Chapter 6 Jms
-
Upload
mullah-fassudin -
Category
Documents
-
view
229 -
download
0
Transcript of 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.
-
8/9/2019 Chapter 6 Jms
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.
-
8/9/2019 Chapter 6 Jms
3/58
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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<"ft
1LT"ft
( * + , T
Shear Stress
Load /iagram ( * + , T
(
Shear Force at #oint )
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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$ant force concentrates at )o% and stern.
ei,ht concentrates at middle of ship.
The lon,itudinal )endin, moment %ill create a si,nificant
stress in the structure called bending stress.
-
8/9/2019 Chapter 6 Jms
10/58
A ship has similar )endin, moments5 )ut the
)uo$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.
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
11/58
Sagging
*ogging
Bendin,
Moment
BowStern Keel : tension
Weather deck : compression
Bendin,
Moment
BowStern
Keel : compression
Weather deck : tension
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
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.
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
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
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
14/58
8uantif$in, Bendin, Stress
$om#ression
ension
Sagging condition
Neutral !is
y
4
B
4
B
I
M y=
Bendin, Stress 7
M& Bending -oment
I & 2nd-oment of area of the cross section
y & ertical distance from the neutral a/is
& tensile 01 or com#ressi+e03 stress
y
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
15/58
8uantif$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
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
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
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
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 $ending
stress at 6eel than dec6.
.4.
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
18/58
4educin, the :ffect of Bendin, stress
Bendin, moment are lar,est at amidship of a ship.
Ship %ill experience the ,reatest )endin, stress at the dec"
and "eel.
The )endin, stress can )e reduced )$ usin,7 hi,her stren,th steel
lar,er cross sectional area of lon,itudinal structural elements
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
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
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
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
'on,itudinal Bendin, Stress
-
8/9/2019 Chapter 6 Jms
21/58
-
8/9/2019 Chapter 6 Jms
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.
-
8/9/2019 Chapter 6 Jms
23/58
Example Problem
!""ft long box shaped barge has an empty weight distribution of#$T%ft. &hat is the total buoyant force floating the empty bargein calm water'
The barge is then loaded with the additional cargo weightdistribution shown abo(e. &hat is the buoyant force distributionin calm water for the loaded barge'
t which point, ), B, C or *+ is the barge under the greatest shear
stress'
s the barge in a hogging or sagging condition'
f a wa(e hits which peaks at the center of the barge and troughs at
the ends, is the condition abo(e mitigated or exacerbated'
100ft
&0ft &0ft 80ft 10ft &0ft
<"ft
9LT"ft
8LT"ft
4 B 3 /
-
8/9/2019 Chapter 6 Jms
24/58
Example nswer
-B Total Empty!""ft/#$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 $oad *iagram Crosses 78 xis
Ends curling up 8 9agging
):itigated by pro(iding additional support at center of barge+
100ft
&0ft &0ft 80ft 10ft &0ft
<"ft
9LT"ft
8LT"ft
4 B 3 /
1.:LT"ft 1.:LT"ft
0.1LT"ft &.1LT"ft 1.1LT"ftLoad /iagram
6 @ Shi St t
-
8/9/2019 Chapter 6 Jms
25/58
6.@ Ship Structure
Structural omponents
Girder
3i,h stren,th structure runnin, lon,itudinall$
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
-
8/9/2019 Chapter 6 Jms
26/58
Structural omponents
*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
-
8/9/2019 Chapter 6 Jms
27/58
Ship Structure
Structural omponents
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>
-
8/9/2019 Chapter 6 Jms
28/58
* i S t
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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$stem
* i S t
-
8/9/2019 Chapter 6 Jms
31/58
Trans#erse *ramin, S$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
-
8/9/2019 Chapter 6 Jms
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$stem
-
8/9/2019 Chapter 6 Jms
33/58
( )l B tt
-
8/9/2019 Chapter 6 Jms
34/58
(ou)le Bottoms
T%o %aterti,ht )ottoms %ith a #oid space in )et%een to %ithstand the upard pressure
bending stresses
bottom damage by grounding and underater shock.
The dou)le )ottom pro#ides a space for storin,
fuel oil
)allast %ater - fresh %ater
smooth inner )ottom %hich ma"e it easier to arran,e car,o -
equipment and clean the car,o hold.
t ti ht B l"h d
-
8/9/2019 Chapter 6 Jms
35/58
aterti,ht Bul"heads
'ar,e )ul"head %hich splits the the hull into separate sectionsrimar$ 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
-
8/9/2019 Chapter 6 Jms
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 $%' of yield
stress.(
M d f St t l * il
-
8/9/2019 Chapter 6 Jms
37/58
&. Buc"lin,
"ubstantial dimension changes and sudden loss of stiffness
caused by the compression of long column or plate
Buc5ling load on shi# & cargo7 wa+es7 im#act loads7 etc.
E/&
)eck buckling * by sagging or hogging, loading on deck !ide plate buckling * by a+es, shock, groundings
column bucking * by excessi+e axial loading
Modes of Structural *ailure
M d f St t l * il
-
8/9/2019 Chapter 6 Jms
38/58
@. *ati,ue *ailure
The failure of a material from repeated application of stresssuch as from +ibration
:ndurance limit 7 stress )elo% %hich %ill not fail from fati,ue
*ati,ue failure is affected )$ 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.
Modes of Structural *ailure
M d f St t l * il
-
8/9/2019 Chapter 6 Jms
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
Modes of Structural *ailure
M d f St t l * il
-
8/9/2019 Chapter 6 Jms
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.
Modes of Structural *ailure
Example Problem6
-
8/9/2019 Chapter 6 Jms
41/58
Example Problem6dentify the following ship structural elements6
;;;;;;;;;;;;
9trength :embers ;;;;
;;;;;;;;;;
;;;;;;; ;;;;;;;;;;
;;;;;
;;;;;;;;;;
9trength :embers ;;;;;
;;;;;
;;;;;;;;; ;;;;;;;
Example nswer6
-
8/9/2019 Chapter 6 Jms
42/58
Example nswer6dentify the following ship structural elements6
$ongitudinal9trength :embers
=eel
$ongitudinal
9tringer
*eck >irder
Plating
Trans(erse
9trength :embers
-rame
-loor
*eck Beam
Plating
-
8/9/2019 Chapter 6 Jms
43/58
Example Problem-or the following components, what is the
primary failure mode of concern and how do
we address that concern'
Thick low carbon steel nuclear reactor pressure(essel
luminum airplane wings where they ?oin the
fuselage
&eapons handling gear
9teel water tower legs
Example nswer
-
8/9/2019 Chapter 6 Jms
44/58
Example nswerThick low carbon steel nuclear reactor pressure (essel
Brittle -racture
;perate primarily abo(e transition temperature :inimi
-
8/9/2019 Chapter 6 Jms
45/58
e(iew of Chapters 28D
Chapter 26 9tability
Chapter 6 Properties of Fa(al :aterials
Chapter D6 9hip 9tructures
e(iew EAuation 5 Con(ersion 9heet
-
8/9/2019 Chapter 6 Jms
46/58
Chapter 26 9tability
nternal ighting :oment
Cur(e of ntact 9tatical 9tability
9tability Characteristics from Cur(e Effect of ertical :otion of > on >G
Effect of Trans(erse :otion of > on >G
*amage 9tability -ree 9urface Correction
:etacentric @eight and 9tability
-
8/9/2019 Chapter 6 Jms
47/58
Chapter 2 +!G< !G< B G (ositive) eutral) egative ,ta$ility
-
8/9/2019 Chapter 6 Jms
48/58
Cur(e of ntact 9tatical 9tability
+ange of ,ta$ility
a +ighting 4rm #G
-
8/9/2019 Chapter 6 Jms
49/58
Chapter 6 Properties of Fa(al :aterials
Classifying $oads
9tress and 9train
9tress89train *iagrams and :aterialBeha(ior
:aterial Properties
Fon8*estructi(e Testing
;ther Engineering :aterials
Ch t
-
8/9/2019 Chapter 6 Jms
50/58
Chapter ,tressC !"4 #l$"inD) 'si or 6si%
ElongationCe!L-L0F ,trainC !e"L0#ft"ft% Elastic odulusC E!"#l$"inD) 'si) 6si%
,tress
,train
T,
,lo'e!E
racture(lastic +egion
Elastic
+egion,train
ardeningy
,tress",train /iagram
aterial
Toughness
-
8/9/2019 Chapter 6 Jms
51/58
Chapter
*uctile to Brittle
TransitionC
-atigue Beha(iorC
3har'y
#Hm'act%
Toughness
#in-l$s%
Tem'erature#I%
TransitionTem'erature
Brittle
Behavior
/uctile
Behavior ,tress
#'si%
3ycles
Endurance Limit
,teel
4luminum
-
8/9/2019 Chapter 6 Jms
52/58
Chapter
F*T External6 T, PT, :T
nternal6 T, HT, Eddy Current ;p tests6 @ydro, &eight%$oad
-
8/9/2019 Chapter 6 Jms
53/58
Chapter D6 9hip 9tructures
HniAue spects of 9hip 9tructures
9hip 9tructural $oads
9hip 9tructure
:odes of -ailure
-
8/9/2019 Chapter 6 Jms
54/58
Chapter D
*istributed -orces
*istributed &eight
*istributed Buoyancy
*istribution/*istanceTotal !$T%ft/Dft02$T%ft/1ft!I$T
#$T%ft/3ft!I$T
9hear 9tress $ocali
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
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
-
8/9/2019 Chapter 6 Jms
58/58
9ummary
EAuation 9heet
ssigned homework problems
@omework problems not assigned Example problems worked in class Example problems worked in text