Common Structural Rules for
Bulk Carriers, January 2006

Background Document
CHAPTER 5 – HULL GIRDER STRENGTH

NOTE:- This TB is published to improve the transparency of CSRs and increase theunderstanding of CSRs in the industry.
- The content of the TB is not to be considered as requirements.
- This TB cannot be used to avoid any requirements in CSRs, and in cases
where this TB deviates from the Rules, the Rules have precedence.
- This TB provides the background for the first version (January 2006) of theCSRs, and is not subject to maintenance.

COMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 2 – CHAPTER 5: HULL GIRDER STRENGTH© IACS - the International Association of Classification Societies and theInternational Association of Classification Societies Limited
All rights reserved.
Except as permitted under current English legislation no part of this work may be
photocopied, stored in a retrieval system, published, performed in public, adapted,
broadcast, transmitted, recorded or reproduced in any form or by means, without
prior permission of the copyright owner.
Where IACS has granted written permission for any part of this publication to bequoted such quotation must include acknowledgement to IACS.
Enquiries should be addressed to the Permanent Secretary,
International Association of Classification Societies Ltd,36 Broadway
London, SW1H 0BH
Telephone: +44 (0)20 7976 0660
Fax: +44 (0)20 7808 1100
Email: PERMSEC@IACS.ORG.UK

Terms and Conditions
The International Association of Classification Societies (IACS), its Member Societies
and IACS Ltd. and their directors, officers, members, employees and agents (onbehalf of whom this notice is issued) shall be under no liability or responsibility incontract or negligence or otherwise howsoever to any person in respect of any
information or advice expressly or impliedly given in this document, or in respect of
any inaccuracy herein or omission herefrom or in respect of any act or omission
which has caused or contributed to this document being issued with the information
or advice it contains (if any).
Without derogating from the generality of the foregoing, neither the International
Association of Classification Societies (IACS) nor IACS Ltd. nor its Member Societies
nor their directors, officers, members, employees or agents shall be liable in contract
or negligence or otherwise howsoever for any direct, indirect or consequential loss toany person caused by or arising from any information, advice, inaccuracy or omission
given or contained herein or any act or omission causing or contributing to any suchinformation, advice, inaccuracy or omission given or contained herein.
Any dispute concerning the provision of material herein is subject to the exclusive
jurisdiction of the English courts and will be governed by English Law.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 3 – CHAPTER 5: HULL GIRDER STRENGTHTABLE OF CONTENTS:
SECTION 1 – YIELDING CHECK ...................................................................................................... 4
1.

STRENGTH CHARACTERISTICS OF HULL TRANSVERSE SECTION ................................. 4
1.1
1.2
1.3
1.4
1.5
1.6

2.

HULL GIRDER STRESSES ......................................................................................................... 5
2.1
2.2

3.

Normal stresses ....................................................................................................................... 6
Shear stresses........................................................................................................................... 7

SECTION MODULUS AND MOMENT OF INERTIA............................................................... 7
4.1
4.2
4.3
4.4
4.5

5.

Normal stress .......................................................................................................................... 5
Shear stress .............................................................................................................................. 6

CHECKING CRITERIA............................................................................................................... 6
3.1
3.2

4.

General .................................................................................................................................... 4
Hull girder transverse sections................................................................................................ 4
Strength deck........................................................................................................................... 5
Section modulus ...................................................................................................................... 5
Moments of inertia .................................................................................................................. 5First moment ........................................................................................................................... 5

General .................................................................................................................................... 7
Section modulus within 0.4L amidships ................................................................................. 8
Section modulus outside 0.4L amidship ................................................................................. 8
Midship section moment of inertia ......................................................................................... 8
Extent of higher strength steel................................................................................................. 8

PERMISSIBLE STILL WATER BENDING MOMENT AND SHEAR FORCE........................... 8
5.1
5.2
5.3

Permissible still water bending moment and shear force in intact condition ......................... 8
Permissible still water bending moment and shear force in harbour condition ..................... 9
Permissible still water bending moment and shear force in flooded condition ...................... 9

SECTION 2 – ULTIMATE STRENGTH CHECK.............................................................................. 10
1.

APPLICATION .......................................................................................................................... 10
1.1

2.

General .................................................................................................................................. 10

HULL GIRDER ULTIMATE STRENGTH CHECK .................................................................. 10
2.1
2.2
2.3

Hull girder loads ................................................................................................................... 10
Hull girder bending moment ................................................................................................ 10
Checking criteria ................................................................................................................... 10

APPENDIX 1 – HULL GIRDER ULTIMATE STRENGTH ............................................................... 111.

HULL GIRDER ULTIMATE STRENGTH CHECK .................................................................. 11
1.1

2.

Introduction........................................................................................................................... 11

CRITERIA FOR THE CALCULATION OF THE CURVE M-Χ ................................................. 11
2.1
2.2

Simplified method based on a incremental-iterative approach ............................................ 11
Load-end shortening curves σ-ε ............................................................................................ 11

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 4 – CHAPTER 5: HULL GIRDER STRENGTHSECTION 1 – YIELDING CHECK
1. STRENGTH CHARACTERISTICS OF HULL TRANSVERSE SECTION
1.1

General

1.1.1
1.1.1.aSince regulations related to design loads were basically specified in Chapter 4 in
CSR, regulations related to strength assessment were specified in Chapter 5,referring to the regulations of hull girder loads of Section 3, Chapter 4.

1.2

Hull girder transverse sections

1.2.1

General1.2.1.aSince CSR is based on the net scantling approach, assessment of hull transverse
section characteristics, stress assessment and so on, were required to be performed
taking scantlings equal to the offered scantling minus 0.5tc. See the technicalbackground of Chapter 3 Section 2.

1.2.2

Continuous trunks and continuous longitudinal hatch coamings

1.2.2.aThis regulation is based on 2.1.2 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

1.2.3

Longitudinal ordinary stiffeners or girders welded above the strength deck

1.2.3.aThis regulation is based on 2.1.3 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

1.2.4

Longitudinal girders between hatchways, supported by longitudinalbulkheads

1.2.4.aThis regulation is based on 2.1.4 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

1.2.5

Longitudinal bulkheads with vertical corrugations

1.2.5.aThis regulation is based on 2.1.5 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

1.2.6

Members in materials other than steel

1.2.6.aThe setting of longitudinal strength member of material other than steel of Young's
Modulus 2.06x 105 N/mm2 was based on 2.1.6, Sec. 1, Chapter 6, Part B of the BV
Rules.

1.2.7

Large opening

1.2.7.aThis regulation is based on 2.1.7 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 5 – CHAPTER 5: HULL GIRDER STRENGTH

1.2.8

Small opening

1.2.8.aThis regulation is based on 2.1.8 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

1.2.9

Lightning holes, draining holes and single scallops

1.2.9.aThis regulation is based on 2.1.9 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

1.3

Strength deck

1.3.1
1.3.1.aThis regulation is based on 2.2.1 of Sec. 1, Chapter 6, Part B of the BV Rules. The
treatment of 0.15L in relation to the application is consistent with the usage categoryof the steel.

1.3.2
1.3.2.a

1.4

This regulation is based on 2.2.2 of Sec. 1, Chapter 6, Part B of the BV Rules. The
treatment of 0.15L in relation to the application is consistent with the usage categoryof the steel.

Section modulus

1.4.1
1.4.1.aThis regulation is based on 2.3.1 of Sec. 1, Chapter 6, Part B of BV Rules.

1.4.2
1.4.2.a

1.5This regulation is based on 2.3.2 of Sec. 1, Chapter 6, Part B of BV Rules inaccordance with IACS UR S5.

Moments of inertia

1.5.1
1.5.1.a

1.6This regulation is based on 2.4.1 of Sec. 1, Chapter 6, Part B of BV Rules.

First moment

1.6.1
1.6.1.aThis regulation is based on 2.5.1 of Sec. 1, Chapter 6, Part B of BV Rules.

2. HULL GIRDER STRESSES
2.1

Normal stress

2.1.1

General2.1.1.aNormal stress when a material other than steel is used is to be calculated bysimplified formula using the ratio of Young's modulus. This regulation is based on
2.1.2 of Sec. 2, Chapter 6, Part B of BV Rules

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 6 – CHAPTER 5: HULL GIRDER STRENGTH

2.1.2

Normal stresses induced by vertical bending moments

2.1.2.a

The calculation formula for normal stress arising from vertical bending moment in
the intact condition (non-flooded condition) is shown, and it is the same as in theexisting rules such as BV Rules 2.1.1, Chapter 6 Section 2.

2.1.3

Normal stresses in flooded conditions of BC-A ships and BC-B ships

2.1.3.aAccording to IACS UR S17, the requirement of longitudinal strength of hull girderin flooded condition is to be complied with in respect of the flooding of any cargohold of bulk carriers with notation BC-A or BC-B. The calculation formula fornormal stress due to vertical bending moment in flooded condition is given, and itis the same as in the existing rules.

2.2

Shear stress

2.2.1

General2.2.1.aShear stress is to be calculated by direct analysis in the CSR. Shear force correction is
to be made considering a simplified calculation method according to this regulation.

2.2.2

Simplified calculation of shear stresses induced by vertical shear forces

2.2.2.aDistribution coefficient of shear force and this correction method are according to
2.4.1 of Sec. 2, Chapter 6, Part B of the BV Rules.

2.2.3

Shear stresses in the flooded conditions of BC-A or BC-B ships

2.2.3.aRegulation for correcting the shear stress is specified similar to the intact condition
if the mass of flooded water is included in the mass of cargo.

3. CHECKING CRITERIA
3.1

Normal stresses

3.1.1
3.1.1.a

IACS UR S11 takes the permissible stress in the 0.4L region amidships based on the
gross scantling approach as 175 N/mm2 (based on mild steel). In CSR which uses
the net scantling approach, since the figure is 0.9 times the original section modulus,
which becomes the renewal criterion of various classification societies for hulltransverse section, the permissible stress in the gross scantling approach is divided
by 0.9 to arrive at the value of 190 N/mm2 as the permissible stress (17.5 kgf/mm2/0.9 x 9.81 = 190). The corrosion amount specified in Section 3, Chapter 3 isapplicable to existing ships (5 types of ships namely VLCC, Aframax, Capesize BC,
Panamax BC and Handymax BC). Fig. 5.1 shows the ratio of the section modulus ofdeck and bottom to the original section modulus for each type of ship. From thisfigure, since the section modulus is about 0.9 times the original section modulus forall ship types, evaluation with the net scantling approach using the permissible
value is equivalent to the method used in the existing rules.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 7 – CHAPTER 5: HULL GIRDER STRENGTH

Ship Z(D ouble H ullO ilTanker and Single Side Skin B ulk C arrier)
1.000
0.919

0.911

0.915

0.909

0.903

0.900

0.906

0.893

0.912

0.894

0.905

0.800
0.700
0.600
0.500

N K P roposal

0.400
0.300
0.200
0.100

)
tto
m

S
SS

SS

S

Ca
pe

Ca
pe

BC

BC

(B
o

(D
e

tto
m
(B
o
BC
ax

m
PS

ck
)

)

(D
ec
k)
BC
ax

S

SS

S
SS

SS

H-

m

Pm

m

ax

ax

BC

BC

(B
o

(D
e

tt
om

)

ck
)

)
tto
m
HS
SS

Af
ra
DH

Af
ra
DH

Ta
nk
er
(B
o

)
(B
o
CC
VL

Ta
nk
er
(D
e

tt
om

ck
)
(D
e
CC
DH

VL
DH

ck
)

0.000

Fig. 5.1 Section modulus considering corrosion of BC and tankers

For ensuring continuity of longitudinal strength also in the region other than the
0.4L midship region, the permissible shear stress at locations in the 0.1L and 0.9L
regions at the ends were taken as 130 N/mm2.
3.1.1.b

3.2

Generally, scantling of members contributing to the hull girder longitudinalstrength may be gradually reduced, outside 0.4L amidships. In CSR, the gradualreduction of scantlings of structural members contributing to hull girder strength
are unified by setting the allowable stress outside 0.4 L amidships.

Shear stresses

3.2.1
3.2.1.a

Similar to stress due to vertical bending, the permissible shear stress by the net
scantling approach was taken as 120 N/mm2, which is equal to the permissible
stress of 110 N/mm2 according to existing rules divided by 0.9.

4. SECTION MODULUS AND MOMENT OF INERTIA
4.1

General

4.1.1
4.1.1.aThis regulation is based on 4.1.1 of Sec. 2, Chapter 6, Part B of BV Rules.

4.1.2
4.1.2.aThis regulation is based on 4.2.3 of Sec. 2, Chapter 6, Part B of BV Rules. See thebackground for Material factor k specified in 2.2.1 of Chapter 3 Section 1.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 8 – CHAPTER 5: HULL GIRDER STRENGTH

4.2

Section modulus within 0.4L amidships

4.2.1
4.2.1.aThis regulation is based on the IACS UR S7 taking into account the coefficient 0.9
based on the net scantling approach.

4.2.2
4.2.2.aThis regulation is based on the IACS UR S11 and UR S17.

4.2.3
4.2.3.aThis regulation is based on 4.2.3 of Sec. 2, Chapter 6, Part B of BV Rules.

4.2.4
4.2.4.a

4.3

This regulation is based on 4.2.4 of Sec. 2, Chapter 6, Part B of BV Rules.

Section modulus outside 0.4L amidship

4.3.1
4.3.1.aThis regulation is based on 4.3.1 of Sec. 2, Chapter 6, Part B of BV Rules.

4.3.2
4.3.2.a

4.4This regulation is based on 4.3.2 of Sec. 2, Chapter 6, Part B of BV Rules.

Midship section moment of inertia

4.4.1
4.4.1.a

4.5This regulation is based on IACS UR S4.

Extent of higher strength steel

4.5.1
4.5.1.aThis regulation is based on 4.5.1 of Sec. 2, Chapter 6, Part B of BV Rules.

4.5.2
4.5.2.aThis regulation is based on 4.5.2 of Sec. 2, Chapter 6, Part B of BV Rules.

5. PERMISSIBLE STILL WATER BENDING MOMENT AND SHEAR FORCE
5.1

Permissible still water bending moment and shear force in intact condition

5.1.1

Permissible still water bending moment

5.1.1.aThis regulation is based on 5.1.1 of Sec. 2, Chapter 6, Part B of BV Rules.

5.1.2

Permissible still water shear force – Direct calculation

5.1.2.aThis regulation is based on 5.2.1 of Sec. 2, Chapter 6, Part B of BV Rules.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 9 – CHAPTER 5: HULL GIRDER STRENGTH

5.1.3

Permissible still water shear force – Simplified calculation

5.1.3.aThis regulation is based on 5.2.2 of Sec. 2, Chapter 6, Part B of BV Rules

5.2

Permissible still water bending moment and shear force in harbour condition

5.2.1

Permissible still water bending moment

5.2.1.aThis regulation is related to the concept on the vertical wave bending moment in
harbour condition specified in Ch 4 Sec 3 in CSR.

5.2.2

Permissible still water shear force

5.2.2.aThis regulation is related to the concepts on the vertical wave shear force in harbour
condition specified in Ch 4 Sec 3 in CSR.

5.3

Permissible still water bending moment and shear force in flooded condition

5.3.1

Permissible still water bending moment

5.3.1.aThis regulation is related to the vertical wave bending moment in flooded condition
specified in Ch 4 Sec 3 in CSR.

5.3.2

Permissible still water shear force – Direct calculation

5.3.2.aThis regulation is related to the concepts on the vertical shear force in flooded
condition by direct calculation method specified in Ch 4 Sec 3 in CSR.

5.3.3

Permissible still water shear force – Simplified calculation

5.3.3.aThis regulation is related to the concepts on the vertical shear force in flooded
condition by simplified calculation method specified in Ch 4 Sec 3 in CSR.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 10 – CHAPTER 5: HULL GIRDER STRENGTHSECTION 2 – ULTIMATE STRENGTH CHECK
1. APPLICATION
1.1

General

1.1.1
1.1.1.a

The hull girder strength is the most important for hull structure. The ships length
becomes longer, this strength is more important. Hence, the hull girder ultimate
strength check is required to ships with length (L) not less than 150m.t

2. HULL GIRDER ULTIMATE STRENGTH CHECK
2.1

Hull girder loads

2.1.1

Bending moment

2.1.1.a

The yielding strength of hull girder is checked by the working stress design method
using the allowable stress as required in Chapter 5 Section 1. However, the working
stress design method cannot be evaluated to the actual capacity of hull girder, eventhough the scantling of hull girder is considered reasonable and practicable. Hence,
to estimate the actual capacity of hull girder, the ultimate strength hull girder ischecked by the partial safety factor design method.

2.1.1.b

Ultimate strength check is required to the ultimate condition such as ultimate wave
loads which is expressed by multiplying the extreme wave loads by the partial
safety factor and flooded condition.

2.2

Hull girder bending moment

2.2.1

Curve M-χ2.2.1.aThis regulation is based on 3.2.1 of Sec. 3, Chapter 6 of RINA Rules.

2.2.2

Hull girder transverse sections

2.2.2.aThis regulation is based on 3.2.2 of Sec. 3, Chapter 6 of RINA Rules.

2.3

Checking criteria

2.3.1
2.3.1.aThis regulation is based on 3.3.1 of Sec. 3, Chapter 6 of RINA Rules.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 11 – CHAPTER 5: HULL GIRDER STRENGTHAPPENDIX 1 – HULL GIRDER ULTIMATE STRENGTH
1. HULL GIRDER ULTIMATE STRENGTH CHECK
1.1

Introduction

1.1.1
1.1.1.aThis Appendix describes details of the calculation method for hull girder ultimate
strength. It is based on Part B, Chapter 6, Appendix 1 of BV Rules for theClassification of Steel Ships (April 2005).

2. CRITERIA FOR THE CALCULATION OF THE CURVE M-Χ
2.1

Simplified method based on a incremental-iterative approach

2.1.1

Procedure

2.1.1.aThis requirement is based on 1.2.1 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.1.2

Assumption

2.1.2.aThis requirement is based on 1.2.2 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2

Load-end shortening curves σ-ε

2.2.1

Plating panels and ordinary stiffeners

2.2.1.aThis requirement is based on 1.3.1 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2.2

Hard corners

2.2.2.aThis requirement is based on 1.3.2 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2.3

Elastic-plastic collapse of structural elements

2.2.3.aThis requirement is based on 1.3.3 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2.4

Beam column buckling

2.2.4.aThis requirement is based on 1.3.4 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2.5

Torsional buckling

2.2.5.aThis requirement is based on 1.3.5 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

COMMON STRUCTURAL RULES FOR BULK CARRIERSCOMMON STRUCTURAL RULES FOR BULK CARRIERS − BACKGROUND DOCUMENT
PAGE 12 – CHAPTER 5: HULL GIRDER STRENGTH

2.2.6

Web local buckling of ordinary stiffeners made of flanged profiles

2.2.6.aThis requirement is based on 1.3.6 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2.7

Web local buckling of ordinary stiffeners made of flat bars

2.2.7.aThis requirement is based on 1.3.7 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

2.2.8

Plate buckling

2.2.8.aThis requirement is based on 1.3.8 of Part B, Chapter 6, Appendix 1 of BV Rules for
Steel Ships.

COMMON STRUCTURAL RULES FOR BULK CARRIERS