Hull Structure

8/12/2019 Hull Structure

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Hull Structure

CourseDNV

2005


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Consequence

of a crack in

this detail?

Where is it likely

to find cracks?

How are theloads taken

up by the

structure?


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Hull Structure Course

Objective:

After completion of the course, the participants

should have gained knowledge of basic hull

strength and understanding of how to perform

better hull inspections.


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Course breakdown:

Day 1

Introduction

Single beams & loads Structural connections

Hull structure failure types

Day 2

Fore & aft ship Hull structural breakdown Oil Tanker

Day 3

Hull structural breakdown Bulk Carrier

Day 4

Fore & aft ship

Hull structural breakdown Container Carrier


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Agenda day 1

09.00-09.15 Welcome & Introduction

09.15-09.45 Expectation & presentation of participants10.00-11.30 Beams + Buzz group

11.30-12.30 Loads

12.30-13.15 Lunch

13.15-14.15 Structural connections

14.15-15.45 Failure mode fatigue

15.45-16.45 Buckling & Indent16.45-17.45 Corrosion

17.45-18.00 Review questions


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Agenda day 209.00 09.15 Answers to review questions

09.15 10.30 Structural breakdown fore and aft ship

10.30 10.45 Introduction to tank

10.45 11.00 Coffee break11.00 11.45 Ship side & longitudinal bulkhead

11.45 12.15 Webframes

12.15 13.00 Lunch

13.00 13.30 Case: Oil Tanker Part A

13.45 14.30 Deck

14.30 15.00 Bottom

15.00 15.15 Coffee break15.15 16.15 Case: Oil Tanker Part B

16.15 16.45 Transverse Bulkhead

16.45 17.00 Review quiz


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Agenda day 309.00 - 09.30 Answers to review questions

09.30 - 10.00 Introduction to Bulk

10.00 - 10.45 Side

10.45 11.00 Coffee break11.00 - 11.45 Bottom

11.45 - 12.15 Deck

12.15 - 13.00 Lunch

13.00 - 13.45 Case: Side hold no 1

13.45 - 14.30 Transverse Bulkhead

14.30 - 15.00 Hopper tank & topside tank

15.00 15.15 Coffee break15.15 - 15.45 Hatch coaming & covers

15.45 16.30 Case: Ore Carrier

16.30 - 17.00 Review Quiz and closing


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Agenda day 409.00 - 09.30 Answers to review questions from day 1

09.30 - 10.30 Structural breakdown fore and aft ship

10.30 - 11.00 Introduction Container Carriers

11.00 11.15 Coffee break11.15 12.15 Bottom and Ship Sides

12.15 - 13.00 Lunch

13.00 14.00 Hatch Covers, Deck & Hatch Coamings

14.00 15.00 Case: Container Carriers

15.00 - 15.15 Coffee Break

15.15 15.45 Bulkheads

15.45 16.00 Closing16.00 16.30 Review Quiz


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Slide 2

Basic Hull StrengthObjectives

After completion of this module the participants should have

gained:

1. Understanding of:

The behaviour of simple beams with loads and corresponding

shear forces and moments.

The applicable local and global loads on the hull girder and thecorresponding shear forces and bending moments.


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Slide 3

Basic Hull Strength

Load

Simple beam properties

Tension

Compression

Shear

force

Shear area: The beam has to have a sufficient cross sectional area to

take up the external load and transfer this towards the end supports.

Bending: When a beam is loaded it will bend dependent on its stiffness

and its end connections. A single load from above causes compression

stress on the upper side and tension stress on the lower side of the beam.

A

A

Section A-A

Bending

moment


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Slide 4

Basic Hull Strength

Simply supported beam

- concentrated load

F

Single beam withconcentrated load,

simply supported ends

ShearForce

Bending

Moment

F/2 F/2

M=Q x

Q=F/2

Q=F/2

F

L/2

L/2


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Slide 5

Basic Hull Strength

Simply supported beam

distributed load

p

L

Single beam with

distributed load,simply supported ends

Bending

Moment

ShearForce

Q=pL/2

pL/2 pL/2

Q=pL2

M=pL2/8


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Slide 6

Basic Hull StrengthBeam with fixed ends - distributed load

L

ShearForce

BendingMoment

Single beamwith distributedload, fixed ends

p

M=pL2/24

M=pL2/12

pL/2pL/2

Q=pL/2

Q=pL/2

No rotation!


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Slide 7

Basic Hull StrengthBeam with spring supported ends

p

Shear force and bending moment distribution varies with degree of

end fixation (spring stiffness)

Degree of end fixation = 0

Spring Springkk

Degree of end fixation = 1

Simply supported

Fixed ends


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Slide 8

Basic Hull Strength

Symmetrical load full fixation

End fixation

Structural clamping spring support


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Slide 9

Basic Hull Strength

Load on structure is important with regard to fixation

bottom longs connection to transverse bulkhead

Beam fixation at ends

Non symmetry in loadsgives less fixation or even

forced rotation

Symmetric load gives fullfixation

LoadedEmptyEmptyEmpty Empty


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Slide 10

Basic Hull StrengthAxial stress

Area

Force

Stress = ForceArea

= x E (Hooks Law)

: Relative elongation

E : Youngs modulus(2,06E5 N/mm - steel)


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Slide 11

Basic Hull StrengthStress levels elastic & inelastic region

Elastic region: yield- A beam exposed to a stress level below

the yield stress, will return to its originalshape after the load is removed, Simple

beam theory valid

(elongation)

Yield

fracture

Inelastic regionIn-elastic region: = > yield- A beam exposed to stresses above the

yield stress will have a permanent

deformation after removing the load

(yielding, buckling, fractures)

Elastic region

= * E


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Slide 12

Basic Hull StrengthHigh Tensile Steel (HTS)

Material grades NVA - NVE Measure for ductility of material (prevent brittle fracture)

Material grade dependent on location of structure and

thickness of plate.

NVA

NVB

NVD

NVE

MS

HT28

HT32

HT36

HT40


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Slide 13

Basic Hull StrengthBending stress - Simple beam with load

R1 R2

A

A

A

A

Section A-A

Area effective in

transferring the bending

of the beam

Distribution of stress

caused by bending

Max stress at flanges.Zero stress at neutral axis:

F

n.a


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Slide 14

Basic Hull StrengthShear stress - Simple beam with load

R1 R2

A

A

A

A

Area effective in

transferring load

to the supports

Distribution of the

stress

Max shear stress at

neutral axisis of profile:

Section A-A

F


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Slide 16

Basic Hull StrengthBeam stiffness and section modulus

As the axial stresses are transferred in the flange of a beam, it is the flange

area that is governing a beams bending stiffness

n.a x

y

1yIZ xx =Section modulus:

The Section Modulus is expressing the beams ability to withstand bending

y1

Aflange

2

13 212

1yAblI flangex +=Moment of Inertia:

lb

XZ

M=Bending Stress:


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Slide 17

Basic Hull StrengthShear stress & shear area

The load is carried in shear towards the supports by the web

n.a x

y

thAs =Shear area :

sA

Q=Shear stress:

th

QShear force :


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Slide 19

Basic Hull Strength

An angle bar profile will twist when exposed to lateral loads due

to asymmetric profile which gives additional stress at supports

due to skew bending

Additional bending

stress in web

POSTFEM 5.6-02 5 SEP 2SESAM

XY

Z

MODEL: T1-1 DEF = 2034: LINEAR ANALYSISNODAL DISPLACE ALLMAX = 1.46 MIN = 0

.696E-1

.139

.209

.278

.348

.418

.487

.557

.626

.696

.766

.835

.905

.9741.041.111.18

1.251.321.39

Side longs

internal pressure

Angle bar (rolled / built up)


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Slide 21

Basic Hull StrengthHierarchy of hull structures

Plate Stiffener Stringer / girder Panel Hull

Stresses in a hull plate due to external sea pressure, are transferred

further into the hull structure through the hierarchy of structures.


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Slide 22

Basic Hull StrengthLevel 1: Plate - simple beam

Water pressure

StiffenerPlating

A strip of platingconsidered as a beam

with fixed ends and

evenly distributed load

PLATE AS A BEAM

NO

ROTATION


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Slide 24

Basic Hull StrengthLevel 3 : Transverse web - simple beam

Beam with fixed ends and

concentrated loads from the

bottom longitudinals

BM

SF

Max shear and bending

moment towards ends

(side & long bhd.)


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Slide 25

Basic Hull Strength

Level 3 Longitudinal girder with

transverse webframes

Longitudinal girder between two

transverse bulkheads

Max shear and bendingmoment towards


Single beam with fixed ends and concentrated loads from the transverse web frames

Max Shear and bending moment towards ends


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Slide 26

Basic Hull StrengthBeams, load transfer

Double bottom structure

Centre girder

Floor / transverse

bottom girderSide girder

Stiffeners supported

by floors

Loads taken up by the bottom platingare transferred through the hierarchy

of structures into the hull


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Slide 28

Basic Hull StrengthDamage experience

Level 1 Plate supported at stiffeners

Level 2 Stiffener supported at webframe

Level 3 Webframe supported at panel

Level 4 Panel hull girder

Consequences of damages level 1-4 above!


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Slide 29

Basic Hull StrengthSingle beam VS Hull girder

A vessels hull has many of the same properties as a single beam.

Hence simple beam theory may be applied when describing the nature of a

vessels hullThe term Hull girder is used when thinking of the hull as a single beam

Single

beam

Hull


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Slide 30

Basic Hull StrengthHull girder bending

When a vessels hull is exposed to loading, it will bend similarly as a

single beam


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Slide 31

Basic Hull StrengthSingle beam VS Hull girder

Section A-A

Hull Girder

Shear stress,

Bending stress,

Compression

Tension

A

A

A

A

F

Deck and bottom acts as flanges in the hull girder, while ship sides

and longitudinal bulkheads, act as the web


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Slide 32

Basic Hull StrengthStress hierarchy in ship structure

Local stress : Plate / stiffener

Girder stresses: Webframes / Girders /Floors

Hull girder stresses; Deck & bottom / Side /long. Bhd.


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Slide 33

Basic Hull StrengthCase Module 2: Loads Buzz Groups

For a beam with fixed ends and evenly distributed

load, i.e. from sea pressure, is it true that:

Bending stresses are zero at one location

Reaction forces are equal at both ends

No rotation at ends

Bending stresses are positive (tension) in one flange

and negative (compression) in the other in the middle

of the span

Shear stresses are highest in the middle of the span

Shear forces are carried by the web


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Slide 34

Basic Hull StrengthCase Module 2: Beams Buzz Groups

Is it correct that the transverse girders aresupported by the longitudinal stiffeners?

Are the longitudinals inside a tank structure forexample bottom longitudinals between

webframes normally fixed or simply supported?


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Slide 35

Basic Hull StrengthSummary: Beams

BM and Shear force

Stress axial / bending / shear Section modulus / Moment of inertia / Shear area

Stress distribution Bending and shear

BM and SF distribution depending on load andend fixation

Profile types and properties

Structural hierarchy plates-stiffeners-girder-panel


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Slide 37

Basic Hull StrengthLoads acting on a ship structure

1. Internal loads: - Cargo

- Ballast

- Fuel

- Flooding

- Loading/unloading

2. External loads: - Sea

- Ice

- Wind Anchor


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Slide 38

Basic Hull StrengthStatic and Dynamic loads

Static local load: The local load, internal and external

due to cargo / ballast pressure

Dynamic local load: External - dynamic wave loads,Internal - due to acceleration

Static global loads: Global Bending Moment and ShearForce

Wave loads: Dynamic Bending Moment and ShearForce


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Slide 39

Basic Hull StrengthStatic and Dynamic loads

Total external local load acting on a vessel:

Max at the bottom

Note the relative size of static / dynamic pressure is not to scale!

Static Dynamic

Max around the waterline


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Slide 40

Basic Hull Strength

Plotted sea pressure curveis a sum of the static anddynamic contribution

Constant in the midshiparea, increasing towardsends

Sea Pressure static and dynamic contribution

Local sea pressure

(example for a bottom longitudinal)

p (kN/m2)

aft fwd

St ti d D i l d


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Slide 41

Basic Hull Strength

Global dynamic vertical and horizontal wave bending

moments give longitudinal dynamic stresses in deck, bottom

and side

Highest global dynamic loads for all longitudinal members

in the midship area

Static and Dynamic loads

L d f hi


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Slide 42

Basic Hull StrengthLoads on foreship

Bottom Slamming PressureInduced by waves in shallow draft

condition (ballast condition)

Dominant for flat bottom structure

forward

Bow Impact PressureInduced by waves, vessel speed, flare

and waterline angle important factors

Dominant for ship sides in the bow at

full draught


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W i ht d b


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Slide 44

Basic Hull StrengthWeights and buoyancy

Steel weight, equipmentand machinery

Buoyancy

Weight distribution of

cargo and fuel

Static Dynamic

B i H ll St thBulk Carrier typical load


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Slide 45

Basic Hull Strength

Static internal

load from cargo

Static external sea

pressure

Dynamic internalload from cargo

Bulk Carrier typical load

Dynamic external

sea pressure


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Basic Hull StrengthNet load on structure empty hold


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Slide 47

Basic Hull Strength

Static and dynamic

sea pressure

Net load on structure - empty hold

Net load from sea pressure

Basic Hull StrengthAlternate loading condition


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Slide 48

Basic Hull StrengthAlternate loading condition


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Basic Hull Strength

Hull girder still water bending


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Slide 50

g

moment and shear force

Example: SF and BM distribution for a double hull tanker in a fully loaded condition


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Basic Hull StrengthCase 2 Module 2 Loads/Materials


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Slide 52

Case 2 Module 2 Loads/Materials

Where in the hull girder cross section of a hull girder are

the local dynamic loads due to sea pressure highest?

Where along the hull girder are the dynamic seapressure loads highest?

Where in the hull girder is the global dynamic bending

moment highest? Does a vessel in sagging condition experience

compression or tension in deck?

A vessel in sagging condition experience flooding of a

empty tank in midship. Will the hull girder bending

moment increase or decrease?

Basic Hull StrengthSummary: Loads


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Slide 53

Summary: Loads

Static & dynamic

Internal & external Load distribution

Net load

Longitudinal strength SF & BM


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Module 3:

Structural ConnectionsModule 3: Structural Connections


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Slide 1

Objectives of this Module:

After completion of this module the participants should have gained:

Knowledge about connections between structural elements

Understanding of the transfer of forces between structural elements

and the relevant stress distributions

Knowledge about how to improve the design of structural

connections


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Module 3:

Structural ConnectionsWeld Types Fillet welds


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Slide 4

Fillet welds:

The most common type

Transferring shear forces (between profile and plate)

Building welded sections

Connections to other members

NDT by magnetic particle or

dye penetrant

Leg length

Throat thickness

Throat thickness-

measure 3.5 mm

= leg length 5.0 mm

Weld Types Fillet welds


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Module 3:

Structural ConnectionsConnections of stiffeners


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Slide 6

Connections of stiffeners

What forces are to be transferred?

ShearForce

L

Bending

Moment

Module 3:

Structural ConnectionsLoad from stiffener to webframe


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Slide 7

How is the

forces

transferredfrom the

stiffener to

webframe

How are the

forces

transferredfrom the

stiffener to

webframe


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Module 3:

Structural ConnectionsConnections of stiffeners


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Slide 12

Common crack locations

= =

Longitudinal

StiffenerWeb-plating

Design improvement

Module 3:

Structural ConnectionsEnd-brackets on girders - forces


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Slide 13

Full Centre TankEmptyWing

Tank

Net loadNet load


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Module 3:

Structural ConnectionsEnd-brackets on girders


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Slide 16

Girder bracket

Typical crack location

Ref. iii b) previous fig.


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Module 3:

Structural ConnectionsKnuckles


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Slide 20

Vertical Brackets

Module 3:



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Slide 21

Crack in shell plate at

knuckle:

New Brackets


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Module 3:



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Slide 23

Preferred design:

No misalignment in the connection.

No lugs or scallops


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Module 3:

Structural Connections

Intersecting Hull Elements


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Slide 25

WINGTANK

DIESELSUPPLYTANK

TOP SIDE

TANK NO. 7

CRACKS

ENGINEROOM

BULKHEAD

CRACKS

ENGINE ROOM BULKHEAD

A

A

EXISTING BRACKETTO BE REMOVED

NEW BRACKETS INLINE WITH BOTTOM

PLATE IN TOP SIDETANK

Section A-AENGINE ROOM BULKHEAD

iii

ADDIT IONA LBRACKET

SLANTING TANK TOPPLATING

TO BE IN LINE


LONGITUDINAL BULKHEAD


TANK TOP

STR LON

GITUDINAL

BULKHEAD

BKT.

iv

Cracks

Reinforcements

A - A


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Contents of Module 5


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Slide 3

1. Fwd and aft structural parts2. Oil Tankers structures in cargo area

3. Bulk Carriers structures in cargo area

4. Container Ship structures in cargo area


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Fore

ship Structural build up fore ship


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Slide 7

Vertical side frames Horizontal side longs


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Hull damages in fore shipFore

ship


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Slide 14

Characteristic damages fore ship

1. Corrosion lost ship side fore peak

2. Buckling of stringers

3. Bow impact

4. Damages to the wave breaker

5. Bottom slamming

Fore ship specially

prone to hull

damages.

Of top 10 damages

on tankers are 6 of

them in the fore

ship!


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Buckling of stringer

Impact of function

Oil Tanker

302,419 DWT built 1992

Buckling of stringers in fore peak tank

(after 1 year)

Fore

ship


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Slide 19

Buckled / deformed stringers may

develop cracks penetrating the shell causeleak impact on trim draught

If stringers are significantly reduced in

strength the webframes loose their support.

Side longitudinals loose their support at

webframes.

Side longitudinals with excessive loadsmay collapse and ship side collapse

flooding of fore structure.

Bow Impact DamageContainer ship

1 yearFore

ship


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Slide 20

A recent damage in 2001..Occurred during the first year of operation

Bow Impact DamageContainer ship

1 yearFore

ship


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Slide 21


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Structural build up aft ship

Transom stern plate

Aft ship


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Slide 30

Transom stern plate

Engine room bulkhead

Floors

Webframes

Structural build up aft ship

Engine room platform

Aft ship


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Slide 31

Engine room platform

Side plate &

longitudinals

Webframe side

Webframe deck

Structural build up aft peak tank

Vertical side framesHorizontal side longs

Aft ship


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Slide 32

g

Structural functions of aft ship

Aft ship


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Slide 33

Loads are taken up by the hull plating, stresses are transferred from plate to stiffener

Shell must withstand static and dynamic sea pressure, bottom

slamming may introduce additional loads Internal pressure from ballast

Dynamic impulses from the propeller

Functions of aft ship

Web in hull girder (global strength)

Aft ship


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Slide 34

Side plating is acting

as web in the hull

girder beam

Global loads are

acting on the hullgirder beam

Cont.

Ship side together with the

longitudinal swash

bulkheads are taking up

global shear forces from

net load on the hull girder

in the aft end

High shear

forces fwd. of

engine room

full load

conditions


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Hull damages in aft ship

Characteristic damages for the aft ship:

Aft ship


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Slide 37

Characteristic damages for the aft ship:

1. Buckling of engine room stringers

2. Stern Slamming

3. Cracks due to vibration4. Cavitation damages to the rudder


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External sea pressure

BucklingAft ship


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Slide 39

Bending + shear

exceed the

buckling capacity

of the plate

Bending

moment


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Repaired

connection area/

ll

Stern Slamming Container ShipAft ship


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Slide 42

Scallop and stiffener

connection to outer shelllongitudinals in ballast tanksin after body area were foundfractured in several locations.

scallop

Stern Slamming Container ShipAft ship


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Slide 43

F

F

Side longitudinals may loose their support at

b f

Stern SlammingImpact of function

Container ShipAft ship


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Slide 44

web frames

Crack may penetrate the shell plating - loss ofwatertight integrity - flooding possible scenario

Cracks in aft peak tank due to vibrationsAft ship


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Slide 45

Vibrati

onalcracks

Cracks in Trans. at Steering Gear Flat

Supporting structure belowoscillating machinery

Passage doors in engine room area


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Pressure

Pressure distribution aroundtypical rudder profile

Aft ship Rudder Cavitation


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Slide 49

distribution(suction)

Positivepressure

U = speed ofambient water

Pressure distribution due to

shape of profile

Pressure distribution due tothickness of profile

Cavitation of rudder blade depend on:

Shape of profile

Thickness of profile

Rudder angle

Speed of water over profile

Stainless steel shielding

Preferred solution welded



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Slide 50

Preferred solution welded

with continuous weld insmall pieces not slot

welds



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Slide 51

This is how it may end ifthe shielding is not

welded properly

Cracks may occur which could lead to reduced

rudder support and maneuverability

Rudder CavitationImpact on function

Aft ship


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Slide 52

rudder support and maneuverability


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Oil

Tankers


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18.02.2005Slide 1

Oil Tankers - Hull Structure

Oil

Tankers Contents Oil tankers

1. Introduction


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18.02.2005Slide 2

2. Hull structural breakdown function of hull elements:

Side, bottom, deck, transverse bulkhead, longitudinal bulkhead,

web frames including relevant hull damages for all structural

elements

3. Case

Oil

Tankers Characteristics for Oil tankers

- High number of tanks good capability of survival

Any

proposals?


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18.02.2005Slide 3

- Low freeboard, green seas on deck

- Pollution / public attention / fire explosion hazards

- Fatigue

- Liquid cargo sloshing in wide tanks and stability aspect

-Hull inspection environment

- Fully utilizes BM limits hogging/sagging (double hull tankers)

Oil

Tankers Size categories of tankers

Oil TankersType DWT


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18.02.2005Slide 4

Type DWT

ULCC 320,000+

VLCC 200 - 320,000

Suezmax 120 - 200,000Aframax 75 - 120,000

Panamax 55 - 70,000

Products 10 - 50,000Source: INTERTANKO

Oil

Tankers Size categories of tankers

Panamax (55 - 75,000 dwt): Max size tanker able to transit the Panama Canal

L(max): 274.3 m


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18.02.2005Slide 5

( )

B(max): 32.3 m

Typical vessel: 60,000 dwt, L=228,6m, B=32,2m, T=12,6m

Aframax (75 120,000 dwt): AFRA= Average Freight Rate Assessment

Traditionally employed on a wide variety of short andmedium-haul crude oil trades

Biggest tanker in US ports is 100,000 dwt


Source: INTERTANKO Age distribution

Age distribution

Oil

Tankers

Suezmax (120 200,000 dwt):

Notation is soon to become redundant as the project ofdeepening the Suez Canal to 18,9m is completed

Size categories of tankers


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18.02.2005Slide 6


VLCC (200 320,000 dwt):

Were prompted by the rapid growth in global oil consumptionduring the 60s and the 1967 closing of the Suez canal

Today the most effective way of transporting large volumesof oil over relatively long distances

Typical vessel: 280,000 dwt, L=335,0m, B=57,0m, T=21,0mSource: INTERTANKO

Age distribution

Age distribution


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Oil

Tankers Single Skin Oil Tanker

Ship data:

L = 310m

B 56


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18.02.2005Slide 8

- Old design, build up to 1993

B = 56m

D = 31,4m284,497 DWT

Oil

Tankers Single bottom with side ballast tanks

Ship data:

L = 236m

B = 42m


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18.02.2005Slide 9

B = 42m

D = 19,2m

88,950 DWT

- Built in the 80s,

considered as single skin

Oil

Tankers Double Hull Two Longitudinal Bulkheads

Ship data:

L = 320m

B = 58m


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18.02.2005Slide 10

- Common VLCC design

of today

B = 58m

D = 26,8m298,731 DWT

Oil

Tankers Double Hull CL Longitudinal Bulkhead

Ship data:

L = 264m

B = 48m


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18.02.2005Slide 11

B = 48m

D = 23,2m159,681 DWT - Common Aframax andSuezmax design of today

Oil

Tankers Double Hull no CL bulkhead

Ship data:

L = 218m

B = 32,2m


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18.02.2005Slide 12

B 32,2m

D = 19,7m63,765 DWT - Older design

Oil

TankersNomenclature for a typical double hull oil

tanker


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18.02.2005Slide 13

Oil

Tankers

-A vessels hull can be divided into different hull structural

elements

Structural breakdown of hull


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18.02.2005Slide 14

- Each element has its own function contributing to the integrity

of the hull

- In order to assess the structure of an oil tanker, one needs tounderstand the function of each structural element

Oil

Tankers Damages and repairs


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18.02.2005Slide 15

WWW.witherbys.com

Oil

Tankers Function of hull elements

Deck:

Ship side:


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18.02.2005Slide 16Bottom:

Transverse bulkhead:

Longitudinal bulkhead:Webframes:

Ship side:

Oil

Tankers Hull Structural Breakdown

1.

2.

3.

Side

Bottom

Deck


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18.02.2005Slide 17

4.

5.

6.

ec

Transverse bulkhead

Longitudinal bulkhead

Web frames


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Oil

Tankers 1. SideHull Structural Breakdown -

Ship side

1.

2.

3.

Side

Bottom

Deck


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18.02.2005Slide 1

4.

5.

6.

Transverse bulkhead


Web frames

Oil

Tankers 1. SideStructural build up of ship side

single skin tanker

Side plating with

longitudinals


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18.02.2005Slide 2

Cross ties

Transverse

bulkhead

g

Web frameStringers

Oil

Tankers 1. SideStructural build-up of a double

hull ship side

Side plating with

longitudinals Inner side plating

with longitudinals


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18.02.2005Slide 3

Stringers

Web frame

g

Oil

Tankers 1. SideStructural functions of ship side

Watertight integrity

- Take up external sea loads and transfer these into the

hull girder


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18.02.2005Slide 4

g

- Resist internal pressure from cargo and ballast

Web in hull girder

- Side plating act as the web in the hull girder beam

Oil

Tankers 1. SideLoads on the ship side - example

Ballast conditionFully loadedcondition


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18.02.2005Slide 5 Full centre tankFull wing tank

Net force

Water

Line

Net force

WaterLine

Oil

Tankers 1. SideLocal function: Watertight integrity

External loads induces shear forces and

bending moments in the side longitudinals as


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18.02.2005Slide 6

single beams (between each web frame)

Side long.as a single beam

between two web frames BM and SF distribtion for a single beam

with evenly distributed load and fixed ends

Oil

Tankers 1. SideLocal function: Watertight integrity

-Side longs are supported at the web frames

- Web frames are supported at the cross ties

and at the deck and bottom


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18.02.2005Slide 7 Part of web frame supported

at two cross ties, shear max

towards su orts

Shear

forceBending

moment

Oil

Tankers 1. SideDouble hull ship side

The structural functions of a double hull ship side is the same as for a

single hull:

As there are no cross ties,

side web frame is supported


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18.02.2005Slide 8

at the deck and bottom

High shear stress

Oil

Tankers 1. SideGlobal function: Web in hull girder

Global shear forces resulting from uneven distribution of

cargo and buoyancy are taken up in the ship side plating


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18.02.2005Slide 9

Shear stress distribution resulting from

global loads for midship section

Area effective in

transferring shear

force

Oil

Tankers 1. SideStringers in a double side

Stringers contribute to the stiffness of the doublehull ship side, which means:

15mm


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18.02.2005Slide 10

High shear stress in

stringer towards the

transverse bulkhead

15mm

20mm

25mm

20mm

Oil

Tankers 1. SideCharacteristic damages for ship

side:

1. Cracks in side longitudinals at web frames

2 C k i f l i di l


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18.02.2005Slide 11

2. Cracks in cut-outs for longitudinals

3. Cracks in side longitudinals at transverse bulkheads

4. Indents of side shell and stiffeners

Oil

Tankers 1. SideCrack in side longitudinals

Oil Tanker285,690 DWT built 1990

Cracking in side longitudinal web frame

connection

(after 3 years)


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18.02.2005Slide 12

Crack in side longitudinal

tripping bracket connection to

web frame (various wing tanks)

Side longitudinal flatbar

connection to web frame

Oil

Tankers 1. SideCause for cracking in side longitudinals


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18.02.2005Slide 13

Dynamic loads (sea

and cargo) are forcing

the side longitudinal to

flex in and out

High alternating bending stresses towards the end

supports (web frames)

Highly stressed areas created around geometrichard points (bracket toes, scallops, flat bars)

Oil

Tankers 1. Side

More Stress concentration factors ;

Kg : Gross Geometry (from FEM analysis)

Kw : Weld Geometry (typical 1,5)

Stress concentration factors


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18.02.2005Slide 14

Kn : Unsymmetrical Stiffeners (L& bulb-profiles)

Oil

Tankers 1. SideStandard repair proposal longs / webframes


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18.02.2005Slide 15

Oil

Tankers 1. SideCracks in web frame cut outs


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18.02.2005Slide 16

Cracks around openings for

side longitudinals in web

frames

Cracks

Oil

Tankers 1. SideCause for cracking in cut outs

for longitudinals

Sea loads induce shear stresses in the web frame


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18.02.2005Slide 17

Shear stress

Shear stress

High shear stresses

around openings etc,

where shear area is

reduced

Oil

Tankers 1. SideConsequence of crack in web frame

Side longitudinals

loose their support

How does this damage impact on the function of the web frame?


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18.02.2005Slide 18

Re-distribution of shear

stresses in web frame

May lead to overloading

of adacent structure

Oil

Tankers 1. SideCrack in side longitudinal at

transverse bulkhead


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18.02.2005Slide 19

Side longitudinal connections

to transverse bulkheads

Cracks in side longitudinal connection to

stringers at transverse bulkhead

Oil

Tankers 1. Side

Relative deflections occur between

the rigid transverse bulkhead and

the flexible web frame construction

Why cracking at transverse bhd.?

Ship side


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18.02.2005Slide 20

Sea

pressure

the flexible web frame construction

The relative deflection inducesadditional

bending stresses at the end connection of side

longitudinals to the transverse bulkhead. Also

important at wash bulkheads.

Oil

Tankers 1. SideFEM plot of double hull oil tanker


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18.02.2005Slide 21

Loading condition:

External dynamic

sea pressure at full

draught

Relative

deflection

Oil

Tankers 1. SideConsequence of damage

Cracks in side longitudinals:- oil leakage and pollution

- longitudinal may break off

- in worst case (a series of cracks i

same area) could induce a larger

fracture (loss of ship side)

Suggestions?


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18.02.2005Slide 22

fracture (loss of ship side)

leakage

Oil

Tankers 1. SideIndents of side shell with stiffeners

Mainly from contact damages:


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18.02.2005Slide 23

The terms indents and buckling should not be mixed up with each

other, as the cause for these damages are different:

-Indents: Mainly due to contact damages

-Buckling: Due to excessive in-plane stresses

Oil

Tankers 1. SideConsequense of indents


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18.02.2005Slide 24

Oil

Tankers 1. SideConsequense of indents

Large area set in (plating and stiffeners)

gives reduced buckling capacity

Adjacent areas may then be overloaded


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18.02.2005Slide 25

Sharp indents may lead tocracks and possible leakage

Oil

Tankers 2. BottomHull Structural Breakdown -

Bottom

1.

2.

3.

4.

Side

Bottom

Deck

Transverse bulkhead


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18.02.2005Slide 1

5.

6.


Web frames

Oil

Tankers 2. Bottom


Resist external sea pressure

Resist internal pressure from cargo and ballast

Structural functions of bottom


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18.02.2005Slide 2

Flange in hull girder

Bottom plating and longitudinals act together as the lower

flange in the hull girder beam

Oil

Tankers 2. BottomStructural build up of bottom

single skin tanker


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18.02.2005Slide 3

Bottom platingw/longitudinals

Web frameCL girder

Bilge

Keel plate

Oil

Tankers 2. BottomStructural build-up of a double

bottom structure


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18.02.2005Slide 4 Bottom plating with

longitudinals

Buttress

Inner bottom plating (tank

top) with longitudinals

Transverse

girder / floor

CL double

bottom girder

Outboard girder

(margin girder)

Hopper

plating with

longitudinals

Hopper web

plating

Oil

Tankers 2. Bottom

External loads induce shear forces and bending moments

in the bottom longitudinals, acting as single beams

(between each web frame)

Function: Watertight integrity

Fixation?


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18.02.2005Slide 5

Bottom longitudinal as a single beam between two web

framesCont.

BM and SF distribtion for a

single beam with distributed

load and fixed ends

Oil

Tankers 2. Bottom

Bottom plating with longitudinals are also acting asflange for the transverse web frame

Function: Watertight integrity


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18.02.2005Slide 6

Transverse bottom girder/web frame is supported at the

longitudinal bulkheads (max. shear force towards long. bhds.)BM

SF

pL

Oil

Tankers 2. BottomBottom is supported by ship side and

longitudinal bulkhead

Double span for double bottom

without CL longitudinal

bulkhead


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18.02.2005Slide 7

Shear stress in

double bottom floordue to external sea

pressure

Oil

Tankers 2. BottomFunction: Flange in hull girder

Global bending moment induces longitudinal stresses in the

bottom plating and longitudinals

L


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18.02.2005Slide 8

Longitudinal stresses (+/-) are acting in

the bottom plating and longitudinals

due to bending of hull girder

Section A-A

L

Oil

Tankers 2. BottomDouble bottom structure

Load distribution

in double bottom

girder system


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18.02.2005Slide 9

Oil

Tankers 2. BottomLoad response double bottom

Stresss flow

shortest way to

support

Stresss flow

shortest way to

support


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18.02.2005Slide 10

Cont.

Oil

Tankers 2. Bottom

The double bottom is a grillage structure built up by

transverse girders/floors and longitudinal girders

Double bottom structure

With few longitudinal girders, double

bottom stresses resulting from the net

load on the girder system are mainly


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18.02.2005Slide 11

Double bottom transverse

girder (web frame) as a

single I-beam

Net load

Shear force

High shear stresses in

floors & girders in way of

transv. Bhd. And hoppertank

load on the girder system are mainly

transferred in the transverse direction

Shearforce

Oil

Tankers 2. BottomCharacteristic damages

1. Bilge keel terminations crack in hull plating

2. Fatigue cracking in bottom longitudinalconnections to web frame and transverse bulkhead


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18.02.2005Slide 12

3. Corrosion of bottom structures

4. Hopper knuckle cracks

Oil

Tankers 2. BottomBilge keel cracking

Oil Tanker

285,690 DWT built 1990

Crack in hull plating i.w.o. bilge keel

terminations

Bilge keel


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18.02.2005Slide 13

Crack in hull plating in

way of bilge keel toes

Oil


Hot spotBilge keel


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18.02.2005Slide 14

Longitudinalstress

Oil


Web frame/BilgeBracket

All measures in mm

125

Edges to be grindedsmooth


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18.02.2005Slide 15

10-15mm

1600

Bilge Keel

Pad plate

200

Ship side

10025100

Full pen. weld

Oil

Tankers 2. BottomCracking in bottom longitudinals


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18.02.2005Slide 16

Bottom long. flat

bar connection

Bottom long.

tripping bracket

connection

Similar cracking in bottom longitudinals is also

valid for double hull tankers

Oil

Tankers 2. BottomCause for cracking in bottom

longitudinals

Bottom longitudinals are subject to both:

MM

WebWeb/

Trans bhd

p


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18.02.2005Slide 17

1. Local stress from

lateral dynamic sea

loading

2. Longitudinal stresses

from hull girder bending

Oil

Tankers 2. BottomConsequences of cracks in

bottom longitudinals:

-Leakage of oil

- Crack may propagate

further into bottom

plating and induce alarger transverse fracture


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18.02.2005Slide 18

larger transverse fracture

Oil

Tankers 2. BottomExample: Cracks in inner bottom

Oil Tanker

95,371 DWTCrack in tank top plating at toes of

transverse bulkhead buttress P/S

Crack in toe of big brackets connecting

transverse bulkhead and tank top plating


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18.02.2005Slide 19

transverse bulkhead and tank top plating

(in various cargo tanks along ships length)

Crack in

bracket toeCrack propagating

through tank top

plating (a few cases)

Oil

Tankers 2. BottomCracking in double bottomlongitudinals


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18.02.2005Slide 20

Cracks in flatbar connections for bottom and inner


Oil

Tankers 2. BottomCause for cracking in double


In a ballast condition there is a net overpressure in the double bottom ballast tank(full ballast tank and empty cargo tank)

In a loaded condition there will be a negative net pressure on the double bottom

(empty ballast tank, full draft and full cargo tank)


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18.02.2005Slide 21

This effect may cause yield stress in hot spots at flat bar connections

Due to the dynamic +/- variation of stresses, low cycle fatigue may occur

Oil

Tankers 2. BottomIllustration double bottom flatbar

connections

Tensile stresses in critical structural details


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18.02.2005Slide 22

The double bottom structure is

exposed to large forces both in

ballast and loaded condition

Oil

Tankers 2. BottomCorrosion of bottom structures


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18.02.2005Slide 23

Local corrosion (pitting): may occur

all over the bottom plating, but area

below and around bell-mouth is

particularly exposed

Pitting is also applicable for double hull

tankers i.w.o. tank top plating

Oil

Tankers 2. BottomCorrosion of bottom structures

- Pittings and local corrosion may cause leakage, in general not anystructural problem

- General corrosion will reduce the bottom sectional area, which can lead to

an increased stress level:

1. Higher risk for fatigue cracks in bottom longitudinals

2 Higher risk for buckling of plate fields in the bottom


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18.02.2005Slide 24

2. Higher risk for buckling of plate fields in the bottom

A

FL =

Increased risk for fatigue cracking and buckling ofbottom panels if general corrosion has developed

over the cross section

Longitudinal

stress

Area

Force

Oil

Tankers 2. BottomCracking in hopper knuckle


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18.02.2005Slide 25

Crack in hopper knuckle at web

frame connections

Oil

Tankers 2. Bottom

- Bending of double bottom due to external and internal

dynamic loads induces membrane stresses in the inner

bottom (flange in the double bottom transverse girder)

Cause for cracking in hopperknuckle


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18.02.2005Slide 26

Bending moment

L

L

Bending stress in double

bottom girderBending stress in

inner bottom plating

Oil

Tankers 2. Bottom

- Inner bottom membrane stresses are transferred into the hopper plating

- The turn of the stress direction (inner bottom to hopper plating) results

in an unbalanced stress component

Cause for cracking in hopperknuckle

Resulting membrane

stress in hopper plating


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18.02.2005Slide 27

- This effect together with the knuckle being a geometric hard point atweb frame connections, induce very high stresses in the knuckle point

Un-balanced

stress component

Membrane stress from

bending of transverse girder

Oil

Tankers 3. DeckHull Structural Breakdown -Deck

1.

2.

3.

4.

5.

SideBottom

Deck

Transverse bulkhead



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18.02.2005Slide 1

6. Web frames

Oil

Tankers 3. DeckStructural functions of deck

Flange in hull girder

- Deck plating and longitudinals act as the upper flange in

the hull girder beam


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18.02.2005Slide 2

Oil

Tankers 3. DeckStructural build up of deck single skin tanker

Deck CL girderDeck plating

w/longitudinals

Transverse deck

girder / Web frame


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18.02.2005Slide 3

Oil

Tankers 3. Deck

Longitudinal stresses (+/-) are set up in

the deck plating and longitudinals dueto bending of hull girder

Function: Flange in hull girder

Hull girder bending moment induces longitudinal stresses in

the deck plating and longitudinals


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18.02.2005Slide 4

L

Oil

Tankers 3. DeckLongitudinal stresses in deck

Longitudinal stresses from bending of hull girder is

maximum at midshipMidship area most

susceptible to fatigue

cracking and buckling


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18.02.2005Slide 5

Bending

moment

Max

OilTankers 3. DeckCharacteristic damages

1. Cracks in deck longitudinals

2. Crack in deck plating3. Corrosion of deckhead


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18.02.2005Slide 6

4. Buckling of deck

OilTankers 3. Deck

Deck longitudinal

Cracking in deck longitudinals


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18.02.2005Slide 7

Deck longitudinal

connection to web frames

Deck longitudinal

connection to

transverse bulkhead

OilTankers 3. DeckCracking in deck longitudinals

Oil Tanker

135,000 DWT built 1991Crack main deck plating


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18.02.2005Slide 8

Crack in underdeck support for hose

handling crane (P/S, midship area)

OilTankers 3. Deck

The wave induced excitation of the hull girder leads todynamic axial stress in the deck longitudinals

Cause for cracking in decklongitudinals

+

_

+

_


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18.02.2005Slide 9

The cyclic variation of axial stress may lead to fatigue cracks

initiating at hot spots

A loaded condition will normally induce compression stress in the deck (sagging)

A ballast condition will normally induce tension stress in the deck (hogging)

OilTankers 3. DeckCracks in deck longitudinals


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18.02.2005Slide 10

- May result in oil spill on deck

- Corrosion is highly influencing the fatigue life

of a detail- A crack could develop further in the deck

plating (brittle fracture)

OilTankers 3. DeckOpenings in deck

Kg.Kw.


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18.02.2005Slide 11

Longitudinalstress-flow around

manhole in deck

Increased stress level around

openings in deck!


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OilTankers 3. DeckCrack in deck plating

Tanker for Oil

99328 DWTbuilt 1996

Crack in deck plating


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18.02.2005Slide 13

Crack in deck plating at hose

saddle support (midship area)

OilTankers 3. DeckCorrosion of deckhead


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18.02.2005Slide 14

The ullage space (deckhead) is an area

susceptible to general corrosion


A reduction of the deck transverse sectional area due to general corrosionwill lead to an increased stress level in deck

A

F

L =

Longitudinal

stress

Force

L

Higher stress

level in deck

n.a.


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18.02.2005Slide 15

Reduced sectional area in deck may lead to plate buckling

Area

Longitudinal

stress distribution

L

Long. stress distribution

(with reduced deck

sectional area)


Higher stress level in deck

due to general corrosion

L

Longitudinal

stressForce


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18.02.2005Slide 16

L

A

F

L =

Area

A reduction of the deck transverse sectional area due to general corrosion will lead

to an increased stress level in deck may lead to buckling problems


Flatbars have poor

buckling capacity


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18.02.2005Slide 17

L-profiles have good

buckling capacity

OilTankers 3. DeckBuckling in deck

Buckling in deck is most likely to occur in the midshipregion where the hull girder bending moment is at its

maximum


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18.02.2005Slide 18

Buckling of a plate field (plating with stiffeners)

OilTankers 3. DeckCause for buckling in deck

Buckling in deck is a result of in plane compression forces in excess ofthe buckling capacity of the deck plate field

Such a situation may occur if the transverse section of the deck is reduced

due to general corrosion and the vessel is in a fully loaded (sagging)

condition


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18.02.2005Slide 19

The deck buckling may take the form of one

plate between two deck longitudinals or in

worst case a complete plate field (both deck

plating with stiffeners)Buckling of complete plate field

OilTankers 3. DeckCorrosion of deckhead / buckling:

- heavy corrosion of deck may lead tobuckling

- small buckles (plate between

stiffeners) is a strong warning sign thatlongitudinal stresses are high

- large buckles (plate field) may lead to

l f l b l h d i


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18.02.2005Slide 20

loss of global strength and in worst case

a total collapse of the hull girder

Remember max 10% diminution of deck transversesectional area!

OilTankers 4.

Transverse

bulkheadHull Structural Breakdown -Transverse bulkhead

1.

2.

3.

4.

5.

6.

SideBottom

Deck

Transverse bulkheadLongitudinal bulkhead

Webframes


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18.02.2005Slide 1

OilTankers 4.

Transverse

bulkheadStructural build up oftransverse bulkhead

Transverse bulkhead

plating w/stiffeners


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18.02.2005Slide 2

Stringers

Buttress

OilTankers 4.

Transverse

bulkhead

Watertight integrity- Resist internal pressure from cargo and ballast

(cargo boundary)

- Safety against collapse if water ingress (boundary forflooding)

Hull girder stiffness

Structural functions


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18.02.2005Slide 3

g

- Transverse bulkhead is an important contributor to thehull girder transverse stiffness

OilTankers 4.

Transverse

bulkhead

The transverse bulkhead must withstandinternal pressure loads from cargo and ballast

The distribution of cargo and ballast introduces

alternate loading on sections of the transverse

bulkheads (single skin tanker)

Functions of transverse bulkhead


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18.02.2005Slide 4

Typical fully loaded

condition (single skin)

Typical ballast condition

(single skin)

OilTankers 4.

Transverse

bulkheadFunction: tank boundary

Stringer

Shear

force


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18.02.2005Slide 5Stiffener

Bending

moment

OilTankers 4.

Transverse

bulkheadFunction: tank boundary


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18.02.2005Slide 6

One sided loading on the transverse bulkhead

introduces stresses in the transverse bulkhead as a panel

Bulkhead will flex out and high stresses occur at end

connections towards deck and bottom

OilTankers 4.

Transverse

bulkhead

Transverse bulkheads are an important contributorto the hull girder strength

Function: transverse stiffness


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18.02.2005Slide 7

Transverse

stiffness

Seapressure

Seapressure

OilTankers 4.

Transverse

bulkheadCharacteristic damages

1. Stringer toes cracking

2. Bottom longitudinal bracket connection to

transverse bulkhead - cracks

3. Cracking of transverse bulkhead stiffeners

connection to stringers


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18.02.2005Slide 8

OilTankers 4.

Transverse

bulkheadCracking in stringer toe

Cracks in stringer toes and heel


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18.02.2005Slide 9

OilTankers 4.

Transverse

bulkheadCracking in stringer toe


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18.02.2005Slide 10

OilTankers 4.

Transverse

bulkhead

Full cargo tank

Cause for cracking in stringer toe

Compression/tension stresses

from one sided loading


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18.02.2005Slide 11

Full cargo tankSea

pressure

Very high alternating bending stresses in stringer toe

OilTankers 4.

Transverse

bulkheadCracks in stringer

Stringer flange

Crack


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18.02.2005Slide 12

May cause contamination of ballast water andsmall oil spills

Stringer webLongitudinal bulkhead

OilTankers 4.

Transverse

bulkhead

17.

Cracks in bottom longitudinals


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18.02.2005Slide 13

Cracks in toe of transverse bulkhead

bracket ending at bottom longitudinals

(wing tanks, midship area)

OilTankers 4.

Transverse

bulkheadCause - cracks in bottom brackets

Crack in bracket


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18.02.2005Slide 14

One sided loading at the transverse bulkhead

induce high local alternating bending stresses at

the bracket toe

toe (hot spot)

OilTankers 4.

Transverse

bulkheadDouble btm at transverse bulkhead

Similarily, one sided alternate loading at the transverse bulkhead also

induces high stresses for a double bottom structure

Modern designs have no

longitudinal girders in

double bottom giving large


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18.02.2005Slide 15

Critical areas

relative deflection

OilTankers 4.

Transverse

bulkheadCrack in transverse bulkheadstiffeners connection to stringers


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18.02.2005Slide 16

Connection of stringer to transverse

bulkhead with associated brackets

OilTankers 4.

Transverse

bulkheadCause for cracking in transversebulkhead stiffeners

One sided internal loading from cargo and ballast sets up ashear stress distribution in the bulkhead stiffener

Highly stressed areas are

created around geometric

hard points at stiffener

end connections to the


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18.02.2005Slide 17

stringer

-may cause ballast water contamination and possible oil spills

OilTankers 5.

LongitudinalBulkhead

Hull Structural Breakdown -Longitudinal bulkhead

1.

2.

3.

4.

5.

6.

SideBottom

Deck

Transverse bulkhead

Web frames



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18.02.2005Slide 1

OilTankers 5.


Structural build up oflongitudinal bulkhead

Cross ties

Longitudinal

bulkhead plating

with stiffeners

Web frame


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18.02.2005Slide 2

OilTankers 5.


Structural functions of long.bhd


- Resist internal pressure from cargo and ballast (cargo boundary)

- Safety against collapse if water ingress (boundary for flooding)

Web in hull girder

- Contributes to hull girder longitudinal stiffness


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18.02.2005Slide 3

OilTankers 5.


Function : Cargo boundary

Internal loads induce shear forces and

bending moments in the longitudinal

bulkhead longitudinal (between each webframe)


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18.02.2005Slide 4

Stresses are loaded onto the web framesand further into the hull girder structure

OilTankers 5.


Function: Web in hull girder

Longitudinal bulkhead together with ship side is taking up global shear

forces from wave induced loads and weight/buoyancy distribution along

the vessel length

R1 R2

A

A

A

A

F


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18.02.2005Slide 5 Section A-ASF

Shear force distribution

resulting from global

loads for midship section

OilTankers 5.


Characteristic damages

1. Cracks in bulkhead longitudinals connection to

stringers at transverse bulkhead

2. Shear buckling of longitudinal bulkhead


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18.02.2005Slide 6

OilTankers 5.


Crack in long.bhd longitudinalsconnection to stringers


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18.02.2005Slide 7

Connection of longitudinal

bulkhead longitudinals to stringers

with associated brackets

OilTankers 5.


Cause for cracking in long.bhdat stringer connections

Longitudinal bulkhead is flexing depending on the

loading condition (filling of tanks)


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18.02.2005Slide 8

High bending stresses towards the supports

(transverse bulkheads)

Fully loaded condition Ballast condition

OilTankers 5.


Cause for cracking in long.bhdstringer connections

Hotspot

Full ballast

tank


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18.02.2005Slide 9

May cause contamination of ballast water

and small oil spills

OilTankers 5.


Shear buckling of longitudinalbulkhead


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18.02.2005Slide 10

Shear buckling is most likely to occur in

areas towards the transverse bulkheads, butmay also occur in other areas depending on

the thickness of the bulkhead plating

OilTankers 5.


Shear buckling of longitudinalbulkhead

SF maximum at



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18.02.2005Slide 11

Longitudinal shear force

distribution an example

OilTankers 5.


Cause for shear buckling

Result of excessive shear stress in the bulkhead plating

Corrosion increases possibility for shear buckling

SFSF


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Shear buckled panels will have a reduced shear strength,

which may lead to an overload of adjacent areas

Shear buckling (middle and upper area of

bulkhead most exposed due to corrosion

risk and reduced original scantlings)

OilTankers 6. Web framesHull Structural Breakdown -Web frames

1.

2.

3.

4.

5.

6.

SideBottom

Deck

Transverse bulkhead

Web frames



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18.02.2005Slide 1

OilTankers 6. Web framesStructural build up of web

frame

Web frame flange

Web frames


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18.02.2005Slide 2

Cross tie

OilTankers 6. Web framesFunction of web frames

- Web frames are supports for the longitudinal stiffeners

- Web frames contributes to the hull girder transverse strength


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18.02.2005Slide 3

OilTankers 6. Web framesFunction of web frame

Web frames are supportsfor the longitudinals

Web frames take up local

loads from the

longitudinal stiffeners and

transfer them further into

the hull girder

Web frames keep the

Internal

pressure


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18.02.2005Slide 4

Web frames keep thecross sections together

and contribute to the

transverse stiffness

Sea

pressure

OilTankers 6. Web framesCharacteristic damages

1. Corrosion / buckling of web frame

2. Corrosion / cracking of cross tie connection

3. Cracking of tripping bracket connection to webframe flange


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OilTankers 6. Web framesShear buckling of web frame

High shear stress

SF


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SF

OilTankers 6. Web framesTYP. WEB SEC. (SHEAR STRESS)

LC 2

Shear buckling may occur in areaswhere shear stress is high


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OilTankers 6. Web framesCorrosion of cross tie

Cross ties are subject to both

compression and tension stressdepending on loading condition

Corrosion

Reduced Buckling capacity

Increased stress level


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18.02.2005Slide 10

g p y

Cross tie collapse?

+/- Axial stress

OilTankers 6. Web framesCrack in tripping bracketconnection to web frame flange


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18.02.2005Slide 11

Weld connection of large curved flanges

and tripping brackets on webframes

OilTankers 6. Web framesCause for cracking in web frameflange

Cracks occur due to additional

bending stresses from the presence

of a tripping bracket in the curved

part of the flange

- If flange is exposed to tension,

the flange will bend outwards


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18.02.2005Slide 12

- If exposed to compression,

the flange will bend inwards

Deflection pattern

of free flange

OilTankers 6. Web framesFEM plot of cross tie with deflections


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18.02.2005Slide 13

Oil

Tankers 6. Web framesCracks in web frame

Webframe support forlongidudinals reduced

support excessive load on

longitudinals

Increased loads on adjacent

webframes

May lead to loss of stiffened


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18.02.2005Slide 14

panel

Bulk

Carriers Bulk Carriers - Hull Structure


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Bulk

Carriers Contents Bulk Carriers

1. Introduction to Bulk carrier hull structure

2. Hull structural breakdown function of hull elements:

Side, bottom, deck, transverse bulkhead, longitudinal bulkhead,

web frames including relevant hull damages for all structuralelements

3. Case


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18.02.2005Slide 2

Bulk

Carriers Characteristics for Bulk Carriers

Single skin / hopper & top-wing tanks

Heavy cargoes

Large net load on double bottom

High shear stresses shell side

Sensitive to leakage - total structural loss High loading rate

Transverse strength

Green seas Not much public attention (no vetting)


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Not much public attention (no vetting)

Low survival capability when flooded

High number of vessels lost

Bulk

Carriers Bulk Carrier loading flexibility

Bulk Carrier HC/EA Any hold empty at full draught

Bulk Carrier HC/E hold 2,4,6 . Empty

Given combination of holds empty at full draught

Bulk Carrier HC Any hold empty at 80% of full draught

Bulk CarrierR

educedflex

ibility


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18.02.2005Slide 4

Bulk Carrier Any hold empty at 60% of full draught

Bulk

Carriers History

Built in 1954 - Cassiopeia

First bulk carrier with hopper

tank topside tank cross

section


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18.02.2005Slide 5

Bulk

Carriers Bulk Carrier particulars

5 cargo holds

7 cargo holds

9 cargo holds


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Bulk

Carriers Nomenclature


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18.02.2005Slide 7

Bulk

Carriers Nomenclature


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18.02.2005Slide 8

Bulk

Carriers

- A vessels hull can be divided into different hull

structural elements

- Each element has its function in the structure

- In order to assess the structure of a Bulk Carrier you

need to understand the function of the structural element

you are looking at

Structural breakdown of hull


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18.02.2005Slide 9

Bulk

Carriers Typical damages and repairs

WWW.witherbys.com


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18.02.2005Slide 10

Bulk

Carriers

5. Topside tank

1.

Side

3. Deck

4.

Transverse bulkhead

Structural breakdown of Bulk Carrier

7. Hatch coaming & cover


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18.02.2005Slide 11 2. Bottom

6.

Hopper tank

Bulk

Carriers Hull Structural Breakdown

1.

2.

3.

4.

5.

6.

Side

Bottom

Deck

Transverse bulkheadHopper tank

Topside tank

7.

Hatch cover & coaming


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18.02.2005Slide 12


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Bulk

Carrier Structural functions of ship side

1. Watertight integrity (local strength)

- Resist external sea pressure

- Resist internal pressure from cargo and ballast

2. Web in hull girder (global strength)

- Side plating act as the web in the hull girder beam

1. Side


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Slide 2

Bulk

Carrier Structural build up of ship side 1. Side

Side

frames

Lower

b k t

Side plating

Upper

bracket


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Slide 3

bracket

Bulk

Carrier Structural functions of ship side

Watertight integrity (local strength)

1. Side

Loads are taken up by the hull plating, stresses are

transferred into the vertical side frames further

into the upper and lower bkts further into the

topwing tank and hopper tank structure

Ship side must withstand static and dynamic

loads from external sea pressure as well internal

pressure from cargo and ballast


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Slide 4

Bulk

Carrier Functions of ship side

1. Side

Watertight integrity (local strength)

Lateral loads induces shear forces

and bending moments in the

vertical side frames. The side

frame is a single beam supported at

hopper / twt bkts

BmSF


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Slide 5

Bulk

Carrier

Net load down cause rotation of hopper tank structure.

additional moment in the mid-field and upper end

Functions of ship side 1. Side

Ore hold load response;

SFBm

Bm


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Slide 6

Bulk

Carrier

Net load up cause rotation of hopper tank structure.

additional moment in the mid-field and lower end

Functions of ship side 1. Side

Empty hold load response;

SFBm

Bm


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Slide 7

Bulk

Carrier Functions of ship side 1. Side

Side plating is acting

as web in hull girder

beam

Global loads are

acting on the hullgirder beam


Ship side is taking up

global shear forces

resulting from the

hull girder bending

moment and

weight/buoyancy

distribution along the

vessel length


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Slide 8

beam

Cont.

Bulk

Carrier

ingmoment

Hogging

0e

arforce

0

Function of ship side (longitudinal shear strength)

force(t

-m)

Shear Distribution at a

cross section Cont.


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Slide 9

Bend

Sagging

She

Sh

earf

Bulk

Carrier Functions of ship side 1. Side

Shear force distribution

resulting from global

loads for midship

section


- Global shear forces are distributed in the ship side plating Cont.


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Slide 10

Bulk

Carrier Hull damages in ship side 1. Side

Two characteristic damages for ship side:1. Cracks in side frames at lower / upper bracket connection

2. Corrosion of side frames and lower bkt. detached bkts


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Slide 11

Bulk

Carrier 1. Side

Vertical side frame lower

bkt. commection

Crack in side longitudinal web frame

connection

Cracking in vertical side frame:


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Slide 12

Bulk

Carrier

The dynamic loads from the sea are taken up by the

side plates supported by the vertical side frames andload is transferred to the upper and lower bkts. This

gives peak of bending moment and shear in way of

lower bkt. connection.

Cause for cracking in vertical side

frames lower bkt. connections1. Side

1a. The sniped termination of the bracket flange creates a local stressconcentration, which may develop cracks from the toe of the bracket

1a.

1b.

hi i hi h b di i fl d


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Slide 13

In this point a high bending stress in flange and a stress

concentration due to weld (overlap) increase the risk for fatigue

cracks.

1b.


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Bulk

Carrier

Side frames and bkts are prone to

corrosion, both general corrosion

as well as grooving corrosion

which may result in :

Local corrosion and grooving

General wastage.

Fractured/detached frames

Fracture in plating/bracket toes

Corrosion of side frames and lower

bkt. connection 1. Side


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Slide 15

Bulk

Carrier

Torig T-min T-subst T-Coat

Hold 1:

Aft end of Hold 1:

Upper bracket web 13,0 9,8 10,6 11,2

Frame web, middle and upper part 13,0 9,8 10,6 11,2

Frame web, Lower part 13,0 11,2 11,6 11,2

Lower bracket web 15,0 11,3 12,2 12,7

Frame flange thickness, middle and upper part 20,0 15,0 16,3 N/A

Frame flange thickness, lower part 20,0 15,0 16,3 N/A

Lower bracket flange thickness 20,0 15,0 16,3 N/A

Middle part of Hold 1:

Upper bracket web 13,0 9,8 10,6 11,2Frame web, middle and upper part 13,0 9,8 10,6 11,2

Frame web, Lower part 13,0 9,9 10,7 11,2

Lower bracket web 15,0 11,3 12,2 12,7




Forward end of Hold 1:

Upper bracket web 13,0 9,8 10,6 11,2Frame web, middle and upper part 13,0 9,8 10,6 11,2

Frame web, Lower part 13,0 13,9 NB! N/A

Lower bracket web 15,0 16,9 NB! N/A


F fl thi k l t 20 0 15 0 16 3 N/A

Upper Bracket

Lower Bracket

Middle and upperpart of Frame

Low er part of Frame

Revised Minimum Thickness List


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Slide 16



Bulk

CarrierCorrosion of side frames and lower

bkt. Connection Consequences 1. Side

Local grooving of side frame support bkts

Shear area of profile web reduced

If angle bar specially critical

Detached lower side frames

Frames simply supported, increase BM buckling

Side plate rupture top of hopper tank - flooding

General corrosion of side frames reduce the sheararea and section modulus. Bending moment stress level increases

Stiffeners may collapse in buckling


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Slide 17

p p p pp g

Bulk

Carrier Damage impact on function 1. Side

1. Cracks in vertical side frame- may increase moment in field for frame- may increase loads on adjacent frames

- may cause water ingress leakage

- may develop to panel collapse

- flooding stability - strength (loss of ship)

2. Corrosion of side frames

- As above


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Slide 18


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Bulk

Carrier 2. Bottom

Hull Structural Breakdown -

Bottom

1.

2.

3.

4.

5.

Side

Bottom

Deck

Transverse bulkhead

Hopper tank

Topside-tank6.


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Slide

1

Bulk

Carrier2.

Bottom

1. Watertight integrity (local strength bottom / inner bottom)

- Resist external sea pressure (bottom)

- Resist internal pressure from cargo/ballast & fuel oil

2. Carry net load on double bottom girder structure

- Inner bottom / bottom plate & stiffn. are girder flanges

- double bottom floors / girders are

Hull Structure

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