5/6/2011Offshore Structures – Offshore Lift Analysis 5/3/2011 1 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis DOUBLE PADEYE MOUNTED ON TOP 5/3/2011 2 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 1 5/6/2011 Offshore Structures – Offshore Lift Analysis PADEYE MOUNTED ON SIDE 5/3/2011 3 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis PADEYE MOUNTED ON TOP 5/3/2011 4 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 2 Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 3 .5/6/2011 Offshore Structures – Offshore Lift Analysis 5/3/2011 5 Dr. S. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis TRUNNION (MAIN PLATE WELDED TO SKIN) Pv P Pipe Ph Internal Rings 5/3/2011 6 Dr. S.5/6/2011 Offshore Structures – Offshore Lift Analysis TRUNNION (MAIN PLATE SLOTTED INTO TUBE) Pipe Pv P Ph External Rings 5/3/2011 7 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 4 . Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis 5/3/2011 8 Dr. 5/6/2011 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. S. gap with selected shackle and add spacers if required Attempt a Structural Analysis for strength and modify either padeye. S.5*Sling Diameter 5/3/2011 10 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis PADEYE ARRANGEMENT Generally one main plate of thickness from 25mm to 90mm can be used Cheek plates should not be more than the thickness of main 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 provided p p plate between shackle and the last cheek or spacer Adequate space (C2)shall be provided between the top of main plate and the underside of shackle and shall be minimum 1. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 5 . shackle or sling as necessary 5/3/2011 9 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis 5/3/2011 12 Dr.5/6/2011 Offshore Structures – Offshore Lift Analysis CLEARANCES 5/3/2011 11 Dr. S. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 6 . Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 7 .5/6/2011 Offshore Structures – Offshore Lift Analysis Pullout shear Plane Main Plate (tm) P Rp FV Rm Rc θ FH P Stiffener Structure Clearance for Shackle FPDL Cheek Plate (tc) h Q B 5/3/2011 13 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Q Offshore Structures – Offshore Lift Analysis Main Plate FPDL/2 FPDL/2 Out-off p plane Force of 5% FPDL Cos θ Cheek Plates Stiffener Plate bs bs 5/3/2011 14 Dr. S. 5/6/2011 Offshore Structures – Offshore Lift Analysis X Y Y 2bs B X 5/3/2011 15 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis Bearing Stress Calculation The bearing stress fb shall be calculated as below: fb = Where FPDL d p (tm + 2tc )R f FPDL = Padeye Design Load dp= Diameter of Pin tm = Thickness of main plate tc = Thickness of cheek plate Rf = Reduction Factor 5/3/2011 16 Dr. S. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 8 . f = s F ⎡( R − R ) t + 2 ( R − R ) t ⎦ ⎤ 2⎣ PDL m p m c p c where FPDL=Padeye design load Rm=Radius of main plate Rc=Radius of cheek plate Rp=Radius of pin tm= Thickness of main plate tc=Thickness of cheek plate 5/3/2011 17 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis TENSILE STRESS AT SECTION P-P f = t F Sin θ ⎡ ⎣2 ( R − R ) t + 4 ( R − R ) t ⎤ ⎦ PDL m p m c p c TENSILE STRESS AT SECTION Q-Q f = t F Sin θ [Bt + 4 b t PDL m s s ] 5/3/2011 18 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 9 . S.5/6/2011 Offshore Structures – Offshore Lift Analysis PULLOUT SHEAR STRESS CALCUALTIONS Pullout shear stress shall be calculated as below. S. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 10 . S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis OUT-OFF PLANE SHEAR STRESSES HORIZONTAL SHEAR STRESS AT SECTION Q-Q f s − op = 0.05 F Cos θ [ 4b t ] PDL s s 5/3/2011 20 Dr.5/6/2011 Offshore Structures – Offshore Lift Analysis INPLANE SHEAR STRESSES HORIZONTAL SHEAR STRESS AT SECTION P-P f s − in = F Cos θ ⎡ ⎣( R − R ) t + 2 ( R − R ) t ⎤ ⎦ PDL m p m c p c HORIZONTAL SHEAR STRESS AT SECTION Q-Q f 5/3/2011 s − in = F Cos θ [ Bt ] PDL m 19 Dr. 05 F hb Cos θ I PDL s YY 3 3 m s s t B ⎛ 8b t ⎞ I = + 2⎜ ⎟ 12 ⎝ 12 ⎠ YY 5/3/2011 22 Dr. S.5/6/2011 Offshore Structures – Offshore Lift Analysis BENDING STRESSES AT SECTION Y-Y INPLANE f b − in F hBCos θ = 2I PDL xx 3 3 2 m s s s ⎛ 2b t t B ⎛B−t ⎞ ⎞ I = + 2⎜ + 4b t ⎜ ⎟ ⎟ 12 ⎝ 2 ⎠ ⎠ ⎝ 12 xx s s 5/3/2011 21 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis BENDING STRESSES AT SECTION Y-Y OUT-OFF PLANE f b − op = 0. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 11 . 75Fy) Von Mises Stress (0.5/6/2011 Offshore Structures – Offshore Lift Analysis COMBINED STRESSES Combined Bending Stress fb = f 2b−in + f 2b−op p fs = f 2s−in + f 2s−op fvon = ft2 +3fs2 + fb2 − ft fb 23 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 5/3/2011 12 .9Fy) Shear Stresses (0.75Fy) 24 Dr.4Fy) Tensile Stresses (0.6Fy) Combined Stresses (0. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Combined Shear Stress Von Mises Stress 5/3/2011 Offshore Structures – Offshore Lift Analysis ALLOWABLE STRESSES Establish stresses induced in the padeye plates and connections and to assure they are within allowable stresses Bearing Stresses (0.6Fy) Bending Stresses (0. S. t c1 t m + t c1 + t c 2 R1 + R2 Fillet Weld Size required between main plate and first cheek plate 2π Rc1. Rc1 Second Cheek Plate : tc2. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis Weld Between Main and Cheek Plates: Force Transmitted between Main plate and First Cheek Plate R1 = w1 = FPDL .707.0.Fyw R2 Fillet Weld Size required between first cheek plate and second cheek plate 5/3/2011 26 Dr.0. Rc2 0. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 13 .Fyw Force Transmitted between First Cheek plate and Second Cheek Plate R2 = w2 = FPDL . S.5/6/2011 Offshore Structures – Offshore Lift Analysis WELDING BETWEEN MAIN AND CHEEK PLATES Main Plate : tm.707.5 FPDL Weld Size w2 R1 R2 R2 R1 5/3/2011 25 Dr.t c 2 t m + t c1 + t c 2 2π Rc 2 .5 FPDL Weld Size w1 0. Rm First Cheek Plate : tc1. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis UNSYMETRIC ARRANGEMENT Many occasions we will be using the unsymetric y arrangement g The vertical load distribution across the main plate is not uniform and it introduces an eccentricity “e” which causes additional moment 5/3/2011 28 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 14 . S.5/6/2011 Offshore Structures – Offshore Lift Analysis 5/3/2011 27 Dr. S.5/6/2011 Offshore Structures – Offshore Lift Analysis UNSYMETRIC ARRANGEMENT X Fv FH FPDL h Y e B X 5/3/2011 29 Y Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis 5/3/2011 30 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 15 . Many different methods of transmitting the forces can be adopted.4Fy 5/3/2011 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis PADEYE MAIN PLATE SLOTTED TO THE DECK EXTENSION Welding between tube and main plate L D Fv e θ FH h FPDL L= FPDL Sin θ 4Tt 0. S.Sin θ ( e+D/2 ) 2Tt D 0. S.5/6/2011 Offshore Structures – Offshore Lift Analysis CONNECTION TO THE MAIN STRUCTURE The loads from the padeye shall be transmitted to the main structure safely y without overstressing. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 16 .4F y + FPDL .4F y 32 − FPDL Cos θ h 2Tt D 0. The simple way of transferring is by either “Direct Direct Shear” Shear or by “Ring Ring Shear” Shear Methods using Bending or combination of Axial and bending shall be avoided 5/3/2011 31 Dr. 4F y + FPDL Cos θ (h + 0. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 5/3/2011 17 . Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 5/3/2011 Offshore Structures – Offshore Lift Analysis PADEYE MAIN PLATE WELDED TO DECK LEG SKIN Welding between tube and main plate L D Fv e θ FH h FPDL L = F PD L S in θ 2 t m 0 . S.5/6/2011 Offshore Structures – Offshore Lift Analysis PADEYE MAIN PLATE SLOTTED TO THE DECK EXTENSION Welding between tube and main plate h Fv FPDL θ FH L D L= FPDL .4Fy 33 Dr. S.4 F y ( Only Vertical Load Transferred) 34 Dr.5 L) 2Tt D 0.Sin θ 4Tt D 0. Otherwise these forces shall have to be transferred by bending 5/3/2011 35 Dr.5 L − h ) L 36 + FPD L Sin θ (e (e+D D /2) L 5/3/2011 Dr. S.5/6/2011 Offshore Structures – Offshore Lift Analysis MAIN PLATE WELDED TO SKIN OF TUBE The Vertical Component of Load (FV) is transferred through the direct shear between main plate and tube Horizontal component (FH) and moments shall be decoupled between top and bottom ring plates These forces on the rings shall be transferred as circumferential shear Hence. Hence the rings shall be complete.5 L + h ) L − FPD L Sin θ (e+D /2) L Bottom Ring Plate FT = FPD L C os θ (0. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 18 . Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis CALCULATION OF RING FORCES Top Ring Plate FT = FPD L C os θ (0. S. FEM analysis will give actual load path Indicate hot spots where local stresses are high 5/3/2011 37 Dr. Manual calculation becomes too complicated. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis FEA – Lifting Pad-eye 5/3/2011 38 Dr. Manual Calculations too conservative due to assumptions made on load path.5/6/2011 Offshore Structures – Offshore Lift Analysis FINITE ELEMENT ANALYSIS Finite element analysis will be carried out when No redundancy in design failure of the component will result in catostrophy. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 19 . catostrophy Multiple / unclear Load path. 5/6/2011 Offshore Structures – Offshore Lift Analysis FEA – Lifting Pad-eye 5/3/2011 39 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 Offshore Structures – Offshore Lift Analysis FEA .Spreader Bar 5/3/2011 40 Dr. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 20 . S. 5/6/2011 Offshore Structures – Offshore Lift Analysis FEA .Spreader Bar 5/3/2011 41 Dr. S. Nallayarasu Department of Ocean Engineering Indian Institute of Technology Madras-36 21 .