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Marine Division92571 Neuilly-sur-Seine Cedex - France

Tel: + 33 (0)1 55 24 70 00 - Fax: + 33 (0)1 55 24 70 25

Marine website: http://www.veristar.com

Email: [email protected]

2008 Bureau Veritas - All rights reserved

November 2008

Guidance NoteNI 532 DT R00 E

Guidelines for Structural Analysis of

Container Ships

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M A R I N E D I V I S I O N

G E N E R A L C O N D I T I O N S

ARTICLE 1

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ARTICLE 2

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Committees consisting of personalities from the Industry contribute to the development of those documents.

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ARTICLE 4

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ARTICLE 7

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ARTICLE 9

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the data relative to the evolution of the Register, to the class suspension and to the survey status of theUnits are passed on to IACS according to the association working rules;

the certificates, documents and information relative to the Units classed with the Society may be reviewedduring IACS audits and are di sclosed upon order of the concerned governmental or inter-governmentalauthorities or of a Court h aving jurisdiction.

The documents and data are subject to a file management plan.

ARTICLE 10

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ARTICLE 11

11.1. - In case of diverging opinions during surveys between the Client and the Societys surveyor, the Societymay designate another of its surveyors at the request of the Client.

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ARTICLE 12

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ARTICLE 13

13.1. - These General Conditions constitute the sole contractual obligations binding together the So-

ciety and the Client, to the exclusion of all other representation, statements, terms, conditions wheth-er express or implied. They may be varied in writing by mutual agreement.

13.2. - The invalidity of one or more stipulations of the present General Conditions does not affect the validityof the remaining p rovisions.

13.3. - The definitions herein take precedence over any definitions serving the same purpose which may ap-pear in other documents issued by the Society.

BV Mod. Ad. ME 545 j - 16 February 2004

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November 2008

GUIDANCE NOTE NI 532

NI 532

Guidelines for Structural Analysis

of Container Ships

SECTION 1 GENERAL

SECTION 2 LOADING CONDITIONS AND LOAD CASES

SECTION 3 HULL GIRDER STRENGTH

SECTION 4 DIRECT STRENGTH ANALYSIS

SECTION 5 DETAILED ASSESSMENT OF SPECIFIC AREAS

SECTION 6 FATIGUE STRENGTH ASSESSMENT

SECTION 7 WAVE IMPACT ASSESSMENT

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2 Bureau Veritas November 2008

Guidelines for Structural Analysis of Container Ships

Section 1 General

1 General 5

1.1 Introduction1.2 Application and class notations1.3 Methodology of assessment1.4 Structure design principles of container ships

Section 2 Loading Conditions and Load Cases

1 Design wave loads 101.1 Bending moments and shear forces1.2 Wave torque and still water torque induced by non symmetrical loading

conditions

2 Loading conditions 12

2.1 General

3 Load cases 12

3.1 Load cases for structural analysis based on partial ship models3.2 Load cases for structural analysis based on complete ship models

4 Flooding cases 15

4.1 General

Section 3 Hull Girder Strength

1 Introduction 18

1.1 Scope1.2 Topics not covered in this section

2 Strength principle 18

2.1 Structural continuity

3 Strength characteristics of the hull girder tranverse sections 18

3.1 Hull girder transverse sections

4 Stresses 18

4.1 Normal stresses induced by vertical bending moments4.2 Normal stresses induced by torque and bending moments4.3 Shear stresses

5 Checking criteria 19

5.1 Normal stresses5.2 Shear stresses

6 Ultimate strength check 20

6.1 Application

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November 2008 Bureau Veritas 3

Section 4 Direct Strength Analysis

1 Methodology 21

1.1 General

2 Warping analysis for hull girder torsional strength assessment 22

2.1 Thin walled beam model

3 3D beam model analysis 24

3.1 General3.2 Boundary conditions3.3 Stress calculations

4 Finite element model analysis 27

4.1 General4.2 Partial model analysis4.3 Complete ship model analysis4.4 Fine mesh and highly stressed area analysis

5 Yielding calculations and criteria 40

5.1 Stress components5.2 Checking criteria

6 Buckling calculation and criteria 42

6.1 General

Section 5 Detailed Assessment of Specific Areas

1 General 43

1.1 General

2 Critical areas 43

2.1 Cargo hold region2.2 Fore end structure

Section 6 Fatigue Strength Assessment

1 General 49

1.1 Methodology1.2 Areas subject to fatigue assessment1.3 Fatigue calculation1.4 Hot spot stresses directly obtained by finite element analysis

2 Fatigue of side shell longitudinals 54

2.1 General2.2 Connections of side shell longitudinals with stiffeners of transverse members2.3 Connections of side shell longitudinals with transverse members (without

stiffener on primary member)

3 Fatigue of hatch corners 58

3.1 Calculation through three dimensional structural model

3.2 Workmanship

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Section 7 Wave Impact Assessment

1 Dynamic hull girder loads 62

1.1 Dynamic hull girder loads due to bow flare impact

2 Reinforcements 62

2.1 Reinforcement of the bow flare area2.2 Reinforcements of the flat area of the bottom aft

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NI 532, Sec 1


SECTION 1 GENERAL

1 General

1.1 Introduction

1.1.1 The purpose of this Guidance Note is to give a methodology to assess hull strength of container ships using BureauVeritas Rules for the Classification of Steel Ships, referred to as Rules for Steel Ships in this Guidance Note.

1.1.2 This Guidance Note does not substitute the designer's liability and does not replace Rules for Steel Ships: it is sim-ply intended to highlight specific features of container ships as regards structural analysis. Reference is made to Part B,Part D and Part E of the Rules for Steel Ships.

1.1.3 The methodology in this Guidance Note explains the different steps of calculations and describes the tools and

ways to perform 2D calculations, 3D calculations (including beam and finite element analysis) and 3D fatigue analysis.The purpose is also to identify the main features of container ships and the way to perform detailed calculations.

The calculations described in this Guidance Note can be performed using Bureau Veritas softwares such as:

Mars 2000: for the structural analysis of transverse 2D sections, transverse bulkheads and evaluation of hull girder tor-sional effects

VeriSTAR-Hull: for the FEM structural analysis concerning partial model (e.g. 3 hold model)

VeriSTAR CSM (Complet Ship Model): the most advanced tool for FEM analysis of whole ship model.

1.1.4 This Guidance Note applies to container ships which are constructed with a single deck, double side skin tanks,passageways and double bottom in cargo area, and intended exclusively to carry containers, in holds, on deck and onhatch covers (See Fig 1).

1.1.5 The present Guidance Note does not address possible hydro-elastic effects that may be present, particularly forlarger container ship structures.

Figure 1 : General view of a container ship

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NI 532, Sec 1


1.2 Application and class notations

1.2.1 Application

This Guidance Note applies to ships complying with Rules for Steel Ships under the service notation container ship asdefined in Pt A, Ch 1, Sec 2, [4.2.5] of the Rules for Steel Ships.

1.2.2 Additionnal class notation VeriSTAR-HULL

A ship may be assigned with the additional class notation VeriSTAR-HULL to demonstrate that her structures have beenchecked by means of 3D FEM structural analysis, possibly including a finite element calculation of the wholeship (VeriSTAR CSM). The requirements for this notation are given in Pt E, Ch 1, Sec 2 of the Rules for Steel Ships.

1.2.3 DFL xx years

The additional class notation VeriSTAR-HULL may be completed by DFL xx years, with xx having values between 25 and40, when a fatigue assessment has been carried out on selected structural details showing that their evaluated designfatigue life is not less than xx years. A default fatigue life of 20 years is used when the additional class notation hereaboveis not assigned. This item is described in Pt E, Ch 1, Sec 2 of the Rules for Steel Ships.

1.2.4 Additional class notation LASHING

The additional class notation LASHING may be assigned to ships initially fitted with mobile container lashing equipmentwhich has been documented, tested and checked, in accordance with Rules for Steel Ships Pt E, Ch 10, Sec 5.

1.3 Methodology of assessment

1.3.1 There are two design review processes when assessing hull strength of container ships: key drawings review asdescribed in [1.3.3] and detail drawings review as described in [1.3.4].

Requirements in ship review process of hull strength of container ships are described in Fig 2.

This Guidance Note is presented with some illustrations from calculations (2D and 3D calculations) of several containerships of different sizes and dimensions without referring to a specific existing design.

Figure 2 : Ship review scheme with structural models to be used regarding ship length

W a r p i n g s t r e s s

M a r s 2 0 0 0

+ t o r s i o n m o d u l e

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3 D p a r t i a l m o d e l :

- b e a m

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3 D T h i n w a l l e d b e a m m o d e l

V e r i s t a r H u l l

2 D s e c t i o n m o d e l

M a r s 2 0 0 0

W a r p i n g s t r e s s

N O

L e n g t h o f s h i p

G r e a t e r t h a n 1 7 0 m

Y E S

3 D F E M p a r t i a l m o d e l

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C o m p l e t e s h i p m o d e l

V e r i s t a r C S M

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NI 532, Sec 1


1.3.2 Net scantling approach and partial safety factors

The structural analysis of each element according to Rules for Steel Ships is carried out considering their net strengthcharacteristics. This means that the strength checks consider the structural scantlings without the corrosion margin, whichare then to be added to the net scantlings to obtain the required gross scantlings. See Rules for Steel Ships Pt B, Ch 4,Sec 2.

Partial Safety Factors (PSF) are defined by the Rules for Steel Ships to be separately applied to the wave induced hullgirder and local loads on one side ("Demand PSF"), to the structural model and the material resistance ("Capacity PSF")on the other. These can be more rationally and precisely defined. The value of the PSFs depends on the associated levelof uncertainty.

1.3.3 Key drawings review process

The following items are to be reviewed with respect to ships length

General and subdivision arrangement

Hull girder strength including torsion strength

Local scantlings

Primary members using direct strength analysis

Structural continuity

Wave bow flare and stern impact

Fatigue analysis for ships greater than 170 m in length.

The structural analysis with FEM calculations should be performed at the very early stage in parallel to the design reviewprocess.

The strength check procedure is summarized in Tab 1.

The strength check criteria require that the structural elements are assessed by means of the Rule formulae, which representthe equations of the limit states considered for plating, ordinary stiffeners and primary supporting members (see Tab 2).

1.3.4 Detail drawings review process

In this process, the procedure is to check structural details (collar plates, flat bars, brackets, openings etc), structuralreinforcements (reinforcements under container corners, insert plates, cell guides, etc...) interface with equipment (hatchcovers for example), welding details (penetration welding, semi penetration welding, edge preparation, welding length,etc) taking into account the hull girder stresses and local stresses.

See detail assessment of specific areas in Sec 5 of this Guidance Note.

1.4 Structure design principles of container ships

1.4.1 The structure design principles and the specific features of the service notation container ship are described inPt B, Ch 4, Sec 1 to Sec 7, Pt B, Ch 12, Sec 2, [2.7] and Pt D, Ch 2, Sec 2 of the Rules for Steel Ships. The following itemsare presented:

a) Materials: Steels for hull structure

b) Design loads

Hull girder loads: Still water loads and wave loads. For wave loads and torsional wave loads see Sec 2 of thisGuidance Note

Forces due to containers

c) Loading conditions for primary structure analysis. See also Sec 4 of this Guidance Note

d) Hull scantlings

Plating

Primary supporting members

e) Strength principles

Local reinforcements

Forces applying on the fixed cargo securing devices


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NI 532, Sec 1


f) Bottom structure

Floor and girder spacing

Reinforcements in way of cell guides

g) Side structure: Framing arrangement

h) Deck structure

Longitudinal girders of cross decks

Cross decks

Connection of face plates of deck girders and deck beams in cross decks

Deck and hatch cover reinforcements

i) Bulkhead structure

Transverse box structure

Primary supporting members

Reinforcements in way of cell guides

j) Other structure: Non-weathertight hatch covers above superstructure deck

k) Fixed cell guide

l) Fixed cargo securing device

m) Construction and testing.

Table 1 : Strength check procedure

Data Review Results

Hull girder strength including torsion strength

Design still water bending moment, still watertorque and shear force at sea and harbour

Checking of section moduli at top,deck and bottom

Ultimate strength of the hull girder (1)

Hull girder bendingstress, shear stress andwarping stress

Local strength plating and ordinary stiffeners

Hull girder bending stress, shear and warpingstress

Scantling draught and ballast draught

All boundaries of compartments checked infull or empty conditions

Air pipe

Design loads (accelerations...)

Transverse sections

Transverse bulkheads

Bow flare

Aft and forward structures

Engine room structure

Superstructures

Thickness of plating

Shear area and sectionmodulus of stiffeners

Dimensions and scant-lings of brackets

Buckling

Transverse primary members, stringers, floors, girders

Design load distribution Minimum dimension from the Rulesfor Steel Ships

3D beam or finite element analysis

Yielding and buckling


Worst loads transferred through the connec-tion

Continuity of strength and avoidanceof abrupt structural changes

Tapering of scantlings

Possible modification ofconnection designs

Fatigue (1)

Full load and ballast conditions Fatigue analysis of longitudinal con-nections

Fatigue analysis of primary memberconnections

Damage ratio or fatiguelife of connections

(1) To be considered for ships greater than 170m in length.

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NI 532, Sec 1


Table 2 : Limit states specified by the Rules for Steel Ships for each type of structural element

YieldingStrength of plating under

lateral pressureBuckling

Ultimatestrength (1)

Fatigue(1)

Hull Girder X X

Plating X XOrdinary stiffeners X X X

Primary supporting members X X X

Structural details X

(1) To be considered for ships greater than 170m in length

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NI 532, Sec 2


SECTION 2 LOADING CONDITIONS AND LOAD CASES

1 Design wave loads

1.1 Bending moments and shear forces

1.1.1 See Pt B, Ch 5, Sec 2, [3] of the Rules for Steel Ships.

1.2 Wave torque and still water torque induced by non symmetrical loading conditions

1.2.1 Wave torque

The wave torque at any hull transverse section is to be calculated considering the ship in two different conditions:

condition 1: ship direction forming an angle of 60 with the prevailing sea direction

condition 2: ship direction forming an angle of 120 with the prevailing sea direction.

The values of the wave torques in these conditions, calculated with respect to the section centre of torsion, are obtained,in kN.m, from the following formula:

where:

FTM, FTQ : Distribution factors defined in Tab 1 for ship conditions 1 and 2 (see also Fig 1 and Fig 2)CM : Wave torque coefficient:

CM = 0,45 B CW2

CQ : Horizontal wave shear coefficient:

CQ = 5 T CB

CW : Waterplane coefficient, to be taken not greater than the value obtained from the following formula:

CW = 0,165 + 0,95 CB

where CB is to be assumed not less than 0,6. In the absence of more precise determination, CW may be taken

equal to the value provided by the above formula.

d : Vertical distance, in m, from the centre of torsion to a point located 0,6 T above the baseline.

H : Wave parameter, defined in Pt B, Ch 5, Sec 2 of the Rules for Steel Ships

n : Navigation coefficient, defined in Pt B, Ch 5, Sec 1 of the Rules for Steel Ships

Table 1 : Distribution factors FTM and FTQ

Ship condition Distribution factor FTM Distribution factor FTQ

1

2

MWTHL4

--------n FTMCM FTQ CQd+( )=

1 2xL

----------cos 2xL

----------sin

1 2 L x( )L

------------------------cos 2 L x( )L

------------------------sin

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NI 532, Sec 2


Figure 1 : Ship condition 1 - Distribution factors F TM and FTQ

Figure 2 : Ship condition 2 - Distribution factors F TM and FTQ

1.2.2 Still water torsional torque

The design still water torsional torque induced by the non-symmetrical distribution of cargo, consumable liquids and bal-last are to be considered. If no specific data are provided by the Designer, it is to be obtained at any hull transverse sec-tion, in kN.m, from the following formula:

MSW, T = 31,4 FT S T B

where:

FT : Distribution factor defined in Tab 2 as a function of the x co-ordinate of the hull transverse section withrespect to the reference co-ordinate system defined in Pt B, Ch 1, Sec 2, [4] of the Rules for Steel Ships

S : Number of container stacks over the breadth B

T : Number of container tiers in cargo hold amidships (excluding containers on deck or on hatch covers)

Where the value of MSW, T obtained from the above formula is greater than 49000 kN.m, the Society may require moredetailed calculations of MSW, T to be carried out by the Designer.

Table 2 : Distribution factor FT

Hull transverse section location Distribution factor FT

0 x < 0,5 L x / L

0,5 L x L (1 x / L)

FTM

, FTQ

0,5

AE0,0

0,25-0,5

-1,0

1,0

1,5

2,0

0,50 0,75

xLFE

F

TMF

TQ

0 1

FTM

, FTQ

0,5

0,0

-0,5

-1,0

1,0

1,5

2,0

0 1

0,25 0,50 0,75

xLFE

FTM

FTQ

AE

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NI 532, Sec 2


2 Loading conditions

2.1 General

2.1.1 The following minimum loading conditions are to be considered:

Full container load associated to scantling draught T

Ballast condition with ballast draught

Partial loading conditions at scantling draught. The condition one empty bay is to be considered even if not includedin the loading manual

Flooding case. Pressure on watertight bulkhead to be considered up to freeboard deck with damage draught, or scant-ling draught if no data available from damage stability calculation.

3 Load cases

3.1 Load cases for structural analysis based on partial ship models3.1.1 The load cases described in this article are those to be used for the following structural element analyses (see Rulesfor Steel Ships Pt B, Ch 5, Sec 4):

The analyses of plating (See Pt B, Ch 7, Sec 1 of the Rules for Steel Ships)

The analyses of ordinary stiffeners (See Pt B, Ch 7, Sec 2 of the Rules for Steel Ships)

The analyses of primary supporting members (See Pt B, Ch 7, Sec 3 of the Rules for Steel Ships)

The fatigue analysis of the structural details of the above elements (See Pt B, Ch 7 Sec 4 of the Rules for Steel Ships),for ship greater than 170 m in length.

These load cases are the mutually exclusive load cases "a", "b", "c" and "d" explained in Pt B, Ch 5, Sec 4 of the Rules forSteel Ships.

Load cases "a" and "b" refer to the ship in upright condition i.e. at rest or having surge, heave and pitch motions ( Fig 3and Fig 4) inducing vertical wave bending moments and shear forces.

Figure 3 : Wave loads in load case a

Positive h1

Z

Y

0,625Qwv 0,625MwvT1

h1

Negative h1

Z

Y

0,625Qwv 0,625MwvT1

h1

Y

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NI 532, Sec 2


Figure 4 : Wave loads in load case b

Load cases "c" and "d" refer to the ship in inclined conditions i.e. having sway, roll and yaw motions ( Fig 5 and Fig 6)inducing:

Vertical wave bending moments and shear forces

Horizontal wave bending moments

Torque for the load case "c"

Figure 5 : Wave loads in load case c

Figure 6 : Wave loads in load case d

Z

Y

0,625Qwv az 0,625Mwv

0,5h1

T1

Z

Y

1

T

2

h

2

h

W V

0 , 2 5 Q

0 , 6 2 5 M

W T

W H

0 , 6 2 5 M

Y

0 , 7 a W V

0 , 2 5 M

0,5

0,5

0,25M

WV0,25Q

Z

Y1,0a

WV

2h

WH0,625M

Y

1T

h 2

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3.2 Load cases for structural analysis based on complete ship models

3.2.1 When primary supporting members are to be analysed through complete ship models (ships greater than 170 m inlength), specific load cases are to be considered. The use of such load cases should include fatigue calculations.

These load cases are to be defined considering the ship as sailing in regular waves with different lengths, heights and

heading angles, each wave being selected in order to maximise a design load parameter. The procedure for the determi-nation of these load cases is specified in Rules for Steel Ships, Pt B, Ch 7, App 3 as summarized in [3.2.2].

3.2.2 Summary of the loading procedures

Applicable cargo loading conditions described in [2.1.1] are analysed through:

The computation of the characteristics of the finite element model with still water loads

The selection of the load cases which are critical for the strength of the resistant structural members

The determination of the design wave characteristics for each load case includes the following steps:

Computation of the Response Amplitude Operators and phase of the dominant load effect

Selection of the wave length and heading

Determination of the wave phase, so as the dominant load effect reaches its maximum

Computation of the wave amplitude corresponding to the design value of the dominant load effect.

3.2.3 Dominant load effects

Each critical load case maximises the value of one of the following load effects having a dominant influence on thestrength of some parts of the structure or a combination of both in order to maximise the total combined stress:

a) Bending moments (Head sea cases)

Vertical wave bending moment in hogging condition at midship section

Vertical wave bending moment in sagging condition at midship section

b) Wave shear forces (Head sea cases)

Vertical wave shear force on transverse bulkhead

c) Horizontal bending moments (Quartering and beam sea cases)

Horizontal wave bending moment at midship section

d) Wave torque (Quartering and beam sea cases)

Wave torque within cargo areas at aft part (maximize warping stress)

Wave torque within cargo areas at fore part (maximize warping stress)

Wave torque within cargo areas at mid part (maximize warping stress)e) Accelerations (Head sea and beam sea cases)

Vertical acceleration in midship (especially with maximum internal loads or heavy cargo loads) and fore body sec-tion

Transverse acceleration at deck at side at midship section

f) Local pressure loads (Head sea and beam sea cases)

Wave pressure at bottom at centreline in upright ship condition at midship section (especially in partial loadingcondition with maximum draught)

Wave pressure at bottom at side in inclined ship condition at mid-ship section (especially in partial loading condi-tion with maximum draught)

Load cases and load effect values are described for reference in Tab 3 and Tab 4 and wave can be combined in order tomaximize vertical bending, horizontal bending and torsion.

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3.2.4 Response Amplitude Operators (RAOs)

The Response Amplitude Operators (RAO's) and associated phase characteristics are to be computed for wave periodsbetween 4 and 22 seconds, using a seakeeping program, for the following motions and load effects:

Heave, sway, pitch, roll and yaw motions

Vertical wave bending moment at 0.5L or at the longitudinal position where the bending moment RAO is maximum Vertical wave shear force at 0.25L and 0.5L

Horizontal wave bending moment at 0.5L

Wave torque at 0.25L (aft part) ,0.5L (mid part) and 0.75L (fore part)

The Response Amplitude Operators (RAO's) are to be calculated for wave headings ranging from following seas (0degree) to head sea (180 degrees) by increment of 15 degrees, using a ship speed of 60% of the maximum service speed.

The amplitude and phase of other dominant load effects may be computed at relevant wave periods, using the RAO'slisted above.

3.2.5 Design waves

For each load case, the ship is considered to encounter a regular wave, defined by its parameters (See Tab 3):

Wave length

Heading angle

Wave height (double amplitude).

The wave phase is to be selected so as to reach load effect values.

The dominant load effect values are described in Tab 4.

3.2.6 Design wave amplitude

The amplitude of the design wave is obtained by dividing the design value of the dominant load effect by the value of the

Response Amplitude Operator of this effect computed for the relevant heading and wave length.

The design values of load effect, heading and wave length are given for each load case in Tab 3 and Tab 4.

The design wave phase is the phase of the dominant load effect.

Application to complete ship finite element model is described in Sec 4, [4.3]:

Finite element loading and lightship distribution

Static calculations: hydrostatic calculations and equilibrium check

Wave load calculations: value of load effects.

4 Flooding cases

4.1 General

4.1.1 Unless otherwise specified, the still water and inertial pressure to be considered as acting on plating (excludingbottom and side shell plating) which constitutes boundary of compartments not intended to carry liquids are obtained inkN/m2 from the formula in Tab 5.

with:

zF : Z co-ordinate, in m, of the freeboard deck at side in way of transverse section considered. Where the results of

damage stability calculations are available, the deepest equilibrium waterline may be considered in lieu of thefreeboard deck; in this case the Society may require transient conditions to be taken into account

aZ1 : Vertical acceleration defined in Pt B, Ch 5, Sec 3 [3.4.1] of the Rules for Steel Ships

d0 : Distance depending on ship length defined in Pt B, Ch 5, Sec 6, Symbols of the Rules for Steel Ships

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Table 3 : Load cases and load effect values

Loadcase

Dominant load effect

Wave parameters (1)

Location(s) NotesWave length

Headingangle

1 Vertical wave bendingmoment in hoggingcondition

Peak value of vertical wavebending moment RAO withoutbeing less than 0,9L

180 Midship section

2 Vertical wave bendingmoment in saggingcondition

Same as load case 1 180 Midship section

3 Vertical wave shearforce

Peak value of vertical waveshear force RAO:

at 0,5L for 0,35L < x < 0,65L

at 0,25L elsewhere

0

or

180

Each transversebulkhead

4 Horizontal wavebending moment

Peak value of horizontal wavebending moment RAO or 0,5L

120

or

135

Midship section Select the heading such thatthe value of Cmax for vertical

wave bending moment is notexceeded

5 Wave torque Peak value of wave torqueRAO or 0,5L

60

or

75

Vicinity of 0,25L

Midship section

Select the heading such thatthe value of Cmax for vertical

wave bending moment is notexceeded

6 Wave torque Peak value of wave torqueRAO within the allowablerange

90 Midship section Wave amplitude may haveto be limited such that thevalue of Cmax for transverse

acceleration and vertical rel-ative motion at side are notexceeded

7 Wave torque Same as load case 5 105or

120

Vicinity of 0,75L

Midship section

Select the heading such thatthe value of Cmax for verticalwave bending moment is notexceeded

8 Vertical accelerationin inclined shipcondition

where:

C = 1,0 for 90 heading

1,15 for 105 heading

CW : Waterplane coefficient at

load waterline

90

or

105

Midship section

9 Vertical accelerationin upright shipcondition

= 1,6 L (0,575 + 0,8 F)2

180 From forwardend of cargoarea to fore end

10 Transverseacceleration

= 1,35 g TR2 / (2)

without being taken greaterthan 756 m

90 Midship section

11 Wave pressure at bot-tom at centreline inupright ship condition

0,7 L 180

or

0

Midship section may have to be increasedto keep the wave steepnessbelow wave breaking limit

12 Wave pressure at bot-tom at side in inclinedship condition

= 0,35 g TR2 / (2)

without being taken less than2,0B

90 Midship section

(1) The forward ship speed is to be taken equal to 0,6 V.

12 3, C

BL CW----------------------=

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Table 4 : Dominant load effect values

Table 5 : Flooding - Still water and inertial pressures

Dominant load effectDesign value

(at 10-5 probability)Combined load

componentsReferences (1)

Vertical wave bending moment inhogging condition

0,625 W1 MWV ,H

MWV,H defined in:

Pt B, Ch 5, Sec 2, [3.1.1]Vertical wave bending moment insagging condition

0,625 W1 FD MWV ,S

MWV,S defined in:Pt B, Ch 5, Sec 2, [3.1.1]

FD defined inPt B, Ch 5, Sec 2, [4.2.1]

Vertical wave shear force0,625 W1 QWV

QWV defined in:

Pt B, Ch 5, Sec 2, [3.4]

Horizontal wave bending moment0,625 W1 MWH

MWH defined in:

Pt B, Ch 5, Sec 2, [3.2.1]

Wave torque 0,625 W1 MWTHorizontal wavebending moment

MT defined in:Pt B, Ch 5, Sec 2, [3.3]

Vertical acceleration at centrelinein upright ship condition W2 aZ1 Vertical relative motionat side at fore end aZ1 defined in:Pt B, Ch 5, Sec 3, [3.4.1]

Vertical acceleration at deck atside in inclined ship condition

W2 aZ2 aZ2 defined in:Pt B, Ch 5, Sec 3, [3.4.1]

Transverse acceleration at deck atside

W2 aY2 Roll angleaY2 defined in:

Pt B, Ch 5, Sec 3, [3.4.1]

Wave pressure at bottom atcentreline in upright shipcondition

W2 pWVertical wave bendingmoment at midship

pW defined in:

Pt B, Ch 7, App 1, Tab 3 for case a

Wave pressure at bottom at side ininclined ship condition W2 pW

pW defined in:

Pt B, Ch 7, App 1, Tab 4 for case c

(1) References in the Rules for the Classification of Steel Ships

Still water pressure pSF , in kN/m2 Inertial pressure pWF , in kN/m2

Compartment located under freeboard deck:

g (zF z)

without being taken less than 0,4 g d0

Compartment located immediately above freeboard deck:

0,32 g d0

Compartment located under freeboard deck:

0,6 aZ1 (zF z)

without being taken less than 0,4 g d0

Compartment located immediately above freeboard deck:

0,32 g d0

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SECTION 3 HULL GIRDER STRENGTH

1 Introduction

1.1 Scope

1.1.1 The purpose of this section is to assess hull girder strength. To this end, hull girder stresses and ways to combinethem are described. References are made to other sections of this Guidance Note in which explanations are made onhow to get such stresses.

1.2 Topics not covered in this section

1.2.1 This section does not take into account:

Minimum section moduli and moment of inertia (see Pt B, Ch 6, Sec 2 of the Rules for Steel Ships). Permissible still water bending moment and shear force during navigation or harbour navigation (see Pt B, Ch 6, Sec 2

of the Rules for Steel Ships).

Ultimate strength (See Pt B, Ch 6, Sec 3 and also Pt B, Ch 7, Sec 2, [5] of the Rules for Steel Ships).

2 Strength principle

2.1 Structural continuity

2.1.1 Attention is to be paid to the structural continuity:

in way of ends of superstructure / machinery space (see Pt B, Ch 9, Sec 3 and Pt B, Ch 9, Sec 4 of the Rules for SteelShips)

in way of the fore and afts parts (see Pt B, Ch 9, Sec 1 and Sec 2 of the Rules for Steel Ships)

See also Pt B, Ch 4, Sec 3, [1.1] and Pt D, Ch 2, Sec 2, [3] of the Rules for Steel Ships.

3 Strength characteristics of the hull girder tranverse sections

3.1 Hull girder transverse sections

3.1.1 General

Hull girder transverse sections are to be considered as being constituted by the members contributing to the hull girder

longitudinal strength, i.e. all continuous longitudinal members below the strength deck defined in Rules for Steel ships,Pt B, Ch 6, Sec 1, [2].

Gross scantlings are used for yielding criteria defined in [4] and [5], net scantlings are used for ultimate strength criteriadefined in [6].

4 Stresses

4.1 Normal stresses induced by vertical bending moments

4.1.1 The normal stresses induced by vertical bending moments are obtained, in N/mm2, from the following formulae:

at any point of the hull transverse section:

1MSW MWV+

ZA----------------------------- 10

3=

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at bottom:

at deck:

MSW : Still water bending moment, in kN.m (hogging and sagging)

MWV : Vertical wave bending moment, in kN.m (hogging and sagging)

ZA : Gross section modulus, in cm3, at any point of the hull transverse section

ZAB,ZAD : Gross section moduli, in cm3, at bottom and deck, respectively.

4.2 Normal stresses induced by torque and bending moments

4.2.1 Definition

They are to be obtained, in N/mm2, from the following formula:

where:

: Warping stress, in N/mm2, induced by the torque MWT and obtained through direct calculation analyses basedon a structural model in accordance with Pt B, Ch 6, Sec 1, [2.6] of the Rules for Steel Ships; it includes thecontribution due to the still water torque MT, SW defined in Pt D, Ch 2, Sec 2, [4.1] of the Rules for Steel Ships

For warping stress assessment see [4.2.2] of this Guidance Note.

y : Y co-ordinate, in m, of the calculation point with respect to the reference co-ordinate system defined in Pt B,Ch 1, Sec 2, [4] of the Rules for Steel Ships.

MWH : Horizontal wave bending moment, in kN.m

IZ : Moment of inertia, in m4, of the hull transverse section about its vertical neutral axis.

4.2.2 Structural models for the calculation of normal warping stresses and shear stresses

The structural models that can be used for the calculation of normal warping stresses, induced by torque, and shearstresses, induced by shear forces or torque, are:

three dimensional finite element models

thin walled beam models.

These models are described in Sec 4 of this Guidance Note.

4.3 Shear stresses

4.3.1 Refer to Pt B, Ch 6, Sec 2 [2.3.1] of the Rules for Steel Ships for shear stress calculation (direct calculation of1).

5 Checking criteria

5.1 Normal stresses

5.1.1 It is to be checked that the normal stresses 1 are in compliance with the following formula:

11,ALL

1MSW MWV+

ZAB-----------------------------10

3=

1MSW MWV+

ZAD-----------------------------10

3=

1MSWZA

-----------0 4M, WV

ZA--------------------

MWHIZ

------------ y + ++=

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where:

1,ALL : Allowable normal stress, in N/mm2, obtained from the following formulae:

k : Material factor, as defined in Rules for Steel Ships Ch 4, Sec 1, [2.3]

x : X co-ordinate, in m, of the calculation point with respect to the reference co-ordinate system defined in Rulesfor Steel Ships Ch 1, Sec 2, [4]

5.2 Shear stresses

5.2.1 It is to be checked that the shear stresses 1 are in compliance with the following formula:

11,ALL

where:

1,ALL : Allowable shear stress, in N/mm2:

1,ALL = 110/k

6 Ultimate strength check

6.1 Application

6.1.1 The requirements for ultimate strength apply to ship equal to or greater than 170m in length. See Pt B, Ch 6, Sec 3and Pt B, Ch 6, App 1 of the Rules for Steel Ships.

1 AL L,119

k----------= for

xL--- 0 1,

1 AL L, 175k---------- 1400

k------------- x

L--- 0 3,

2

= for 0 1, xL--- 0 3,

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