Chapter 6 Jms

8/9/2019 Chapter 6 Jms

1/58

6.1 Unique Aspects of Ship Structures

Ships are BIG!

Three dimensional complex shape.

Multiurpose Support Structure and S"in.

Ships see a #ariet$ of d$namic and randomloads.

Ships operate in a %ide #ariet$ ofen#ironments.


2/58

6.& Ship Structural 'oad

(istri)uted *orces + %ei,ht - )uo$anc$

G

B

WL

s.

B*

< Floating Body in Static Equilibrium>

Resultant weight force due to

the distributed weight

Result Buoyancy force due to

the distributed buoyancy

- Two forces are equal in magnitude.- The centroid of the forces are vertically in line.


3/58


4/58

(istri)uted ei,ht

- "eight of shi# can be #resented as a distributed force.- $ase % & Uniformly distributed weight

2 L!ft

barge

2 L!ft

50 ft

Bs*1//'T0/ft

ft

&'T. ===

(istri)uted *orces


5/58

(istri)uted ei,ht

2 L!ft

barge

' L!ft

50 ft

Bs *1//'T1/ft

ft

1'T1/ft

ft

&'T1/ft

ft

2'T1/ft

ft

&'T1/ft

ft

1'T. ==++++=

- $ase %% &Non-uniformly distributed weight

2 L!ft

( L!ft

2 L!ft' L!ft

10ft

wB! B"L #distri$uted load ! B"length%wB! 100LT ! & LT"ft 50ft

(istri)uted *orces


6/58

Shear stress'resent at 'oints () *) +) , T due to un$alanced forces

at to' and $ottom.

Load diagramcan $e drawn $y summing u' the distri$uted force

vertically. ( L!ft

2 L!ft

' L!ft2 L!ft 2 L!ft

' L!ft

1LT"ft&LT"ft

1LT"ft

( * + , T

Shear Stress

Load /iagram ( * + , T

(

Shear Force at #oint )


7/58

aimum shear stresses occur where the load diagram crossesthe -ais #or equals 0%.

' L!ft ' L!ft

2 L!ft

(

* +

, T

-10 LT

210 LT

Load/iagram

,hear/iagram

Shear Stress


8/58

3o% to 4educe Shear Stress of ship

To chan,e the under%ater hull shape so that )uo$anc$

distri)ution matches that of %ei,ht distri)ution.

The step li"e shape is #er$ inefficient %ith re,ard to

the resistance.

Since the loadin, condition chan,es e#er$ time5 this method

is not feasi)le.

To concentrate the ship hull strength in an area %here lar,e

shear stress exists . This can )e done )$

using higher strength material

increasing the cross sectional area of the structure.

Shear Stress


9/58

'on,itudinal Bendin, Stress

'on,itudinal Bendin, Moment and Stress

Une#en load distri)ution %ill produce a lon,itudinal

Bending Moment.

Bendin, Moment

Buo$ant force concentrates at )o% and stern.

ei,ht concentrates at middle of ship.

The lon,itudinal )endin, moment %ill create a si,nificant

stress in the structure called bending stress.


10/58

A ship has similar )endin, moments5 )ut the

)uo$anc$ and man$ loads are distri)uted o#er the

entire hull instead of ust one point.

The up%ard force is )uo$anc$ and the do%n%ard

forces are %ei,hts.

Most %ei,ht and )uo$anc$ is concentrated in themiddle of a ship5 %here the #olume is ,reatest.



11/58

Sagging

*ogging

Bendin,

Moment

BowStern Keel : tension

Weather deck : compression

Bendin,

Moment

BowStern

Keel : compression

Weather deck : tension



12/58

Sa,,in, - 3o,,in, on a#es

Sagging condition

*ogging condition

Trough3rest

Trough3rest

3rest

Trough

Buoyant force is greater at wa+e crests.



13/58

IM y=

here7M, Bending -oment

I , 2nd-oment of area of the cross section

y , ertical distance from the neutral a/is

, tensile 01 or com#ressi+e03 stress

The longitudinal bending moment creates a significant

structural stress called the bending stress



14/58

8uantif$in, Bendin, Stress

$om#ression

ension

Sagging condition

Neutral !is

y

4

B

4

B

I

M y=

Bendin, Stress 7

M& Bending -oment

I & 2nd-oment of area of the cross section

y & ertical distance from the neutral a/is

& tensile 01 or com#ressi+e03 stress

y



15/58

8uantif$in, Bendin, Stress

*ogging conditiony

$om#ression

ension

Neutral !is

4

B

4

B

9eutral Axis& geometric centroid of the cross section or

transition between com#ression and tension



16/58

:xample 7Bendin, Stress of Ship 3ull

"hip could be at sagging condition e#en in calm water $

%enerally& bending moments are largest at the midship area$

eutral4is

Bow,tern

4

B

/ec6

7eel

B

4

4ec5 & $om#ression

6eel & ension

Tic6nesscrosssection



17/58

:xample 7Bendin, Stress of Ship 3ull

eutral 4is

Bow,tern

4

B

/ec6

7eel

B

4

Tic6nesscrosssection

y

7eel

This shi' has lager $ending

stress at 6eel than dec6.

.4.



18/58

4educin, the :ffect of Bendin, stress

Bendin, moment are lar,est at amidship of a ship.

Ship %ill experience the ,reatest )endin, stress at the dec"

and "eel.

The )endin, stress can )e reduced )$ usin,7 hi,her stren,th steel

lar,er cross sectional area of lon,itudinal structural elements



19/58

3ull Structure Interaction

Bendin, stress at the superstructure is lar,e )ecause of its

distance from the neutral axis.

In Sa,,in, or 3o,,in, condition5 se#ere shear stresses )et%een

dec" of hull and )ottom of the superstructure %ill )e created.

This shear stresses %ill cause crac" in area of sharp corners

%here the hull and superstructure connect.

This stress can )e reduced )$ an Expansion Joint



20/58

Compression orTension on deck

Expansion Joint

By using Expansion Joint, the super structure will be

allowed to flex along with the hull.

Compression or

Tension on bottom



21/58


22/58

;ther 'oads

eapon 'oads

'oadin, due to explosion of %eapons or shoc"

impact,)oth in air and under%ater

9a#al ?essel should resist these forces

9a#al #essel %ill often ,o throu,h a series of shock

trials durin, initial sea trials.


23/58

Example Problem

!""ft long box shaped barge has an empty weight distribution of#$T%ft. &hat is the total buoyant force floating the empty bargein calm water'

The barge is then loaded with the additional cargo weightdistribution shown abo(e. &hat is the buoyant force distributionin calm water for the loaded barge'

t which point, ), B, C or *+ is the barge under the greatest shear

stress'

s the barge in a hogging or sagging condition'

f a wa(e hits which peaks at the center of the barge and troughs at

the ends, is the condition abo(e mitigated or exacerbated'

100ft

&0ft &0ft 80ft 10ft &0ft

&LT"ft

9LT"ft

8LT"ft

4 B 3 /


24/58

Example nswer

-B Total Empty!""ft/#$T%ft#""$T

-B Total $oaded#""$T0#"ft/#$T%ft0

1"ft/2$T%ft0!"ft/1$T%ft13"$T

-B *ist4n13"$T%!""ft1.3$T%ft

Point 5 *6 $oad *iagram Crosses 78 xis

Ends curling up 8 9agging

):itigated by pro(iding additional support at center of barge+

100ft

&0ft &0ft 80ft 10ft &0ft

&LT"ft

9LT"ft

8LT"ft

4 B 3 /

1.:LT"ft 1.:LT"ft

0.1LT"ft &.1LT"ft 1.1LT"ftLoad /iagram

6 @ Shi St t


25/58

6.@ Ship Structure

Structural omponents

Girder

3i,h stren,th structure runnin, lon,itudinall$

eel

'ar,e center plane ,irder

4uns lon,itudinall$ alon, the )ottom of the ship

latin,

Thin pieces enclosin, the top5 )ottom and side of structure

ontri)utes si,nificantl$ to lon,itudinal hull stren,th 4esists the h$drostatic pressure load =or side impact>

*rame

A trans#erse mem)er runnin, from "eel to dec"

4esists h$drostatic pressure5 %a#es5 impact5 etc


26/58


*loor

(eep frame runnin, from the "eel to the turn of the )il,e

*rames ma$ )e attached to the floors

=*rame %ould )e the part a)o#e the floor>

'on,itudinal

Girders runnin, parallel to the "eel alon, the )ottom

Intersects floors at ri,ht an,les

ro#ides lon,itudinal stren,th

Ship Structure


27/58

Ship Structure


Strin,er

Girders runnin, alon, the sides of the ship

T$picall$ smaller than a lon,itudinal

ro#ides lon,itudinal stren,th

(ec" Beams

Trans#erse mem)er of the dec" frame

(ec" Girder

'on,itudinal mem)er of the dec" frame

=dec" lon,itudinal>


28/58

* i S t


29/58

*ramin, S$stem

Increase shipCs stren,th )$7

Addin, framin, elements more densel$ Increasin, the thic"ness of platin, and structural

components

All this %ill increase cost5 reduce space utiliDation and

allo% less missionrelated equipment to )e added

;ptimi


30/58

'on,itudinal *ramin, S$stem

'on,itudinal *ramin, S$stem 7

'on,itudinals are spaced frequentl$ )ut shallo%er

*rames are spaced %idel$

eel5 lon,itudinals5 strin,ers5 dec" ,irders5 plates

Primary roleof lon,itudinal mem)ers 7 to resist the

longitudinal bending stress due to sagging and hogging.

A t$pical %a#e len,th in the ocean is @//ft. Ships of this len,th

or ,reater are li"el$ to experience considera)le lon,itudinal )endin, stress.

Ship that are lon,er than a)out @//ft =lon, ship> tend to ha#e a

,reater num)er of lon,itudinal mem)ers than trans#erse

mem)ers.

*ramin, S$stem

* i S t


31/58

Trans#erse *ramin, S$stem

Trans#erse *ramin, S$stem 7

'on,itudinals are spaced %idel$ )ut deep.

*rames are spaced closel$ and continuousl$

Trans#erse mem)ers 7 frame5 floor5 dec" )eam5 platin,

Primary roleof trans#erse mem)ers 7 to resist h$drostatic

loads. Ships shorter than @//ft and su)mersi)les

*ramin, S$stem

* i S t


32/58

om)ined *ramin, S$stem

om)ination of lon,itudinal and trans#erse framin, s$stem

urpose7

To optimiDe the structural arran,ement for the expected

loadin,

To minimiDe the cost

T$pical com)ination 7 'on,itudinals and strin,ers %ith shallo% frame

(eep frame e#er$ @rd or 2thframe

*ramin, S$stem


33/58

( )l B tt


34/58

(ou)le Bottoms

T%o %aterti,ht )ottoms %ith a #oid space in )et%een to %ithstand the upard pressure

bending stresses

bottom damage by grounding and underater shock.

The dou)le )ottom pro#ides a space for storin,

fuel oil

)allast %ater - fresh %ater

smooth inner )ottom %hich ma"e it easier to arran,e car,o -

equipment and clean the car,o hold.

t ti ht B l"h d


35/58

aterti,ht Bul"heads

'ar,e )ul"head %hich splits the the hull into separate sectionsrimar$ role

!tiffening the ship

"educing the effect of damage

The careful positionin, the )ul"heads allo%s the ship to fulfill

the dama,e sta)ilit$ criteria.

The )ul"heads are often stiffened )$ steel mem)ers in the#ertical and horiDontal directions.

6 2 M d f St t l * il


36/58

6.2 Modes of Structural *ailure

1. Tensile or ompressi#e Eield

"low plastic deformation of a structural component due to an

applied stress greater than yield stress

o a+oid the yield7 Safety factors are considered for shi#

constructions.

"afety factor ' ( or )#Maximum stress on ship hull ill be $%& or $%' of yield

stress.(

M d f St t l * il


37/58

&. Buc"lin,

"ubstantial dimension changes and sudden loss of stiffness

caused by the compression of long column or plate

Buc5ling load on shi# & cargo7 wa+es7 im#act loads7 etc.

E/&

)eck buckling * by sagging or hogging, loading on deck !ide plate buckling * by a+es, shock, groundings

column bucking * by excessi+e axial loading

Modes of Structural *ailure

M d f St t l * il


38/58

@. *ati,ue *ailure

The failure of a material from repeated application of stresssuch as from +ibration

:ndurance limit 7 stress )elo% %hich %ill not fail from fati,ue

*ati,ue failure is affected )$ material composition =impurities5 car)on contents5

internal defects>

surface finish

en#ironments =corrosion5 salinities5 sulfites5 moisture5..>

,eometr$ =sharp corners5 discontinuities>

%or"manship =%eldin,5 fitup>

*ati,ue ,enerall$ createscracks on the ship hull.


M d f St t l * il


39/58

2. Brittle *racture

sudden catastrophic failure ith little or no plastic deformation

Brittle fracture depends on

Material7 'o% tou,hness - hi,h car)on material

Temperature7 Material operatin, )elo% its transition temperature

Geometr$7 ea" point for crac" 7 sharp corners5 ed,es

T$pe F 4ate of 'oadin,7 TensileFimpact loadin,s are %orse


M d f St t l * il


40/58

0. reep

The slo plastic deformation of material due to continuously

applied stresses that are belo its yield stress.

reep is not usuall$ a concern in ship structures.


Example Problem6


41/58

Example Problem6dentify the following ship structural elements6

;;;;;;;;;;;;

9trength :embers ;;;;

;;;;;;;;;;

;;;;;;; ;;;;;;;;;;

;;;;;

;;;;;;;;;;

9trength :embers ;;;;;

;;;;;

;;;;;;;;; ;;;;;;;

Example nswer6


42/58

Example nswer6dentify the following ship structural elements6

$ongitudinal9trength :embers

=eel

$ongitudinal

9tringer

*eck >irder

Plating

Trans(erse

9trength :embers

-rame

-loor

*eck Beam

Plating


43/58

Example Problem-or the following components, what is the

primary failure mode of concern and how do

we address that concern'

Thick low carbon steel nuclear reactor pressure(essel

luminum airplane wings where they ?oin the

fuselage

&eapons handling gear

9teel water tower legs

Example nswer


44/58

Example nswerThick low carbon steel nuclear reactor pressure (essel

Brittle -racture

;perate primarily abo(e transition temperature :inimi


45/58

e(iew of Chapters 28D

Chapter 26 9tability

Chapter 6 Properties of Fa(al :aterials

Chapter D6 9hip 9tructures

e(iew EAuation 5 Con(ersion 9heet


46/58

Chapter 26 9tability

nternal ighting :oment

Cur(e of ntact 9tatical 9tability

9tability Characteristics from Cur(e Effect of ertical :otion of > on >G

Effect of Trans(erse :otion of > on >G

*amage 9tability -ree 9urface Correction

:etacentric @eight and 9tability


47/58

Chapter 2 +!G< !G< B G (ositive) eutral) egative ,ta$ility


48/58

Cur(e of ntact 9tatical 9tability

+ange of ,ta$ility

a +ighting 4rm #G


49/58

Chapter 6 Properties of Fa(al :aterials

Classifying $oads

9tress and 9train

9tress89train *iagrams and :aterialBeha(ior

:aterial Properties

Fon8*estructi(e Testing

;ther Engineering :aterials

Ch t


50/58

Chapter ,tressC !"4 #l$"inD) 'si or 6si%

ElongationCe!L-L0F ,trainC !e"L0#ft"ft% Elastic odulusC E!"#l$"inD) 'si) 6si%

,tress

,train

T,

,lo'e!E

racture(lastic +egion

Elastic

+egion,train

ardeningy

,tress",train /iagram

aterial

Toughness


51/58

Chapter

*uctile to Brittle

TransitionC

-atigue Beha(iorC

3har'y

#Hm'act%

Toughness

#in-l$s%

Tem'erature#I%

TransitionTem'erature

Brittle

Behavior

/uctile

Behavior ,tress

#'si%

3ycles

Endurance Limit

,teel

4luminum


52/58

Chapter

F*T External6 T, PT, :T

nternal6 T, HT, Eddy Current ;p tests6 @ydro, &eight%$oad


53/58

Chapter D6 9hip 9tructures

HniAue spects of 9hip 9tructures

9hip 9tructural $oads

9hip 9tructure

:odes of -ailure


54/58

Chapter D

*istributed -orces

*istributed &eight

*istributed Buoyancy

*istribution/*istanceTotal !$T%ft/Dft02$T%ft/1ft!I$T

#$T%ft/3ft!I$T

9hear 9tress $ocali


55/58

Chapter D6 9hip 9tructural Components

$ongitudinal 9trength

:embers =eel

$ongitudinal

9tringers *eck >irders

Plating

Trans(erse 9trength

:embers -rame

-loor

*eck Beams Plating

,tanchion


56/58

Chapter D6 :odes of 9tructural -ailure

Tensile or Compressi(e ield Exceed ield 9tress

Buckling

Bowing induced bylongitudinal load on

slender structure

,tress

,train

y


57/58

Chapter D

-atigue -ailure

Brittle -racture :aterial

Temperature >eometry

ate of $oading

,tress

#'si%

3ycles

Endurance Limit

,teel

4luminum

/uctile

Brittle

,tress

,train

3har'y

#Hm'act%

Toughness#in-l$s%

Tem'erature#I%

Transition

Tem'erature

Brittle

Behavior

/uctile

Behavior


58/58

9ummary

EAuation 9heet

ssigned homework problems

@omework problems not assigned Example problems worked in class Example problems worked in text

Chapter 6 Jms

Documents

Transcript of Chapter 6 Jms