shipright tankers

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Structural DesignAssessment

Primary Structure of Tankers

Guidance on direct calculations

Notice No.1 to July 2002 versionEffective date: 1 October 2002

ShipRightDesign and construction


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Structural DesignAssessment


Guidance on direct calculations

Notice No.1 to July 2002 versionEffective date: 1 October 2002

ShipRightDesign and construction

Lloyds Register of Shipping, 71 Fenchurch Street, London EC3M 4BS

Switchboard: +44 (0)20 7709 9166, Fax: +44 (0)20 7488 4796, Website: www.lr.org

Direct line: +44 (0)20 7423 + extension no., Fax: +44 (0)20 7423 2061, Email: [email protected]


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Lloyds Register Marine Business Stream

71 Fenchurch StreetLondonEC3M 4BS

Switchboard: +44 (0)20 7709 9166Direct line: +44 (0)20 7423 + extension no.Fax: +44 (0)20 7488 4796Website: www.lr.org

Lloyd's Register Marine Business Stream is a part of Lloyd's Register of Shipping.

Lloyds Register of Shipping, 2002Registered office, 71 Fenchurch Street, London EC3M 4BS

Document History

Document Date Notes

October 1994 New document coveringPrimary Structure ofTankers

April 1996 Primary Structure of Bulk Carriers incorporated

November 2001 Intranet user reviewversion

July 2002 General release(Primary Structure ofBulk Carriers removed)

NOTICE AND TERMS OF USE

The following terms and conditions apply to all services providedby any entity that is part of the "LR Group" as hereinafter defined:

1. In these terms and conditions: (i) "Services" means any and allservices provided to the Client by Lloyd's Register ofShipping ("LR"), or any entity that is part of the LR Group, ashereinafter defined, including any classification of the Client'svessel, equipment or machinery; (ii) the "Contract" meansany agreement for supply of the Services, such as a requestfor services or any other document or agreement relating tothe providing of Services; and (iii) the "LR Group" means LR,its affiliates and subsidiaries, and the officers, directors,

employees, representatives and agents of any of them,individually or collectively.

2. Any damage, defect, breakdown, or grounding that couldinvalidate the conditions for which a class has been assigned,must be reported to LR without delay.

3. If the Client requires classification services relating to vessels,machinery, or equipment classed by LR in a jurisdiction inwhich LR itself does not do business (including withoutlimitation Brazil, Canada, Greece, and the United States ofAmerica), the Client hereby acknowledges and agrees thatthese services will be performed by a subsidiary of LR that ispart of the LR Group and that is authorised to conductclassification surveys and issue certificates on the vessel,machinery, or equipment, or by another person or entity thathas been approved by LR to perform the services. If

classification services are performed by an entity other thanLR in accordance with this paragraph 3, the survey reportsand certificates issued by that entity will be submitted to LRfor acceptance. LR will accept for classification purposes asurvey or certificate issued by any LR Group entity.

4. In providing services, information, or advice, the LR Groupdoes not warrant the accuracy of any information or advicesupplied. Except as set out in these Terms and Conditions,the LR Group will not be liable for any loss, damage, orexpense sustained by any person and caused by any act,omission, error, negligence, or strict liability of any of the LRGroup or caused by any inaccuracy in any information oradvice given in any way by or on behalf of the LR Groupeven if held to amount to a breach of warranty.

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exclusive jurisdiction of the English courts.

Notice No.1 to Primary Structure of Tankers (July 2002) - Effective date: 1 October 2002


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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002

Contents

Lloyds Register of Shipping i

Contents

Chapter 1 Introduction 1Section 1 Application

2 Symbols

3 Direct calculations procedures report

Chapter 2 Primary Structure of Tankers 5

Section 1 Objectives 5

2 Structural modelling 5

3 Boundary conditions 15

3.1 Introduction

3.2 Boundary conditions for local stress loadcases(symmetric loads)

3.3 Boundary conditions for local stress loadcases(asymmetric loads)

3.4 Boundary conditions for global stress loadcases(hull girder bending moments)

3.5 Boundar conditions for global stress loadcases(hull girder shear forces)

4 Loading conditions 27

5 Permissible stresses 38

6 Buckling acceptance criteria 40

7 Deflection of primary members 43


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Chapter 1SECTION 1

Lloyds Register of Shipping 1

Introduction

Section 1: Application

Section 2: Symbols

Section 3: Direct calculation procedure report

Section 1: Application

1.1 The ShipRight Structural Design Assessment (SDA) procedure is mandatory for oil tankers greater than 190 m

in length and for other tankers of abnormal hull form, or of unusual structural configuration or complexity.

1.2 When applied on a mandatory basis, the SDA procedure must be utilised in conjunction with both the

ShipRight Fatigue Design Assessment (FDA) and Construction Monitoring (CM) procedures.

1.3 For tankers, other than those defined in 1.1, the SDA and/or FDA procedures may be applied on a voluntary

basis.

1.4 The SDA procedure requires:

A detailed analysis of the ships structural response to applied static and quasi-dynamic loadings using finiteelement analysis.

Sloshing analysis. When applicable, assessment of the strength of tank boundary structures against collapse due tothe dynamic loads imposed by the sloshing of liquids in partially filled tanks.

Other direct calculations as applicable.

1.5 This document details the SDA procedure for finite element analysis of the ships structure. The requirements for

the sloshing analysis are given in the ShipRight SDA Sloshing Loads and Scantling Assessmentprocedures manual.

1.6 The structural model and applied load cases detailed in this document will enable the following structural

responses to be investigated:

Stresses in longitudinal primary members resulting from local loads and hull girder bending loads. Stresses in transverse primary members including transverse bulkheads. Buckling behaviour of primary structure.

1.7 The direct calculation of the ships structural response is to be based on a three-dimensional finite elementanalysis (3-D FEA) carried out in accordance with this procedure.


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Chapter 1SECTION 1

2 Lloyds Register of Shipping

1.8 A detailed report of the calculations is to be submitted and must include the information detailed in Section 3.

The report must show compliance with the specified required structural design criteria in Sections 5, 6 and 7.

1.9 If the computer programs employed are not recognised by LR, full particulars of the program will also require

to be submitted, seePt 3, Ch 1,3.1 of (LRs)Rules and Regulations for the Classification of Ships(hereinafter referred

to as the Rules for Ships).

1.10 LR may, in certain circumstances, require the submission of computer input and output in suitable electronic

format to further verify the adequacy of the calculations carried out.

1.11 Where alternative procedures are proposed, these are to be agreed with LR before commencement.

1.12 Tankers of unusual form or structural arrangements may need special consideration and additional calculations

to those contained in this procedure may be required.

1.13 For tankers with two longitudinal bulkheads arrangement with a cross-tie in the centre tank, alternative

assessment procedure are specified depending on the operational design requirement. Depending on the procedure

followed restrictions may be applied on the loading conditions permitted in service. Such restrictions are to be included

in the Loading Manual, seepara 4.3.

1.14 It is recommended that the designer consults with LR on the SDA analysis requirements early on in the design

cycle.


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Chapter 1SECTION 2


Section 2: Symbols

2.1 For the purpose of this procedure the following definitions apply:

L = Rule length, in metres, seePt 3, Ch 1,6 of the Rules for Ships

B = moulded breadth, in metres, seePt.3, Ch 1,6 of the Rules for Ships

D = depth of ship, in metres, seePt 3, Ch 1,6 of the Rules for Ships

kL, k= higher tensile steel factor, seePt 3, Ch 2,1.2 of the Rules for Ships

MW = design vertical wave bending moment, including hog and sag factor,f2, and ship service factor,f1,

seePt 3, Ch 4,5 of the Rules for Ships

MWO = design vertical wave bending moment, excluding hogging and sagging factor and ship service

factor, see Pt 3, Ch 4,5 of the Rules for Ships

f1 = the ship service factor, see Pt 3, Ch 4,5 of the Rules for Ships

f2 = the hogging/sagging factor, see Pt 3, Ch 4,5 of the Rules for Ships

MS = Rule permissible still water bending moment, see Pt 3, Ch 4,5 of the Rules for Ships

Ms = design still water bending moment, see Pt 3, Ch 4,5 of the Rules for Ships

MSW = the still water bending moment distribution envelope to be applied to the FE models for stress and

buckling assessments. The values ofMsware to be greater than Ms and less or equal toMS.Msware to be

incorporated into the ships Loading Manual and loading instrument as the assigned permissible still water

bending moment values.Mswis hereinafter referred as the permissible still water bending moment.

Tsc = scantling draught, in metres

Cb = block coefficient, seePt 3, Ch 1,6 of the Rules for Ships

x = longitudinal distance, in metres, from amidships to the centre of gravity of the tank, x is positive

forward of amidships

V = service speed, in knots, seePt 3, Ch 1,6 of the Rules for Ships

g = gravity constant = density of sea-water (specific gravity to be taken as 1,025)h = local head for pressure evaluation

c = density of cargo (specific gravity to be taken not less than 1,025)t = thickness of plating

tc = thickness deduction for corrosion

cr = critical buckling stress corrected for plasticity effects

c = elastic critical buckling stresso = specified minimum yield stress of material (special consideration will be given to steel where

0 2, seePt 3, Ch 2,1 of the Rules for Ships)

L =L

235k

= factor against elastic buckling

e = von Mises equivalent stress, given by

e = x y x y xy

2 2 23+ +

x = direct stress in element x directiony = direct stress in element y directionxy = shear stress in element xy plane = total stress in local bending direction

= mean shear stress over depth of web plate2.2 Consistent units to be used throughout all parts of the analysis. Results presentation in N and mm preferred.

2.3 All Rule equations are to use units as defined in the Rules for Ships.


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Chapter 1SECTION 3


Section 3: Direct calculationprocedure report

3.1 A report is to be submitted to LR for approval of the primary structure of the ship and is to contain:

list of plans used including dates and versions;

detailed description of structural modelling including all modelling assumptions; plots to demonstrate correct structural modelling and assigned properties; details of material properties used; details of boundary conditions; details of all loading conditions reviewed with calculated SF and BM distributions; details of applied loadings and confirmation that individual and total applied loads are correct; plots and results that demonstrate the correct behaviour of the structural model to the applied loads; summaries and plots of global and local deflections; summaries and sufficient plots of von Mises, directional and shear stresses to demonstrate that the design criteria are

not exceeded in any member;

plate buckling analysis and results; tabulated results showing compliance, or otherwise, with the design criteria; proposed amendments to structure where necessary, including revised assessment of stresses and buckling

properties.


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Chapter 2SECTIONS 1 & 2



Section 1: Objectives

Section 2: Structural modelling

Section 3: Boundary conditions

Section 4: Loading conditions

Section 5: Permissible stresses

Section 6: Buckling acceptance criteria

Section 7: Deflection of primary members

Section 1: Objectives

1.1 The objectives of the structural analysis is to verify that the stress level and buckling capability of primary

structures under the applied static and quasi-dynamic loads are within the acceptable limits.

Section 2: Structural modelling

2.1 In general, a 3-D finite plate element model of two-tank length located at about amidships is to be

considered. The ends of the finite element (FE) model are to be located at the mid-tank position. A typical FE model

is shown in Fig. 2.2.1 and Fig. 2.2.2.

2.2 This length of FE model is to enable the ships structure over the major cargo tank region to be assessed. If

the cargo tank structure in the after and forward tank(s) is significantly different from the midships tank arrangement,

then an extended or additional FE model is required.

2.3 The appropriate length of the FE model depends on the tank arrangement and is to be agreed with LR at an

early stage.

2.4 Unless there is asymmetry of the ship about the ships centreline, then only one side of the ship needs to be

represented with appropriate boundary conditions imposed at the centreline. However, it is strongly recommended

that both sides of the ship be modelled, as this will simplify the loading and analysis of asymmetrical loading

conditions. The full depth of the ship is to be modelled.

2.5 The FE model of the ship structure is to adopt should be represented using a right handed Cartesian co-

ordinate system with:

X measured in the longitudinal direction, positive forward,

Y measured in the transverse direction, positive to port from the centreline,

Z measured in the vertical direction, positive upwards from the baseline.


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Chapter 2SECTION 2


2.6 Typical FE arrangements representing a double hull VLCC design with primary members are shown in

Figs. 2.2.1 to 2.2.5. The proposed scantlings, excluding Owners extras or any additional thickness for ShipRight ES

procedure are to be used throughout the FE model. The selected size and type of plate elements are to provide a

satisfactory representation of the deflections and stress distribution within the structure.

2.7 In general the plate element mesh is to follow the primary stiffening arrangement as appropriate. The coarse

mesh size should not be greater than:

transversely, one element between every longitudinal stiffener; longitudinally, two elements between double bottom floors; vertically, one element between longitudinal stiffener; and three or more elements over the depth of double bottom girders, floors and side transverses with adjacent structure

modelled to suit.

Reduced sized elements, in the order of 450mm x 450mm, are to be incorporated at stress concentrations such asbracket toes, hopper knuckles, etc.

2.8 Where the mesh size of the coarse 3-D finite plate element model is insufficiently detailed to represent areas

of localised higher stresses, these are to be investigated by means of separate local fine mesh models with boundary

conditions derived from the main model. Alternatively, local fine mesh regions may be introduced into the main model.

In general the requirements to use fine mesh models or fine mesh regions within the main model will be subject to the

results from the main structural model. Proposals for follow-on fine mesh analysis should be submitted for approval.

2.9 The following structural items are to be investigated by fine mesh models unless it can be demonstrated by

previous finite element investigation that the arrangements proposed are acceptable.

Hopper knuckle. Transverse Stringers

Secondary member end connection in way of primary members, which do not satisfy the relative deflection criteriaspecified in section 7.

2.10 The mesh size in fine mesh regions is to be approximately 15t x15tor 200 x 200 mm, whichever is the lesser,

where tis the primary member thickness. The mesh size is not to be less than t xt.

2.11 In the coarse 3-D model, secondary stiffening members are to be modelled using line elements positioned in

the plane of the plating having axial and bending properties (bars), which may be grouped as necessary. The bar

elements are to have:

a cross-sectional area representing the stiffener area, excluding the area of attached plating (grouped as appropriate);

and

bending properties representing the combined attached plating and stiffener inertia (grouped as appropriate).

2.12 The permissible stresses and buckling criteria are based on membrane stress. However, the use of plate

elements with bending properties may be preferred, as this can avoid the problems of low or zero stiffness for out-of-

plane degrees of freedom associated with pure membrane elements and/or rod elements. In the latter case the membrane

stress result is to be used for comparison with the acceptance stress criteria.

2.13 In general, the use of triangular plate elements is to be kept to a minimum. Where possible they should be

avoided in areas where there are likely to be high stresses or a high stress gradient. These areas include:

in way of lightning /access holes; in way of the connection between the corrugated bulkhead and inner bottom or stool; and adjacent to knuckles or structural discontinuities.


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Chapter 2SECTION 2


2.14 Lightening holes, access openings, etc., in primary structure should be represented in high stress area, such as

double bottom girders adjacent to transverse bulkheads and floor plates adjacent to the hopper knuckle. Additional mesh

refinement may be necessary to model these openings but it may be sufficient to represent the effect of the opening by

deleting the appropriate element.

2.15 Lightening holes, access openings, etc., away from the above locations may be modelled by deleting the

appropriate elements or may be take into account by applying a correction to the resulting shear stresses, see5.5.

2.16 Face plates and plate panel stiffeners of primary members are to be represented by line elements with a cross-

sectional area modified, where appropriate, in accordance with, Table 2.2.1 and Fig. 2.2.6.


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Chapter 2SECTION 2


Fig. 2.2.1

3-D Finite plate element model


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Chapter 2SECTION 2


Fig. 2.2.23-D Finite plate element model


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Chapter 2SECTION 2


Fig. 2.2.3

Typical transverse frame


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Chapter 2SECTION 2


Fig. 2.2.4

Typical transverse bulkhead horizontal girder


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Chapter 2SECTION 2


Fig. 2.2.5

Typical centreline girder


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Chapter 2SECTION 2


1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0

Effective area of face bars = b ftf

0,5b f

Effective Area of Face Bars

R

Effective area of symmetrical face bars

0

tf

Rt f

1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0

Effective area of asymmetric face bars

0

Rtf

b f

R

b f

tf

Effective area of face bars = b ftf

b f

moss227

Fig. 2.2.6

Effective area of face bars


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Chapter 2SECTION 2


Table 2.2.1 Line element effective cross-section area

Structure represented by line

element

Effective area, Ae

Primary member face bars Symmetrical

Asymmetrical

Ae= 100% AnAe= 100% An

Curved bracket face bars

(continuous)

Symmetrical

Asymmetrical From Fig. 2.2.6

Straight bracket face bars

(discontinuous)

Symmetrical

Asymmetrical

Ae= 100% AnAe= 60% An

Straight

portion

Symmetrical

Asymmetrical

Ae= 100% AnAe= 60% AnStraight bracket face bars

(continuous around toe curvature)Curved portion

Symmetrical

AsymmetricalFrom Fig. 2.2.5

Flat bars Ae= 25% stiffener area

Web stiffeners - sniped both endsOther sections

AA

Y

r

Ae P=

+

1 02

Flat bars Ae= 75% stiffener area

Web stiffeners - sniped one end,

connected other end Other sectionsA

A

Y

r

Ae p=

+

12

0

2

Symbols

A = cross-section area of stiffener and associated plating

An = average face bar area over length of line element

Ap = cross-section area of associated plating

I = moment of inertia of stiffener and associated plating

Yo = distance of neutral axis of stiffener and associated plating from median plane of plate

r = radius of gyration =A

I


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Chapter 2SECTION 3


Section 3: Boundary conditions

3.1 Introduction

3.1.1 The boundary conditions to be applied to the FE model are dependent on the extent of ship modelled and the

load case to be analysed. Different boundary conditions need to be applied to analyse the local stress loadcases and

global stress loadcases specified in Section 4.

3.1.2 The boundary conditions described in this section are suitable for the FE model of two cargo tank length

(i.e. tank + 1 tank + tank).

3.1.3 A half-breadth FE model may be used only if the structure is symmetrical about the ships centreline plane.

However, for asymmetrical loading conditions, it is strongly recommended that both sides of the ship be modelled, as

this will simplify the analysis procedure.

3.1.4 The boundary conditions described in this section are preferred. Alternative boundary conditions may be used,subject to LRs agreement, which should be obtained prior to commencement of the analysis.

3.1.5 Stress results derived from the region close to the boundary supports will be influenced by the imposed

boundary conditions and may not be satisfactorily representative of the actual response of the structure. Therefore, these

results may not be suitable for evaluating the structure.

3.1.6 The figure describing the boundary conditions indicate arrangement with one longitudinal bulkhead. For ships

with more than one longitudinal bulkhead constraints applied to Points A, B at lines K and P to be applied to all

longitudinal bulkheads.

3.2 Boundary conditions for local stress loadcases (symmetric loads)

3.2.1 The boundary conditions described in this section are to be applied to remove the effect of global hull girder

bending from the FE model response induced by local loads. These boundary conditions are suitable for the analysis of

the local stress loadcases that comprise symmetric loads.

3.2.2 The boundary conditions are summarised in Table 2.3.1.

3.2.3 Constraints at ends of model

3.2.3.1 The forward and aft ends of the model are to be constrained by means of rigid planes. The grid points relating

to continuous longitudinal material at the model end are to be rigidly linked to an independent grid point in x, yand zdegrees of freedom. This independent point is to be located on the centre-line at a height close to the neutral axis (see

Fig. 2.3.1). This independent point is not to be connected to the model except by the rigid links. The independent points

at each end of the model are to be constrained in accordance with Table 2.3.1.

3.2.4 Transverse constraints

3.2.4.1 Transverse translation constraints, y= 0, are to be applied to the gird points on the upper deck, at theintersection of longitudinal bulkhead with transverse bulkheads, i.e. points A and B in Fig.2.3.1. For ships with more

than one longitudinal bulkhead, the constraints are to be applied to the intersection points on one longitudinal bulkhead

only, preferable on the centre-line. If a longitudinal bulkhead does not exists then the constraints are to be applied to the

intersection of the transverse bulkheads with the centre-line plane at the upper deck.

3.2.4.2 For a half-breadth FE model, see3.2.6.


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Chapter 2SECTION 3


3.2.5 Vertical constraints

3.2.5.1 Spring element method

Grounded spring elements (i.e. spring elements with one end constrained in all 6 degrees of freedom) are to be applied

to the grid points along the vertical part of the lines of intersection of the side shell, inner skin and longitudinal

bulkhead(s) with transverse bulkheads, i.e. lines I, J, K, L, M, N, O, P, Q, R in Fig. 2.3.2. These spring elements are to

have stiffness in zdegree of freedom only.

The stiffness K of the spring elements are calculated as:

nL

AGK

6

5=

Where G = shear modulus of plate material

A = shear area of the side shell, inner skin or longitudinal bulkhead(s)L = length of the cargo tank

n = number of grid points to which the spring elements is applied to the side shell, inner skin or

longitudinal bulkhead(s)

For a half breadth FE model with a centreline longitudinal bulkhead, the values of spring stiffness to be applied to the

lines of intersection of the transverse bulkheads with the centreline longitudinal bulkhead, i.e. lines K and P in Fig.

2.3.2, are to be calculated on the basis of half shear area of the longitudinal bulkhead.

3.2.5.2Force balancing method

As an alternative to the application of grounded spring elements described in 3.2.5.1, balance of the model can be

achieved by applying vertical forces to the grid points along the vertical part of the line of intersection of the side shell,

inner skin and longitudinal bulkhead(s) with transverse bulkheads (i.e. lines I, J, K, L, M, N, O, P, Q, R in Fig. 2.3.2). A

vertical constraint, z= 0, is to be applied to a grid point at the intersection of the side shell and the upper deck at eachtransverse bulkhead position (i.e. points C, D, E and F in Fig. 2.3.1).

Different values of force will be required to apply to each of the lines I, J, K, L, M, N, O, P, Q, R and these values will

also be different for each load cases. The vertical forces applied to each of the lines I, J, K, L, M, N, O, P, Q, R are to

be derived for each load cases considered. The sum of the nodal forces at each of the lines I, J, K, L, M, N, O, P, Q, R

may be derived in accordance with a shear flow calculation or is the ratio of the shear area of the relevant member to the

total shear are of the hull section. The total force along each line may be distributed evenly to the grid points. The total

sum of these forces equals to the out of balance vertical loads from each of the load cases.

For a half breadth FE model, the calculation of the forces to be distributed to the grid points on the lines I, J, K, L, M,

N, O, P, Q, R are to be based on the properties of the full hull section. Where a centreline longitudinal bulkhead exists,

the forces to be applied to the lines of intersection of the transverse bulkheads with the centreline longitudinal bulkhead,

i.e. lines K and P in Fig. 2.3.2, are to be taken as half of the calculated values.

Alternative methods of calculating the applied vertical forces will be considered.

3.2.6 Additional centreline constraints for half-breadth model

3.2.6.1 For a half breadth FE model, symmetry boundary conditions are to be applied to the centreline plane of theFE model. Each grid point in the centreline plane is to be constrained in y, xand zdegrees of freedom(i.e. y= x= z= 0).


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Chapter 2SECTION 3


3.3 Boundary conditions for local stress loadcases (asymmetric loads)

3.3.1 The boundary conditions described in this section are suitable for the analysis of the local stress loadcases that

subject to asymmetric local loads.



3.3.3.1 The constraints specified in 3.2.3 are to be applied to the ends of the FE model.


3.3.4.1 Grounded spring elements are to be applied to the grid points, along the lines of intersection of the upper deck

and bottom shell with the transverse bulkheads, i.e. lines S, T, U, and V in Fig. 2.3.2. These spring elements are to have

stiffness in ydegree of freedom only. The stiffness K of the spring elements is to be calculated in accordance with theformula given in 3.2.5.1, where A is now representing the shear area of the deck or bottom shell.

3.3.4.2 For load cases which only involve asymmetric fill level of cargo tanks, instead of the constraints specified in

3.3.4.1, the transverse constraints given in 3.2.4.1 may be used. For load case C2 in Fig. 2.4.1, in which asymmetric

external pressure loads are applied, the grounded spring constraints specified in 3.3.4.1 are to be used.

3.3.4.3 For half breadth FE model, see3.3.6.


3.3.5.1 The grounded spring element vertical constraints described in 3.2.5.1 are to be applied.

3.3.5.2 For load cases which only involve asymmetric fill level of cargo tanks, as an alternative to 3.3.5.1, the forcebalancing vertical constraints given in 3.2.5.2 may be used. However, for load case C2 in Fig. 2.4.1, in which

asymmetric external pressure loads are applied, the grounded spring constraints specified in 3.3.5.1 are to be used.


3.3.6.1 For a half breadth FE model, the asymmetric load case needs to be divided into two sub loadcases where the

symmetric and anti-symmetric components of the loads are applied separately. These symmetric load and anti-

symmetric load sub loadcases are then applied to the FE model with symmetric and anti-symmetric boundary conditions

respectively. The stress responses from the asymmetric load case are obtained by combining the results from the

symmetric and anti-symmetric load subload cases.

3.3.6.2 Due to the complexity in the analysis outlined in 3.3.6.1, a half breadth FE model is not recommended for the

analysis of asymmetric load cases and a full breadth model should be used.

3.3.6.2The following boundary conditions are included for completeness:

For the anti-symmetric load sub loadcase, anti-symmetry boundary conditions are to be applied to the centrelineplane of the half breadth model. Each grid point in the centreline plane is to be constrained in x, zand ydegreesof freedom (i.e. x= z= y= 0).

For the symmetric load sub loadcase, the boundary conditions specified in 3.2 are to be used.


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Chapter 2SECTION 3


3.4 Boundary conditions for global stress loadcases (hull girder bending moments)

3.4.1 These boundary conditions allow the FE model to deflect globally under the action of hull girder bending

moments and are suitable for analysis of the global hull girder bending moment loadcases described in 4.4.1. The

required bending moment is to be applied to the forward and aft ends of the model in accordance with the 3.4.3. No

other loads are to be applied to the model.



3.4.3.1 Bending moment is to be applied to the forward and aft ends of the FE model. The end planes of the model are

to be restrained to remain plane under the action of the applied bending moment whilst the cross-section is to be free to

rotate. To achieve this objective, all grid points relating to continuous longitudinal material at the model ends are to be

rigidly linked to an independent grid point in x, yand zdegrees of freedom.

3.4.3.2 The independent points are to be located on the centre-line at a height close to the neutral axis position. These

independent points are not to be connected to the model except by the rigid links. The independent points are to be

constrained in accordance with Table 2.3.3. The required vertical bending moment is to be applied to the independent

grid point at each end of the model, seeFig. 2.3.3.


3.4.4.1 Transverse translation constraints, y= 0, are to be applied to the gird points in the bottom shell, on thecentreline, at the positions of the transverse bulkheads, seeFig. 2.3.4.

3.4.4.2 For a half breadth FE model, see3.4.6.


3.4.5.1 Vertical translation constraints, z= 0, are to be applied to the ends of the model, at the intersection points ofthe upper deck and the side shell, seeFig. 2.3.3.


3.4.6.1 For a half breadth FE model, symmetry boundary conditions are to be applied to the centreline plane of the FE

model. Each grid point in the centreline plane is to be constrained in y, xand zdegrees of freedom (i.e. y= x= z= 0).

3.5 Boundary conditions for global stress loadcases (hull girder shear forces)

3.5.1 These boundary are suitable for analysis of the global hull girder shear force loadcases described in 4.4.2. The

required shear forces are to be applied to the fore end of the model. No other loads are to be applied to the model.



3.5.3.1 The boundary conditions for the local stress loadcases described in 3.2.3 are to be applied to the aft end of the

model only.

3.5.3.2 Shear forces are to be applied to the fore end of the FE model by distributing vertical forces to the grid points

along the vertical part of the side shell, inner skin and longitudinal bulkhead(s) in accordance with 4.4.2. The fore endof the model is to be free from constraints.



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Chapter 2SECTION 3


3.5.4.1 Transverse translation constraints, y= 0, are to be applied to the gird points in the bottom shell, on thecentreline, at the positions of the transverse bulkheads, as described in 3.4.4.


3.5.5.1 Grounded spring elements with stiffness in zdegree of freedom are to be applied to the grid points along thevertical part of the side shell, inner skin and longitudinal bulkhead(s) at the aft end of the model. The stiffness K of the

spring elements is to be calculated in accordance with the formula given in 3.2.5.1.

3.5.5.2 For a half breadth FE model with a centreline longitudinal bulkhead, the values of spring stiffness to be applied

to the centreline longitudinal bulkhead are to be calculated based on half shear area of the longitudinal bulkhead.


3.4.6.1 Symmetry boundary conditions as described in 3.4.6 are to be applied to the centreline plane of the FE model.


26/50


Chapter 2SECTION 3


Table 2.3.1 Boundary conditions for local stress loadcases (symmetric loads)

Translation RotationLocation

x y z x y zComments

Constraints at ends of model

Aft end L - - - L LFwd end L - - - L LIndependentpoint aft end

Independentpoint fwd end

-

SeeFig. 2.3.1

Transverse constraints

Points A, B - --

- -See

Fig. 2.3.1

Vertical constraints

Lines I, J, K, L,M, N, O, P, Q,R

- - S

-

- -See Notes1 & 2 andFig. 2.3.2

Or

Points C, D, E,F

- - - - -See

Fig.2.3.2Lines I, J, K, L,M, N, O, P, Q,R

- - F - - -

See Notes3 & 4 andFig. 2.3.2

Additional centre line constraints for half-breadth model

Centreline plane(symmetry)

- - - -

Symbols constraint (fixed)

constraint (fixed) may be required to remove mathematical singularities

- no constraint applied (free)

L rigidly linked to independent point at neutral axis on centreline

S application of grounded springs to grid points

F application of forces to grid pointsNotes1 Different values of spring stiffness are to be applied to each of the lines I, J, K, L, M, N, O, P, Q, R, see 3.2.5.1

2 For a half breadth FE model with a centreline longitudinal bulkhead, the calculation of the values of spring stiffnessfor applying to the lines K and P are to be based on half of the shear area of the longitudinal bulkhead, see 3.2.5.1.

3 Different values of force are to be applied to each of the lines, I, J, K, L, M, N, O, P, Q, R, and these values will bedifferent for each load cases considered, see 3.2.5.2.

4 For a half breadth FE model, the calculation of the forces for applying to the lines, I , J, K, L, M, N, O, P, Q, R, are tobe based on the properties of the full hull section. Where a centreline longitudinal bulkhead exists, the forces to beapplied to the lines, K and P, are to be taken as half of the calculated values, see 3.2.5.2.


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28/50


Chapter 2SECTION 3


Table 2.3.3 Boundary conditions for global stress loadcases (hull girder bending moments)


x y z x y zComments


Aft end L - - - L L

Fwd end L - - - L L

Independentpoint aft end

M

Independentpoint fwd end

- M

SeeFig. 2.3.3


Points K, L - --

- -See

Fig. 2.3.4


Points G, H, I, J - - - - - Fig. 2.3.3



- - -

Symbols

M Bending moment applied to independent point

For other symbols, see Table 2.3.1.

Table 2.3.4 Boundary conditions for global stress loadcases (hull girder shear forces)


x

y

z

x

y

z

Comments


Aft end L - - - L L

Fwd end - - F - - -

Independentpoint aft end


Points K, L - --

- -See

Fig. 2.3.4


Aft end - - S - - -



- - -

Symbols

F Application of vertical forces to the grid points along the vertical part of the side shell, inner skin andlongitudinal bulkhead(s) to represent shear forces, see3.5.3.The values of the total vertical force to beapplied to each structural component are different and are dependent upon the shear area.

S Application of grounded springs to grid points along the vertical part of the side shell, inner skin andlongitudinal bulkhead(s), see 3.5.5.The values of the spring stiffness to be applied to each structuralcomponent are different and are dependent upon the shear area.

For other symbols, seeTable 2.3.1.


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Chapter 2SECTION 3


Fig. 2.3.1

Location for application of constraints for local stress load cases(symmetric loadcases see table 2.3.1, asymmetric loadcases, seeTable 2.3.2)

C

D

A

E

F

B

Independent

point

N.A

N.A

N.A

N.A

Independentpoint


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Chapter 2SECTION 3


Fig. 2.3.2

Location for application of constraints for local stress load cases(symmetric loadcases see table 2.3.1, asymmetric loadcases, seeTable 2.3.2)

I

J

L

M

NO

Q

RK

P

S

T

S

T

U

V


31/50


Chapter 2SECTION 3


Fig. 2.3.3

Boundary conditions for global stress load cases (hull girder bending moments)

z= 0

z= 0

z= 0

z= 0

G

I

H

J

Independentpoint

M

N.A

N.A

M

N.A

N.A


32/50


Chapter 2SECTION 3


Fig. 2.3.4

Boundary conditions for global stress load cases (hull girder bending moments)

K

L

y= 0

y= 0


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Chapter 2SECTION 4


Section 4: Loading conditions

4.1 The loading conditions, which are likely to impose the most onerous local and global load regimes, are to be

investigated by structural analysis.

4.2 Where specified loading conditions are agreed between the Shipbuilder and Shipowner which are not covered

by the loading conditions given in these guidance notes, then these additional loading conditions are to be examined.

Full details of all proposed loading conditions are to be submitted at an early stage for consideration.

4.3 Special loading & assessment conditions for ship with two longitudinal watertight bulkheads

and cross-tie arrangement in the centre tank.

4.3.1 Standard loading conditions to be used in the assessment ar described in paragraph 4.4.

4.3.2 However, additional requirements are applicable to ships with two longitudinal bulkheads and cross-tie

arrangement in the centre tank.

4.3.3 The reason for these additional load cases is that the loading conditions shown in Fig. 2.4.1 (a) are symmetrical

with respect to the transverse distribution of tank fillings. For tankers with two longitudinal bulkheads and cross-tie

arrangement in the centre tank it is possible that unequal fillings of transversely paired wing cargo tanks would result in

more onerous structural response.

4.3.4 For ships, which are not intended to operate in sea-going or sheltered water conditions with unequal filling

levels in transversely paired side wing cargo tanks the additional load cases specified in Fig. 2.4.2 are to be examined

using the stress and buckling criteria given in 5.2 and 6.10 to cater for possible accidental discharge of one side wing

cargo tank during operations in sheltered water conditions.

Such ships will have to comply with the following restrictions, which are to be clearly stated in the Loading Manual.

(a) The ship is not to be operated in sea-going or sheltered water conditions with a difference in filling height in

transversely paired tanks exceeding 5% of the tank depth.

(b) In cargo operations in sheltered water conditions the difference in filling height between transversely paired wing

tanks is not to exceed 25% of the tank depth.

(c) Wing cargo tank testing is always to be carried out with both port and starboard wing cargo tanks full. Strict control

is to be exercised to ensure that the difference in filling levels during filling and discharging does not exceed 25%

of the depth of the tank.

4.3.5 If any asymmetrical filling of transversely paired side wing cargo tanks is envisaged in either sea-going,sheltered water or tank testing conditions, the additional loading conditions specified in Fig. 2.4.2 are to be examined to

verify satisfaction of the stress and buckling criteria given in Table 2.5.1 and 2.6.2.

4.4 Local stress load cases

4.4.1 The standard loading conditions to be applied to the structural model are shown in Fig. 2.4.1. Fig. 2.4.1(a), (b)

and (c) specify the standard loading conditions for tankers with two oiltight longitudinal bulkheads, one centreline

oiltight longitudinal bulkhead and no oiltight longitudinal bulkheads respectively.

4.4.2 The loading conditions shown in Fig. 2.4.1(a) are symmetrical with respect to the transverse distribution of

tank fillings. For tankers with two longitudinal bulkheads it is possible that unequal fillings of transversely paired wing

cargo tanks would result in more onerous structural response, see4.3.


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Chapter 2SECTION 4


4.4.3 The conditions of operation for asymmetrical loading are to be clearly stated in the Ships Loading Manual. If

the ship is not intended to operate in such loading conditions a note is to be included in the Loading Manual stating that

these loading conditions are not permitted. For designs with two longitudinal bulkheads and cross-tie in centre tank see

4.3.

4.4.4 Loads arising from liquids in tanks are to be applied as equivalent pressure loads to all contacted surfaces. The

design specific gravity of the cargo is not to be taken as less than 1,025. Fuel oil tanks and/or other tanks in the double

bottom in way of cargo tanks are to be included in the model.

4.4.5 The additional pressure on the external plating due to a wave crest is to be applied as local loads in accordance

with the pressure head distribution given in Fig. 2.4.3.

4.5 Global stress load cases

4.5.1 Global hull girder bending moments

4.5.1.1 The following global hull girder bending moments are to be considered:

Maximum permissible still water bending moment (sagging and hogging). Combined maximum permissible still water and Rule design vertical wave bending moment (sagging and hogging).

4.5.1.2 Stress responses are to be determined by applying a suitable bending moment to the model ends, using the

boundary conditions given in 3.4. No other loads are to be applied to the FE model.This bending moment should be

applied as a separate load case.

4.5.2 Global hull girder shear forces

4.5.2.1 For the cargo loaded conditions specified in Fig. 2.3.1 (a) 3, (b) 3 and (c) 1 with all tanks abreast empty, the

structure is also to be assessed against the combination of local loads (see4.4) and global shear loads.

4.5.2.2 The shear forces to be applied to the FE model are the summation of global design wave shear forces (seePt 3,

Ch 4,6 of the Rules for Ships) and maximum permissible still water shear force assigned to the ship minus the

maximum shear force developed in the local loads case. Both positive and negative shear forces are to be considered.

No other loads are to be applied to the FE model.

4.5.2.3 The shear forces are to be represented by vertical forces distributed to the grid points along the vertical part of

the side shell, inner skin and longitudinal bulkhead(s) and applied to the fore end of the FE model. The vertical force, f,

at each nodal points of a structural component is to be calculated as:

where F is the total shear force

A is the total shear area of structural components

a is the shear area of each structural component

n is the number of grid points on each structural component

4.5.2.4 The boundary conditions to be applied to the FE model are described in 3.5. This shear force should be applied

as a separate load case.

4.5.3 Alternative method may be used to apply the global hull girder loads. In this case, the proposed method shouldbe submitted for LRs agreement prior to commencement of the analysis.

nA

aFf=


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Chapter 2SECTION 4


4.6 Combination of Load Cases

4.6.1 The stresses derived from the local stress load cases are to be combined with the stresses derived from the

global stress load cases, in accordance with Tables 2.5.1 and 2.6.1, for checking compliance with the permissible stress

and buckling criteria.

4.6.2 For cargo loaded and ballast conditions, the local stresses are to be combined with the global stresses arising

from the application of combined maximum assigned still water moment (Msw) and Rule vertical wave design bending

moment (Mw). For tank testing conditions, the local stresses may be combined with the global stresses arising from the

application of maximum assigned still water bending moment only. Both hogging and sagging bending moments are to

be considered for stress combination to give maximum stresses for comparison with the permissible stress criteria and

buckling assessment.

4.6.3 For the cargo loaded conditions specified in Fig. 2.3.1 (a) 3, (b) 3 and (c) 1, compliance with the permissible

stress criteria is also to be verified for the combined local stress and global stress from the application of design wave

shear force and maximum permissible still water shear force. Both positive and negative global shear forces are to beconsidered for stress combination to give maximum stresses for comparison with the permissible stress criteria and

buckling assessment.


36/50


Chapter 2SECTION 4


Fig. 2.4.1 Part (a)

Standard load casesTankers with two oiltight longitudinal bulkheads (seecontinuation)


37/50


Chapter 2SECTION 4


Fig. 2.4.1 Part (a)

Standard load casesTankers with two oiltight longitudinal bulkheads (seecontinuation)


38/50


Chapter 2SECTION 4


Fig. 2.4.1 Part (b)Standard load cases

Tankers with one centreline oiltight longitudinal bulkhead (seecontinuation)


39/50


Chapter 2SECTION 4


Fig. 2.4.1 Part (b)

Standard load caseTankers with one centreline oiltight longitudinal bulkhead (seecontinuation)


40/50


Chapter 2SECTION 4


Additional internal head above top of tanks in metres:h1 = 0,125D1+ R(b1-0,6B)

minimum value of h1=h2h2 = 0,125D1

External draught in metres:T1 = 0,4D+0,5RBT2 = 0,4D-0,5RB

Where

R =

+

127054,00,10,45

L

B

L

L, B, D = seeCh 1,2D1 = seeNote 1b1 = largest horizontal distance, in metres, from the tank corner at top of tank, either

side to mid point of span of member concerned. SeealsoPt 4, Ch 9,6.2 of theRules for Ships.

Fig. 2.4.1 Part (c)

Standard load casesTankers with no oiltight longitudinal bulkheads (seecontinuation)


41/50


Chapter 2SECTION 4


Fig. 2.4.1 Part (c)

Standard load casesTankers with no oiltight longitudinal bulkheads (conclusion)

NOTES1. All tanks which are loaded are to include an additional internal head measured above the top of the tank as follows:

1.1 2,45 m in tank test conditions.

1.2 D1/8 m in cargo and ballast conditions (except condition 2(c)).D1is the moulded depth of the ship in metres, but is not to be taken greater than 16,0 m.

2. The specific gravity in loaded tanks is not to be taken as less than 1,025.

3. Where applicable, the additional wave head, in metres, is to be applied as given in Fig. 2.4.3.

4. Transverse bulkheads are to be examined with the loading applied from both sides of bulkhead. Where the structuralmodel only includes one transverse bulkhead, two separate load cases will be required.

5. For designs having two longitudinal bulkheads and cross-ties in the centre tank, wing cargo tank testing is always tobe carried out with both port and starboard cargo tanks full. Strict control is to be exercised to ensure that thedifference in levels during filling and discharge does not exceed 25 per cent of the depth of the tank.This restriction is to be included as a Note in the Loading Manual. However, this restriction will not apply if theadditional load cases indicated in Fig. 2.4.2 has been analysed and the stress and buckling capability comply withTable 2.5.1 and Table 2.6.2 (seealso 4.3).

6. For single hull tankers the loading conditions will be specially considered.


42/50


Chapter 2SECTION 4


(a) Tankers with two oiltight longitudinal bulkheads with a cross-tie in the centre tank

Fig. 2.4.2

Additional load cases


43/50


Chapter 2SECTION 4


Wave crest

P H hWL W= +

P Hh

TH W

sc

=

1 0 7,

whereHw = 0,0771Le

-0,0044Lm for L< 227 m

= 6,446 m for L e = 2,7183h = distance below the still waterline, m

Hw

Hw

h

Tsc

Pressur eacting inward

PW= PH

PW= PWL

NOTEPressure due to immersion of draught, Tsc, is also to be applied.

Fig. 2.4.3

Pressure head distribution Pwfor local wave crest


44/50


Chapter 2SECTION 5


Section 5: Permissible stresses

5.1 The stresses resulting from the application of the standard and/or specified loading conditions are not to exceed

the maximum permissible values given in Table 2.5.1. The assessment of the primary scantlings is to be based on the

most severe criteria.

5.2 For the asymmetrical loading conditions specified in Fig. 2.4.2, if these conditions are not intended to be

operated in sheltered water or sea-going conditions, the calculated direct stresses and combined stresses are not to

exceed the yield stress of the material and the calculated shear stresses are not to exceed 0,58 of the tensile yield stress.

For operation in sheltered water and sea-going conditions, the stress criteria given in Table 2.5.1 are to be complied

with, see4.3.

5.3 The permissible stress criteria in Table 2.5.1 are based on the recommended mesh size indicated in Section 2.

5.4 Where indicated in Table 2.5.1, the stresses derived from the local stress load cases are to be combined withthe hull girder stresses in order to check compliance with the permissible stress criteria, see 4.4. Both hogging and

sagging bending moments are to be considered for stress combination to give the maximum compressive and tensile

stress values with local stresses.

5.5 The mean shear stress, , is to be taken as the average shear stress over the depth of the web of the primarymember. Where openings are not represented in the structural model, both the mean shear stress, , and the element

shear stress, xy, are to be increased in direct proportion to the modelled web shear area divided by the actual web area.The revised xy is to be used to calculate the combined equivalent stress, e. Where the resulting stresses are greater than90 per cent of the maximum permitted, a more detailed analysis using a fine mesh representing the opening may be

required.

5.6 The structural items indicated in Table 2.5.1 are provided for guidance as to the most likely critical areas. All

stresses for all parts of the model are to be examined for high values.


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Chapter 2SECTION 5


Table 2.5.1 Maximum permissible membrane stresses

Permissible stresses, N/mm2

Structural Item Applied stresses

e

(a) Local stress and hullgirder stress, seeNote 2

0,460 0Longitudinal girders in double hull

SeeNote 1

(b) Local stress only 0,350 0,750

Longitudinal girders in single hull:

Web plateFace plate


0,830face plate only

0,920

SeeNote 1 (b) Local stress only 0,350 0,750


0,920 seenote 2.3 0Plating of inner and outer hulldouble hulls and longitudinal

bulkheads

SeeNotes 1 and 3 (b) Local stress only 0,630 0,750

Transverse structure excluding thetoes of primary member brackets

All local stresses

Web plate 0,350 0,750

Face plate 0,750

SeeNote 5

Areas of stress concentrationadjacent to welds including toes ofprimary

SeeNote 4

All local stressesmember brackets

245

Fine mesh regions

Average combined stress, averageand

Average shear stress, averageSeeNote 6

All cases 0,460 0

Individual element, see5.2 All cases


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Chapter 2SECTION 6


Section 6: Buckling acceptance criteria

6.1 Plate panel buckling is to be investigated for the web plating of longitudinal girders and transverse primary

structure including all stress components. Panel buckling is also to be investigated in the attached plating to primary

members, e.g. deck, shell, inner hull and transverse and longitudinal bulkhead plating.

6.2 Panel buckling calculations are to be based on the proposed thickness reduced by the standard thickness

deduction for corrosion given in Table 2.6.1.

6.3 The combined interaction of bi-axial compressive stresses, shear stresses and in plane bending stresses are to

be included in the buckling calculation. In general, the average stresses acting within the plate panel are to be used for

the buckling calculation.

6.4 Where indicated in Table 2.6.1, the stresses derived from the local stress load cases are to be combined with

the hull girder bending stresses for the assessment of panel buckling capability, see4.5. Both hogging and sagging

bending moments are to be considered for stress combination to give the maximum compressive stress values with local

stresses.

6.5 The stresses derived from the local load cases are to be increased by a factor equal to the original thickness

divided by the thickness after the corrosion deduction given in 6.2. For hull girder stresses, it is permissible not to

apply the stress increases due to corrosion reduction of thickness.

6.6 The factor against elastic buckling are to be derived using the computer program LR Buckle (ShipRight IS) or

program Buckling of flat rectangular plate panels (ShipRight Direct Calculation program no. 10403) or equivalent.

6.7 In calculating the factors against buckling, the edge restraint factor 'c' defined in Pt 3, Ch 4,7 of the Rules for

Ships may be taken into account in calculating the critical buckling stress of wide panels subjected to compressive

loading on the long edge of the panel. The edge restraint factor c is not to be used in the calculation of the critical

buckling stress for compression applied on the short edges.

6.8 When the calculated elastic critical buckling stress exceeds 50 per cent of the specified minimum yield stress

then the buckling stress is to be adjusted for the effects of plasticity using the JohnsonOstenfeld correction formula,

given below:

cr= o o c)

6.9 The applied stresses which are to be included in the buckling calculation, and the required minimum factor

against elastic buckling, , given in Table 2.6.2.

6.10 For the asymmetrical loading conditions specified in Fig. 2.4.2, if these conditions are not intended to be

operated in sheltered water or sea-going conditions, minimum factors against buckling of not less than 1,0 is acceptable.

For operations in sheltered water and sea-going conditions, the buckling criteria in Table 2.6.2 are to be satisfied. See

4.3.


47/50


Chapter 2SECTION 6


Table 2.6.1 Standard thickness deductions, to be used to derive design applied and critical

buckling stresses

Position Thickness deduction, mmDeck and shell plating 1,0

Longitudinal bulkhead and inner hull 2,0Within 1,5 m ofweather deck Internal structure including transverse bulkheads

SeeNote 1

2,0

Shell plating 1,0

Longitudinal bulkhead and inner hull 1,0Elsewhere

Internal structure including transverse bulkheads

SeeNote 1

1,0

NOTES1. In uncoated tanks for refined oils where an inert gas system is not fitted the thickness deduction is to beincreased by 1,0 mm.

2. A mean value is to be taken for tanks in which the contents vary and for internal plating which separates regionshaving different thickness deductions.


48/50


Chapter 2SECTION 6


Table 2.6.2 Plate panel buckling: Required factor against elastic buckling,

Structural Item Applied stressesFactor againstelastic buckling

Longitudinal girder in double hull (a) Local stress only

(b) Local stress and hull girder stress, seeNote 3

1,2

1,0

Longitudinal girder in single hull Local stress and hull girder stress, seeNote 3 1,0

Plating of deck, shell, inner hull,longitudinal and transverse bulkhead

Local stresses and hull girder stress, seeNote 3 1,0

Web plating of transverse structureincluding midship web frame and bulkheadhorizontal and vertical webs

All local stresses 1,1

Symbols

=Calculated critical buckling stress

Applied stress

NOTES

1. Local stresses are to be derived from the finite plate element calculation increased in direct proportion to platethickness to account for stresses after standard thickness deduction.

2. Critical buckling stress is to be calculated using the net plate thickness taking account of the standardthickness deduction.

3. Local stress and hull girder stress combination

3.1 For cargo and ballast conditions, the hull girder bending stresses, corresponding to the combined maximumpermissible still water bending moment (Msw) and Rule wave vertical bending moment (Mw),.is to be added to

the local stresses for checking compliance with the maximum permissible stresses criteria.3.2 For tank testing conditions, the hull girder bending stress may be based only on the maximum permissible still

water bending moment, see4.4.

3.3 For the cargo loaded conditions specified in Fig. 2.3.1 (a) 3, (b) 3 and (c) 1, compliance with the permissiblestress criteria is also to be verified for the combined local stress and global stress from the application ofdesign wave shear force and maximum permissible still water shear force. Thickness deduction for the globalcomponent need not be applied.

4. Still water hull girder bending stress is to correspond to the permissible still water bending moment and thescantlings without applying the thickness deduction.

5. Wave hull girder bending stress is to be derived as for the still water stress using the Rule wave bending moment.

6. For deck and bottom structure the maximum combined bending moments for sagging and hoggingrespectively are to be used.


49/50


Chapter 2SECTION 7


Section 7: Deflection of primary members

7.1 Where the relative deflection between adjacent primary transverse members exceeds the values given below,

particular attention is to be paid to the design of the end connections of the longitudinals and stiffeners in way (seealso

2.9):

(a) For deck and bottom transverse, floors and transverse bulkhead girders:

S2180= mm for asymmetrical longitudinals and stiffeners

d

S2205= mm for symmetrical longitudinals and stiffener

(b) For side transverses and vertical webs of longitudinal bulkheads:

S2160= mm for asymmetrical longitudinals and stiffeners

S2185= mm for symmetrical longitudinals and stiffener

where

d = depth of longitudinal, in mm

S = spacing of transverse, in metres

= maximum permitted relative deflection of primary members without special consideration being given tothe end connections of the longitudinals and stiffeners in way, in mm

7.2 The critical regions are normally between transverse or swash bulkheads and the adjacent transverse frame or

between the deck or bottom structure and the adjacent transverse bulkhead horizontal girder.

7.3 In addition to the relative deflection criteria given in 7.1, the maximum deflection of an individual primary

member m, is not in general to exceed the following values:

(a) For deck and bottom transverses, floors and transverse bulkhead girders:

m = 1,3lmm

(b) For side transverses and vertical webs of longitudinal bulkheads:

m = 1,0lmm

wherel = overall length of the primary member, in metres, as defined in Pt 3, Ch 3,3.2.1 of the Rules for Ships. In

the case of side transverses and the vertical webs of the longitudinal bulkheads, cross ties are to be

neglected in determining l

m = maximum deflection of the primary member, in mm, measured relative to a straight line joining the endsof the overall length.


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