacing of stiffeners in mIa = moment of inertia of stiffener in cm4

Ib = moment of inertia of transverse girder in cm4

t = plate thickness in mmta = equivalent plate thickness of stiffener area in mm

The critical buckling stress σc is found from A102.202 The critical buckling stress found from 201 and A102 is not to be less than:

σa = calculated compressive stressη = 0.75.

H 300 Buckling of effective flange301 Plating acting as effective flange for girders which support crossing stiffeners is to have a satisfactorybuckling strength.302 Compressive stresses arising in the plating due to local loading of girders are to be less than ηG x thecritical buckling strength, see 303. When calculating the compressive stress the section modulus of the girdermay be based on a plate flange breadth equal to the distance between girders (100% effective flange).ηG: see D100.303 The critical buckling strength is given in D101 and A102, when l = span of stiffener or distance fromgirder to eventual buckling stiffener parallel to the girder.304 Elastic buckling of deck plating may be accepted after special consideration.Reference is made to G.The additional PA, and the corresponding additional moment capacity, will, however, refer to a girder sectionwith effective width of deck plating = be.

=

0.75ls-- 1+-----------

σel 1.38 π2

S2 t ta+( )-----------------------

IaIbsl

---------=

stiffener areastiffener spacing---------------------------------------

σcσaη-----≥

DET NORSKE VERITAS


H 400 Shear buckling of web401 See D200, for constant shear force over l.

Guidance note:For variable shear force over l of panel, a reduced l may be considered in formula.


DET NORSKE VERITAS

hull structural design, aluminium alloy · a 200 aluminium alloys 201 the alloy grades are listed...

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