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Offshore Structures Offshore Lift Analysis
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
DOUBLE PADEYEMOUNTED ON
TOP
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
PADEYEMOUNTED ONSIDE
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
PADEYEMOUNTED ONTOP
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
TRUNNION (MAIN PLATE WELDED TO SKIN)
PPvPipe
Ph
InternalRings
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
TRUNNION (MAIN PLATE SLOTTED INTO TUBE)
PPvPipe
Ph
ExternalRings
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
DESIGN PROCEDURE
Establish Maximum Sling Load (Fmax)
Select suitable Sling Diameter
Select Suitable Shackle
Check Suitability of Shackle and Slings
Select Suitable Main Plates and Cheek Plates
Check Suitability of Spacing, gap withselected shackle and add spacers if required
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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modify either padeye, shackle or sling asnecessary
Offshore Structures Offshore Lift Analysis
PADEYE ARRANGEMENT
Generally one main plate of thickness from 25mm to90mm can be used
Cheek lates should not be more than the thickness ofmain plates
More than one cheek plate on each face shall be avoided
Second cheek plate shall be considered as spacer plate Boring shall be done after welding the cheek plates to
main plate
A minimum clear gap (S) of 5mm shall be providedbetween shackle and the last cheek or s acer late
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Adequate space (C2)shall be provided between the top ofmain plate and the underside of shackle and shall beminimum 1.5*Sling Diameter
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Offshore Structures Offshore Lift Analysis
CLEARANCES
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
Rm
Rc
FPDLPullout shear
Plane
Main Plate(tm)
Cheek Plate(tc)
FV
Rp
P P
Structureh
Clearance for
Stiffener
FH
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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B
Shackle
Q Q
Offshore Structures Offshore Lift Analysis
Cheek Plates
FPDL/2FPDL/2Main Plate
Out-off plane
Stiffener Plate
Force of 5%FPDLCos
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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bs bs
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Offshore Structures Offshore Lift Analysis
X
Y Y
2bs
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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X
Offshore Structures Offshore Lift Analysis
The bearing stress fb shall be calculated as below:
PDLF=
Bearing Stress Calculation
fcmp Rttd 2+
WhereFPDL =Padeye Design Load
dp=Diameter of Pin
tm =Thickness of main plate
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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tc =Thickness of cheek plate
Rf=Reduction Factor
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Offshore Structures Offshore Lift Analysis
PDLF
=
PULLOUT SHEAR STRESS CALCUALTIONSPullout shear stress shall be calculated as below.
( ) ( )2 2sm p m c p c
R R t R R t +
where
FPDL=Padeye design load
Rm=Radius of main plate
Rc=Radius of cheek plate
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Rp
=Radius of pin
tm= Thickness of main plate
tc=Thickness of cheek plate
Offshore Structures Offshore Lift Analysis
PDL
t
F Sinf
=
TENSILE STRESS AT SECTION P-P
m p m c p c
t t +
F Sin
TENSILE STRESS AT SECTION Q-Q
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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[ ]4t
m s sB t b t
=+
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Offshore Structures Offshore Lift Analysis
HORIZONTAL SHEAR STRESS AT SECTION P-P
INPLANE SHEAR STRESSES
( ) ( )2PDL
s in
m p m c p c
F Cosf
R R t R R t
= +
HORIZONTAL SHEAR STRESS AT SECTION Q-Q
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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[ ]PDL
s in
m
F CosfBt
=
Offshore Structures Offshore Lift Analysis
HORIZONTAL SHEAR STRESS AT SECTION Q-Q
OUT-OFF PLANE SHEAR STRESSES
[ ]
0.05
4PDL
s op
s s
F Cosf b t
=
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
INPLANE
BENDING STRESSES AT SECTION Y-Y
23 3
xx2I
PDL
b in
F hBCosf
=
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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2 412 12 2m s s s
xx s sI b t
= + +
Offshore Structures Offshore Lift Analysis
OUT-OFF PLANE
BENDING STRESSES AT SECTION Y-Y
3 3
YY
0.05
I
PDL s
b op
F hb Cosf
=
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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212 12m s s
YYI = +
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Offshore Structures Offshore Lift Analysis
COMBINED STRESSES
2 2
b b in b of f f
= +Combined Bending Stress
2 2
s s in s opf f f
= +Combined Shear Stress
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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2 2 23von t s b t bf f f f f f= + + Von Mises Stress
Offshore Structures Offshore Lift Analysis
ALLOWABLE STRESSES
Establish stresses induced in the padeyeplates and connections and to assure they are
Bearing Stresses (0.9Fy)
Shear Stresses (0.4Fy)
Tensile Stresses (0.6Fy)
Bending Stresses (0.6Fy)
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Combined Stresses (0.75Fy)
Von Mises Stress (0.75Fy)
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Offshore Structures Offshore Lift Analysis
0.5 FPDL0.5 FPDL
Weld Size w1WELDING BETWEEN MAIN AND
CHEEK PLATES
Main Plate : tm, Rm
Weld Size w2First Cheek Plate : tc1, Rc1
Second Cheek Plate : tc2, Rc2
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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11
R2R2
Offshore Structures Offshore Lift Analysis
Weld Between Main and Cheek Plates:
1
1
1 2
.PDL c
m c c
F tR
t t t=
+ +Force Transmitted betweenMain plate and First Cheek Plate
1 2
112 .0.707.c yw
R Rw
R F
+=
2
2
.PDL c
F tR
t t t=
+ +
Force Transmitted between FirstCheek plate and Second Cheek Plate
Fillet Weld Size required betweenmain plate and first cheek plate
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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2
2
22 .0.707.
c yw
Rw
R F=Fillet Weld Size required between first
cheek plate and second cheek plate
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Offshore Structures Offshore Lift Analysis
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
UNSYMETRIC ARRANGEMENT
Many occasions we will be using theunsymetric arrangement
The vertical load distribution across the
main plate is not uniform and itintroduces an eccentricity e whichcauses additional moment
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
X
FH
FPDLF
v
UNSYMETRIC
ARRANGEMENT
YY
h
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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XB
e
Offshore Structures Offshore Lift Analysis
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
CONNECTION TO THE MAIN STRUCTURE
The loads from the padeye shall betransmitted to the main structure safelywithout overstressing.
Many different methods of transmittingthe forces can be adopted.
The simple way of transferring is by either
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Methods using Bending or combination ofAxial and bending shall be avoided
Offshore Structures Offshore Lift Analysis
FPDL
FH
Fv
h
e
PADEYE MAIN PLATE SLOTTED
TO THE DECK EXTENSION
Welding betweentube and main plate
DL
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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( )
y y y
. e+D/2
4 0.4F 2 0.4F 2 0.4FPDL PDL PDL
t t t
F Sin F Sin F Cos hL
T T D T D
= +
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Offshore Structures Offshore Lift Analysis
PADEYE MAIN PLATE SLOTTED
TO THE DECK EXTENSION
Welding betweentube and main plate
FPDL
FH
Fv
h
DL
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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y y
. ( 0.5 )
4 0.4F 2 0.4F
PDL PDL
t t
F Sin F Cos h LL
T D T D
+= +
Offshore Structures Offshore Lift Analysis
PADEYE MAIN PLATE WELDED TO
DECK LEG SKIN
Welding betweentube and main plate
FPDL
FH
Fv
h
e
DL
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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y
2 0 .4 F
P D L
m
F S i nL
t
= ( Only Vertical Load
Transferred)
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Offshore Structures Offshore Lift Analysis
MAIN PLATE WELDED TO SKIN OF TUBE
The Vertical Component of Load (FV) istransferred through the direct shear between
Horizontal component (FH) and moments shallbe decoupled between top and bottom ringplates
These forces on the rings shall be transferred ascircumferential shear
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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,
these forces shall have to be transferred bybending
Offshore Structures Offshore Lift Analysis
CALCULATION OF RING FORCES
Top Ring Plate
(0.5 ) (e+D/2)PD L P D L
T
F C os L h F SinF
L L
+=
+
Bottom Ring Plate
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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.P D L PD L
TF
L L= +
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Offshore Structures Offshore Lift Analysis
FINITE ELEMENT ANALYSIS
Finite element analysis will be carried out when
No redundancy in design failure of the.
Multiple / unclear Load path.
Manual Calculations too conservative dueto assumptions made on load path.
Manual calculation becomes toocomplicated.
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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FEM analysis will give actual load path
Indicate hot spots where local stresses are high
Offshore Structures Offshore Lift Analysis
FEA Lifting Pad-eye
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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Offshore Structures Offshore Lift Analysis
FEA - Spreader Bar
5/3/2011 Dr. S. NallayarasuDepartment of Ocean Engineering
Indian Institute of Technology Madras-36
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