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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
transverse bulkheads
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:
Structural ConnectionsKnuckles
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Slide 21
Crack in shell plate at
knuckle:
New Brackets
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Module 3:
Structural ConnectionsKnuckles
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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
ENGINE ROOM BULKHEAD
LONGITUDINAL BULKHEAD
ENGINE ROOM 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
Aft ship Rudder Cavitation
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Slide 50
Preferred solution welded
with continuous weld insmall pieces not slot
welds
Aft ship Rudder Cavitation
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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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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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- 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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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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( )
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
Typical vessel: 100,000 dwt, L=253,0m, B=44,2m, T=11,6m
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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Typical vessel: 150,000 dwt, L=274,0m, B=50,0m, T=14,5m
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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- 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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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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- 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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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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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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- 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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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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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
Longitudinal 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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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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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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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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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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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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Kn : Unsymmetrical Stiffeners (L& bulb-profiles)
Oil
Tankers 1. SideStandard repair proposal longs / webframes
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Oil
Tankers 1. SideCracks in web frame cut outs
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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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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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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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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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5.
6.
Longitudinal bulkhead
Web frames
Oil
Tankers 2. Bottom
Watertight integrity
Resist external sea pressure
Resist internal pressure from cargo and ballast
Structural functions of bottom
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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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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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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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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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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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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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Oil
Tankers 2. BottomLoad response double bottom
Stresss flow
shortest way to
support
Stresss flow
shortest way to
support
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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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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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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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Crack in hull plating in
way of bilge keel toes
Oil
Tankers 2. BottomBilge keel cracking
Hot spotBilge keel
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Longitudinalstress
Oil
Tankers 2. BottomBilge keel cracking
Web frame/BilgeBracket
All measures in mm
125
Edges to be grindedsmooth
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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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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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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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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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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
bottom longitudinals
Oil
Tankers 2. BottomCause for cracking in double
bottom longitudinals
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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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
Longitudinal bulkhead
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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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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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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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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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Bending
moment
Max
OilTankers 3. DeckCharacteristic damages
1. Cracks in deck longitudinals
2. Crack in deck plating3. Corrosion of deckhead
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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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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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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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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
OilTankers 3. DeckCorrosion of deckhead
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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Reduced sectional area in deck may lead to plate buckling
Area
Longitudinal
stress distribution
L
Long. stress distribution
(with reduced deck
sectional area)
OilTankers 3. DeckCorrosion of deckhead
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
OilTankers 3. DeckCorrosion of deckhead
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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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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OilTankers 4.
Transverse
bulkheadStructural build up oftransverse bulkhead
Transverse bulkhead
plating w/stiffeners
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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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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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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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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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OilTankers 4.
Transverse
bulkheadCracking in stringer toe
Cracks in stringer toes and heel
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OilTankers 4.
Transverse
bulkheadCracking in stringer toe
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OilTankers 4.
Transverse
bulkhead
Full cargo tank
Cause for cracking in stringer toe
Compression/tension stresses
from one sided loading
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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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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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Critical areas
relative deflection
OilTankers 4.
Transverse
bulkheadCrack in transverse bulkheadstiffeners connection to stringers
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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
Longitudinal bulkhead
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OilTankers 5.
LongitudinalBulkhead
Structural build up oflongitudinal bulkhead
Cross ties
Longitudinal
bulkhead plating
with stiffeners
Web frame
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OilTankers 5.
LongitudinalBulkhead
Structural functions of long.bhd
Watertight integrity
- 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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OilTankers 5.
LongitudinalBulkhead
Function : Cargo boundary
Internal loads induce shear forces and
bending moments in the longitudinal
bulkhead longitudinal (between each webframe)
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Stresses are loaded onto the web framesand further into the hull girder structure
OilTankers 5.
LongitudinalBulkhead
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.
LongitudinalBulkhead
Characteristic damages
1. Cracks in bulkhead longitudinals connection to
stringers at transverse bulkhead
2. Shear buckling of longitudinal bulkhead
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OilTankers 5.
LongitudinalBulkhead
Crack in long.bhd longitudinalsconnection to stringers
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Connection of longitudinal
bulkhead longitudinals to stringers
with associated brackets
OilTankers 5.
LongitudinalBulkhead
Cause for cracking in long.bhdat stringer connections
Longitudinal bulkhead is flexing depending on the
loading condition (filling of tanks)
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High bending stresses towards the supports
(transverse bulkheads)
Fully loaded condition Ballast condition
OilTankers 5.
LongitudinalBulkhead
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.
LongitudinalBulkhead
Shear buckling of longitudinalbulkhead
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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.
LongitudinalBulkhead
Shear buckling of longitudinalbulkhead
SF maximum at
transverse bulkheads
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Longitudinal shear force
distribution an example
OilTankers 5.
LongitudinalBulkhead
Cause for shear buckling
Result of excessive shear stress in the bulkhead plating
Corrosion increases possibility for shear buckling
SFSF
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18.02.2005Slide 12
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
Longitudinal bulkhead
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OilTankers 6. Web framesStructural build up of web
frame
Web frame flange
Web frames
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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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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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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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g p y
Cross tie collapse?
+/- Axial stress
OilTankers 6. Web framesCrack in tripping bracketconnection to web frame flange
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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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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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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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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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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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Bulk
Carriers Nomenclature
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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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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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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
Web in hull girder (global strength)
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
Web in hull girder (global strength)
- 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
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
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
Frame flange thickness, middle and upper part 20,0 15,0 16,3 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
Frame flange thickness, lower part 20,0 15,0 16,3 N/A
Lower bracket flange thickness 12,5 9,4 10,2 N/A
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