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Hull Structure
Course
DNV
2005
How are the
loads taken
up by the
structure?
Consequence
of a crack in
this detail?

Where is it likely
to find cracks?
Hull Structure Course
Objective:
After completion of the course, the participants
should have gained knowledge of basic hu...
Hull Structure Course
Purpose:
To train technical personnel about the basics of hull
structure.
Target group is technical ...
Course breakdown:
Day 1
•
•
•
•
Day 2
•
•
Day 3
•
Day 4
•
•

Introduction
Single beams & loads
Structural connections
Hull...
Agenda day 1
09.00-09.15
09.15-09.45
10.00-11.30
11.30-12.30

Welcome & Introduction
Expectation & presentation of partici...
Agenda day 2
09.00 – 09.15
09.15 – 10.30
10.30 – 10.45
10.45 – 11.00
11.00 – 11.45
11.45 – 12.15

Answers to review questi...
Agenda day 3
09.00 - 09.30
09.30 - 10.00
10.00 - 10.45
10.45 – 11.00
11.00 - 11.45
11.45 - 12.15

Answers to review questi...
Agenda day 4
09.00 - 09.30
09.30 - 10.30
10.30 - 11.00
11.00 – 11.15
11.15 – 12.15

Answers to review questions from day 1...
Module 2: Basic Hull Strength

Slide 1

Basic Hull Strength
Objectives

Basic Hull Strength

After completion of this module the participants should have
gained:
1. Understanding of:...
Simple beam properties

Basic Hull Strength

Bending
moment

Load

A

Compression
Section A-A

A

Tension

Shear
force

Be...
Simply supported beam
- concentrated load
L/2
ℓ

Basic Hull Strength

F

Single beam with
concentrated load,
simply suppor...
Simply supported beam
– distributed load

Basic Hull Strength

p

Single beam with
distributed load,
simply supported ends...
Beam with fixed ends - distributed load

Basic Hull Strength

No rotation!
p

Single beam
with distributed
load, fixed end...
Beam with spring supported ends

Basic Hull Strength

p

Spring

k

k

Spring

Shear force and bending moment distribution...
End fixation

Basic Hull Strength

Structural clamping – spring support

Symmetrical load – full fixation

Slide 8
Beam – fixation at ends

Basic Hull Strength

• Load on structure is important with regard to fixation
bottom longs connec...
Axial stress

Basic Hull Strength

Force

Stress

=

Force
Area

Area

σ

= ε x E (Hook’s Law)
ε : Relative elongation
You...
Stress levels – elastic & inelastic region
Elastic region: σ

< σyield

- A beam exposed to a stress level below
the yield...
High Tensile Steel (HTS)

Basic Hull Strength

Material grades NVA - NVE
• Measure for ductility of material (prevent brit...
Bending stress - Simple beam with load

A

R1

F

A

A
A

R2

Area effective in
transferring the bending
of the beam

n.a
...
Shear stress - Simple beam with load

A

R1

F
A

A

A

R2

Distribution of the
stress

Area effective in
transferring loa...
Bending and shear stress flow
A

R1

A

F

Basic Hull Strength

A
A

R2

Compression

Bending stress is
transferred in the...
Beam stiffness and section modulus

Basic Hull Strength

As the axial stresses are transferred in the flange of a beam, it...
Shear stress & shear area

Basic Hull Strength

The load is carried in shear towards the supports by the web
Shear force :...
Conventional profiles in ship structures

Basic Hull Strength

Flatbar (slabs)
Easy with regard to production, flatbar sti...
Angle bar (rolled / built up)

Basic Hull Strength

An angle bar profile will twist when exposed to lateral loads due
to a...
Conventional ship structure profiles

Basic Hull Strength

Bulb profile (single / double bulb)
Bulb profiles are favourabl...
Hierarchy of hull structures

Plate

–

Stiffener

–

Stringer / girder

–

Basic Hull Strength

Panel

–

Stresses in a h...
Level 1: Plate - simple beam

Basic Hull Strength

Stiffener

NO
ROTATION

Plating

Water pressure
A strip of plating
cons...
Level 2 Longitudinal - simple beam

Basic Hull Strength

Longitudinal between two web frames

Max shear and bending moment...
Level 3 : Transverse web - simple beam

Basic Hull Strength

Beam with fixed ends and
concentrated loads from the
bottom l...
Level 3 Longitudinal girder with
transverse webframes

Basic Hull Strength

Longitudinal girder between two
transverse bul...
Beams, load transfer

Basic Hull Strength

Double bottom structure

Loads taken up by the bottom plating
are transferred t...
Beams, load transfer

Basic Hull Strength

Longitudinal
bulkhead

Single skin structure
Loads taken up by the bottom plati...
Damage experience
• Level 1

Plate supported at stiffeners

• Level 2

Stiffener supported at webframe

• Level 3

Webfram...
Single beam VS Hull girder

Basic Hull Strength

A vessel’s hull has many of the same properties as a single beam.
Hence s...
Hull girder bending

Basic Hull Strength

When a vessel’s hull is exposed to loading, it will bend similarly as a
single b...
Single beam VS Hull girder
A
A

F

A
A

Bending stress, σ

Compression

Tension

Hull Girder
Section A-A

Shear stress, τ
...
Stress hierarchy in ship structure

Local stress :
Girder stresses:
Hull girder stresses;

Slide 32

Basic Hull Strength

...
Case Module 2: Loads Buzz Groups

Basic Hull Strength

• For a beam with fixed ends and evenly distributed
load, i.e. from...
Case Module 2: Beams Buzz Groups

Basic Hull Strength

• Is it correct that the transverse girders are
supported by the lo...
Summary: Beams
•
•
•
•
•

Basic Hull Strength

BM and Shear force
Stress axial / bending / shear
Section modulus / Moment ...
Loads acting on a ship structure

Slide 36

Basic Hull Strength
Loads acting on a ship structure
1. Internal loads:

- Cargo
- Ballast
- Fuel
- Flooding
- Loading/unloading

2. External ...
Static and Dynamic loads
Static local load:

Basic Hull Strength

The local load, internal and external
due to cargo / bal...
Static and Dynamic loads

Basic Hull Strength

Total external local load acting on a vessel:

Static

Max at the bottom

D...
Sea Pressure – static and dynamic contribution

Basic Hull Strength

Plotted sea pressure curve
is a sum of the static and...
Static and Dynamic loads

Basic Hull Strength

• Global dynamic vertical and horizontal wave bending
moments give longitud...
Loads on foreship

Basic Hull Strength

Bow Impact Pressure
•Induced by waves, vessel speed, flare
and waterline angle imp...
Loads on deck

Slide 43

Green Seas Loading:
• Dominant for hatch covers and fwd deck structure
(incl. deck equipment, doo...
Weights and buoyancy

Basic Hull Strength

Weight distribution of
cargo and fuel

Steel weight, equipment
and machinery

B...
Bulk Carrier typical load
Static external sea
pressure
Dynamic external
sea pressure

Slide 45

Basic Hull Strength

Stati...
Net load on structure – ‘Ore hold’
Internal load
- External load
= Net load on double bottom

Static and dynamic
internal ...
Net load on structure - empty hold
Net load from sea pressure

Slide 47

Static and dynamic
sea pressure

Basic Hull Stren...
Alternate loading condition

Slide 48

Basic Hull Strength
Weights and buoyancy

Basic Hull Strength

Buoyancy and weights are not evenly distributed along
a ships length…

…hence, ...
Hull girder still water bending
moment and shear force

Basic Hull Strength

Slide 50

Example: SF and BM distribution for...
Total BM acting on a vessel

Basic Hull Strength

Total hull girder bending moment MTotal = Mstill water + M wave

Slide 5...
Case 2 Module 2 – Loads/Materials

Basic Hull Strength

• Where in the hull girder cross section of a hull girder are
the ...
Summary: Loads
•
•
•
•
•

Slide 53

Static & dynamic
Internal & external
Load distribution
Net load
Longitudinal strength ...
Basic Hull Strength

End of Module 2: Basic Hull Strength

Slide 54
Module 3: Structural Connections

Module 3:
Structural Connections

• Objectives of this Module:
After completion of this ...
Contents

•
•
•
•
•

Slide 2

Types of welds
Connections of stiffeners
Connections of girders/web frames
Connections betwe...
Module 3:

Weld Types

Structural Connections

We will briefly touch upon the following types:
• Fillet welds
• Full penet...
Module 3:

Weld Types – Fillet welds

Structural Connections

Throat thickness

Fillet welds:
• The most common type
Leg l...
Module 3:

Weld Types – Full penetration

Structural Connections

Full penetration welds:
• To be used where stress level ...
Module 3:

Connections of stiffeners
• What forces are to be transferred?

L

Shear
Force

Bending
Moment

Slide 6

Struct...
Load from stiffener to webframe

How arethe
How is the
forces
transferred
from the
stiffener to
webframe
Slide 7

Module 3...
Module 3:

Connections of stiffeners

Web fr.
Slide 8

Stiffener

Web fr.

b)

a)

+

+

+

c)

d)

Web fr.

+

Structural...
Module 3:

Connections of stiffeners

Structural Connections

Effect of brackets on the max bending stress

No or negative...
Connections of stiffeners
Web-plating

Stiffener

Slide 10

=

Structural Connections

Common crack locations in longitudi...
Static stress in stiffener on top

Module 3:
Structural Connections

Stress distribution for different details

ballast

σ...
Connections of stiffeners
Common crack locations
Web-plating

Stiffener
Longitudinal

=

=
Design improvement

Slide 12

M...
End-brackets on girders - forces

Empty
Wing
Tank

Structural Connections

Full Centre Tank

Net load

Slide 13

Module 3:...
End-brackets on girders

Module 3:
Structural Connections

Improved design

Transverse welding of
flange outside curved ar...
Stringer connection to inner side

Module 3:
Structural Connections

Repair

Original Design
Inner side
Ship side

Stringe...
End-brackets on girders

Module 3:
Structural Connections

Girder bracket

Typical crack location
Ref. iii b) previous fig...
Module 3:

Cross-Ties

Full Centre Tank
Empty Centre Tank

Full Centre/Empty Wing at full draught
= Max. Compression in Cr...
Module 3:

Knuckles

Structural Connections

helikopter

Out of plane forces

Deformation/low stiffness

Slide 18
Knuckles

Module 3:
Structural Connections

Support as close to the knuckle as possible

Slide 19
Knuckles

Module 3:
Structural Connections

Vertical Brackets

Slide 20
Module 3:

Knuckles
Crack in shell plate at
knuckle:

New Brackets

Slide 21

Structural Connections
Module 3:

Knuckles

Structural Connections

Crack Locations

Stress Concentrations
In way of Webs

Slide 22
Module 3:

Knuckles

Structural Connections

Preferred design:
• No misalignment in the connection.
• No lugs or scallops
...
Module 3:

Intersecting Hull Elements
Crossing Panel - No bracket

Structural Connections

Crossing Panel - With bracket

...
Module 3:

Intersecting Hull Elements

Structural Connections

TOP SIDE
TANK NO. 7

ENGINE ROOM BULKHEAD

DIESEL
SUPPLY
TA...
Notches, Drain/Lightening Holes

i)

Crack

Common notch
in way of weld

Slide 26

Reduced risk of cracking

Module 3:
Str...
Module 3:

Summary module 3
•
•
•
•
•
•
•

Slide 27

Welding
Connection stiffener – girder
Girder – panel
Cross tie
Knuckl...
Module 5
Hull Structural Breakdown
Oil Tanker
Bulk Carrier
Container Ship

Slide 1
Hull Structural Breakdown
Oil Tanker – Bulk Carrier – Container Ship

Objective of Module 5:

After completion of this mod...
Contents of Module 5

1. Fwd and aft structural parts
2. Oil Tankers – structures in cargo area
3. Bulk Carriers – structu...
Fore
ship

Contents – Fwd and aft structural parts

1. Hull structure breakdown – fwd part of ship
2. Hull structure break...
Fore
ship

Structural functions of fore ship

1. Watertight integrity (local strength)
- Resist external sea pressure / Bo...
Fore
ship

Structural build up fore ship
Collision bhd.

Chain locker

Stringer decks

Breast hook

Side webframes

Bulbou...
Fore
ship

Structural build up fore ship

Vertical side frames

Slide 7

Horizontal side longs
Fore
ship

Structural functions of fore ship

•
•
Slide 8

•

Shell side must withstand static and dynamic
loads from exte...
Fore
ship

Structural build up fore peak
Horizontal stiffening

Plate supported by side longs
Side longs supported at webf...
Fore
ship

Structural build up fore peak
Horizontal stiffening

Reduced
efficiency
due to flare
angle

Slide 10
Fore
ship

Structural build up fore peak
Vertical stiffening
Plate supported by side
frames
Side frames supported by
strin...
Fore
ship

Functions of fore peak global strength
2. Web in hull girder (global strength)
•

Ship side / longitudinal swas...
Fore
ship

Functions of fore peak Global strength
2. Deck and Bottom in hull girder (global strength)
-

The global bendin...
Fore
ship

Hull damages in fore ship

Characteristic damages fore ship
1.
2.

Buckling of stringers

3.

Bow impact

4.

D...
Fore
ship

Lost shipside

Oil Tanker 357 000
DWT built 1973
20 years

Heavy
local
corrosion

Experience feedback

• Local ...
Fore
ship

Lost shipside - Impact of function

Oil Tanker 357 000
DWT built 1973
20 years

• Shell side lost its watertigh...
Fore
ship

Slide 17

Buckling of stringer in fore
peak tank

Oil Tanker
302,419 DWT built 1992
Buckling of stringers in fo...
Fore
ship

Buckling of stringer in fore peak
tank

Oil Tanker
302,419 DWT built 1992
Buckling of stringers in fore peak ta...
Fore
ship

Buckling of stringer
Impact of function

Oil Tanker
302,419 DWT built 1992
Buckling of stringers in fore peak t...
Fore
ship

Bow Impact Damage

Container ship
1 year

A recent damage in 2001…..
Occurred during the first year of operatio...
Fore
ship

Slide 21

Bow Impact Damage

Container ship
1 year
Fore
ship

Bow Impact Damage

Container ship
1 year

Bow impact: Peak pressure

Important factors:
Flare angle, α
Waterlin...
Fore
ship

Bow Impact Damage

Container ship
1 year

Local plate buckling

Slide 23
Fore
ship

Bow Impact Damage
Impact of function

Container ship
1 year

• Buckled plating may lead to leakage
• Damages to...
Fore
ship

Bottom slamming fore ship

Bulk Carrier
220 000Dwt
Built 1997

•

Bottom plate set in

•

Bottom longs tripped ...
Fore
ship

Bottom slamming fore ship

Plates set in and punctured
Floors twisted and damaged
Mostly for small ships in
bal...
Fore
ship

Bottom slamming fore ship

Feeder
L = 100 m

Parametres:

T
BF

= Ballast draught forward. Increasing ballast d...
Fore
ship

Bottom slamming
Impact of Function

• Bottom longs tripped will not efficiently support
plate
– Bottom plate + ...
Aft ship

Contents – Fwd and aft structural parts

1. Hull structure breakdown – fwd part of ship
2. Hull structure breakd...
Aft ship

Structural build up aft ship

Transom stern plate
Engine room bulkhead
Webframes

Floors

Slide 30
Aft ship

Structural build up aft ship
Engine room platform
Side plate &
longitudinals
Webframe side
Webframe deck

Slide ...
Aft ship

Structural build up aft peak tank

Horizontal side longs

Slide 32

Vertical side frames
Aft ship

•
•
•
Slide 33

Structural functions of aft ship

Shell must withstand static and dynamic sea pressure, bottom
s...
Aft ship

Functions of aft ship

Web in hull girder (global strength)
Ship side together with the
longitudinal swash
bulkh...
Aft ship

Functions of Aft ship

2. Deck and Bottom in hull girder (global strength)
-

The global bending moments are alw...
Aft ship

Functions of Aft ship

• Ensure adequate stiffness for:
– Main engine support (double bottom engine room)
– Stee...
Aft ship

Hull damages in aft ship

Characteristic damages for the aft ship:
1. Buckling of engine room stringers
2. Stern...
Aft ship

Buckling

Oil Tanker
Built 1992
Buckling of stringers in engine room
(after 1 year)

Buckling of stringers aft i...
Aft ship

Buckling

External sea pressure

Bending
moment

Bending + shear
exceed the
buckling capacity
of the plate

Slid...
Aft ship

Buckling
Impact of function

• Stiffeners may loose their support and areas
may be overloaded
• Collapse of pane...
Aft ship

Stern Slamming

Container Ship

• Flat stern structure is prone to be high stern slamming impact
load - the wide...
Aft ship

Container Ship

Stern Slamming

Repaired
connection area/
scallop

Slide 42

Scallop and stiffener
connection to...
Aft ship

Container Ship

Stern Slamming

F

F
Slide 43
Aft ship

Stern Slamming

Container Ship

Impact of function

• Side longitudinals may loose their support at
web frames
•...
Aft ship

Cracks in aft peak tank due to vibrations

Cracks in Trans. at Steering Gear Flat

Supporting structure below
os...
Aft ship

Cracks in aft peak tank due to vibrations
Crack in weld between
web frame and shell side

Crack

Repair;
Crack c...
Aft ship

Vibration damages
Impact of function

• The supporting structure may get less effective
• If the cracks are in t...
Aft ship

Rudder Cavitation

Typical repair;
• Grind the affected area
• Pre-heat
Slide 48

• Re-weld

Typical on Containe...
Aft ship

Rudder Cavitation
Pressure distribution around
typical rudder profile

Pressure
distribution
(suction)

Positive...
Aft ship

Rudder Cavitation

• Stainless steel shielding
– Preferred solution welded
with continuous weld in
small pieces ...
Aft ship

Rudder Cavitation

This is how it may end if
the shielding is not
welded properly

Slide 51
Aft ship

Rudder Cavitation
Impact on function

• Cracks may occur which could lead to reduced
rudder support and maneuver...
End of Module 5 Fore & aft ship

Slide 53
Oil
Tankers

Oil Tankers - Hull Structure

Slide 1

18.02.2005
Oil
Tankers

Contents – Oil tankers

1. Introduction
2. Hull structural breakdown – function of hull elements:
•

3.

Slid...
Oil
Tankers

Characteristics for Oil tankers

Any
proposals?

- High number of tanks – good capability of survival
- Low f...
Oil
Tankers

Size categories of tankers

Oil Tankers
Type
ULCC
VLCC
Suezmax
Aframax
Panamax
Products

DWT
320,000+
200 - 3...
Oil
Tankers

Size categories of tankers
Panamax (55 - 75,000 dwt):
• Max size tanker able to transit the Panama Canal

• L...
Oil
Tankers

Size categories of tankers
Suezmax (120 – 200,000 dwt):
• Notation is soon to become redundant as the project...
Oil
Tankers

Size categories of tankers

ULCC (320,000+ dwt):
• Most ships of this type built in the mid to late 70’s

• O...
Oil
Tankers

Single Skin Oil Tanker

Ship data:
L = 310m
B = 56m
D = 31,4m
284,497 DWT

Slide 8

- Old design, build up to...
Oil
Tankers

Single bottom with side ballast tanks

Ship data:
L = 236m
B = 42m
D = 19,2m
88,950 DWT

- Built in the 80’s,...
Oil
Tankers

Double Hull – Two Longitudinal Bulkheads

Ship data:
L = 320m
B = 58m
D = 26,8m
298,731 DWT

Slide 10

- Comm...
Oil
Tankers

Double Hull – CL Longitudinal Bulkhead

Ship data:
L = 264m
B = 48m
D = 23,2m
159,681 DWT

Slide 11

- Common...
Oil
Tankers

Double Hull – no CL bulkhead

Ship data:
L = 218m
B = 32,2m
D = 19,7m
63,765 DWT

Slide 12

- Older design

1...
Oil
Tankers

Slide 13

Nomenclature for a typical double hull oil
tanker

18.02.2005
Oil
Tankers

Structural breakdown of hull

-A vessel’s hull can be divided into different hull structural
elements

- Each...
Oil
Tankers

Damages and repairs

WWW.witherbys.com

Slide 15

18.02.2005
Oil
Tankers

Function of hull elements

Deck:
Ship side:

Webframes:

Slide 16

18.02.2005

Longitudinal bulkhead:

Bottom...
Oil
Tankers

Hull Structural Breakdown

2.

Side
Bottom

3.

Deck

4.

Transverse bulkhead
Longitudinal bulkhead
Web frame...
Oil
Tankers

End of Oil Tanker session

Slide 18

18.02.2005
Oil
Tankers

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Ship side
Side
Bottom
Deck
Transverse bulkhead
Longitud...
Oil
Tankers

Structural build up of ship side
– single skin tanker

Side plating with
longitudinals
Transverse
bulkhead
Cr...
Oil
Tankers

Structural build-up of a double
hull ship side

Side plating with
longitudinals

Inner side plating
with long...
Oil
Tankers

Structural functions of ship side

1.

Side

Watertight integrity
- Take up external sea loads and transfer t...
Oil
Tankers

Loads on the ship side - example

1.

Side

Fully loaded
condition

Ballast condition
Water
Line

Net force

...
Oil
Tankers

Local function: Watertight integrity

1.

Side

External loads induces shear forces and
bending moments in th...
Oil
Tankers

Local function: Watertight integrity

1.

Side

-Side longs are supported at the web frames
- Web frames are ...
Oil
Tankers

Double hull ship side

1.

Side

• The structural functions of a double hull ship side is the same as for a
s...
Oil
Tankers

Global function: Web in hull girder

1.

Global shear forces resulting from uneven distribution of
cargo and ...
Oil
Tankers

Stringers in a double side

• Stringers contribute to the stiffness of the double
hull ship side, which means...
Oil
Tankers

Characteristic damages for ship
side:

1.

Side

1. Cracks in side longitudinals at web frames
2. Cracks in c...
Oil
Tankers

Crack in side longitudinals

Oil Tanker
285,690 DWT built 1990
Cracking in side longitudinal web frame
connec...
Oil
Tankers

Cause for cracking in side longitudinals

1.

Side

Dynamic loads (sea
and cargo) are forcing
the side longit...
Oil
Tankers

Stress concentration factors

More Stress concentration factors ;
•

Kg

: Gross Geometry (from FEM analysis)...
Oil
Tankers

Slide 15

Standard repair proposal longs / webframes

18.02.2005

1.

Side
Oil
Tankers

Cracks in web frame cut outs

Cr
ac
ks

Slide 16

18.02.2005

1.

Side

Cracks around openings for
side longi...
Oil
Tankers

Cause for cracking in cut outs
for longitudinals

1.

Side

Sea loads induce shear stresses in the web frame
...
Oil
Tankers

Consequence of crack in web frame

1.

Side

How does this damage impact on the function of the web frame?
Si...
Oil
Tankers

Crack in side longitudinal at
transverse bulkhead

1.

Side longitudinal connections
to transverse bulkheads
...
Oil
Tankers

Why cracking at transverse bhd.?

Ship side

1.

Side

Relative deflections occur between
the ’rigid’ transve...
Oil
Tankers

FEM plot of double hull oil tanker

1.

Side

Loading condition:
External dynamic
sea pressure at full
draugh...
Oil
Tankers

Suggestions?

Consequence of damage

1.

Side

Cracks in side longitudinals:
-

leakage
Slide 22

18.02.2005
...
Oil
Tankers

Indents of side shell with stiffeners

1.

Side

Mainly from contact damages:

The terms ’indents’ and ’buckl...
Oil
Tankers

Slide 24

Consequense of indents

18.02.2005

1.

Side
Oil
Tankers

Consequense of indents

1.

Side

Large area set in (plating and stiffeners)
gives reduced buckling capacity
...
Oil
Tankers

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Bottom
Side
Bottom
Deck
Transverse bulkhead
Longitudina...
Oil
Tankers

Structural functions of bottom

2.

Bottom

Watertight integrity
•

Resist external sea pressure

•

Resist i...
Oil
Tankers

Structural build up of bottom –
single skin tanker

Bilge
Bottom plating
w/longitudinals
Keel plate
Slide 3

...
Oil
Tankers

Structural build-up of a double
bottom structure

Inner bottom plating (tank
top) with longitudinals

2.

Bot...
Oil
Tankers

Function: Watertight integrity

2.

Bottom

Fixation?

External loads induce shear forces and bending moments...
Oil
Tankers

Function: Watertight integrity

2.

Bottom

Bottom plating with longitudinals are also acting as
flange for t...
Oil
Tankers

Bottom is supported by ship side and
longitudinal bulkhead

2.

Bottom

Double span for double bottom
without...
Oil
Tankers

Function: Flange in hull girder

2.

Bottom

Global bending moment induces longitudinal stresses in the
botto...
Oil
Tankers

Double bottom structure

2.

Bottom

Load distribution
in double bottom
girder system

Slide 9

18.02.2005
Oil
Tankers

Load response double bottom

2.

Bottom

Stresss flow
shortest way to
support

Cont.

Slide 10

18.02.2005
Oil
Tankers

Double bottom structure

2.

Bottom

The double bottom is a grillage structure built up by
transverse girders...
Oil
Tankers

Characteristic damages

2.

Bottom

1. Bilge keel terminations – crack in hull plating
2. Fatigue cracking in...
Oil
Tankers

Bilge keel cracking

2.

Bottom

Oil Tanker
285,690 DWT built 1990
Crack in hull plating i.w.o. bilge keel
te...
Oil
Tankers

Bilge keel cracking

2.

Hot spot
Bilge keel

Longi

Slide 14

18.02.2005

tudina
l stres

s

Bottom
Oil
Tankers

Bilge keel cracking

2.

Web frame/Bilge
Bracket
All measures in mm

125
Edges to be grinded
smooth
Ship side...
Oil
Tankers

Cracking in bottom longitudinals

Bottom long. flat
bar connection

Similar16
Slide cracking in bottom longit...
Oil
Tankers

Cause for cracking in bottom
longitudinals

Bottom

2.

Bottom longitudinals are subject to both:
Web/
Trans ...
Oil
Tankers

Consequences of cracks in
bottom longitudinals:

2.

Bottom

-Leakage of oil
- Crack may propagate
further in...
Oil
Tankers

Example: Cracks in inner bottom

2.

Bottom

Oil Tanker
95,371 DWT
Crack in tank top plating at toes of
trans...
Oil
Tankers

Cracking in double bottom
longitudinals

2.

Bottom

Cracks in flatbar connections for bottom and inner
botto...
Oil
Tankers

Cause for cracking in double
bottom longitudinals

2.

Bottom

In a ballast condition there is a net overpres...
Oil
Tankers

Illustration – double bottom flatbar
connections

2.

Bottom

Tensile stresses in critical structural details...
Oil
Tankers

Corrosion of bottom structures

2.

Bottom

Local corrosion (pitting): may occur
all over the bottom plating,...
Oil
Tankers

Corrosion of bottom structures

2.

Bottom

- Pittings and local corrosion may cause leakage, in general not ...
Oil
Tankers

Slide 25

Cracking in hopper knuckle

18.02.2005

Crack in hopper knuckle at web
frame connections

2.

Botto...
Oil
Tankers

Cause for cracking in hopper
knuckle

2.

Bottom

- Bending of double bottom due to external and internal
dyn...
Oil
Tankers

Cause for cracking in hopper
knuckle

2.

Bottom

- Inner bottom membrane stresses are transferred into the h...
Oil
Tankers

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Deck
Side
Bottom
Deck
Transverse bulkhead
Longitudinal ...
Oil
Tankers

Structural functions of deck

3.

Deck

Flange in hull girder
- Deck plating and longitudinals act as the upp...
Oil
Tankers

Structural build up of deck –
single skin tanker
Deck plating
w/longitudinals

Transverse deck
girder / Web f...
Oil
Tankers

Function: Flange in hull girder

3.

Deck

Hull girder bending moment induces longitudinal stresses in
the de...
Oil
Tankers

Longitudinal stresses in deck

3.

Longitudinal stresses from bending of hull girder is
maximum at midship

M...
Oil
Tankers

Characteristic damages

1. Cracks in deck longitudinals
2. Crack in deck plating
3. Corrosion of deckhead
4. ...
Oil
Tankers

Cracking in deck longitudinals

3.

Deck

Deck longitudinal
connection to web frames

Deck longitudinal
conne...
Oil
Tankers

Cracking in deck longitudinals
Oil Tanker
135,000 DWT built 1991
Crack main deck plating

Slide 8

Crack in u...
Cause for cracking in deck
longitudinals

Oil
Tankers

3.

The wave induced excitation of the hull girder leads to
dynamic...
Oil
Tankers

Cracks in deck longitudinals

- May result in oil spill on deck
- Corrosion is highly influencing the fatigue...
Oil
Tankers

Openings in deck

3.

Deck

σ
Kg.Kw. σ

σ

Longitudinal
stress-flow around
manhole in deck

Slide 11

18.02.2...
Oil
Tankers

Example: crack in scallop in deck
longitudinal

3.

Deck

Oil Tanker
123,000 DWT built 2000
Crack main deck p...
Oil
Tankers

Crack in deck plating

3.

Tanker for Oil
99328 DWT
built 1996
Crack in deck plating

Crack in deck plating a...
Oil
Tankers

Corrosion of deckhead

The ullage space (deckhead) is an area
susceptible to general corrosion

Slide 14

18....
Oil
Tankers

Corrosion of deckhead

3.

Deck

A reduction of the deck transverse sectional area due to general corrosion
w...
Oil
Tankers

Corrosion of deckhead

3.

Deck

Higher stress level in deck
due to general corrosion

σL

Longitudinal
stres...
Oil
Tankers

Corrosion of deckhead

3.

Deck

Flatbars have poor
buckling capacity

Slide 17

18.02.2005

L-profiles have ...
Oil
Tankers

Buckling in deck

Buckling in deck is most likely to occur in the midship
region where the hull girder bendin...
Oil
Tankers

Cause for buckling in deck

3.

Deck

Buckling in deck is a result of in plane compression forces in excess o...
Oil
Tankers

Corrosion of deckhead / buckling:

3.

Deck

- heavy corrosion of deck may lead to
buckling
- small buckles (...
Oil
Tankers

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Transverse bulkhead
Side
Bottom
Deck
Transverse bulkhea...
Oil
Tankers

Structural build up of
transverse bulkhead

Transverse bulkhead
plating w/stiffeners

Stringers

Buttress
Sli...
Oil
Tankers

Structural functions

4.

Transverse
bulkhead

Watertight integrity
- Resist internal pressure from cargo and...
Oil
Tankers

Functions of transverse bulkhead

The transverse bulkhead must withstand
internal pressure loads from cargo a...
Oil
Tankers

Function: tank boundary

4.

Transverse
bulkhead

Stringer

Shear
force

Bending
moment

Slide 5
Stiffener

1...
Oil
Tankers

Function: tank boundary

One sided loading on the transverse bulkhead
introduces stresses in the transverse b...
Oil
Tankers

Function: transverse stiffness

4.

Transverse
bulkhead

Transverse bulkheads are an important contributor
to...
Oil
Tankers

Characteristic damages

1. Stringer toes – cracking
2. Bottom longitudinal bracket connection to
transverse b...
Oil
Tankers

Cracking in stringer toe
Cracks in stringer toes and heel

Slide 9

18.02.2005

4.

Transverse
bulkhead
Oil
Tankers

Slide 10

Cracking in stringer toe

18.02.2005

4.

Transverse
bulkhead
Oil
Tankers

Cause for cracking in stringer toe
Compression/tension stresses
from one sided loading

Full cargo tank

Sea
...
Oil
Tankers

Cracks in stringer

4.

Transverse
bulkhead

Crack
Stringer flange

Longitudinal bulkhead
Stringer web

Slide...
Oil
Tankers

Cracks in bottom longitudinals

4.

Transverse
bulkhead

17.

Cracks in toe of transverse bulkhead
bracket en...
Oil
Tankers

Cause - cracks in bottom brackets

4.

Transverse
bulkhead

Crack in bracket
toe (hot spot)

Slide 14

18.02....
Oil
Tankers

Double btm at transverse bulkhead

4.

Transverse
bulkhead

Similarily, one sided alternate loading at the tr...
Oil
Tankers

Crack in transverse bulkhead
stiffeners connection to stringers

Connection of stringer to transverse
bulkhea...
Oil
Tankers

Cause for cracking in transverse
bulkhead stiffeners

4.

Transverse
bulkhead

One sided internal loading fro...
Oil
Tankers

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Longitudinal bulkhead
Side
Bottom
Deck
Transverse bulkh...
Oil
Tankers

Structural build up of
longitudinal bulkhead

5.

Longitudinal
bulkhead plating
with stiffeners

Web frame

S...
Oil
Tankers

Structural functions of long.bhd

5.

Longitudinal
Bulkhead

Watertight integrity
- Resist internal pressure ...
Oil
Tankers

Function : Cargo boundary

5.

Longitudinal
Bulkhead

Internal loads induce shear forces and
bending moments ...
Oil
Tankers

Function: Web in hull girder

5.

Longitudinal
Bulkhead

Longitudinal bulkhead together with ship side is tak...
Oil
Tankers

Characteristic damages

5.

Longitudinal
Bulkhead

1. Cracks in bulkhead longitudinals connection to
stringer...
Oil
Tankers

Crack in long.bhd longitudinals
connection to stringers

5.

Longitudinal
Bulkhead

Connection of longitudina...
Oil
Tankers

Cause for cracking in long.bhd
at stringer connections

5.

Longitudinal bulkhead is flexing depending on the...
Oil
Tankers

Cause for cracking in long.bhd
stringer connections

Full ballast
tank
H
ot

sp

ot

May cause contamination ...
Oil
Tankers

Slide 10

Shear buckling of longitudinal
bulkhead

18.02.2005

Shear buckling is most likely to occur in
area...
Oil
Tankers

Shear buckling of longitudinal
bulkhead

SF maximum at
transverse bulkheads

Longitudinal shear force
distrib...
Oil
Tankers

Cause for shear buckling

5.

Longitudinal
Bulkhead

Result of excessive shear stress in the bulkhead plating...
Oil
Tankers

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Web frames
Side
Bottom
Deck
Transverse bulkhead
Longitu...
Oil
Tankers

Structural build up of web
frame
Web frame flange

Web frames

Cross tie

Slide 2

18.02.2005

6. Web frames
Oil
Tankers

Function of web frames

6. Web frames

- Web frames are supports for the longitudinal stiffeners
- Web frames...
Oil
Tankers

Function of web frame

6. Web frames

• Web frames are supports
for the longitudinals
• Web frames take up lo...
Oil
Tankers

Characteristic damages

6. Web frames

1. Corrosion / buckling of web frame
2. Corrosion / cracking of cross ...
Oil
Tankers

Shear buckling of web frame

High shear stress
SF

SF

Slide 6

18.02.2005

6. Web frames
Oil
Tankers

TYP. WEB SEC. (SHEAR STRESS)
LC 2

Shear buckling may occur in areas
where shear stress is high

Slide 7

18....
Oil
Tankers

Shear buckling of web frame:

Corrosion of web frame
increases the risk for
shear buckling
Corroded cut outs ...
Oil
Tankers

Corrosion of cross tie

Weld connection of straight part
of cross tie to the side and
longitudinal bulkhead

...
Oil
Tankers

Corrosion of cross tie

6. Web frames

Cross ties are subject to both
compression and tension stress
dependin...
Oil
Tankers

Crack in tripping bracket
connection to web frame flange

Weld connection of large curved flanges
and trippin...
Oil
Tankers

Cause for cracking in web frame
flange

6. Web frames

Cracks occur due to additional
bending stresses from t...
Oil
Tankers

Slide 13

FEM plot of cross tie with deflections

18.02.2005

6. Web frames
Oil
Tankers

Cracks in web frame

6. Web frames

•

•

18.02.2005

Increased loads on adjacent
webframes

•

Slide 14

Web...
Bulk
Carriers

Slide 1

Bulk Carriers - Hull Structure

18.02.2005
Bulk

Contents – Bulk Carriers

Carriers

1. Introduction to Bulk carrier hull structure
2. Hull structural breakdown – fu...
Bulk
Carriers

Characteristics for Bulk Carriers

•
•
•
•
•
•
•
•
•
•
•

Single skin / hopper & top-wing tanks
Heavy cargo...
Bulk
Carriers

Bulk Carrier loading flexibility
• Bulk Carrier HC/EA

Reduced flexibility

– Any hold empty at full draugh...
Bulk
Carriers

History

• Built in 1954 - Cassiopeia

• First bulk carrier with hopper
tank – topside tank cross
section

...
Bulk
Carriers

Bulk Carrier particulars
5 cargo holds
7 cargo holds
9 cargo holds

Slide 6

18.02.2005
Bulk
Carriers

Slide 7

Nomenclature

18.02.2005
Bulk
Carriers

Slide 8

Nomenclature

18.02.2005
Bulk
Carriers

Structural breakdown of hull

-

A vessel’s hull can be divided into different hull
structural elements

-
...
Bulk

Typical damages and repairs

Carriers

WWW.witherbys.com

Slide 10

18.02.2005
Bulk
Carriers

Structural breakdown of Bulk Carrier
7.

Hatch coaming & cover
3.

4.
1.

5.

Topside tank

Transverse bulk...
Bulk

Hull Structural Breakdown

Carriers

1.

Side

2.

Bottom

3.

Deck

4.

Transverse bulkhead

5.

Hopper tank

6.

T...
Bulk
Carrier

1.
2.
3.
4.
5.
6.

Slide 1

Hull Structural Breakdown Ship side
Side
Bottom
Deck
Transverse bulkhead
Hopper ...
Bulk
Carrier

Structural functions of ship side

1.

1. Watertight integrity (local strength)
- Resist external sea pressu...
Bulk
Carrier

Structural build up of ship side

1.

Upper
bracket
Side plating
Side
frames
Lower
bracket

Slide 3

Side
Bulk
Carrier

Structural functions of ship side

1.

Watertight integrity (local strength)
Ship side must withstand static...
Bulk
Carrier

Functions of ship side

Watertight integrity (local strength)
Lateral loads induces shear forces
and bending...
Bulk
Carrier

Functions of ship side

1.

Side

Ore hold load response;
Net load down cause rotation of hopper tank struct...
Bulk
Carrier

Functions of ship side

1.

Side

Bm

Bm

Empty hold load response;
Net load up cause rotation of hopper tan...
Bulk
Carrier

Functions of ship side

1.

Side

Web in hull girder (global strength)
Ship side is taking up
global shear f...
Bulk
Carrier

Function of ship side (longitudinal shear strength)
Shear Distribution at a

0

Sagging

Bending force
Shear...
Bulk
Carrier

Functions of ship side

1.

Side

Web in hull girder (global strength)
- Global shear forces are distributed...
Bulk
Carrier

Hull damages in ship side

1.

Two characteristic damages for ship side:
1.
2.

Slide 11

Cracks in side fra...
Bulk
Carrier

Crack in side longitudinal web frame
connection

1.

Side

Cracking in vertical side frame:

Vertical side f...
Bulk
Carrier

Cause for cracking in vertical side
frames lower bkt. connections

1.

1b.

1a.

The dynamic loads from the ...
Bulk
Carrier

Crack in side longitudinal web frame connection
Possible consequence
1.
Side
•

As these cracks develop, the...
Bulk
Carrier

Corrosion of side frames and lower
bkt. connection

1.

Side frames and bkt’s are prone to
corrosion, both g...
Bulk
Carrier

Revised Minimum Thickness List
Torig

Hold 1:
Aft end of Hold 1:
Upper bracket web
Frame web, middle and upp...
Bulk
Carrier

Corrosion of side frames and lower
bkt. Connection – Consequences

• General corrosion of side frames reduce...
Bulk
Carrier

Damage impact on function

1.

Cracks in vertical side frame
- may increase moment in field for frame
- may ...
Bulk
Carrier

1.
2.
3.
4.
5.
6.

Slide
1

Hull Structural Breakdown Bottom
Side
Bottom
Deck
Transverse bulkhead
Hopper tan...
Bulk
Carrier

Structural functions of bottom

2.

Bottom

1. Watertight integrity (local strength bottom / inner bottom)
-...
Bulk
Carrier

Structural build up of bottom

Longitudinal girders
Floor
Slide
3

Pipe tunnel

2.

Bottom
Bulk
Carrier

Structural functions of bottom

2.

Bottom

1. Watertight integrity (local strength)
Bottom plate must withs...
Bulk
Carrier

•

Structural functions of bottom
Stress distribution in a double bottom structure
•

Forces are taken up by...
Bulk
Carrier

Functions of inner bottom (local

2.

Bottom

stiffener level)

Cargo hold boundary (local strength)
Externa...
Bulk
Carrier

Load response double bottom

2.

Bottom

Stresss flow
shortest way to
support

Cont.

Slide
7
Bulk
Carrier

Double bottom girders load response

2.

Bottom

• girders & floors carry the net load to hopper tank and
tr...
Bulk
Carrier

Functions of double bottom girder

Net Load on double bottom

Simple
beam
model

Longitudinal girders repres...
Bulk
Carrier

Floors / girders- design

2.

Bottom

Long. Db.
girder
High Shear force – No
cut-outs / increased
thickness
...
Bulk
Carrier

2.

Functions of bottom

Bottom

2. Bottom flange in hull girder (global strength)
The bottom and inner
bott...
TM

Bending moment

Bulk
Carrier

Moment diagram

Reduced global
bending but high
double bottom
stresses
Still water bendi...
Bulk
Carrier

Highly stressed areas

2.

Bottom

Deck

Tanktop

+

NA

Inner bottom level

Bottom

Bottom

Global bending
...
Bulk
Carrier

Hull damages bottom / inner
bottom

2.

Bottom

Three characteristic damages for bottom are:
1.
2.

Crack / ...
Bulk
Carrier

Cracks in way of hopper knuckle

2.

• Heavy ballast condition – tension in inner bottom plate

Fractures

S...
Bulk
Carrier

Cracks in way of hopper knuckle

Hopper plate

Inner bottom plating
Slide
16

2.

Bottom
Bulk
Carrier

Cracks in way of hopper knuckle
Impact on function

2.

Bottom

• Loss of watertight integrity – leak ballas...
Bulk
Carrier

Fractures in connection of
floors i.w.o. hopper

Damage bottom
Inner
Fractures

Repair
A

2.

Full penetrati...
Bulk
Carrier

Crack in floor

2.

• Floor in way of high shear stress
• Connection at bottom longitudinals
Repair A
Lug

D...
Bulk
Carrier

Crack in floor impact on function

2.

Bottom

• Loss of support of longs – increased stresses at
adjacent f...
Bulk
Carrier

Slide
21

Indents of inner bottom plate

2.

Bottom
Bulk
Carrier

Indents of inner bottom plate

2.

Impact on function

• Difficult with discharge of cargo – cleaning
• Seve...
Bulk
Carrier

Fracture in longitudinals at stool
connection

Damage

Bottom

Cause
Stool
Inner bottom
longitudinal

Fractu...
Bulk
Carrier

Fracture in longitudinals at
stool connection

2.

Bottom

Repair
Stool

Too large brackets may cause
furthe...
Bulk
Carrier

Fracture in longitudinals at
stool connection

Damage

Repair

Stool
Inner bottom

Modified brackets
with so...
Bulk
Carrier

1.
2.
3.
4.
5.
6.
7.

Slide 1

Hull Structural Breakdown - Deck
Side
Bottom
Deck
Transverse bulkhead
Hopper ...
Bulk
Carrier

Structural functions of deck

1. Watertight integrity (local strength)
- Resist external sea pressure
2. Tra...
Bulk
Carrier

Structural build up of deck

• Main deck outside line of hatches
• Deck between hatches
• Longitudinal hatch...
Bulk
Carrier

Structural functions of deck

1. Watertight integrity (local strength)
Deck plate must withstand static and ...
Bulk
Carrier

•

Slide 5

Structural functions of deck
Stress distribution in deck

3.

Deck
Bulk
Carrier

•

Structural functions of deck
Deck between hatches

Flexing in transverse direcction

Slide 6

3.

Deck
Bulk
Carrier

Structural functions of deck

3.

• The element contributing to transverse strength:
– Deck plate and transv...
Bulk
Carrier

3.

Functions of deck

Deck

2. Upper flange in hull girder (global strength)
The deck plating and
longs out...
Bulk
Carrier

Hull damages deck

3.

Deck

Characteristic damages for deck are:
1.
2.

Buckling of deck between hatches

3...
Bulk
Carrier

Crack in deck plate at
hatch coaming end

3.

Deck

• Longitudinal stresses are going into the side hatch co...
Bulk
Carrier

Buckling of deck between hatches

3.

• Ore carrier (250 000 DWT) Local buckling of deck
plates and transver...
Bulk
Carrier

Slide 12

Buckling of deck between hatches

3.

Deck
Bulk
Carrier

Buckling of deck between hatches

3.

• Buckling caused by excessive stresses in
transverse direction deck b...
Bulk
Carrier

Buckling of deck between hatches

3.

• Possible consequences of buckling of deck
between hatches:
- Ships t...
Bulk
Carrier

Hull Structural Breakdown Bulkhead

1.

Side

2.

Bottom

3.

Deck

4.

Transverse bulkhead

5.

Hopper tank...
Bulk
Carrier

Structural functions of bhd.

1. Cargo hold boundary (local strength)
- Resist internal pressure from cargo ...
Bulk
Carrier

Structural build up of deck

4.

Bhd.

Corrugated bhd.
Lower stool
Upper stool

Slide 3
Bulk
Carrier

Structural build up of deck

4.

Bhd.

Upper stool diaphragm
Hatch coaming bkt
Lower stool diaphragm
Shedder...
Bulk
Carrier

Structural functions of bhd.

1. Cargo hold boundary (local strength)
Transverse bhd. plate must withstand s...
Bulk
Carrier

Slide 6

4.

Bhd.
Bulk
Carrier

Structural functions of bhd.

4.

Bhd.

Design load conditions
• Water flooding
• ” Light cargo ” full hold
...
Bulk
Carrier

Structural functions of bhd.

flange

Web

Slide 8

4.

Bhd.
Bulk
Carrier

Structural functions of bhd.

Moment

4.

Bhd.

One sided load on bhd. Introduce a moment
in lower stool.
Si...
Bulk
Carrier

Structural functions of bhd.

4.

Bhd.

• Transverse bhd. Supports the double bottom long. girders

Moment o...
Bulk
Carrier

Structural functions of bhd.
•

Transverse bhd. Carry
global shear from
double bottom to ship
side

Net load...
Bulk
Carrier

Structural functions of bhd.

• Upper and lower stool transverse strenght of hull

Flexible part

Slide 12

...
Bulk
Carrier

Hull damages transverse
bulkhead

4.

Bhd.

Two characteristic damages for transverse bulkheads:
1.
2.

Slid...
Bulk
Carrier

4.

Collapse of transverse bulkhead

Capesize Bulk Carrier 9 holds – 20 years
•

Loaded with pellets alterna...
Bulk
Carrier

Bulk Carrier loaded with pellets
1.

2.

3.

Slide 15

4.

Collapse of transverse bulkhead

Bhd.

LO W
E
DIA...
Bulk
Carrier

Collapse of transverse bulkhead
Impact on function

• No boundary between cargo holds
• Transverse strength ...
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Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
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Dnv   hull structure course
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Dnv   hull structure course
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Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
Dnv   hull structure course
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Transcript of "Dnv hull structure course"

  1. 1. Hull Structure Course DNV 2005
  2. 2. How are the loads taken up by the structure? Consequence of a crack in this detail? Where is it likely to find cracks?
  3. 3. 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.
  4. 4. Hull Structure Course Purpose: To train technical personnel about the basics of hull structure. Target group is technical personnel within ship owner / manager organization in need of improved competence in structural matters, with special focus on Bulk Carriers and Oil Tankers.
  5. 5. Course breakdown: Day 1 • • • • Day 2 • • Day 3 • Day 4 • • Introduction Single beams & loads Structural connections Hull structure failure types Fore & aft ship Hull structural breakdown Oil Tanker Hull structural breakdown Bulk Carrier Fore & aft ship Hull structural breakdown Container Carrier
  6. 6. Agenda day 1 09.00-09.15 09.15-09.45 10.00-11.30 11.30-12.30 Welcome & Introduction Expectation & presentation of participants Beams + Buzz group Loads 12.30-13.15 Lunch 13.15-14.15 14.15-15.45 15.45-16.45 16.45-17.45 17.45-18.00 Structural connections Failure mode fatigue Buckling & Indent Corrosion Review questions
  7. 7. Agenda day 2 09.00 – 09.15 09.15 – 10.30 10.30 – 10.45 10.45 – 11.00 11.00 – 11.45 11.45 – 12.15 Answers to review questions Structural breakdown fore and aft ship Introduction to tank Coffee break Ship side & longitudinal bulkhead Webframes 12.15 – 13.00 Lunch 13.00 – 13.30 13.45 – 14.30 14.30 – 15.00 15.00 – 15.15 15.15 – 16.15 16.15 – 16.45 16.45 – 17.00 Case: Oil Tanker Part A Deck Bottom Coffee break Case: Oil Tanker Part B Transverse Bulkhead Review quiz
  8. 8. Agenda day 3 09.00 - 09.30 09.30 - 10.00 10.00 - 10.45 10.45 – 11.00 11.00 - 11.45 11.45 - 12.15 Answers to review questions Introduction to Bulk Side Coffee break Bottom Deck 12.15 - 13.00 Lunch 13.00 - 13.45 13.45 - 14.30 14.30 - 15.00 15.00 – 15.15 15.15 - 15.45 15.45 – 16.30 16.30 - 17.00 Case: Side hold no 1 Transverse Bulkhead Hopper tank & topside tank Coffee break Hatch coaming & covers Case: Ore Carrier Review Quiz and closing
  9. 9. Agenda day 4 09.00 - 09.30 09.30 - 10.30 10.30 - 11.00 11.00 – 11.15 11.15 – 12.15 Answers to review questions from day 1 Structural breakdown fore and aft ship Introduction – Container Carriers Coffee break Bottom and Ship Sides 12.15 - 13.00 Lunch 13.00 – 14.00 14.00 – 15.00 15.00 - 15.15 15.15 – 15.45 15.45 – 16.00 16.00 – 16.30 Hatch Covers, Deck & Hatch Coamings Case: Container Carriers Coffee Break Bulkheads Closing Review Quiz
  10. 10. Module 2: Basic Hull Strength Slide 1 Basic Hull Strength
  11. 11. Objectives Basic Hull Strength 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 the corresponding shear forces and bending moments. Slide 2
  12. 12. Simple beam properties Basic Hull Strength Bending moment Load A Compression Section A-A A Tension Shear force 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. 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. Slide 3
  13. 13. Simply supported beam - concentrated load L/2 ℓ Basic Hull Strength F Single beam with concentrated load, simply supported ends F/2 Shear Force F F/2 Q=F/2 Q=F/2 Bending Moment L/2 M=Q x ℓ Slide 4
  14. 14. Simply supported beam – distributed load Basic Hull Strength p Single beam with distributed load, simply supported ends pL/2 Shear Force L pL/2 Q=pL2 Q=pL/2 Bending Moment M=pL2/8 Slide 5
  15. 15. Beam with fixed ends - distributed load Basic Hull Strength No rotation! p Single beam with distributed load, fixed ends pL/2 Shear Force L pL/2 Q=pL/2 Q=pL/2 Bending Moment 2 M=pL /12 2 M=pL /24 Slide 6
  16. 16. Beam with spring supported ends Basic Hull Strength p Spring k k Spring Shear force and bending moment distribution varies with degree of end fixation (spring stiffness) Degree of end fixation = 0 Degree of end fixation = 1 Slide 7 Simply supported Fixed ends
  17. 17. End fixation Basic Hull Strength Structural clamping – spring support Symmetrical load – full fixation Slide 8
  18. 18. Beam – fixation at ends Basic Hull Strength • Load on structure is important with regard to fixation bottom longs connection to transverse bulkhead Symmetric load gives full fixation Non symmetry in loads gives less fixation or even forced rotation Slide 9 Empty Empty Loaded
  19. 19. Axial stress Basic Hull Strength Force Stress = Force Area Area σ = ε x E (Hook’s Law) ε : Relative elongation Youngs modulus E: (2,06E5 N/mm² - steel) Slide 10
  20. 20. Stress levels – elastic & inelastic region Elastic region: σ < σyield - A beam exposed to a stress level below the yield stress, will return to its original shape after the load is removed, Simple beam theory valid In-elastic region: σ σ fracture Yield = > σyield Inelastic region - A beam exposed to stresses above the yield stress will have a permanent deformation after removing the load (yielding, buckling, fractures) ε (elongation) Elastic region Slide 11 Basic Hull Strength σ=ε*E
  21. 21. High Tensile Steel (HTS) Basic Hull Strength 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 Slide 12 MS HT28 HT32 HT36 HT40
  22. 22. Bending stress - Simple beam with load A R1 F A A A R2 Area effective in transferring the bending of the beam n.a Section A-A Slide 13 Distribution of stress caused by bending Max stress at flanges. Zero stress at neutral axis: Basic Hull Strength
  23. 23. Shear stress - Simple beam with load A R1 F A A A R2 Distribution of the stress Area effective in transferring load to the supports Max shear stress at neutral axisis of profile: Section A-A Slide 14 Basic Hull Strength
  24. 24. Bending and shear stress flow A R1 A F Basic Hull Strength A A R2 Compression Bending stress is transferred in the Tension flanges, σ Shear stress is transferred in the web, τ Section A-A Slide 15
  25. 25. Beam stiffness and section modulus Basic Hull Strength As the axial stresses are transferred in the flange of a beam, it is the flange area that is governing a beam’s ‘bending stiffness’ Aflange y Bending Stress: b n.a l M σ= ZX y1 x Section modulus: Moment of Inertia: Ix Zx = y1 1 3 2 I x = bl + 2 A flange y1 12 The ‘Section Modulus’ is expressing the beam’s ability to withstand bending Slide 16
  26. 26. Shear stress & shear area Basic Hull Strength The load is carried in shear towards the supports by the web Shear force : n.a Slide 17 h As = h ⋅ t Shear stress: t Q Shear area : y Q τ= As x
  27. 27. Conventional profiles in ship structures Basic Hull Strength Flatbar (slabs) Easy with regard to production, flatbar stiffeners have poor buckling strength properties, low section modulus mostly applied in deck and upper part of side - long. bhd. Angle bar (rolled and welded) Angle bar will twist when exposed to lateral load due to nonsymmetric profile. This effect gives additional stress at supports due to skew bending. Angle bars are more prone to fatigue cracking than symmetrical profiles (Ref. sketch next page) Due to the skew bending, which gives a moment in the web-plate at welded connection to the plate, angle bars are also more critical with regard to grooving (necking) corrosion. Slide 18
  28. 28. Angle bar (rolled / built up) 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 POSTFEM 5.6-02 MODEL: T1-1 DEF = 203 4: LINEAR ANALYSIS NODAL DISPLACE ALL MAX = 1.46 MIN = 0 SESAM 5 SEP 2 Side longs internal pressure Additional bending stress in web Z Y X Slide 19 1.39 1.32 1.25 1.18 1.11 1.04 .974 .905 .835 .766 .696 .626 .557 .487 .418 .348 .278 .209 .139 .696E-1
  29. 29. Conventional ship structure profiles Basic Hull Strength Bulb profile (single / double bulb) Bulb profiles are favourable with regard to coating application. Single bulb which is most common will (as for the L-profile) have some skew bending when exposed to lateral load. T- Profile The T-profile is symmetrical and will not be prone to skew bending. Favourable with regard to fatigue strength. The profile may have large section modulus. Some T-profiles on single skin VLCC’s have been found critical with regard to buckling due to a high and thin web-plate with a small flange on top. Slide 20
  30. 30. Hierarchy of hull structures Plate – Stiffener – Stringer / girder – Basic Hull Strength Panel – Stresses in a hull plate due to external sea pressure, are transferred further into the hull structure through the hierarchy of structures. Slide 21 Hull
  31. 31. Level 1: Plate - simple beam Basic Hull Strength Stiffener NO ROTATION Plating Water pressure A strip of plating considered as a beam with fixed ends and evenly distributed load Slide 22 PLATE AS A BEAM
  32. 32. Level 2 Longitudinal - simple beam Basic Hull Strength Longitudinal between two web frames Max shear and bending moment at supports (web frames) Symmetric load fwd and aft of web frames gives no rotation fixed ends Slide 23
  33. 33. Level 3 : Transverse web - simple beam Basic Hull Strength Beam with fixed ends and concentrated loads from the bottom longitudinals SF Slide 24 BM Max shear and bending moment towards ends (side & long bhd.)
  34. 34. Level 3 Longitudinal girder with transverse webframes Basic Hull Strength Longitudinal girder between two transverse bulkheads Max shear and bending moment towards transverse bulkheads Single beam with fixed ends and concentrated loads from the transverse web frames Max Shear and bending moment towards ends Slide 25
  35. 35. Beams, load transfer Basic Hull Strength Double bottom structure Loads taken up by the bottom plating are transferred through the hierarchy of structures into the hull Side girder Floor / transverse bottom girder Centre girder Stiffeners supported by floors Slide 26
  36. 36. Beams, load transfer Basic Hull Strength Longitudinal bulkhead Single skin structure Loads taken up by the bottom plating are transferred through the hierarcy of structures into the hull Transverse bottom girder /web frame Bottom longitudinals with plating Slide 27 CL girder
  37. 37. Damage 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! Slide 28 Basic Hull Strength
  38. 38. Single beam VS Hull girder Basic Hull Strength A vessel’s 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 hull The term ‘Hull girder’ is used when thinking of the hull as a single beam Single beam Hull Slide 29
  39. 39. Hull girder bending Basic Hull Strength When a vessel’s hull is exposed to loading, it will bend similarly as a single beam Slide 30
  40. 40. Single beam VS Hull girder A A F A A Bending stress, σ Compression Tension Hull Girder Section A-A Shear stress, τ Deck and bottom acts as flanges in the ‘hull girder’, while ship sides and longitudinal bulkheads, act as the web Slide 31 Basic Hull Strength
  41. 41. Stress hierarchy in ship structure Local stress : Girder stresses: Hull girder stresses; Slide 32 Basic Hull Strength Plate / stiffener Webframes / Girders /Floors Deck & bottom / Side / long. Bhd.
  42. 42. Case Module 2: Loads Buzz Groups Basic Hull Strength • 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 Slide 33
  43. 43. Case Module 2: Beams Buzz Groups Basic Hull Strength • Is it correct that the transverse girders are supported by the longitudinal stiffeners? • Are the longitudinals inside a tank structure for example bottom longitudinals between webframes normally fixed or simply supported? Slide 34
  44. 44. Summary: Beams • • • • • Basic Hull Strength 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 and end fixation • Profile types and properties • Structural hierarchy plates-stiffeners-girder-panel Slide 35
  45. 45. Loads acting on a ship structure Slide 36 Basic Hull Strength
  46. 46. Loads acting on a ship structure 1. Internal loads: - Cargo - Ballast - Fuel - Flooding - Loading/unloading 2. External loads: - Sea - Ice - Wind Slide 37 Basic Hull Strength Anchor
  47. 47. Static and Dynamic loads Static local load: Basic Hull Strength 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 Shear Force Wave loads: Dynamic Bending Moment and Shear Force Slide 38
  48. 48. Static and Dynamic loads Basic Hull Strength Total external local load acting on a vessel: Static Max at the bottom Dynamic Max around the waterline Note the relative size of static / dynamic pressure is not to scale! Slide 39
  49. 49. Sea Pressure – static and dynamic contribution Basic Hull Strength Plotted sea pressure curve is a sum of the static and dynamic contribution p (kN/m2) Constant in the midship area, increasing towards ends aft fwd Local sea pressure (example for a bottom longitudinal) Slide 40
  50. 50. Static and Dynamic loads 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 Slide 41
  51. 51. Loads on foreship Basic Hull Strength Bow Impact Pressure •Induced by waves, vessel speed, flare and waterline angle important factors •Dominant for ship sides in the bow at full draught Bottom Slamming Pressure •Induced by waves in shallow draft condition (ballast condition) •Dominant for flat bottom structure forward Slide 42
  52. 52. Loads on deck Slide 43 Green Seas Loading: • Dominant for hatch covers and fwd deck structure (incl. deck equipment, doors, openings etc) Basic Hull Strength
  53. 53. Weights and buoyancy Basic Hull Strength Weight distribution of cargo and fuel Steel weight, equipment and machinery Buoyancy Slide 44 Static Dynamic
  54. 54. Bulk Carrier typical load Static external sea pressure Dynamic external sea pressure Slide 45 Basic Hull Strength Static internal load from cargo Dynamic internal load from cargo
  55. 55. Net load on structure – ‘Ore hold’ Internal load - External load = Net load on double bottom Static and dynamic internal load from cargo Slide 46 Static and dynamic sea pressure Basic Hull Strength
  56. 56. Net load on structure - empty hold Net load from sea pressure Slide 47 Static and dynamic sea pressure Basic Hull Strength
  57. 57. Alternate loading condition Slide 48 Basic Hull Strength
  58. 58. Weights and buoyancy Basic Hull Strength Buoyancy and weights are not evenly distributed along a ships length… …hence, a global shear force and bending moment distribution is set up on the hull girder Slide 49
  59. 59. Hull girder still water bending moment and shear force Basic Hull Strength Slide 50 Example: SF and BM distribution for a double hull tanker in a fully loaded condition
  60. 60. Total BM acting on a vessel Basic Hull Strength Total hull girder bending moment MTotal = Mstill water + M wave Slide 51 Hogging Sagging BM limits Mtotal Mstill water Mwave
  61. 61. Case 2 Module 2 – Loads/Materials Basic Hull Strength • 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 sea pressure 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? Slide 52
  62. 62. Summary: Loads • • • • • Slide 53 Static & dynamic Internal & external Load distribution Net load Longitudinal strength SF & BM Basic Hull Strength
  63. 63. Basic Hull Strength End of Module 2: Basic Hull Strength Slide 54
  64. 64. Module 3: Structural Connections Module 3: Structural Connections • Objectives of this Module: After completion of this module the participants should have gained: • • • Slide 1 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
  65. 65. Contents • • • • • Slide 2 Types of welds Connections of stiffeners Connections of girders/web frames Connections between panels Design details Module 3: Structural Connections
  66. 66. Module 3: Weld Types Structural Connections We will briefly touch upon the following types: • Fillet welds • Full penetration welds (Full pen) (Ref. Rules Pt.3 Ch.1 Sec.11) Slide 3
  67. 67. Module 3: Weld Types – Fillet welds Structural Connections Throat thickness Fillet welds: • The most common type Leg length Transferring shear forces (between profile and plate) • Building welded sections • Connections to other members • NDT by magnetic particle or dye penetrant Slide 4 Throat thicknessmeasure 3.5 mm = leg length 5.0 mm
  68. 68. Module 3: Weld Types – Full penetration Structural Connections Full penetration welds: • To be used where stress level normal to the weld is high t Gap <3 mm Throat thickness Root Face 2-4 mm for full penetration welds σ Slide 5 Transferring shear forces and forces normal to the weld • Connections to other members in highly stressed locations • NDT by ultrasonic, dye penetrant or magnetic particle
  69. 69. Module 3: Connections of stiffeners • What forces are to be transferred? L Shear Force Bending Moment Slide 6 Structural Connections
  70. 70. Load from stiffener to webframe How arethe How is the forces transferred from the stiffener to webframe Slide 7 Module 3: Structural Connections
  71. 71. Module 3: Connections of stiffeners Web fr. Slide 8 Stiffener Web fr. b) a) + + + c) d) Web fr. + Structural Connections
  72. 72. Module 3: Connections of stiffeners Structural Connections Effect of brackets on the max bending stress No or negative effect = Slide 9 =
  73. 73. Connections of stiffeners Web-plating Stiffener Slide 10 = Structural Connections Common crack locations in longitudinal Longitudinal = Module 3:
  74. 74. Static stress in stiffener on top Module 3: Structural Connections Stress distribution for different details ballast σx Slide 11 loaded σx
  75. 75. Connections of stiffeners Common crack locations Web-plating Stiffener Longitudinal = = Design improvement Slide 12 Module 3: Structural Connections
  76. 76. End-brackets on girders - forces Empty Wing Tank Structural Connections Full Centre Tank Net load Slide 13 Module 3: Net load
  77. 77. End-brackets on girders Module 3: Structural Connections Improved design Transverse welding of flange outside curved area a Increased stress at support bkts. i) i iii iii) iiib) High Stress Areas High Stress Areas Soft bkts. recommended High Stress Areas iv) ii) ii Slide 14 Flange attached and supported
  78. 78. Stringer connection to inner side Module 3: Structural Connections Repair Original Design Inner side Ship side Stringer Trv. Bhd. Crack Slide 15 Original thickness 16mm Insert 20 to 25 mm Bracket with thickness 20 to 25 mm
  79. 79. End-brackets on girders Module 3: Structural Connections Girder bracket Typical crack location Ref. iii b) previous fig. Slide 16
  80. 80. Module 3: Cross-Ties Full Centre Tank Empty Centre Tank Full Centre/Empty Wing at full draught = Max. Compression in Cross Tie Empty Centre/Full Wing at ballast draught = Max. Tension in Cross Tie Slide 17 Structural Connections Empty Full Wing Wing Tank Tank
  81. 81. Module 3: Knuckles Structural Connections helikopter Out of plane forces Deformation/low stiffness Slide 18
  82. 82. Knuckles Module 3: Structural Connections Support as close to the knuckle as possible Slide 19
  83. 83. Knuckles Module 3: Structural Connections Vertical Brackets Slide 20
  84. 84. Module 3: Knuckles Crack in shell plate at knuckle: New Brackets Slide 21 Structural Connections
  85. 85. Module 3: Knuckles Structural Connections Crack Locations Stress Concentrations In way of Webs Slide 22
  86. 86. Module 3: Knuckles Structural Connections Preferred design: • No misalignment in the connection. • No lugs or scallops Slide 23
  87. 87. Module 3: Intersecting Hull Elements Crossing Panel - No bracket Structural Connections Crossing Panel - With bracket Panel 2 Panel 1 Connecting area ~ (a+b) · t Connecting area ~ t · t b t t a Slide 24
  88. 88. Module 3: Intersecting Hull Elements Structural Connections TOP SIDE TANK NO. 7 ENGINE ROOM BULKHEAD DIESEL SUPPLY TANK Cracks ENGINE ROOM BULKHEAD CRACKS LONGITUDINAL WING TANK CRACKS STR BK TANK TOP BULKHEAD iv iii T. ENGINE ROOM BULKHEAD A EXISTING BRACKET TO BE REMOVED ADDITIONAL BRACKET NEW BRACKETS IN LINE WITH BOTTOM PLATE IN TOP SIDE TANK A ENGINE ROOM BULKHEAD SLANTING TANK TOP PLATING ENGINE ROOM BULKHEAD Slide 25 LONGITUDINAL BULKHEAD Section A-A A-A Reinforcements TO BE IN LINE
  89. 89. Notches, Drain/Lightening Holes i) Crack Common notch in way of weld Slide 26 Reduced risk of cracking Module 3: Structural Connections iii) Notch away from weld
  90. 90. Module 3: Summary module 3 • • • • • • • Slide 27 Welding Connection stiffener – girder Girder – panel Cross tie Knuckles Intersection of plates / panels Cut-outs and notches Structural Connections
  91. 91. Module 5 Hull Structural Breakdown Oil Tanker Bulk Carrier Container Ship Slide 1
  92. 92. Hull Structural Breakdown Oil Tanker – Bulk Carrier – Container Ship Objective of Module 5: After completion of this module the participants should have gained: • Understanding of hull structural design for Oil Tankers, Bulk Carriers and Container Ships through application of basic hull strength theory • Slide 2 Knowledge of typical structural damages and their consequences
  93. 93. Contents of Module 5 1. Fwd and aft structural parts 2. Oil Tankers – structures in cargo area 3. Bulk Carriers – structures in cargo area 4. Container Ship – structures in cargo area Slide 3
  94. 94. Fore ship Contents – Fwd and aft structural parts 1. Hull structure breakdown – fwd part of ship 2. Hull structure breakdown – aft part of ship 3. Slide 4 Case
  95. 95. Fore ship Structural functions of fore ship 1. Watertight integrity (local strength) - Resist external sea pressure / Bow impact / bottom slamming - Resist internal pressure from ballast 2. Web in hull girder (global strength) - Side plating act as the web in the hull girder beam Slide 5
  96. 96. Fore ship Structural build up fore ship Collision bhd. Chain locker Stringer decks Breast hook Side webframes Bulbous bow Slide 6
  97. 97. Fore ship Structural build up fore ship Vertical side frames Slide 7 Horizontal side longs
  98. 98. Fore ship Structural functions of fore ship • • Slide 8 • Shell side must withstand static and dynamic loads from external sea pressure. Bow impact and bottom slamming introduce additional loads Internal pressure from ballast
  99. 99. Fore ship Structural build up fore peak Horizontal stiffening Plate supported by side longs Side longs supported at webframes Webframes supported at stringer flats BM and SF distribution for a single beam with distributed load and fixed ends Slide 9
  100. 100. Fore ship Structural build up fore peak Horizontal stiffening Reduced efficiency due to flare angle Slide 10
  101. 101. Fore ship Structural build up fore peak Vertical stiffening Plate supported by side frames Side frames supported by stringer flats SF Slide 11 Bm
  102. 102. Fore ship Functions of fore peak global strength 2. Web in hull girder (global strength) • Ship side / longitudinal swash bulkhead carry global shear forces from net load in fore peak to the collision bhd. Side plating is acting as web in the hull girder beam Full draught with empty fore peak most critical Cont. Slide 12
  103. 103. Fore ship Functions of fore peak Global strength 2. Deck and Bottom in hull girder (global strength) - The global bending moments are always zero at fwd / aft end. - The longitudinal stresses in deck and bottom are moderate in fore structure - If large flare – wave induced compression stresses in deck may critical Slide 13
  104. 104. Fore ship Hull damages in fore ship Characteristic damages fore ship 1. 2. Buckling of stringers 3. Bow impact 4. Damages to the wave breaker 5. Slide 14 Corrosion – lost ship side fore peak Bottom slamming Fore ship specially prone to hull damages. Of top 10 damages on tankers are 6 of them in the fore ship!
  105. 105. Fore ship Lost shipside Oil Tanker 357 000 DWT built 1973 20 years Heavy local corrosion Experience feedback • Local heavy corrosion – increase stress level - reduced buckling strength • local buckling stiffener collapse – web frame buckling/collapse Slide 15 • Side longs double span – overload and collapse
  106. 106. Fore ship Lost shipside - Impact of function Oil Tanker 357 000 DWT built 1973 20 years • Shell side lost its watertight integrity • Lost buoyancy – increased fwd. draught – impact on longitudinal strength • Reduced shear carrying capacity for hull girder • Collision bhd. Exposed to dynamic sea loads Slide 16
  107. 107. Fore ship Slide 17 Buckling of stringer in fore peak tank Oil Tanker 302,419 DWT built 1992 Buckling of stringers in fore peak tank (after 1 year) Buckling in stringer no 1, 2 & 3 in fore peak tank. Stringer no 1 shown, other stringers similar buckling pattern
  108. 108. Fore ship Buckling of stringer in fore peak tank Oil Tanker 302,419 DWT built 1992 Buckling of stringers in fore peak tank (after 1 year) Stringer as beam Local web buckling due to lateral load axial stress in web Buckling of stringer due to high shear / compression stresses Experience feedback Slide 18
  109. 109. Fore ship Buckling of stringer Impact of function Oil Tanker 302,419 DWT built 1992 Buckling of stringers in fore peak tank (after 1 year) • Buckled / deformed stringers may develop cracks penetrating the shell – cause leak – 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 loads may collapse and ship side collapse – flooding of fore structure. Slide 19
  110. 110. Fore ship Bow Impact Damage Container ship 1 year A recent damage in 2001….. Occurred during the first year of operation Slide 20
  111. 111. Fore ship Slide 21 Bow Impact Damage Container ship 1 year
  112. 112. Fore ship Bow Impact Damage Container ship 1 year Bow impact: Peak pressure Important factors: Flare angle, α Waterline angle, β Height above waterline Vessel speed Roll and pitch α Sea Pressure: ”Evenly” distributed β Slide 22 h0
  113. 113. Fore ship Bow Impact Damage Container ship 1 year Local plate buckling Slide 23
  114. 114. Fore ship Bow Impact Damage Impact of function Container ship 1 year • Buckled plating may lead to leakage • Damages to longitudinals may reduce their load carrying capacity • Damages to stringers and webs could lead to reduced support of longitudinals which again may lead to ship side collapse and flooding. Slide 24
  115. 115. Fore ship Bottom slamming fore ship Bulk Carrier 220 000Dwt Built 1997 • Bottom plate set in • Bottom longs tripped ( L-profiles) • Webframes buckled between longs and access holes Slide 25
  116. 116. Fore ship Bottom slamming fore ship Plates set in and punctured Floors twisted and damaged Mostly for small ships in ballast condition Slide 26 Feeder L = 100 m
  117. 117. Fore ship Bottom slamming fore ship Feeder L = 100 m Parametres: T BF = Ballast draught forward. Increasing ballast draught B B = Breadth of flat bottom. “V” shape forward reduces slamming load. X = Distance from FP. Pitch component of relative velocity, and therefore slamming load, decreases with distance from FP decreases slamming load. Slamming Pressure Slide 27 Slamming Pressure
  118. 118. Fore ship Bottom slamming Impact of Function • Bottom longs tripped will not efficiently support plate – Bottom plate + longs will be set in – In plane buckling capacity significantly reduced • not critical in this area due to low vertical bending moment • Bottom floors buckled, webframes reduced their load carrying capacity • Loss of watertight integrity – flooding possible scenario – impact on trim - draught Slide 28
  119. 119. Aft ship Contents – Fwd and aft structural parts 1. Hull structure breakdown – fwd part of ship 2. Hull structure breakdown – aft part of ship 3. Slide 29 Case
  120. 120. Aft ship Structural build up aft ship Transom stern plate Engine room bulkhead Webframes Floors Slide 30
  121. 121. Aft ship Structural build up aft ship Engine room platform Side plate & longitudinals Webframe side Webframe deck Slide 31
  122. 122. Aft ship Structural build up aft peak tank Horizontal side longs Slide 32 Vertical side frames
  123. 123. Aft ship • • • Slide 33 Structural functions of aft ship Shell must withstand static and dynamic sea pressure, bottom slamming may introduce additional loads Internal pressure from ballast Dynamic impulses from the propeller Loads are taken up by the hull plating, stresses are transferred from plate to stiffener
  124. 124. Aft ship Functions of aft ship Web in hull girder (global strength) 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 Global loads are acting on the hull girder beam Side plating is acting as web in the hull girder beam Cont. Slide 34
  125. 125. Aft ship Functions of Aft ship 2. Deck and Bottom in hull girder (global strength) - The global bending moments are always zero at fwd / aft end - The longitudinal stresses in deck and bottom are moderate in fore peak Slide 35
  126. 126. Aft ship Functions of Aft ship • Ensure adequate stiffness for: – Main engine support (double bottom engine room) – Steering gear support (steering gear flat / aft peak) – Rudder horn (aft peak structure) Slide 36
  127. 127. Aft ship Hull damages in aft ship Characteristic damages for the aft ship: 1. Buckling of engine room stringers 2. Stern Slamming 3. Cracks due to vibration 4. Cavitation damages to the rudder Slide 37
  128. 128. Aft ship Buckling Oil Tanker Built 1992 Buckling of stringers in engine room (after 1 year) Buckling of stringers aft in engine room 7100 / 11150 mm above baseline Buckling of side stringer 7700 mm above baseline in engine room (P/S) Slide 38
  129. 129. Aft ship Buckling External sea pressure Bending moment Bending + shear exceed the buckling capacity of the plate Slide 39
  130. 130. Aft ship Buckling Impact of function • Stiffeners may loose their support and areas may be overloaded • Collapse of panels and leakage may be a possible scenario Slide 40
  131. 131. Aft ship Stern Slamming Container Ship • Flat stern structure is prone to be high stern slamming impact load - the wider beam, the higher impact pressure and total load on the stern Slide 41
  132. 132. Aft ship Container Ship Stern Slamming Repaired connection area/ scallop Slide 42 Scallop and stiffener connection to outer shell longitudinals in ballast tanks in after body area were found fractured in several locations.
  133. 133. Aft ship Container Ship Stern Slamming F F Slide 43
  134. 134. Aft ship Stern Slamming Container Ship Impact of function • Side longitudinals may loose their support at web frames • Crack may penetrate the shell plating - loss of watertight integrity - flooding possible scenario Slide 44
  135. 135. Aft ship Cracks in aft peak tank due to vibrations Cracks in Trans. at Steering Gear Flat Supporting structure below oscillating machinery Passage doors in engine room area Slide 45 ibr V l ona ati s ack cr
  136. 136. Aft ship Cracks in aft peak tank due to vibrations Crack in weld between web frame and shell side Crack Repair; Crack caused by vibration of the web frame due to impulses from the propeller Crack start in scallop Slide 46 Additional intercostals to change natural frequency for side webs
  137. 137. Aft ship Vibration damages Impact of function • The supporting structure may get less effective • If the cracks are in the side shell frames or webs, this may lead to crack in the shell plate and thereby leakage. Slide 47
  138. 138. Aft ship Rudder Cavitation Typical repair; • Grind the affected area • Pre-heat Slide 48 • Re-weld Typical on Container Ship
  139. 139. Aft ship Rudder Cavitation Pressure distribution around typical rudder profile Pressure distribution (suction) Positive pressure Cavitation of rudder blade depend on: U = speed of ambient water Pressure distribution due to shape of profile Pressure distribution due to thickness of profile Slide 49 • • • • Shape of profile Thickness of profile Rudder angle Speed of water over profile
  140. 140. Aft ship Rudder Cavitation • Stainless steel shielding – Preferred solution welded with continuous weld in small pieces – not slot welds Slide 50
  141. 141. Aft ship Rudder Cavitation This is how it may end if the shielding is not welded properly Slide 51
  142. 142. Aft ship Rudder Cavitation Impact on function • Cracks may occur which could lead to reduced rudder support and maneuverability Slide 52
  143. 143. End of Module 5 Fore & aft ship Slide 53
  144. 144. Oil Tankers Oil Tankers - Hull Structure Slide 1 18.02.2005
  145. 145. Oil Tankers Contents – Oil tankers 1. Introduction 2. Hull structural breakdown – function of hull elements: • 3. Slide 2 Side, bottom, deck, transverse bulkhead, longitudinal bulkhead, web frames including relevant hull damages for all structural elements Case 18.02.2005
  146. 146. Oil Tankers Characteristics for Oil tankers Any proposals? - High number of tanks – good capability of survival - 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) Slide 3 18.02.2005
  147. 147. Oil Tankers Size categories of tankers Oil Tankers Type ULCC VLCC Suezmax Aframax Panamax Products DWT 320,000+ 200 - 320,000 120 - 200,000 75 - 120,000 55 - 70,000 10 - 50,000 Source: INTERTANKO Slide 4 18.02.2005
  148. 148. 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 • B(max): 32.3 m • Typical vessel: 60,000 dwt, L=228,6m, B=32,2m, T=12,6m Age distribution Aframax (75 – 120,000 dwt): • AFRA= Average Freight Rate Assessment • Traditionally employed on a wide variety of short and medium-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 Slide 5 18.02.2005 Age distribution
  149. 149. Oil Tankers Size categories of tankers Suezmax (120 – 200,000 dwt): • Notation is soon to become redundant as the project of deepening the Suez Canal to 18,9m is completed • Typical vessel: 150,000 dwt, L=274,0m, B=50,0m, T=14,5m Age distribution VLCC (200 – 320,000 dwt): • Were prompted by the rapid growth in global oil consumption during the 60’s and the 1967 closing of the Suez canal • Today the most effective way of transporting large volumes of oil over relatively long distances • Typical vessel: 280,000 dwt, L=335,0m, B=57,0m, T=21,0m Source: INTERTANKO Slide 6 18.02.2005 Age distribution
  150. 150. Oil Tankers Size categories of tankers ULCC (320,000+ dwt): • Most ships of this type built in the mid to late 70’s • Ordered to take advantage of the economies of scale in a buoyant market • Less than 40 of these ships remaining • Rather inflexible, may enter very few ports • Typical vessel: 410,000 dwt, L=377,0m, B=68,0m, T=23,0m Source: INTERTANKO Slide 7 18.02.2005
  151. 151. Oil Tankers Single Skin Oil Tanker Ship data: L = 310m B = 56m D = 31,4m 284,497 DWT Slide 8 - Old design, build up to 1993 18.02.2005
  152. 152. Oil Tankers Single bottom with side ballast tanks Ship data: L = 236m B = 42m D = 19,2m 88,950 DWT - Built in the 80’s, considered as ‘single skin’ Slide 9 18.02.2005
  153. 153. Oil Tankers Double Hull – Two Longitudinal Bulkheads Ship data: L = 320m B = 58m D = 26,8m 298,731 DWT Slide 10 - Common VLCC design of today 18.02.2005
  154. 154. Oil Tankers Double Hull – CL Longitudinal Bulkhead Ship data: L = 264m B = 48m D = 23,2m 159,681 DWT Slide 11 - Common Aframax and Suezmax design of today 18.02.2005
  155. 155. Oil Tankers Double Hull – no CL bulkhead Ship data: L = 218m B = 32,2m D = 19,7m 63,765 DWT Slide 12 - Older design 18.02.2005
  156. 156. Oil Tankers Slide 13 Nomenclature for a typical double hull oil tanker 18.02.2005
  157. 157. Oil Tankers Structural breakdown of hull -A vessel’s hull can be divided into different hull structural elements - 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 to understand the function of each structural element Slide 14 18.02.2005
  158. 158. Oil Tankers Damages and repairs WWW.witherbys.com Slide 15 18.02.2005
  159. 159. Oil Tankers Function of hull elements Deck: Ship side: Webframes: Slide 16 18.02.2005 Longitudinal bulkhead: Bottom: Transverse bulkhead:
  160. 160. Oil Tankers Hull Structural Breakdown 2. Side Bottom 3. Deck 4. Transverse bulkhead Longitudinal bulkhead Web frames 1. 5. 6. Slide 17 18.02.2005
  161. 161. Oil Tankers End of Oil Tanker session Slide 18 18.02.2005
  162. 162. Oil Tankers 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Ship side Side Bottom Deck Transverse bulkhead Longitudinal bulkhead Web frames 18.02.2005 1. Side
  163. 163. Oil Tankers Structural build up of ship side – single skin tanker Side plating with longitudinals Transverse bulkhead Cross ties Stringers Web frame Slide 2 18.02.2005 1. Side
  164. 164. Oil Tankers Structural build-up of a double hull ship side Side plating with longitudinals Inner side plating with longitudinals Stringers Web frame Slide 3 18.02.2005 1. Side
  165. 165. Oil Tankers Structural functions of ship side 1. Side Watertight integrity - Take up external sea loads and transfer these into the hull girder - Resist internal pressure from cargo and ballast Web in hull girder - Side plating act as the web in the hull girder beam Slide 4 18.02.2005
  166. 166. Oil Tankers Loads on the ship side - example 1. Side Fully loaded condition Ballast condition Water Line Net force Net force Water Line Slide 5 18.02.2005 Full wing tank Full centre tank
  167. 167. Oil Tankers Local function: Watertight integrity 1. Side External loads induces shear forces and bending moments in the side longitudinals as single beams (between each web frame) Side long.as a single beam between two web frames Slide 6 18.02.2005 BM and SF distribtion for a single beam with evenly distributed load and fixed ends
  168. 168. Oil Tankers Local function: Watertight integrity 1. Side -Side longs are supported at the web frames - Web frames are supported at the cross ties and at the deck and bottom Shear force Slide 7 18.02.2005 Part of web frame supported at two cross ties, shear max towards supports Bending moment
  169. 169. Oil Tankers Double hull ship side 1. 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 at the deck and bottom High shear stress Slide 8 18.02.2005
  170. 170. Oil Tankers Global function: Web in hull girder 1. Global shear forces resulting from uneven distribution of cargo and buoyancy are taken up in the ship side plating Area effective in transferring shear force Slide 9 18.02.2005 Shear stress distribution resulting from global loads for midship section Side
  171. 171. Oil Tankers Stringers in a double side • Stringers contribute to the stiffness of the double hull ship side, which means: 1. Side 15mm 20mm 25mm 20mm High shear stress in stringer towards the Slide 10 18.02.2005 transverse bulkhead 15mm
  172. 172. Oil Tankers Characteristic damages for ship side: 1. Side 1. Cracks in side longitudinals at web frames 2. Cracks in cut-outs for longitudinals 3. Cracks in side longitudinals at transverse bulkheads 4. Indents of side shell and stiffeners Slide 11 18.02.2005
  173. 173. Oil Tankers Crack in side longitudinals Oil Tanker 285,690 DWT built 1990 Cracking in side longitudinal web frame connection (after 3 years) Side longitudinal flatbar connection to web frame Slide 12 18.02.2005 Crack in side longitudinal tripping bracket connection to web frame (various wing tanks) 1. Side
  174. 174. Oil Tankers Cause for cracking in side longitudinals 1. Side 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 geometric ’hard points’ (bracket toes, scallops, flat bars) Slide 13 18.02.2005
  175. 175. Oil Tankers Stress concentration factors More Stress concentration factors ; • Kg : Gross Geometry (from FEM analysis) • Kw : Weld Geometry (typical 1,5) • Kn : Unsymmetrical Stiffeners (L& bulb-profiles) Slide 14 18.02.2005 1. Side
  176. 176. Oil Tankers Slide 15 Standard repair proposal longs / webframes 18.02.2005 1. Side
  177. 177. Oil Tankers Cracks in web frame cut outs Cr ac ks Slide 16 18.02.2005 1. Side Cracks around openings for side longitudinals in web frames
  178. 178. Oil Tankers Cause for cracking in cut outs for longitudinals 1. Side Sea loads induce shear stresses in the web frame High shear stresses around openings etc, where shear area is reduced Shear stress Shear stress Slide 17 18.02.2005
  179. 179. Oil Tankers Consequence of crack in web frame 1. Side How does this damage impact on the function of the web frame? Side longitudinals loose their support Re-distribution of shear stresses in web frame May lead to overloading of adacent structure Slide 18 18.02.2005
  180. 180. Oil Tankers Crack in side longitudinal at transverse bulkhead 1. Side longitudinal connections to transverse bulkheads Slide 19 18.02.2005 Cracks in side longitudinal connection to stringers at transverse bulkhead Side
  181. 181. Oil Tankers Why cracking at transverse bhd.? Ship side 1. Side Relative deflections occur between the ’rigid’ transverse bulkhead and the flexible web frame construction Sea pressure The relative deflection induces additional bending stresses at the end connection of side longitudinals to the transverse bulkhead. Also important at wash bulkheads. Slide 20 18.02.2005
  182. 182. Oil Tankers FEM plot of double hull oil tanker 1. Side Loading condition: External dynamic sea pressure at full draught Slide 21 18.02.2005 Relative deflection
  183. 183. Oil Tankers Suggestions? Consequence of damage 1. Side Cracks in side longitudinals: - leakage Slide 22 18.02.2005 oil leakage and pollution longitudinal may break off in worst case (a series of cracks in same area) could induce a larger fracture (loss of ship side)
  184. 184. Oil Tankers Indents of side shell with stiffeners 1. Side Mainly from contact damages: 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 Slide 23 18.02.2005 -Buckling: Due to excessive in-plane stresses
  185. 185. Oil Tankers Slide 24 Consequense of indents 18.02.2005 1. Side
  186. 186. Oil Tankers Consequense of indents 1. Side Large area set in (plating and stiffeners) gives reduced buckling capacity Adjacent areas may then be overloaded Sharp indents may lead to cracks and possible leakage Slide 25 18.02.2005
  187. 187. Oil Tankers 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Bottom Side Bottom Deck Transverse bulkhead Longitudinal bulkhead Web frames 18.02.2005 2. Bottom
  188. 188. Oil Tankers Structural functions of bottom 2. Bottom Watertight integrity • Resist external sea pressure • Resist internal pressure from cargo and ballast Flange in hull girder • Bottom plating and longitudinals act together as the lower flange in the hull girder beam Slide 2 18.02.2005
  189. 189. Oil Tankers Structural build up of bottom – single skin tanker Bilge Bottom plating w/longitudinals Keel plate Slide 3 18.02.2005 CL girder Web frame 2. Bottom
  190. 190. Oil Tankers Structural build-up of a double bottom structure Inner bottom plating (tank top) with longitudinals 2. Bottom Buttress Hopper plating with longitudinals Hopper web plating Outboard girder (margin girder) Slide 4 CL double bottom girder 18.02.2005 Bottom plating with longitudinals Transverse girder / floor
  191. 191. Oil Tankers Function: Watertight integrity 2. Bottom Fixation? External loads induce shear forces and bending moments in the bottom longitudinals, acting as single beams (between each web frame) Bottom longitudinal as a single beam between two web frames Slide 5 18.02.2005 Cont. BM and SF distribtion for a single beam with distributed load and fixed ends
  192. 192. Oil Tankers Function: Watertight integrity 2. Bottom Bottom plating with longitudinals are also acting as flange for the transverse web frame p L SF Transverse bottom girder/web frame is supported at the longitudinal bulkheads (max. shear force towards long. bhds.) Slide 6 18.02.2005 BM
  193. 193. Oil Tankers Bottom is supported by ship side and longitudinal bulkhead 2. Bottom Double span for double bottom without CL longitudinal bulkhead Shear stress in double bottom floor due to external sea pressure Slide 7 18.02.2005
  194. 194. Oil Tankers Function: Flange in hull girder 2. Bottom Global bending moment induces longitudinal stresses in the bottom plating and longitudinals σL σL Section A-A Slide 8 18.02.2005 Longitudinal stresses (+/-) are acting in the bottom plating and longitudinals due to bending of hull girder
  195. 195. Oil Tankers Double bottom structure 2. Bottom Load distribution in double bottom girder system Slide 9 18.02.2005
  196. 196. Oil Tankers Load response double bottom 2. Bottom Stresss flow shortest way to support Cont. Slide 10 18.02.2005
  197. 197. Oil Tankers Double bottom structure 2. Bottom The double bottom is a grillage structure built up by transverse girders/floors and longitudinal girders With few longitudinal girders, double bottom stresses resulting from the net load on the girder system are mainly transferred in the transverse direction Net load Shear force Shear fo Double bottom transverse girder (web frame) as a Slide 11 18.02.2005 single I-beam rce High shear stresses in floors & girders in way of transv. Bhd. And hopper tank
  198. 198. Oil Tankers Characteristic damages 2. Bottom 1. Bilge keel terminations – crack in hull plating 2. Fatigue cracking in bottom longitudinal connections to web frame and transverse bulkhead 3. Corrosion of bottom structures 4. Hopper knuckle – cracks Slide 12 18.02.2005
  199. 199. Oil Tankers Bilge keel cracking 2. Bottom Oil Tanker 285,690 DWT built 1990 Crack in hull plating i.w.o. bilge keel terminations Bilge keel Crack in hull plating in way of bilge keel toes Slide 13 18.02.2005
  200. 200. Oil Tankers Bilge keel cracking 2. Hot spot Bilge keel Longi Slide 14 18.02.2005 tudina l stres s Bottom
  201. 201. Oil Tankers Bilge keel cracking 2. Web frame/Bilge Bracket All measures in mm 125 Edges to be grinded smooth Ship side Pad plate 10-15mm Bilge Keel 200 Full pen. weld 1600 100 25 100 Slide 15 18.02.2005 Bottom
  202. 202. Oil Tankers Cracking in bottom longitudinals Bottom long. flat bar connection Similar16 Slide cracking in bottom longitudinals is also 18.02.2005 valid for double hull tankers 2. Bottom Bottom long. tripping bracket connection
  203. 203. Oil Tankers Cause for cracking in bottom longitudinals Bottom 2. Bottom longitudinals are subject to both: Web/ Trans bhd Web M M p 1. Local stress from lateral dynamic sea loading 2. Longitudinal stresses from hull girder bending Slide 17 18.02.2005
  204. 204. Oil Tankers Consequences of cracks in bottom longitudinals: 2. Bottom -Leakage of oil - Crack may propagate further into bottom plating and induce a larger transverse fracture Slide 18 18.02.2005
  205. 205. Oil Tankers Example: Cracks in inner bottom 2. Bottom Oil Tanker 95,371 DWT Crack 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 (in various cargo tanks along ships length) Crack propagating through tank top plating (a few cases) Slide 19 18.02.2005 Crack in bracket toe
  206. 206. Oil Tankers Cracking in double bottom longitudinals 2. Bottom Cracks in flatbar connections for bottom and inner bottom longitudinals Slide 20 18.02.2005
  207. 207. Oil Tankers Cause for cracking in double bottom longitudinals 2. Bottom 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) 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 Slide 21 18.02.2005
  208. 208. Oil Tankers Illustration – double bottom flatbar connections 2. Bottom Tensile stresses in critical structural details The double bottom structure is exposed to large forces both in ballast and loaded condition Slide 22 18.02.2005
  209. 209. Oil Tankers Corrosion of bottom structures 2. Bottom 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 23 Slide i.w.o. tank top plating 18.02.2005
  210. 210. Oil Tankers Corrosion of bottom structures 2. Bottom - Pittings and local corrosion may cause leakage, in general not any structural 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 Longitudinal stress Force F σL = A Area Increased risk for fatigue cracking and buckling of bottom panels if general corrosion has developed over the cross section Slide 24 18.02.2005
  211. 211. Oil Tankers Slide 25 Cracking in hopper knuckle 18.02.2005 Crack in hopper knuckle at web frame connections 2. Bottom
  212. 212. Oil Tankers Cause for cracking in hopper knuckle 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) σL Bending moment Bending stress in inner bottom plating Slide 26 18.02.2005 Bending stress in double bottom girder σL
  213. 213. Oil Tankers Cause for cracking in hopper knuckle 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 Resulting membrane stress in hopper plating Membrane stress from bending of transverse girder Un-balanced stress component - This effect together with the knuckle being a geometric ‘hard point’ at web frame connections, induce very high stresses in the knuckle point Slide 27 18.02.2005
  214. 214. Oil Tankers 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Deck Side Bottom Deck Transverse bulkhead Longitudinal bulkhead Web frames 18.02.2005 3. Deck
  215. 215. Oil Tankers Structural functions of deck 3. Deck Flange in hull girder - Deck plating and longitudinals act as the upper flange in the hull girder beam Slide 2 18.02.2005
  216. 216. Oil Tankers Structural build up of deck – single skin tanker Deck plating w/longitudinals Transverse deck girder / Web frame Slide 3 18.02.2005 Deck CL girder 3. Deck
  217. 217. Oil Tankers Function: Flange in hull girder 3. Deck Hull girder bending moment induces longitudinal stresses in the deck plating and longitudinals Longitudinal stresses (+/-) are set up in the deck plating and longitudinals due to bending of hull girder σL Slide 4 18.02.2005 σ L
  218. 218. Oil Tankers Longitudinal stresses in deck 3. Longitudinal stresses from bending of hull girder is maximum at midship Midship area most susceptible to fatigue cracking and buckling Bending moment Slide 5 18.02.2005 Max Deck
  219. 219. Oil Tankers Characteristic damages 1. Cracks in deck longitudinals 2. Crack in deck plating 3. Corrosion of deckhead 4. Buckling of deck Slide 6 18.02.2005 3. Deck
  220. 220. Oil Tankers Cracking in deck longitudinals 3. Deck Deck longitudinal connection to web frames Deck longitudinal connection to transverse bulkhead Slide 7 18.02.2005
  221. 221. Oil Tankers Cracking in deck longitudinals Oil Tanker 135,000 DWT built 1991 Crack main deck plating Slide 8 Crack in underdeck support for hose handling crane (P/S, midship area) 18.02.2005 3. Deck
  222. 222. Cause for cracking in deck longitudinals Oil Tankers 3. The wave induced excitation of the hull girder leads to dynamic axial stress in the deck longitudinals + + _ _ 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) Slide 9 18.02.2005 Deck
  223. 223. Oil Tankers Cracks in deck longitudinals - 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) Slide 10 18.02.2005 3. Deck
  224. 224. Oil Tankers Openings in deck 3. Deck σ Kg.Kw. σ σ Longitudinal stress-flow around manhole in deck Slide 11 18.02.2005 Increased stress level around openings in deck!
  225. 225. Oil Tankers Example: crack in scallop in deck longitudinal 3. Deck Oil Tanker 123,000 DWT built 2000 Crack main deck plating (after 3 years) Slide 12 Scallop in deck18.02.2005 longitudinal is close to access opening in deck. This will give an additional accumulated stress in the longitudinal, which is believed to be the cause for the damage.
  226. 226. Oil Tankers Crack in deck plating 3. Tanker for Oil 99328 DWT built 1996 Crack in deck plating Crack in deck plating at hose saddle support (midship area) Slide 13 18.02.2005 Deck
  227. 227. Oil Tankers Corrosion of deckhead The ullage space (deckhead) is an area susceptible to general corrosion Slide 14 18.02.2005 3. Deck
  228. 228. Oil Tankers Corrosion of deckhead 3. Deck A reduction of the deck transverse sectional area due to general corrosion will lead to an increased stress level in deck Higher stress σL Longitudinal stress level in deck Force F σL = A n.a. Area σL Longitudinal stress distribution Long. stress distribution (with reduced deck sectional area) Reduced sectional area in deck may lead to plate buckling Slide 15 18.02.2005
  229. 229. Oil Tankers Corrosion of deckhead 3. Deck Higher stress level in deck due to general corrosion σL Longitudinal stress Force F σL = A Area σL A reduction of the deck transverse sectional area due to general corrosion will lead may lead to buckling problems to an increased stress level in deck Slide 16 18.02.2005
  230. 230. Oil Tankers Corrosion of deckhead 3. Deck Flatbars have poor buckling capacity Slide 17 18.02.2005 L-profiles have good buckling capacity
  231. 231. Oil Tankers Buckling in deck Buckling in deck is most likely to occur in the midship region where the hull girder bending moment is at its maximum Buckling of a plate field (plating with stiffeners) Slide 18 18.02.2005 3. Deck
  232. 232. Oil Tankers Cause for buckling in deck 3. Deck Buckling in deck is a result of in plane compression forces in excess of the 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 Buckling of complete plate field Slide 19 18.02.2005 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)
  233. 233. Oil Tankers Corrosion of deckhead / buckling: 3. Deck - heavy corrosion of deck may lead to buckling - small buckles (plate between stiffeners) is a strong warning sign that longitudinal stresses are high - large buckles (plate field) may lead to loss of global strength and in worst case a total collapse of the hull girder Remember max 10% diminution of deck transverse sectional area! Slide 20 18.02.2005
  234. 234. Oil Tankers 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Transverse bulkhead Side Bottom Deck Transverse bulkhead Longitudinal bulkhead Webframes 18.02.2005 4. Transverse bulkhead
  235. 235. Oil Tankers Structural build up of transverse bulkhead Transverse bulkhead plating w/stiffeners Stringers Buttress Slide 2 18.02.2005 4. Transverse bulkhead
  236. 236. Oil Tankers Structural functions 4. Transverse bulkhead Watertight integrity - Resist internal pressure from cargo and ballast (cargo boundary) - Safety against collapse if water ingress (boundary for flooding) Hull girder stiffness - Transverse bulkhead is an important contributor to the hull girder transverse stiffness Slide 3 18.02.2005
  237. 237. Oil Tankers Functions of transverse bulkhead The transverse bulkhead must withstand internal pressure loads from cargo and ballast The distribution of cargo and ballast introduces alternate loading on sections of the transverse bulkheads (single skin tanker) Typical fully loaded condition (single skin) Slide 4 18.02.2005 Typical ballast condition (single skin) 4. Transverse bulkhead
  238. 238. Oil Tankers Function: tank boundary 4. Transverse bulkhead Stringer Shear force Bending moment Slide 5 Stiffener 18.02.2005
  239. 239. Oil Tankers Function: tank boundary 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 Slide 6 18.02.2005 4. Transverse bulkhead
  240. 240. Oil Tankers Function: transverse stiffness 4. Transverse bulkhead Transverse bulkheads are an important contributor to the hull girder strength Sea pressure Sea pressure Transverse stiffness Slide 7 18.02.2005
  241. 241. Oil Tankers Characteristic damages 1. Stringer toes – cracking 2. Bottom longitudinal bracket connection to transverse bulkhead - cracks 3. Cracking of transverse bulkhead stiffeners connection to stringers Slide 8 18.02.2005 4. Transverse bulkhead
  242. 242. Oil Tankers Cracking in stringer toe Cracks in stringer toes and heel Slide 9 18.02.2005 4. Transverse bulkhead
  243. 243. Oil Tankers Slide 10 Cracking in stringer toe 18.02.2005 4. Transverse bulkhead
  244. 244. Oil Tankers Cause for cracking in stringer toe Compression/tension stresses from one sided loading Full cargo tank Sea pressure Slide 11 Full cargo tank 18.02.2005 Very high alternating bending stresses in stringer toe 4. Transverse bulkhead
  245. 245. Oil Tankers Cracks in stringer 4. Transverse bulkhead Crack Stringer flange Longitudinal bulkhead Stringer web Slide 12 May cause contamination of ballast water and small oil spills 18.02.2005
  246. 246. Oil Tankers Cracks in bottom longitudinals 4. Transverse bulkhead 17. Cracks in toe of transverse bulkhead bracket ending at bottom longitudinals (wing tanks, midship area) Slide 13 18.02.2005
  247. 247. Oil Tankers Cause - cracks in bottom brackets 4. Transverse bulkhead Crack in bracket toe (hot spot) Slide 14 18.02.2005 One sided loading at the transverse bulkhead induce high local alternating bending stresses at the bracket toe
  248. 248. Oil Tankers Double btm at transverse bulkhead 4. 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 relative deflection Critical areas Slide 15 18.02.2005
  249. 249. Oil Tankers Crack in transverse bulkhead stiffeners connection to stringers Connection of stringer to transverse bulkhead with associated brackets Slide 16 18.02.2005 4. Transverse bulkhead
  250. 250. Oil Tankers Cause for cracking in transverse bulkhead stiffeners 4. Transverse bulkhead One sided internal loading from cargo and ballast sets up a shear stress distribution in the bulkhead stiffener Highly stressed areas are created around geometric ’hard points’ at stiffener end connections to the stringer -may cause ballast water contamination and possible oil spills Slide 17 18.02.2005
  251. 251. Oil Tankers 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Longitudinal bulkhead Side Bottom Deck Transverse bulkhead Longitudinal bulkhead Web frames 18.02.2005 5. Longitudinal Bulkhead
  252. 252. Oil Tankers Structural build up of longitudinal bulkhead 5. Longitudinal bulkhead plating with stiffeners Web frame Slide 2 18.02.2005 Cross ties Longitudinal Bulkhead
  253. 253. Oil Tankers Structural functions of long.bhd 5. Longitudinal Bulkhead 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 Slide 3 18.02.2005
  254. 254. Oil Tankers Function : Cargo boundary 5. Longitudinal Bulkhead Internal loads induce shear forces and bending moments in the longitudinal bulkhead longitudinal (between each web frame) Stresses are loaded onto the web frames and further into the hull girder structure Slide 4 18.02.2005
  255. 255. Oil Tankers Function: Web in hull girder 5. Longitudinal Bulkhead Longitudinal bulkhead together with ship side is taking up global shear forces from wave induced loads and weight/buoyancy distribution along the vessel length A R1 F A A R2 A Shear force distribution resulting from global loads for midship section Slide 5 18.02.2005 Section A-A SF
  256. 256. Oil Tankers Characteristic damages 5. Longitudinal Bulkhead 1. Cracks in bulkhead longitudinals connection to stringers at transverse bulkhead 2. Shear buckling of longitudinal bulkhead Slide 6 18.02.2005
  257. 257. Oil Tankers Crack in long.bhd longitudinals connection to stringers 5. Longitudinal Bulkhead Connection of longitudinal bulkhead longitudinals to stringers with associated brackets Slide 7 18.02.2005
  258. 258. Oil Tankers Cause for cracking in long.bhd at stringer connections 5. Longitudinal bulkhead is flexing depending on the loading condition (filling of tanks) Fully loaded condition Ballast condition High bending stresses towards the supports (transverse bulkheads) Slide 8 18.02.2005 Longitudinal Bulkhead
  259. 259. Oil Tankers Cause for cracking in long.bhd stringer connections Full ballast tank H ot sp ot May cause contamination of ballast water and small oil spills Slide 9 18.02.2005 5. Longitudinal Bulkhead
  260. 260. Oil Tankers Slide 10 Shear buckling of longitudinal bulkhead 18.02.2005 Shear buckling is most likely to occur in areas towards the transverse bulkheads, but may also occur in other areas depending on the thickness of the bulkhead plating 5. Longitudinal Bulkhead
  261. 261. Oil Tankers Shear buckling of longitudinal bulkhead SF maximum at transverse bulkheads Longitudinal shear force distribution – an example Slide 11 18.02.2005 5. Longitudinal Bulkhead
  262. 262. Oil Tankers Cause for shear buckling 5. Longitudinal Bulkhead Result of excessive shear stress in the bulkhead plating Corrosion increases possibility for shear buckling SF SF Shear buckling (middle and upper area of bulkhead most exposed due to corrosion risk and reduced original scantlings) Shear buckled panels will have a reduced shear strength, 18.02.2005 which may lead to an overload of adjacent areas Slide 12
  263. 263. Oil Tankers 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Web frames Side Bottom Deck Transverse bulkhead Longitudinal bulkhead Web frames 18.02.2005 6. Web frames
  264. 264. Oil Tankers Structural build up of web frame Web frame flange Web frames Cross tie Slide 2 18.02.2005 6. Web frames
  265. 265. Oil Tankers Function of web frames 6. Web frames - Web frames are supports for the longitudinal stiffeners - Web frames contributes to the hull girder transverse strength Slide 3 18.02.2005
  266. 266. Oil Tankers Function of web frame 6. Web frames • Web frames are supports for the longitudinals • Web frames take up local loads from the longitudinal stiffeners and transfer them further into the hull girder • Web frames keep the cross sections together and contribute to the transverse stiffness Slide 4 18.02.2005 Sea pressure Internal pressure
  267. 267. Oil Tankers Characteristic damages 6. Web frames 1. Corrosion / buckling of web frame 2. Corrosion / cracking of cross tie connection 3. Cracking of tripping bracket connection to web frame flange Slide 5 18.02.2005
  268. 268. Oil Tankers Shear buckling of web frame High shear stress SF SF Slide 6 18.02.2005 6. Web frames
  269. 269. Oil Tankers TYP. WEB SEC. (SHEAR STRESS) LC 2 Shear buckling may occur in areas where shear stress is high Slide 7 18.02.2005 6. Web frames
  270. 270. Oil Tankers Shear buckling of web frame: Corrosion of web frame increases the risk for shear buckling Corroded cut outs and openings in web frame are exposed to buckling, because of the reduced shear area (high τshear) Slide 8 18.02.2005 6. Web frames
  271. 271. Oil Tankers Corrosion of cross tie Weld connection of straight part of cross tie to the side and longitudinal bulkhead Slide 9 18.02.2005 6. Web frames
  272. 272. Oil Tankers Corrosion of cross tie 6. Web frames Cross ties are subject to both compression and tension stress depending on loading condition Corrosion Increased stress level Reduced Buckling capacity Cross tie collapse? Slide 10 18.02.2005 +/- Axial stress
  273. 273. Oil Tankers Crack in tripping bracket connection to web frame flange Weld connection of large curved flanges and tripping brackets on webframes Slide 11 18.02.2005 6. Web frames
  274. 274. Oil Tankers Cause for cracking in web frame flange 6. Web frames 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 - If exposed to compression, the flange will bend inwards Slide 12 18.02.2005 Deflection pattern of free flange
  275. 275. Oil Tankers Slide 13 FEM plot of cross tie with deflections 18.02.2005 6. Web frames
  276. 276. Oil Tankers Cracks in web frame 6. Web frames • • 18.02.2005 Increased loads on adjacent webframes • Slide 14 Webframe support for longidudinals – reduced support – excessive load on longitudinals May lead to loss of stiffened panel
  277. 277. Bulk Carriers Slide 1 Bulk Carriers - Hull Structure 18.02.2005
  278. 278. Bulk Contents – Bulk Carriers Carriers 1. Introduction to Bulk carrier hull structure 2. Hull structural breakdown – function of hull elements: • 3. Slide 2 Side, bottom, deck, transverse bulkhead, longitudinal bulkhead, web frames including relevant hull damages for all structural elements Case 18.02.2005
  279. 279. 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) Low survival capability when flooded High number of vessels lost Slide 3 18.02.2005
  280. 280. Bulk Carriers Bulk Carrier loading flexibility • Bulk Carrier HC/EA Reduced flexibility – 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 Carrier – Any hold empty at 60% of full draught Slide 4 18.02.2005
  281. 281. Bulk Carriers History • Built in 1954 - Cassiopeia • First bulk carrier with hopper tank – topside tank cross section Slide 5 18.02.2005
  282. 282. Bulk Carriers Bulk Carrier particulars 5 cargo holds 7 cargo holds 9 cargo holds Slide 6 18.02.2005
  283. 283. Bulk Carriers Slide 7 Nomenclature 18.02.2005
  284. 284. Bulk Carriers Slide 8 Nomenclature 18.02.2005
  285. 285. Bulk Carriers Structural breakdown of hull - A vessel’s 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 Slide 9 18.02.2005
  286. 286. Bulk Typical damages and repairs Carriers WWW.witherbys.com Slide 10 18.02.2005
  287. 287. Bulk Carriers Structural breakdown of Bulk Carrier 7. Hatch coaming & cover 3. 4. 1. 5. Topside tank Transverse bulkhead Side 6. Slide 11 Deck 2. Bottom 18.02.2005 Hopper tank
  288. 288. Bulk Hull Structural Breakdown Carriers 1. Side 2. Bottom 3. Deck 4. Transverse bulkhead 5. Hopper tank 6. Topside tank 7. Hatch cover & coaming Slide 12 18.02.2005
  289. 289. Bulk Carrier 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Ship side Side Bottom Deck Transverse bulkhead Hopper tank Topside-tank 1. Side
  290. 290. Bulk Carrier Structural functions of ship side 1. 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 Slide 2 Side
  291. 291. Bulk Carrier Structural build up of ship side 1. Upper bracket Side plating Side frames Lower bracket Slide 3 Side
  292. 292. Bulk Carrier Structural functions of ship side 1. Watertight integrity (local strength) Ship side must withstand static and dynamic loads from external sea pressure as well internal pressure from cargo and ballast Loads are taken up by the hull plating, stresses are transferred into the vertical side frames – further into the upper and lower bkt’s further into the topwing tank and hopper tank structure Slide 4 Side
  293. 293. Bulk Carrier Functions of ship 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 bkt’s Bm SF Slide 5 1. Side
  294. 294. Bulk Carrier Functions of ship side 1. Side Ore hold load response; Net load down cause rotation of hopper tank structure. additional moment in the mid-field and upper end SF Slide 6 Bm Bm
  295. 295. Bulk Carrier Functions of ship side 1. Side Bm Bm Empty hold load response; Net load up cause rotation of hopper tank structure. additional moment in the mid-field and lower end SF Slide 7
  296. 296. Bulk Carrier Functions of ship side 1. Side 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 Global loads are acting on the hull girder beam Side plating is acting as web in hull girder beam Slide 8 Cont.
  297. 297. Bulk Carrier Function of ship side (longitudinal shear strength) Shear Distribution at a 0 Sagging Bending force Shear moment Shear force (t-m) Hogging cross section Slide 9 Cont.
  298. 298. Bulk Carrier Functions of ship side 1. Side Web in hull girder (global strength) - Global shear forces are distributed in the ship side plating Shear force distribution resulting from global loads for midship section Slide 10 Cont.
  299. 299. Bulk Carrier Hull damages in ship side 1. Two characteristic damages for ship side: 1. 2. Slide 11 Cracks in side frames at lower / upper bracket connection Corrosion of side frames and lower bkt. – detached bkt’s Side
  300. 300. Bulk Carrier Crack in side longitudinal web frame connection 1. Side Cracking in vertical side frame: Vertical side frame lower bkt. commection Slide 12
  301. 301. Bulk Carrier Cause for cracking in vertical side frames lower bkt. connections 1. 1b. 1a. The dynamic loads from the sea are taken up by the side plates supported by the vertical side frames and load is transferred to the upper and lower bkt’s. This gives peak of bending moment and shear in way of lower bkt. connection. 1a. 1b. Slide 13 The sniped termination of the bracket flange creates a local stress concentration, which may develop cracks from the toe of the bracket In this point a high bending stress in flange and a stress concentration due to weld (overlap) increase the risk for fatigue cracks. Side
  302. 302. Bulk Carrier Crack in side longitudinal web frame connection Possible consequence 1. Side • As these cracks develop, the lower end fixation of the side frame is reduced: – higher bending moment in the middle of the frame – some of the load will be carried by adjacent frames • Crack through stiffener: – beam simply supported lower end, profile may buckle at midfield • Side shell may crack. • Adjacent frames crack – panel collapse, possible water flooding. Slide 14
  303. 303. Bulk Carrier Corrosion of side frames and lower bkt. connection 1. Side frames and bkt’s are prone to corrosion, both general corrosion as well as grooving corrosion which may result in : • Fracture in plating/bracket toes • Fractured/detached frames • Local corrosion and grooving • General wastage. Slide 15 Side
  304. 304. Bulk Carrier Revised Minimum Thickness List Torig Hold 1: Aft end of Hold 1: Upper bracket web Frame web, middle and upper part Frame web, Lower part Lower bracket web Frame flange thickness, middle and upper part Frame flange thickness, lower part Lower bracket flange thickness Middle part of Hold 1: Upper bracket web Frame web, middle and upper part Frame web, Lower part Lower bracket web Frame flange thickness, middle and upper part Frame flange thickness, lower part Lower bracket flange thickness Forward end of Hold 1: Upper bracket web Frame web, middle and upper part Frame web, Lower part Lower bracket web Frame flange thickness, middle and upper part Frame flange thickness, lower part Lower bracket flange thickness Slide 16 T-min T-subst T-Coat 13,0 13,0 13,0 15,0 20,0 20,0 20,0 9,8 9,8 11,2 11,3 15,0 15,0 15,0 10,6 10,6 11,6 12,2 16,3 16,3 16,3 11,2 11,2 13,0 13,0 13,0 15,0 20,0 20,0 20,0 9,8 9,8 9,9 11,3 15,0 15,0 15,0 10,6 10,6 10,7 12,2 16,3 16,3 16,3 13,0 13,0 13,0 15,0 20,0 20,0 12,5 9,8 9,8 13,9 16,9 15,0 15,0 9,4 10,6 10,6 NB! NB! 16,3 16,3 10,2 11,2 12,7 N/A N/A N/A 11,2 11,2 11,2 12,7 Upper Bracket Middle and upper part of Frame Low er part of Frame N/A N/A N/A 11,2 11,2 N/A N/A N/A N/A N/A Low er Bracket
  305. 305. Bulk Carrier Corrosion of side frames and lower bkt. Connection – Consequences • General corrosion of side frames reduce the shear area and section modulus. – Bending moment stress level increases – Stiffeners may collapse in buckling • Local grooving of side frame support bkt’s – 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 Slide 17 1. Side
  306. 306. Bulk Carrier Damage impact on function 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 Slide 18 1. Side
  307. 307. Bulk Carrier 1. 2. 3. 4. 5. 6. Slide 1 Hull Structural Breakdown Bottom Side Bottom Deck Transverse bulkhead Hopper tank Topside-tank 2. Bottom
  308. 308. Bulk Carrier Structural functions of bottom 2. 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 webs in double bottom girders 2. Bottom flange in hull girder (global strength) - Bottom and inner bottom structure is the bottom flange in the hull girder Slide 2
  309. 309. Bulk Carrier Structural build up of bottom Longitudinal girders Floor Slide 3 Pipe tunnel 2. Bottom
  310. 310. Bulk Carrier Structural functions of bottom 2. Bottom 1. Watertight integrity (local strength) Bottom plate must withstand static and dynamic loads from external sea pressure as well internal pressure from ballast or fuel oil Inner bottom plate must withstand static and dynamic loads from cargo hold as well as static and dynamic pressure from ballast or fuel oil Cont. Slide 4
  311. 311. Bulk Carrier • Structural functions of bottom Stress distribution in a double bottom structure • Forces are taken up by the stiffest structure • • Slide 5 Middle of hold more stresses in transverse direction Towards bhd. – more stresse in longitudinal direction 2. Bottom
  312. 312. Bulk Carrier Functions of inner bottom (local 2. Bottom stiffener level) Cargo hold boundary (local strength) External loads induce shear forces and bending moments in the inner bottom longitudinals as single beams (between floors) BM and SF distribtion for a single beam with distributed load and fixed ends Cont. Slide 6
  313. 313. Bulk Carrier Load response double bottom 2. Bottom Stresss flow shortest way to support Cont. Slide 7
  314. 314. Bulk Carrier Double bottom girders load response 2. Bottom • girders & floors carry the net load to hopper tank and transverse bulkhead • floors carry most of the loads in middle of hold • longitudinal girders carry most of the load towards transverse bulkhead • length / width ratio is important for the distribution of loads between girders & floors • The stiffest elements are taking most of the load / stresses seek the shortest way to supports Slide 8
  315. 315. Bulk Carrier Functions of double bottom girder Net Load on double bottom Simple beam model Longitudinal girders represented by springs Slide 9 2. Bottom
  316. 316. Bulk Carrier Floors / girders- design 2. Bottom Long. Db. girder High Shear force – No cut-outs / increased thickness Floor Slide 10
  317. 317. Bulk Carrier 2. Functions of bottom Bottom 2. Bottom flange in hull girder (global strength) The bottom and inner bottom longs and longitudinal girders are carrying the vertical bending moments from still water and wave induced bending moments along the vessel length Slide 11 Global loads are acting on the hull girder beam Bottom structure is acting as web in hull girder beam Cont.
  318. 318. TM Bending moment Bulk Carrier Moment diagram Reduced global bending but high double bottom stresses Still water bending moment [intact] Max allowable bending moment [intact] Slide 12 2. Bottom
  319. 319. Bulk Carrier Highly stressed areas 2. Bottom Deck Tanktop + NA Inner bottom level Bottom Bottom Global bending Double bottom bending Bottom plate/longs middle of empty holds (compression ) Bottom plate in loaded holds (tension) Inner bottom plate middle of loaded holds (compression ) Slide 13
  320. 320. Bulk Carrier Hull damages bottom / inner bottom 2. Bottom Three characteristic damages for bottom are: 1. 2. Crack / Corrosion of floors – girders in ballast tanks 3. Slide 14 Cracks in inner bottom plate in way of knuckle to hopper tank Indents of inner bottom plate due to cargo handling
  321. 321. Bulk Carrier Cracks in way of hopper knuckle 2. • Heavy ballast condition – tension in inner bottom plate Fractures Slide 15 Bottom
  322. 322. Bulk Carrier Cracks in way of hopper knuckle Hopper plate Inner bottom plating Slide 16 2. Bottom
  323. 323. Bulk Carrier Cracks in way of hopper knuckle Impact on function 2. Bottom • Loss of watertight integrity – leak ballast – cargo • Cracks extending from one webframe to another severe impact on double bottom strength Slide 17
  324. 324. Bulk Carrier Fractures in connection of floors i.w.o. hopper Damage bottom Inner Fractures Repair A 2. Full penetration weld connection to the inner bottom and hopper plating A Double bottom floor Collar plate Hopper transverse web Edge chamfered for full penetration weld Side girder Reinforcement A View A-A Alternatively, may stop at longitudinals where fitted Transverse fractures in hopper web plating possibly extending into the hopper sloping plate Reinforcement B Inner bottom Slide 18 Floor or transverse web plating Fracture in the floor/web of the hopper transverse Intermediate brackets (i.e. between floors) Face plate of transverse web Inner bottom Scarfing brackets View B-B Bottom
  325. 325. Bulk Carrier Crack in floor 2. • Floor in way of high shear stress • Connection at bottom longitudinals Repair A Lug Damage Floor or transverse web frame Longitudinal Buckling and/or fracturing Fractures New plating of enhanced thickness Repair B Bottom shell plating, inner bottom plating, side shell plating or hopper sloping plate Slide 19 Fractures Full collar plate Bottom
  326. 326. Bulk Carrier Crack in floor impact on function 2. Bottom • Loss of support of longs – increased stresses at adjacent floors – longs • Large crack in floor – increased stresses in adjacent floors - girders Slide 20
  327. 327. Bulk Carrier Slide 21 Indents of inner bottom plate 2. Bottom
  328. 328. Bulk Carrier Indents of inner bottom plate 2. Impact on function • Difficult with discharge of cargo – cleaning • Severe indents – cracks – leak • Impact on buckling capacity of panel Slide 22 Bottom
  329. 329. Bulk Carrier Fracture in longitudinals at stool connection Damage Bottom Cause Stool Inner bottom longitudinal Fractures Bottom shell longitudinal Slide 23 2. Damage due to stress concentrations and large relative deflections (bulkhead stool - first floor) leading to accelerated fatigue in this region.
  330. 330. Bulk Carrier Fracture in longitudinals at stool connection 2. Bottom Repair Stool Too large brackets may cause further problems. Additional brackets with soft toes Where required the longitudinal to be cropped and part renewed Slide 24
  331. 331. Bulk Carrier Fracture in longitudinals at stool connection Damage Repair Stool Inner bottom Modified brackets with soft toes Bilge well Fracture Additional bracket with soft toes Fracture Slide 25 Where required the longitudinals to be cropped and part renewed 2. Bottom
  332. 332. Bulk Carrier 1. 2. 3. 4. 5. 6. 7. Slide 1 Hull Structural Breakdown - Deck Side Bottom Deck Transverse bulkhead Hopper tank Topside-tank Hatch cover & coaming 3. Deck
  333. 333. Bulk Carrier Structural functions of deck 1. Watertight integrity (local strength) - Resist external sea pressure 2. Transverse strength of the hull girder 3. Upper flange in hull girder (global strength) Slide 2 3. Deck
  334. 334. Bulk Carrier Structural build up of deck • Main deck outside line of hatches • Deck between hatches • Longitudinal hatch coaming • Transverse hatch coaming • Deck webframe Slide 3 3. Deck
  335. 335. Bulk Carrier Structural functions of deck 1. Watertight integrity (local strength) Deck plate must withstand static and dynamic loads from green sea pressure as well as internal pressure from ballast tank Slide 4 3. Deck
  336. 336. Bulk Carrier • Slide 5 Structural functions of deck Stress distribution in deck 3. Deck
  337. 337. Bulk Carrier • Structural functions of deck Deck between hatches Flexing in transverse direcction Slide 6 3. Deck
  338. 338. Bulk Carrier Structural functions of deck 3. • The element contributing to transverse strength: – Deck plate and transverse stiffener between hatches – Hatch end girder – Upper stool tank Slide 7 Deck
  339. 339. Bulk Carrier 3. Functions of deck Deck 2. Upper flange in hull girder (global strength) The deck plating and longs outside line of hatches are carrying the vertical bending moments from still water and wave induced bending moments along the vessel length Global loads are acting on the hull girder beam Deck structure is acting as web in hull girder beam Cont. Slide 8
  340. 340. Bulk Carrier Hull damages deck 3. Deck Characteristic damages for deck are: 1. 2. Buckling of deck between hatches 3. Slide 9 Cracks in deck plate at end of longitudinal hatch coaming Crack in deck plate in way of hatch corner
  341. 341. Bulk Carrier Crack in deck plate at hatch coaming end 3. Deck • Longitudinal stresses are going into the side hatch coamings • At the toe of the bkt. There is a local stress concentration Possible consequences: - Water leak to cargo - Long crack – longitudinal strength problem Slide 10
  342. 342. Bulk Carrier Buckling of deck between hatches 3. • Ore carrier (250 000 DWT) Local buckling of deck plates and transverse stiffeners. • Deck plates and transv. Stiffn. buckled • Slide 11 Deck
  343. 343. Bulk Carrier Slide 12 Buckling of deck between hatches 3. Deck
  344. 344. Bulk Carrier Buckling of deck between hatches 3. • Buckling caused by excessive stresses in transverse direction deck between hatches 2 adjacent holds filled Slide 13 Deck
  345. 345. Bulk Carrier Buckling of deck between hatches 3. • Possible consequences of buckling of deck between hatches: - Ships transverse strength severely affected - Ships sides comes in - Hatch coamings deformed - Loss of weather tight integrity Slide 14 Deck
  346. 346. Bulk Carrier Hull Structural Breakdown Bulkhead 1. Side 2. Bottom 3. Deck 4. Transverse bulkhead 5. Hopper tank 6. Topside tank 7. Hatch cover & coaming Slide 1 4. Bhd.
  347. 347. Bulk Carrier Structural functions of bhd. 1. Cargo hold boundary (local strength) - Resist internal pressure from cargo / ballast - Resist water flooding 2. Transverse strength of the hull girder Slide 2 4. Bhd.
  348. 348. Bulk Carrier Structural build up of deck 4. Bhd. Corrugated bhd. Lower stool Upper stool Slide 3
  349. 349. Bulk Carrier Structural build up of deck 4. Bhd. Upper stool diaphragm Hatch coaming bkt Lower stool diaphragm Shedder plate Slide 4
  350. 350. Bulk Carrier Structural functions of bhd. 1. Cargo hold boundary (local strength) Transverse bhd. plate must withstand static and dynamic loads from bulk cargo and ballast The bulkhead must also withstand the water pressure from flooding of cargo hold without collapse Slide 5 4. Bhd.
  351. 351. Bulk Carrier Slide 6 4. Bhd.
  352. 352. Bulk Carrier Structural functions of bhd. 4. Bhd. Design load conditions • Water flooding • ” Light cargo ” full hold SF High stress lower / upper end & midfield Slide 7 Bm
  353. 353. Bulk Carrier Structural functions of bhd. flange Web Slide 8 4. Bhd.
  354. 354. Bulk Carrier Structural functions of bhd. Moment 4. Bhd. One sided load on bhd. Introduce a moment in lower stool. Size of moment incrase by narrow lower stool ( s – on sketch) High stress at intersection lower stool diaphrame and longitudinal girders s Slide 9 Narrow stool – high shear stress in diaphrames
  355. 355. Bulk Carrier Structural functions of bhd. 4. Bhd. • Transverse bhd. Supports the double bottom long. girders Moment on lower stool Empty hold Slide 10 Loaded hold
  356. 356. Bulk Carrier Structural functions of bhd. • Transverse bhd. Carry global shear from double bottom to ship side Net load from cargo Slide 11 4. Bhd.
  357. 357. Bulk Carrier Structural functions of bhd. • Upper and lower stool transverse strenght of hull Flexible part Slide 12 4. Bhd.
  358. 358. Bulk Carrier Hull damages transverse bulkhead 4. Bhd. Two characteristic damages for transverse bulkheads: 1. 2. Slide 13 Collapse of bulkhead due to corrosion in lower stool diaphrames. Shear buckling of corrugated bulkhead due to excessive corrosion
  359. 359. Bulk Carrier 4. Collapse of transverse bulkhead Capesize Bulk Carrier 9 holds – 20 years • Loaded with pellets alternate holds • Bhd. Hold 8/9 collapsed at bottom • Hatch coamings / covers pulled down • Inspection revealed heavy corrosion in lower stool • Void space – humidity – heating in double bottom below. Heavy corrosion Slide 14 Moment s Bhd.
  360. 360. Bulk Carrier Bulk Carrier loaded with pellets 1. 2. 3. Slide 15 4. Collapse of transverse bulkhead Bhd. LO W E DIA R STO PHR O AM L E Transverse bulkhead collapsed at connection between lower stool and tank-top Inspection revealed excessive corrosion at the lower end of the diaphrames in excess of 50%. Bulkhead collapsed due to insufficient shear area at connection to tank-top Casualty information SF Bm
  361. 361. Bulk Carrier Collapse of transverse bulkhead Impact on function • No boundary between cargo holds • Transverse strength of hull girder lost • Watertight integrity lost upper deck • To be repaired before leaving port Slide 16 4. Bhd.
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