2 Finite Element Analysis

2.1 Structural details to be assessed

2.1.1 General

Critical structural details to be checked for fatigue by finite element analysis according to Ch 9, Sec 5 are given in [2.1.2] to [2.1.4].

Table 4 to Table 18 give the list of hot spots for structural details.

2.1.2 Details to be checked by very fine mesh analysis

Critical structural details to be assessed for fatigue by very fine mesh analysis according to Ch 9, Sec 5, [1] to Ch 9, Sec 5, [4] are provided in Table 1, irrespective of their compliance with the design standard given in Ch 9, Sec 6.

2.1.3 Details to be checked by screening fatigue assessment

The structural details listed in Table 2 for which FE fine mesh models have been analysed according to yielding requirements given in Ch 7, Sec 3 are to be assessed using the screening fatigue procedure as given in Ch 9, Sec 5, [6] or to be assessed by very fine mesh analysis according to Ch 9, Sec 5, [1] to Ch 9, Sec 5, [4].

2.1.4 Details in accordance with detail design standard

Table 3 gives critical structural details for which fatigue assessment by very fine mesh analysis can be omitted if their design is in accordance with detail design standard given in Ch 9, Sec 6.

Table 1 : Structural details to be assessed by very fine mesh analysis

No	Critical detail	Applicability
No	Critical detail	Oil tanker	Bulk carrier
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. ⁽¹⁾	One cargo tank ⁽⁴⁾	Ballast hold
2	Radiused lower hopper knuckle connection (intersection of knuckled inner bottom plate, longitudinal girder, floor and transverse web) at the most critical frame location. ⁽¹⁾	One cargo tank ⁽⁴⁾	Ballast hold
3	Welded upper knuckle connection (intersection of hopper sloping 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.⁽¹⁾	One cargo tank (4)	Ballast hold of double side bulk carrier
4	Connections of transverse bulkhead lower stools to the inner bottom plating in way of double bottom girders. ⁽²⁾⁽³⁾	One cargo tank ⁽⁴⁾	Ballast hold
5	Upper side frame bracket toe in case of flat bottom of top wing tank. ⁽¹⁾	N/A	FA hold ⁽⁴⁾,EA hold ⁽⁴⁾ and ballast hold of single skin bulk carrier
6	Deckplating and longitudinal hatch coaming end bracket toe.	N/A	Two aftermost holds, midship hold and two foremost holds
(1) The most critical frame position is generally, but not necessarily, located closest to the mid length of the hold. Where a swash bulkhead is fitted, this is generally located closest to the mid length between the swash bulkhead and the oil-tight bulkhead. (2) Stool connections at each end of the hold are to be checked unless these are symmetrical about mid-hold. (3) Positionat the mid breadth location of the largest hold. (4) Cargo hold located closest to the midship.

Table 2 : Structural details for screening fatigue assessment

No	Critical detail	Applicability
No	Critical detail	Oiltanker	Bulk carrier
1	Bracket toe of transverse web frame	Applicable ⁽¹⁾	N/A
2	Toe of horizontal stringer	Applicable ⁽¹⁾	N/A
3	Lower hopper knuckle connection in EA hold ⁽²⁾ and in FA hold ⁽²⁾ not assigned as a ballast hold	N/A	Applicable⁽¹⁾
4	Connections of transverse bulkhead lower stool to inner bottom in EA hold ⁽²⁾ and in FA hold ⁽²⁾ where the ballast hold is not assigned to the ship	N/A	Applicable⁽¹⁾
(1) Fordetails assessed by fine mesh analysis according to Ch 7, Sec 3 [3.2]. (2) Cargohold located closest to the midship

Table 3 : Structural details to be assessed by very fine mesh analysis if not designed in accordance with detail design standard

No	Critical detail	Corresponding detail design standard	Applicability
No	Critical detail	Corresponding detail design standard	Oil tanker	Bulk carrier
1	Radi used upper hopper knuckle connection (intersection of knuckled inner side plate, side girder and transverse web) at the most critical frame location. ⁽¹⁾	Ch 9, Sec 6, [4]	One cargo tank⁽⁴⁾	Ballast hold of double side bulk carrier
2	Corrugations of bulkheads to lower stool or inner bottom plating connection. ⁽²⁾⁽³⁾	Ch 9, Sec 6, [6] and Ch 9, Sec 6, [7]	One cargo tank⁽⁴⁾	Ballast hold
3	Corrugations of transverse bulkheads to upper stool. ^{(2) (3)}	Ch 9, Sec 6, [6]	N/A	Ballast hold
4	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.	Ch 9, Sec 6, [5]	One cargo tank ⁽⁴⁾	N/A
5	Lower and upper side frame bracket toes at the most critical frame position.⁽¹⁾	Ch 9, Sec 6, [8]	N/A	FA hold ⁽⁴⁾,EA hold ⁽⁴⁾and ballast hold of single skin bulk carrier
6	Cut out for longitudinal stiffeners in web-frame without web stiffener connection.	Ch 9, Sec 6, [2.1]	One cargo tank ⁽⁴⁾	FA hold (4), EA hold ⁽⁴⁾and ballast hold
7	Scallops in way of block joints on strength deck close to mid hold (and down to 0.1D from deck corner).	Ch 9, Sec 6, [3]	One cargo tank ⁽⁴⁾	FA hold ⁽⁴⁾,EA hold ⁽⁴⁾ and ballast hold
(1) The most critical frame position is generally, but not necessarily, located closest to the mid length of the hold. Where a swash bulkhead is fitted, this is generally located closest to the mid length between the swash bulkhead and the oil-tight bulkhead. (2) Stool connections at each end of the hold are to be checked unless these are symmetrical about mid-hold. (3) Position at the mid breath or length location of the largest hold in the considered transverse or longitudinal section. (4) Cargo hold located closest to the midship.

Table 4 : Hot spots for welded lower hopper knuckle connection

Hotspot location	Procedure for calculation of hot spot stress
Hot spot 1: Inner bottom plate, on cargo tank side Hot spot 2: Hopper sloping plate, on cargo tank side	Ch 9, Sec 5, [4.2]
Hot spot 3: Hopper web, outboard of side girder Hot spot 4: Double bottom floor, inboard the side girder Hot spot 5: Side girder	Ch 9, Sec 5, [4.3]
Hot spot 6: Scarfing bracket to the inner bottom plate	Ch 9, Sec 5, [3.1], type ‘b’

Table 5 : Hot spots for radiused lower hopper knuckle connection

Hot spot location

Procedure for calculation of hot spot stress

Hot spot 1: Inner bottom plate on ballast tank side, inboard of the side girder

Hot spot 2: Radiused hopper sloping plate on ballast tank side outboard of the side girder

Hot spot 3: Radiused hopper sloping plate on ballast tank side, outboard of the side girder, towards transverse web

Hot spot 4: Hopper web, outboard of side girder

Hot spot 5: Double bottom floor, inboard of the side girder

Hot spot 6: Side girder

Ch 9, Sec 5, [3.3]

Table 6 : Hot spots for welded upper knuckle connection

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Side stringer on ballast tank side Hot spot 2: Hopper sloping plate, on ballast tank side	Ch 9, Sec 5, [4.2]
Hot spot 3: Transverse web, below stringer. Hot spot 4: Transverse side web, above stringer Hot spot 5: Inner hull longitudinal bulkhead on ballast tank side	Ch 9, Sec 5, [4.3]

Table 7 : Hot spots for connections of transverse bulkhead lower stools to the inner bottom plating in way of double bottom girders

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Inner bottom plate, on cargo hold sideHot spot 2: Stool sloping plate, on cargo hold side	Ch 9, Sec 5, [4.2]
Hot spot 3: Longitudinal girder, under hold, to supporting floor in line with stool plate Hot spot 4: Longitudinal girder, under stool space to supporting floor in line with stool plate Hot spot 5: Double bottom supporting floor in line with stool plate	Ch 9, Sec 5, [4.3]

Table 8 : Hot spots for corrugated bulkhead to lower stool connection

Hot spot location	Procedure for calculation of hot spot stress
Hot spots 1 and 3: Corrugation web above shedder plate Hot spot 4: Corrugation web below shedder plate Hotspot 5, 7 and 8: Corrugation flange Hot spot 6: Gusset plate Hot spot 9: Lower stool plate to stool top plate Hot spot 10: Corrugation corner to stool top plate Hot Spot 11: Gusset plate in way of corrugation corner	Ch 9, Sec 5, [3.1], type ‘a’
Hot spot 2: Corrugation web below shedder plate	Ch 9, Sec 5, [4.3]

Table 9 : Hot spots for corrugated bulkhead to lower stool - Intersecting shedder plates and single sided shedder plate

Intersecting shedder plates
Hot spot location	Procedure for calculation of hot spot stress
Hotspot 12: Intersection of shedder plates	Ch 9, Sec 5, [3.1], type ‘a‘

Single sided shedder plate
Welded connection of web and flange of corrugation to lower stool top For details of hot spots see Table 10, hot spots 1-3 If supported brackets are fitted, see Table 10 for hot spots 4	Ch 9, Sec 5, [3.1], type ‘a‘

Table 10 : Hot spots for corrugated bulkhead to lower stool or inner bottom plating connection

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Inner bottom/lower stool top Hot spot 2: Corner of corrugation flange in way of inner bottom/lower stool top Hot spot 3: Corner of corrugation web in way of inner bottom/lower stool top Hot spot 4: Inner bottom/lower stool top in way of brackets supporting corrugation web	Ch 9, Sec 5, [3.1], type ‘a’
Hot spot 5: Edge of supporting brackets	Ch 9, Sec 5, [3.2].

Table 11 : Hot spots for connections of corrugated longitudinal bulkhead to lower stool top

Hot spot location	Procedure for calculation of hot spot stress
See Table 9	Ch 9, Sec 5, [3.1], type ‘a‘

Table 12 : Hot spots for connections of corrugated transverse bulkhead to upper stool bottom plate or to deck plate for tanker design without top stool

Hot spot location	Procedure for calculation of hot spot stress
See Table 8 and Table 9 Additional bending stresses in the deck stiffeners in way of corrugation flange induced by the bulkhead need to be considered

Table 13 : Hot spots for connection between transverse bulkhead and inner hull longitudinal bulkhead in way of transverse bulkhead horizontal stringer and side stringer without backing bracket at stringer heel

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Inner hull longitudinal bulkhead plate on cargo tank side connection to plane side of transverse bulkhead (i.e. opposite side to stiffening) at heel of transverse bulkhead horizontal stringer Hot spot 2: Transverse bulkhead plate on plane side (i.e. opposite stiffening) at heel of transverse bulkhead horizontal stringer	Ch 9, Sec 5, [4.2]
Hot spot 3: Heel of transverse bulkhead horizontal stringer Hot spot 4: Side stringer in double side diagonally opposite horizontal stringer Hot spot 5: Side stringer in double side in line with horizontal stringer	Ch 9, Sec 5, [4.3]

Table 14 : Hot spots for connection between transverse bulkhead and inner hull longitudinal bulkhead in way of transverse bulkhead horizontal stringer and side stringer, with backing bracket at stringer heel

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Bracket edge where a face plate is not fitted to the bracket Hot spot 4: Radius of bracket toe	Ch 9, Sec 5, [3.2]
Hot spot 2: Inner longitudinal bulkhead at bracket toe Hot spot 3: Transverse bulkhead at bracket toe Hot spot 6: Side stringer, in way of bracket toe Hot spot 7: Horizontal stringer in way of bracket toe	Ch 9, Sec 5, [3.1], type ‘a’
Hot spot 5: Where a face plate is fitted to the bracket, the weld connection of face plate to bracket in way of the face plate termination	Ch 9, Sec 5, [3.1], type ‘b’

Table 15 : Hot spots for lower side frame bracket toe

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Hopper sloping plate in way of hold frame toe	Ch 9, Sec 5, [3.1], type ‘a’
Hot spot 2: Hold frame toe in way of face plate termination	Ch 9, Sec 5, [3.1], type ‘b’

Table 16 : Hot spots for connection of longitudinal stiffener and transverse web including cut-outs and lug plates

Hot spot location	Procedure for calculation of hot spot stress
The critical hot spot has to be decided for each design in agreement with the Society. Typically the following three hot spot types are to be considered:
Hot spot 1: Corners of the cut-out edge	Ch 9, Sec 5, [3.2].
Hot spot 2: Connection of transverse web/lug-plate to longitudinal stiffener web in way of slot Hot spot 3: Overlapping connection between transverse web and lug plate	Ch 9, Sec 5, [3.1], type ‘b’

Table 17 : Hot spots for scallops in way of block connections joints at deck

Hot spot location

Procedure for calculation of hot spot stress

Hot spot 1: Butt weld in longitudinal stiffener web in way of scallop.

Hot spot 2: Deck plate in way of scallop.

Ch 9, Sec 5, [3.1], type ’a’

Table 18 : Hot spots for deck plating and longitudinal hatch coaming end bracket toe

Hot spot location	Procedure for calculation of hot spot stress
Hot spot 1: Hatch corner radiused edge Hot spot 3: Radius of hatch coaming bracket toe	Ch 9, Sec 5, [3.2]
Hot spot 2: Deck plating in way of hatch coaming bracket toe	Ch 9, Sec 5, [3.1], type ‘a’
Hot spot 4: Where a face plate is fitted to the bracket, the weld connection of face plate to bracket in way of the face plate termination	Ch 9, Sec 5, [3.1], type ‘b’