1. A study on Fatigue Strength for Tank Structures subject to
Harmonized CSR
Sungdong Shipbuilding
& Marine Engineering
Hyangduk Seo
TSCF 2016 Shipbuilders Meeting

2. Contents Backgrounds Information of Target Vessel FE Analysis Result
Conclusion

3. Contents Backgrounds Information of Target Vessel FE Analysis Result
Conclusion

4. Class Rules to IMO for GBS verification audit
I. Backgrounds
IACS Plan
Harmonized CSR
1 Jul 2015
Submission of each
Class Rules to IMO for GBS verification audit
IMO GBS
2011
2012
2013
2014
2015
2016
External review periods
Technical Committee review
Adoption
1st revision
Entry in to force
IMO
(GBS)

5. Fatigue Strength Assessment
I. Backgrounds
Fatigue Strength Assessment
Simplified stress analysis
Hot spot stress at weld toe of longitudinal stiffener end connection
Hot spot stresses are obtained by multiplying nominal stresses by SCF
Finite element stress analysis
Hot spot stress from very fine mesh model.
Hot spot stress is generally highly dependent on the finite element model used for representing the structure.
Procedure
Screening with fine mesh model
Evaluate with very fine mesh model
Mandatory area for fatigue strength calculation
Omit fatigue evaluation with design standard

6. Fatigue Strength Assessment
I. Backgrounds
Fatigue Strength Assessment
Structural details toe be assessed by very fine mesh analysis
Structural details to be assessed by very fine mesh analysis
If not designed in accordance with detail design standard No
Critical detail 1
Welded lower hopper knuckle connection (intersection of hopper sloping plate, inner bottom plate, longitudinal girder, floor and transverse web) at the most critical frame location. 2
Radiused lower hopper knuckle connection (intersection of knuckle inner bottom plate, longitudinal girder, floor and transverse web) at the most critical frame location. 3
Welded upper knuckle connection (intersection of hopper slopping plate, inner hull longitudinal bulkhead, transverse web and side stringer) where the angle between hopper plate and inner hull longitudinal bulkhead is less than 130 deg, at the most critical frame location. 4
Connection of transverse bulkhead lower stools to the inner bottom plating in wat of double bottom girders. No
Critical detail 1
Radiused upper hopper knuckle connection (intersection of knuckled inner side plate, side girder and transverse web) at the most critical frame location. 2
Corrugations of transverse bulkheads to lower stool or inner bottom plating connection. 3
Cruciform heel connections between side stringers in double side and transverse bulkhead horizontal stringers, for the stringer closest to the mid depth and for the uppermost one. 4
Cut out for longitudinal stiffeners in web frame without web stiffener connection. 5
Scallops in way of block joints on strength deck close to mid hold (and down to 0.1D from deck corner)

7. Hot spot stress for not Cruciform joints
I. Backgrounds
Hot spot stress for not Cruciform joints
Type “a” and “b”
Free surface
Cruciform joints in H-CSR : Hopper knuckle connection, transverse bulkhead lower stool to inner bottom connection and horizontal stringer heel
Calculation of hot spot stress of Type “a” A
Two principal hot spot stress ranges extrapolated from each side of line A-A in between load case ‘i1’ and ‘i2’.
The angle between the direction x of the element and the principal direction should be calculated.

8. Hot spot stress for Cruciform joints
I. Backgrounds
Hot spot stress for Cruciform joints
Cruciform joints in H-CSR : Hopper knuckle connection, transverse bulkhead lower stool to inner bottom connection and horizontal stringer heel
Calculation of hot spot stress

9. I. Backgrounds Details different from web stiffened cruciform joints
Fatigue strength assessment method for H-CSR
Details different from web stiffened cruciform joints
Weld
Type
Assessment area
Element type
Element or beam size
Welded
Type “a”
Weld toe on plate surface
Shell
tnet50 x tnet50
Type “b”
Weld toe around
the plat edge
Dummy beam
10 x 10
Non welded
Base material
Free surface
Details from web stiffened cruciform joints
Type
Assessment area
Shift stress
Element type
Element size
Hot spot stress at flange
Flange
Applied
Shell
tnet50 x tnet50
Hot spot stress in the web
Web
Bent hopper knuckle
Bent plate

10. Contents Backgrounds Information of Target Vessel FE Analysis Result
Conclusion

11. II. Information of Target Vessel
75K Tanker
115K Tanker
158K Tanker
Principal Dimension
· Length (O.A) : m
· Length (B.P) : m
· Length (Scant.) : m
· Breadth (Mld.) : m
· Depth (Mld.) : 20.9 m
· Draught (Scant.) : m
Principal Dimension
· Length (O.A) : m
· Length (B.P) : m
· Length (Scant.) : m
· Breadth (Mld.) : 44.0 m
· Depth (Mld.) : 21.5 m
· Draught (Scant.) : 15.1 m
Principal Dimension
· Length (O.A) : m
· Length (B.P) : m
· Length (Scant.) : m
· Breadth (Mld.) : 48.0 m
· Depth (Mld.) : 23.1 m
· Draught (Scant.) : m

12. Contents Backgrounds Information of Target Vessel FE Analysis Result
Conclusion

13. Boundary condition & Loading condition
III. FE Analysis
Boundary condition & Loading condition
Boundary Condition
Loading Condition

14. Fatigue Strength Assessment
III. FE Analysis
Fatigue Strength Assessment
Area for Fatigue life evaluation by very fine mesh
Fatigue Check Location 1 : Upper Hopper knuckle connection (Bend type)
Fatigue Check Location 2 : Lower Hopper knuckle connection (Weld type)

15. Fatigue Strength Assessment
III. FE Analysis
Fatigue Strength Assessment
Area for Fatigue life evaluation by very fine mesh
Fatigue Check Location 3-1 : Back bracket of No.1 horizontal stringer
Fatigue Check Location 4-1 : Toe of No.1 horizontal stringer

16. Fatigue Strength Assessment
III. FE Analysis
Fatigue Strength Assessment
Area for Fatigue life evaluation by very fine mesh
Fatigue Check Location 3-2 : Back bracket of No.2 horizontal stringer
Fatigue Check Location 4-2 : Toe of No.2 horizontal stringer

17. Fatigue Strength Assessment
III. FE Analysis
Fatigue Strength Assessment
Area for Fatigue life evaluation by very fine mesh
Fatigue Check Location 5-1 : Knuckle connection of Inner Hull to Upper Deck
Fatigue Check Location 5-2 : Knuckle connection of Inner Hull to Inner Bottom

18. Contents Backgrounds Information of Target Vessel FE Analysis Result
Conclusion

19. Position of Fatigue Check Location
IV. Result
Position of Fatigue Check Location
FCL.1 & 2
FCL.3 & 4
FCL.5

20. IV. Result Fatigue life at FCL.1 ~ 5 Summary of results Location
Member Type
75K
115K
158K
FCL. 1
Hopper Plate
26 years
17 years
84 years
Along the T-Web.
Inner Skin
32 years
13 years
39 years
Hopper plate
81 years
33 years
35 years
Along the No.3 STR
Web Section
47 years
23 years
53 years
57 years
123 years
No.3 STR.
193 years
Over 300 years
232 years
207 years
220 years
FCL. 2
Inner Bottom
19 years
28 years
16 years
25 years
44 years
105 years
42 years
18 years
31 years
24 years
Side Girder
102 years
172 years
112 years
109 years
180 years
113 years
Scarfing Bracket
99 years
74 years
55 years
204 years
259 years
62 years
FCL. 3
No.1 STR
Bracket Edge
173 years
218 years
88 years
Bracket toe
22 years
21 years
(Inner Skin)
184 years
241 years
163 years
(Transverse BHD.)
Stringer Toe
20 years
8 years
Stringer Toe edge
48 years
STR. Face plate End
15 years
Location
Member Type
75K　
115K　
158K　
FCL. 4
No.2 STR
Bracket Edge
85 years
50 years　
36 years
Bracket toe
44 years
38 years
20 years
(Inner Skin)
28 years　
50 years
23 years
(Transverse BHD.)
Stringer Toe
30 years
32 years
24 years
Stringer Toe edge
54 years
202 years
60 years
STR. Face plate End
20 years　
48 years
FCL. 5
Upper Deck
Inner Skin
83 years　
37 years
63 years
129 years
83 years
91 years　
92 years　
127 years　
53 years
35 years
Over 300 years
Inner Bottom
71 years　
141 years　
291 years　
59 years
109 years
61 years
90 years
56 years
Bracket

21. IV. Result
Fatigue life at FCL.1 ~ 5
Summary of results

22. IV. Result Comparison study I
Standard design for heel bracket of horizontal stringer
Standard size of Bracket
VLCC : 800 X 800 X 30, R600
Other Tankers : 800 X 600 X25, R550
Minimum yield stress is not to be less than
315 N/mm2

23. IV. Result Comparison study I Result Location Ship Size Hot spot 1
(Bkt Edge)
(Inner Skin)
(Trans. BHD)
No.1 STR.
75K
54 years
22 years
45 years
115K
107 years
17 years
151 years
158K
136 years
16 years
58 years
No.2 STR.
15 years
25 years
34 years
32 years

24. IV. Result Comparison study I Time in corrosive environment, TC
→ Initiation of Fatigue crack in air condition

25. IV. Result Comparison study II
Results of modification for corrosive years
Location
Member Type
75K
115K
158K
FCL. 1
Hopper Plate
26 years
16 years
84 years
Along the T-Web.
Inner Skin
32 years
13 years
39 years
Hopper plate
81 years
30 years
35 years
Along the No.3 STR
Web Section
47 years
20 years
53 years
57 years
23 years
123 years
No.3 STR.
193 years
Over 300 years
232 years
207 years
220 years
FCL. 2
Inner Bottom
19 years
25 years
29 years
44 years
101 years
42 years
18 years
28 years
24 years
Side Girder
102 years
168 years
112 years
109 years
176 years
113 years
Scarfing Bracket
99 years
70 years
55 years
204 years
255 years
62 years
FCL. 3
No.1 STR
Bracket Edge
173 years
215 years
88 years
Bracket toe
22 years
(Inner Skin)
184 years
237 years
163 years
(Transverse BHD.)
Stringer Toe
17 years
8 years
Stringer Toe edge
45 years
STR. Face plate End
15 years
Location
Member Type
75K
115K
158K
FCL. 4
No.2 STR
Bracket Edge
85 years
47 years　
36 years
Bracket toe
44 years
34 years
20 years
(Inner Skin)
28 years　
47 years
23 years
(Transverse BHD.)
Stringer Toe
30 years
29 years
24 years
Stringer Toe edge
54 years
198 years
60 years
STR. Face plate End
20 years　
45 years
48 years
FCL. 5
Upper
Deck
Inner Skin
83 years　
63 years
129 years
46 years
83 years
Upper Deck
91 years　
88 years　
127 years　
53 years
32 years
Over 300 years
Inner
Bottom
71 years　
137 years　
291 years　
59 years
105 years
Inner Bottom
61 years
86 years
56 years
Bracket

26. IV. Result Comparison study II
Results of modification for corrosive years
Location
Member Type
75K
115K
158K
FCL. 1
Hopper Plate
26 years
17 years
84 years
Along the T-Web.
Inner Skin
32 years
13 years
39 years
Hopper plate
81 years
33 years
35 years
Along the No.3 STR
Web Section
47 years
23 years
53 years
57 years
123 years
No.3 STR.
193 years
Over 300 years
232 years
207 years
220 years
FCL. 2
Inner Bottom
19 years
28 years
16 years
25 years
44 years
105 years
42 years
18 years
31 years
24 years
Side Girder
102 years
172 years
112 years
109 years
180 years
113 years
Scarfing Bracket
99 years
74 years
55 years
204 years
259 years
62 years

27. Contents Backgrounds Information of Target Vessel FE Analysis Result
Conclusion

28. V. Conclusion Fatigue assessment points are increased than CSR-OT
- Standard design suggested to omit the FE analysis.
Performed Fatigue assessment for various size of Tankers(Panamax, Aframax, Suezmax)
- Hopper connection point is still weak area for fatigue strength from CSR-OT.
- Fatigue strength tendency is quite similar but no relation with ship size.
- Fatigue strength for knuckle plate(reinforced within 75mm) shows better result than
rule guidance(within 50mm).
Corrosive year changed from 5 to 10 in urgent rule change 2016.
- Generally, fatigue life reduced 0 ~ 20% before.
Standard design for bracket of transverse stringer in hold.
- Fatigue life is not enough despite standard size applied.
- Different tendency by shape(include property) and location of bracket.

29. Thank you for your attention!