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8/2/2019 08 - DNVs Hull Str for WW - Hull Str - Cargo Area - Deck
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DNVs
Hull Structure course for
World Wide Shipping
8 - Hull Structure cargo area
Deck
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16.03.2004Slide 2
3. Deck
Hull Structural Breakdown -
Deck
1. Side
Bottom
Deck
Transverse bulkhead
Longitudinal bulkheadWeb frames
2.
3.
4.
5.
6.
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16.03.2004Slide 3
3. DeckStructural functions of deck
Flange in hull girder
- Deck plating and longitudinals act as the upper flange inthe hull girder beam
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16.03.2004Slide 4
3. Deck
Structural build up of deck
single skin tanker
Deck CL girderDeck plating
w/longitudinals
Transverse deck
girder / Web frame
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16.03.2004Slide 5
3. DeckLongitudinal stresses in deck
Longitudinal stresses from bending of hull girder is
maximum at midship
Bending
moment
Midship area mostsusceptible to fatigue
cracking and buckling
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16.03.2004Slide 6
3. DeckCharacteristic damages
1. Cracks in deck longitudinals2. Crack in deck plating
3. Corrosion of deckhead
4. Buckling of deck
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16.03.2004Slide 7
3. DeckCracking in deck longitudinals
Deck longitudinal
connection to web frames
Deck longitudinal
connection to
transverse bulkhead
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16.03.2004Slide 8
3. DeckCause for cracking in deck
longitudinals
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 cracksinitiating 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)
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16.03.2004Slide 9
3. DeckCracks 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 deckplating (brittle fracture)
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16.03.2004Slide 10
3. DeckCracking in deck longitudinals
Crack in underdeck support for hose
handling crane (P/S, midship area)
Oil Tanker
135,000 DWT built 1991
Crack main deck plating
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16.03.2004Slide 11
3. DeckCharacteristic damages
1. Cracks in deck longitudinals2. Crack in deck plating
3. Corrosion of deckhead
4. Buckling of deck
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16.03.2004Slide 12
3. DeckOpenings in deck
Longitudinal
stress-flow aroundmanhole in deck
Increased stress level aroundopenings in deck!
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16.03.2004Slide 13
3. DeckExample: crack in scallop in deck
longitudinal
Scallop in deck 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.
Oil Tanker
123,000 DWT built 2000
Crack main deck plating (after 3 years)
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16.03.2004Slide 14
3. DeckCrack in deck plating
Tanker for Oil
99328 DWT
built 1996
Crack in deck plating
Crack in deck plating at hose
saddle support (midship area)
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16.03.2004Slide 15
3. DeckCharacteristic damages
1. Cracks in deck longitudinals2. Crack in deck plating
3. Corrosion of deckhead
4. Buckling of deck
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16.03.2004Slide 16
3. DeckCorrosion of deckhead
The ullage space (deckhead) is an area
susceptible to general corrosion
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16.03.2004Slide 17
3. DeckCorrosion of deckhead
A reduction of the deck transverse sectional area due to general corrosion
will lead to an increased stress level in deck
A
F
L
=
Longitudinal
stress
Area
Force
Longitudinal
stress distribution
L
L
Higher stress
level in deck
Long. stress distribution(with reduced deck
sectional area)
n.a.
Reduced sectional area in deck may lead to plate buckling
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16.03.2004Slide 18
3. DeckCorrosion of deckhead
Higher stress level in deck
due to general corrosion
L
L
A
F
L=
Longitudinalstress
Area
Force
A reduction of the deck transverse sectional area due to general corrosion will lead
to an increased stress level in deck may lead to buckling problems
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16.03.2004Slide 19
3. DeckCorrosion of deckhead
Flatbars have poor
buckling capacity
L-profiles have goodbuckling capacity
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16.03.2004Slide 20
3. DeckCharacteristic damages
1. Cracks in deck longitudinals2. Crack in deck plating
3. Corrosion of deckhead
4. Buckling of deck
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16.03.2004Slide 21
3. DeckBuckling in deck
Buckling of a plate field (plating with stiffeners)
Buckling in deck is most likely to occur in the midship
region where the hull girder bending moment is at its
maximum
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16.03.2004Slide 22
3. DeckCause for buckling in 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 reduceddue to general corrosion and the vessel is in a fully loaded (sagging)
condition
The deck buckling may take the form of one
plate between two deck longitudinals or in
worst case a complete plate field (both deck
plating with stiffeners)Buckling of complete plate field
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16.03.2004Slide 23
3. DeckCorrosion of deckhead / buckling:
- 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!
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16.03.2004Slide 24
3. Deck
Questions ?
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