08 - DNVs Hull Str for WW - Hull Str - Cargo Area - Deck

DNV’s Hull Structure course for  World Wide Shipping 8 - Hull ull Stru Struct ctu ure – carg cargo o area area Deck

Hull Structural Breakdown Deck  1.

Side

2.

Bottom

3.

Deck 

4.

Transverse bulkhead

5.

Longitudinal bulkhead

6.

Web frames

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3.

Deck 

Structural functions of deck 

3.

Deck 

Flange in hull girder  - Deck Deck platin plating g and long longitu itudin dinals als act as as the the upper upper flang flangee in the hull girder beam

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Structural build up of deck –  single skin tanker Deck Deck plat platin ing g w/longitudinals Transv Transvers ersee deck  deck  girder girder / Web Web frame frame

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Deck Deck CL girder  girder 

3.

Deck 

Longitudinal stresses in deck 

Longitudinal stresses from bending of hull girder is maximum at midship Midshi Midship p area area most most susceptible to fatigue cracking and buckling

Bending moment

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3.

Deck 

Characteristic damages

1. Crack rackss in dec deck lon longit gitudin udinal alss 2. Crack in in de deck pl plating 3. Corrosion of deckhead 4. Buckling of deck 

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3.

Deck 

Cracking in deck longitudinals longitudinals

3.

Deck 

Deck Deck longit longitudi udinal nal connection connection to web frames

Deck Deck longit longitudi udinal nal conn connec ecti tion on to transv transvers ersee bulkhe bulkhead ad

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Cause for cracking in deck  longitudinals

3.

The wave induced excitation of the hull girder leads to dynamic axial stress in the deck longitudinals +

+

 _ 

 _ 

The cyclic vari ariati ation of axi axial stress may lead to fatigue cracks initia initiatin ting g at hot spots spots A loaded condition will normally induce compression stress in the deck  (sagging) ASlideballast condition 8 16.03.2004 will normally induce tension stress in the deck  (hogging)

Deck 

Cracks in deck longitudinals longitudinals

- May resu result lt in in oil oil spill spill on deck  deck  - Corros Corrosion ion is highly influe influencing ncing the fatigue fatigue life life of a detail - A crack crack could could develop develop furt further her in the the deck  plating (brittle fracture)

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3.

Deck 

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

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Crack in underde underdeck ck support support for hose hose handling handling crane crane (P/S, midshi midship p area)

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3.

Deck 

Characteristic damages

1. Crack rackss in dec deck lon longit gitudin udinal alss 2. Crack in in de deck pl plating 3. Corrosion of deckhead 4. Buckling of deck 

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3.

Deck 

Openings in deck 

Longitudinal stress-flow around manhole in deck 

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3.

Deck 

Increased stress level around openings in deck!

Example: crack in scallop in deck  longitudinal

3.

Deck 

Oil Tanker 123,000 123,000 DWT built built 2000 Crack main deck plating (after 3 years)

Slide 13 Scallop in deck16.03.2004 longitudinal is close to access opening in deck. deck. This will give an additional

Crack in deck plating

3.

Tanker for Oil 99328 DWT built 1996 Crack in deck plating

Crack in deck plating at hose saddle support support (midshi (midship p area) Slide 14

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Deck 

Characteristic damages

1. Crack rackss in dec deck lon longit gitudin udinal alss 2. Crack in in de deck pl plating 3. Corrosion of deckhead 4. Buckling of deck 

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3.

Deck 

Corrosion of deckhead

The The ulla ullage ge space space (dec (deckh khead ead)) is an an area area susceptible to general corrosion

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3.

Deck 

Corrosion of deckhead

3.

Deck 

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

Higher str Higher stress ess level le vel in deck  deck 

σ L

Longitudinal stress

Force

σ  

 L

 F  =

n.a.

 A Area σ L

Longitudinal stress distribution

Long. stress distribution (wit (with h redu reduce ced d deck  deck  sectio sectional nal area) area)

Reduced sectional area in deck may lead to plate buckling Slide 17

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Corrosion of deckhead

3.

Deck 

Higher High er st stre ress ss lev level el in dec deck  k  due to general corrosion σ L

Longitudinal stress

Force

σ  

 L

 F  =

 A Area

σ L

A reduction of the deck deck transverse sectional sectional area due to general corrosion will lead Slide 18

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may lead to buckling problems

Corrosion of deckhead

3.

Deck 

Flatba Flatbars rs have have poor  poor   buckling capacity

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L-profiles have good  buckling capacity

Characteristic damages

1. Crack rackss in dec deck lon longit gitudin udinal alss 2. Crack in in de deck pl plating 3. Corrosion of deckhead 4. Buckling of deck 

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3.

Deck 

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

Buck Buckli ling ng of a plate plate fiel field d (pla (plati ting ng with with stif stiffe fene ners rs)) Slide 21

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3.

Deck 

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 situation may occur if the transverse transverse section of the deck deck is reduced due to general corrosion and the vessel is in a fully loaded (sagging) condition

Buckling of complete plate field Slide 22

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The deck buckling may take the form of one  plate  plate between between two deck deck longitud longitudinals inals or in worst case a complete plate field (both deck   plating with stiffeners)

Corros Corrosion ion of of dec deckhe khead ad / buckli buckling: ng:

3.

Deck 

- heavy corrosion corrosion of of deck deck may lead lead to to  buckling - small buckles buckles (plate (plate between between stiffeners) is a strong warning sign that longitudinal stresses are high - large buckle buckless (plate (plate field) field) may may lead to 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 23

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3.

Questions ?

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Deck