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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
Primary Structure of Tankers
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.
5. Nevertheless, if the Client uses the LR Group's services orrelies on any information or advice given by or on behalf ofthe LR Group and as a result suffers loss, damage, or expensethat is proved to have been caused by any negligent act,omission, or error of the LR Group or any negligentinaccuracy in information or advice given by or on behalf ofthe LR Group, then the LR Group entity providing theservice, information, or advice will pay compensation to theClient for its proved loss up to but not exceeding the amountof the fee (if any) charged by the LR Group entity for thatparticular service, information, or advice.
6. Notwithstanding the previous clause, the LR Group will notbe liable for any loss of profit, loss of contract, loss of user, or
any indirect or consequential loss, damage, or expensesustained by any person caused by any act, omission, or erroror caused by any inaccuracy in any information or advicegiven in any way by or on behalf of the LR Group.
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8. Any dispute, claim, or litigation between LR and the Clientarising from or in connection with the Services provided byLR or any Contract with LR shall be subject to the exclusivejurisdic tion of the English courts and will be governed byEnglish law.
9. Any dispute, claim or litigation between the Client and anyentity in the LR Group that performs services as provided forin Paragraph 2 shall be subject to the jurisdiction of the courtsin the jurisdiction in which that LR Group entity is locatedand will be governed by English law, including theprovisions on the recovery of legal costs. Notwithstandingthe foregoing, if the Client asserts or initiates any dispute,claim or litigation against an entity in the LR Group in anyproceeding in which LR is also named as a party or that arisesin whole or in part from the subject matter of a dispute, claimor proceeding that also has been asserted or initiated againstLR, that dispute, claim or proceeding shall be subject to the
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 1SECTION 2
Lloyds Register of Shipping 3
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 1SECTION 3
4 Lloyds Register of Shipping
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTIONS 1 & 2
Lloyds Register of Shipping 5
Primary Structure of Tankers
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 2
6 Lloyds Register of Shipping
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 2
Lloyds Register of Shipping 7
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
8 Lloyds Register of Shipping
Fig. 2.2.1
3-D Finite plate element model
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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 2
Lloyds Register of Shipping 9
Fig. 2.2.23-D Finite plate element model
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Chapter 2SECTION 2
10 Lloyds Register of Shipping
Fig. 2.2.3
Typical transverse frame
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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 2
Lloyds Register of Shipping 11
Fig. 2.2.4
Typical transverse bulkhead horizontal girder
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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 2
12 Lloyds Register of Shipping
Fig. 2.2.5
Typical centreline girder
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Chapter 2SECTION 2
Lloyds Register of Shipping 13
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 2
14 Lloyds Register of Shipping
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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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 3
Lloyds Register of Shipping 15
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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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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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.
3.3.2 The boundary conditions are summarised in Table 2.3.2.
3.3.3 Constraints at ends of model
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 Transverse constraints
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 Vertical constraints
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 Additional centreline constraints for half-breadth model
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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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.
3.4.2 The boundary conditions are summarised in Table 2.3.3.
3.4.3 Constraints at ends of 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 Transverse constraints
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 Vertical constraints
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 Additional centreline constraints for half-breadth model
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.
3.5.2 The boundary conditions are summarised in Table 2.3.4.
3.5.3 Constraints at ends of 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.
3.5.4 Transverse constraints
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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 Vertical constraints
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.
3.5.6 Additional centreline constraints for half-breadth model
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.
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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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Table 2.3.3 Boundary conditions for global stress loadcases (hull girder bending moments)
Translation RotationLocation
x y z x y zComments
Constraints at ends of model
Aft end L - - - L L
Fwd end L - - - L L
Independentpoint aft end
M
Independentpoint fwd end
- M
SeeFig. 2.3.3
Transverse constraints
Points K, L - --
- -See
Fig. 2.3.4
Vertical constraints
Points G, H, I, J - - - - - Fig. 2.3.3
Additional centre line constraints for half-breadth model
Centreline plane(symmetry)
- - -
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)
Translation RotationLocation
x
y
z
x
y
z
Comments
Constraints at ends of model
Aft end L - - - L L
Fwd end - - F - - -
Independentpoint aft end
Transverse constraints
Points K, L - --
- -See
Fig. 2.3.4
Vertical constraints
Aft end - - S - - -
Additional centre line constraints for half-breadth model
Centreline plane(symmetry)
- - -
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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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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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
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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
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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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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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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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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.
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Fig. 2.4.1 Part (a)
Standard load casesTankers with two oiltight longitudinal bulkheads (seecontinuation)
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Fig. 2.4.1 Part (a)
Standard load casesTankers with two oiltight longitudinal bulkheads (seecontinuation)
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Fig. 2.4.1 Part (b)Standard load cases
Tankers with one centreline oiltight longitudinal bulkhead (seecontinuation)
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Fig. 2.4.1 Part (b)
Standard load caseTankers with one centreline oiltight longitudinal bulkhead (seecontinuation)
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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)
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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.
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(a) Tankers with two oiltight longitudinal bulkheads with a cross-tie in the centre tank
Fig. 2.4.2
Additional load cases
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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
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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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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
(a) Local stress and hullgirder stress, seeNote 2
0,830face plate only
0,920
SeeNote 1 (b) Local stress only 0,350 0,750
(a) Local stress and hullgirder stress, seeNote 2
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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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.
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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 6
Lloyds Register of Shipping 41
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.
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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 6
42 Lloyds Register of Shipping
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.
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Notice No.1 to Primary Structure of Tankers (July 2002) Effective date: 1 October 2002
Chapter 2SECTION 7
Lloyds Register of Shipping 43
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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