Clasification Society Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, January 2016 - Part 10 SHIP UNITS - Chapter 3 Scantling Requirements - Section 2 Cargo tank region
Section 2 Cargo tank region
2.1 Symbols
2.1.1 The symbols used in this Chapter are defined as follows:
| k | = | higher strength steel factor, defined in Pt 10, Ch 1, 3.1 General 3.1.7. |
2.2 General
- The requirements of this Section apply to the hull structure within the cargo tank region of the ship unit.
- Structural design details are to comply with the requirements given in Pt 10, Ch 3, 1.7 Standard construction details to Pt 10, Ch 3, 1.12 Local reinforcement.
- The scantlings are to be assessed to ensure that the strength criteria are satisfied at all longitudinal positions, where applicable.
- Local scantlings are to be increased where applicable to account
for:
- local variations, such as increased spacing or increased stiffener spans;
- green sea pressure loads;
- fore and aft end strengthening requirements, see Pt 10, Ch 3, 3 Forward of the forward cargo tank and Pt 10, Ch 3, 5 Aft end;
- local deflection requirements to limit interaction between the hull structure and liquefied gas cargo containment systems where fitted; and
- in way of anti-roll chocks, anti-flotation chocks and other similar items where fitted.
- Where the hull structure forms part of, or provides direct support to, a liquefied gas cargo containment system, the scantlings are to be sufficient to meet the requirements of the containment system design and the loads imposed by it. A structural analysis of the hull structure will be required using direct calculation procedures which are to be agreed with LR at as early a stage as possible.
- Where a membrane type liquefied gas cargo containment system is
fitted inside the hull, the scantlings of the hull providing direct support to
the containment system are to comply with the requirements in this Part
outlined for cargo tanks and other tanks designed for liquid filling. However,
the tank pressure is to be taken as:
For static load cases:
P in-tk + P o
For dynamic load cases:
P in-tk + P in-dyn + P o
where
P o is the design vapour pressure defined in Pt 11, Ch 4, 1.1 Definitions 1.1.2.
For the operating and inspection/maintenance conditions the liquid density is to be taken as that of the liquefied gas cargo, see Pt 10, Ch 2, 1.2 Definitions 1.2.3.
The design of membrane tanks is to comply with Pt 11, Ch 4 Cargo Containment.
- Where an independent tank is fitted inside the hull, the scantlings of the hull structure surrounding, but not forming, part of the independent tank are to be as required for watertight boundaries. The scantlings of independent tanks are to comply with Pt 11, Ch 4 Cargo Containment.
- The hull structure is to comply with the applicable requirements
of:
- hull girder longitudinal strength, see Pt 10, Ch 3, 1 Scantling requirements;
- strength against sloshing and impact loads, see Pt 10, Ch 3, 6 Evaluation of structure for sloshing and impact loads;
- hull girder ultimate strength, see LR ShipRight Procedure for Ship Units;
- strength assessment (FEM), see LR ShipRight Procedure for Ship Units;
- fatigue strength, see LR ShipRight Procedure for Ship Units;
- buckling, see Pt 10, Ch 1, 18 Buckling.
- The net section modulus, shear areas and other sectional properties of the local and primary support members are to be determined in accordance with Pt 10, Ch 1, 12 Corrosion additions.
- The thickness of plating and stiffeners in the cargo tank region
is to comply with the appropriate minimum thickness requirements given in Pt 10, Ch 3, 2.2 General 2.2.4.
Table 3.2.1 Minimum net thickness for plating and local support members in the cargo tank region
Scantling location Net thickness (mm) Plating Shell Keel plating 6,0 + 0,04L2 Bottom shell/bilge/side shell 4,5 + 0,03L2 Upper deck 4,5 + 0,02L2 Other structure Hull internal tank boundaries 4,5 + 0,02L2 Non-tight bulkheads, bulkheads between dry spaces and other plates in general 4,5 + 0,01L2 Local support members Local support members on tight boundaries 3,5 + 0,015L2 Local support members on other structure 2,5 + 0,015L2 Tripping brackets 5,0 + 0,015L2
- The thickness of web plating and face plating of primary support
members in the cargo tank region is to comply with the appropriate minimum
thickness requirements given in Pt 10, Ch 3, 2.2 General 2.2.5.
Table 3.2.2 Minimum net thickness for primary support members in cargo tank region
Scantling location Net thickness (mm) Bottom centreline girder 5,5 + 0,025L2 Other bottom girders 5,5 + 0,02L2 Bottom floors, web plates of side transverses and stringers in double hull 5,0 + 0,015L2 Web and flanges of vertical web frames on longitudinal bulkheads, horizontal stringers on transverse bulkhead, deck transverses (above and below upper deck) and cross ties 5,5 + 0,015L2
2.3 Hull envelope plating
- Keel plating is to extend over the flat of bottom for the complete length of the ship unit. The breadth, bkl , is not to be less than:
- The thickness of the keel plating is to comply with the requirements given in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
- The thickness of the bottom shell plating is to
comply with the requirements in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
Table 3.2.3 Thickness requirements for plating
The minimum net thickness, tnet , is to be taken as the greatest value for all applicable design load sets, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, and given by Acceptance criteria set Structural member βa αa Ca-max AC1 Longitudinal strength members Longitudinally stiffened plating 0,9 0,5 0,8 Transversely or vertically stiffened plating 0,9 1,0 0,8 Other members 0,8 0 0,8 AC2 Longitudinal strength members Longitudinally stiffened plating 1,05 0,5 0,95 Transversely or vertically stiffened plating 1,05 1,0 0,95 Other members, including watertight boundary plating 1,0 0 1,0 AC3 All members 1,0 0 1,0 where σhg = hull girder bending stress for the design load set being considered and calculated at the load calculation point = 
N/mm2
Mh-total = design horizontal bending moment at the longitudinal position under consideration for the design load set being considered, in kNm Iv-net50 = net vertical hull girder moment of inertia, at the longitudinal position being considered, in m4
- The thickness of bilge plating is not to be less than that required for the adjacent bottom shell, see Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2, or adjacent side shell plating, see Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4, whichever is the greater.
- The net thickness of bilge plating, tnet
, without longitudinal stiffening is not to be less than:
where
Pex = design sea pressure from Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 calculated at the lower turn of bilge, in kN/m2 r0 = radius of curvature, in mm, see Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.3 a = distance between the lower turn of bilge and the outermost bottom longitudinal, in mm, see Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.3 and Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.1. Where the outermost bottom longitudinal is within the curvature, this distance is to be taken as zero b = distance between the upper turn of bilge and the lowest side longitudinal, in mm, see Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.3 and Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.1. Where the lowest side longitudinal is within the curvature, this distance is to be taken as zero Where the plate seam is located in the flat plate just below the lowest stiffener on the side shell, any increased thickness required for the bilge plating does not have to extend to the adjacent plate above the bilge, provided that the plate seam is not more than Sb /4 below the lowest side longitudinal. Similarly, for flat part of adjacent bottom plating, any increased thickness for the bilge plating does not have to be applied, provided that the plate seam is not more than Sa /4 beyond the outboard bottom longitudinal. Regularly longitudinally-stiffened bilge plating is to be assessed as a stiffened plate. The bilge keel is not considered as ‘longitudinal stiffening’ for the application of this requirement.
Figure 3.2.1 Unstiffened bilge plating
- Where bilge longitudinals are omitted, the bilge plate thickness outside 0,4L amidships will be considered in relation to the support derived from the hull form and internal stiffening arrangements. In general, outside 0,4L amidships the bilge plate scantlings and arrangement are to comply with the requirements of ordinary side or bottom shell plating in the same region. Consideration is to be given where there is increased loading in the forward region.
- The thickness of the side shell plating is to comply with the requirements in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
- The net thickness, tnet , of the side plating within the range as specified in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4 is not to be less than:
- The thickness in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4 is to be applied to the following extent
of the side shell plating, see Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4:
- longitudinal extent:
- between a section aft of amidships where the breadth at the waterline exceeds 0,9B, and a section forward of amidships where the breadth at the waterline exceeds 0,6B.
- vertical extent:
- between 300 mm below the minimum design waterline at the light load draught, TLT , amidships to 0,25TSC or 2,2 m, whichever is greater, above the draught TSC .
Figure 3.2.2 Extent of side shell plating
- longitudinal extent:
- The sheerstrake is to comply with the requirements in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.4.
- The welding of deck fittings to rounded sheerstrakes is to be avoided within 0,6L of amidships.
- Where the sheerstrake extends above the deck stringer plate, the top edge of the sheerstrake is to be kept free from notches and isolated welded fittings, and is to be smooth with rounded edges. Grinding may be required if the cutting surface is not smooth. Drainage openings with a smooth transition in the longitudinal direction may be permitted.
- The thickness of the deck plating is to comply with the requirements given in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
2.4 Hull envelope framing
- The bottom shell, inner bottom and deck are to be longitudinally framed in the cargo tank region. The side shell, inner hull bulkheads and longitudinal bulkheads are generally to be longitudinally framed. Suitable alternatives which take account of resistance to buckling will be specially considered.
- Where longitudinals are omitted in way of the bilge, a longitudinal is to be fitted at the bottom and at the side, close to the position where the curvature of the bilge plate starts. The distance between the lower turn of bilge and the outermost bottom longitudinal, a, is generally not to be greater than one third of the spacing between the two outermost bottom longitudinals, sa . Similarly, the distance between the upper turn of the bilge and the lowest side longitudinal, b, is generally not to be greater than one third of the spacing between the two lowest side longitudinals, sb . See Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.3.
- The section modulus and thickness of the hull envelope framing are
to comply with the requirements given in Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2 and Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2.
Table 3.2.4 Section modulus requirements for stiffeners
The minimum net section modulus, Znet , is to be taken as the greatest value calculated for all applicable design load sets, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, and given by: where fbdg = bending moment factor: = 12 for horizontal stiffeners = for continuous stiffeners and where end connections are fitted consistent with idealisation of the stiffener as having as fixed ends: = 10 for vertical stiffeners for stiffeners with reduced end fixity, see Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3
Sign of hull girder bending stress, σhg Side pressure acting on Acceptance criteria Tension (+ve) Stiffener side but not to be taken greater than Cs-max
Compression (-ve) Plate side Tension (+ve) Plate side Compression (-ve) Stiffener side Acceptance criteria set Structural member βs αs Cs-max AC1 Longitudinal strength member 0,85 1,0 0,75 Transverse or vertical member 0,75 0 0,75 AC2 Longitudinal strength member 1,0 1,0 0,9 Transverse or vertical member 0,9 0 0,9 Watertight boundary stiffeners 0,9 0 0,9 AC3 All members 1,0 0 1,0 σhg = hull girder bending stress for the design load set being considered and calculated at the reference point = 
N/mm2
Mv-total = design vertical bending moment at longitudinal position under consideration for the design load set being considered, in kNm. Mv-total is to be calculated in accordance with Pt 10, Ch 2, 6.1 Symbols 6.1.1 in Pt 10, Ch 2 Loads and Load Combinations using the permissible hogging or sagging still water bending moment, Msw-perm , to be taken as: Stiffener location Msw-perm Pressure acting on plate side Pressure acting on stiffener side Above neutral axis Sagging SWBM Hogging SWBM Below neutral axis Hogging SWBM Sagging SWBM Mh-total = design horizontal bending moment at longitudinal position under consideration for the design load set being considered, in kNm Iv-net50 = net vertical hull girder moment of inertia, at the longitudinal position being considered, in m4 Table 3.2.5 Web thickness requirements for stiffeners
The minimum net web thickness, tw-net , is to be taken as the greatest value calculated for all applicable design load sets, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, and given by where fshr = shear force distribution factor: for continuous stiffeners and where end connections are fitted consistent with idealisation of the stiffener as having as fixed ends:
= 0,5 for horizontal stiffeners = 0,7 for vertical stiffeners for stiffeners with reduced end fixity, see Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3
2.5 Inner bottom
- The thickness of the inner bottom plating is to comply with the requirements given in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
- In way of a welded hopper knuckle, the inner bottom is to be scarphed to ensure adequate load transmission to surrounding structure and reduce stress concentrations.
- In way of corrugated bulkhead stools, where fitted, particular attention is to be given to the through thickness properties, and arrangements for continuity of strength, at the connection of the bulkhead stool to the inner bottom.
- The section modulus and web plate thickness of the inner bottom longitudinals are to comply with the requirements given in Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2 and Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2.
2.6 Bulkheads
- The inner hull and longitudinal bulkheads are generally to be longitudinally framed, and plane. Corrugated bulkheads are to comply with the requirements given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.6.
- Where bulkheads are penetrated by cargo or ballast piping, the structural arrangements in way are to be adequate for the loads imparted to the bulkheads by the hydraulic forces in the pipes.
- The thickness of the longitudinal tank boundary bulkhead plating is to comply with the requirements given in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
- Inner hull and longitudinal bulkheads are to extend as far forward and aft as practicable and are to be effectively scarphed into the adjoining structure.
- Knuckles in the hopper tank plating are to be supported by side girders and stringers, or by a deep longitudinal.
- The thickness of the transverse tank boundary bulkhead plating is to comply with the requirements given in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2.
- The section modulus and web thickness of stiffeners on longitudinal or transverse tank boundary bulkheads are to comply with the requirements given in Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2 and Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2.
- In general, corrugated bulkheads are to be designed with the
corrugation angles, φ, between 55° and 90°, see
Pt 10, Ch 3, 2.6 Bulkheads 2.6.6.
Figure 3.2.3 Definition of parameters for corrugated bulkhead (units with longitudinal bulkhead at centreline)
- The global strength of corrugated bulkheads, lower stools and upper stools, where fitted, and attachments to surrounding structures are to be verified with the cargo tank FEM model, in accordance with the LR ShipRight Procedure for Ship Units, in the midship region. The global strength of corrugated bulkheads outside of midship region is to be considered, based on results from the cargo tank FEM model and using the appropriate pressure for the bulkhead being considered. Additional FEM analysis of cargo tank bulkheads forward and aft of the midship region may be necessary if the bulkhead geometry, structural details and support arrangement details differ significantly from bulkheads within the mid cargo tank region.
- The net thicknesses, tnet
, of the web and flange plates of corrugated bulkheads are to be taken as
the greatest value calculated for all applicable design load sets, as given in
Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, and given by
where
bp = breadth of plate: = b f for flange plating, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 = b w for web plating, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 - Where the corrugated bulkhead is built with
flange and web plate of different thickness, the thicker net plating thickness,
tm-net
, is to be taken as the greatest value calculated for all applicable design
load sets, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, and given by:
where
- In addition to the requirements of Pt 10, Ch 3, 2.6 Bulkheads 2.6.6, vertically corrugated bulkheads are also to comply with the following requirements.
- The net plate thicknesses as required by Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 and Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 are to be maintained for two thirds of the corrugation length, lcg , from the lower end, where lcg is as defined in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7. Above that, the net plate thickness may be reduced by 20 per cent.
- Where a lower stool is fitted, the net web
plating thickness of the lower 15 per cent of the corrugation,
tw-net
, is to be taken as the greatest value calculated for all applicable design
load sets from Pt 10, Ch 3, 2.6 Bulkheads 2.6.7.
where
P1 = design pressure for the design load set being considered, calculated at the lower end of the corrugation, in kN/m2 Pu = design pressure for the design load set being considered, calculated at the upper end of the corrugation, in kN/m2 scg = spacing of corrugation, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 lcg = length of corrugation, which is defined as the distance between the lower stool and the upper stool or the upper end where no upper stool is fitted, in metres, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 dcg = depth of corrugation, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 and Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 Ct-cg = permissible shear stress coefficient = 0,75 for acceptance criteria set AC1 = 0,90 for acceptance criteria set AC2 = for acceptance criteria set AC3. Table 3.2.6 Design load sets for plating and local support members (see continuation)
Structural member Space type Operation on site Inspection/maintenance Transit Flooded Draught S S+D Draught S S+D Draught S S+D Draught S S+D Load Load Load Load Load Load Load Load EXTERNAL MEMBERS Acceptance criteria AC1 AC2 AC1 AC2 AC1 AC2 AC2 AC3 Exposed deck Space above deck Green sea Deep load Pex Deep load Pex Deep load Pex Flooded Pex Space below deck Tanks designed for liquid filing Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Watertight boundaries/Void space Light load
Deep load
Pin Pin Dry spaces Bilge, side shell, sheerstrake External sea Sea water Deep load Pex Pex Deep load Pex Pex Deep load Pex Pex Flooded Pex Pex Inboard space Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Watertight boundaries/Void space Light load
Deep load
Pin Pin Dry spaces Keel, bottom shell External sea Sea water Deep load Pex Pex Deep load Pex Pex Deep load Pex Pex Flooded Pex Pex Space above the panel Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Watertight boundaries/Void space Light load
Deep load
Pin Pin Dry spaces Light load
Deep load
Pdk Pdk Light load
Deep load
Pdk Pdk Light load
Deep load
Pdk Pdk INTERNAL MEMBERS Inner decks, inner bottom tanktops Space above deck Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Flooded Pin Pin Watertight boundaries/void space Light load
Deep load
Pin Pin Flooded Pin Pin Dry spaces Light load
Deep load
Pdk Pdk Light load
Deep load
Pdk Pdk Light load
Deep load
Pdk Pdk Flooded Pdk +Pin Pdk +Pin Space below deck Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Flooded Pin Pin Watertight boundaries/void space Light load
Deep load
Pin Pin Flooded Pin Pin Dry spaces Flooded Pin Pin Bilge, side shell, sheerstrake Outboard space Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Flooded Pin Pin Watertight boundaries/void space Light load
Deep load
Pin Pin Flooded Pin Pin Dry spaces Flooded Pin Pin Inboard space Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Flooded Pin Pin Watertight boundaries/void space Light load
Deep load
Pin Pin Flooded Pin Pin Dry spaces Flooded Pin Pin INTERNAL MEMBERS Transverse bulkheads Space forward of bulkhead Tanks designed for liquid Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Flooded Pin Pin Watertight boundaries/void space Light load
Deep load
Pin Pin Flooded Pin Pin Dry spaces Flooded Pin Pin Space aft of bulkhead Tanks designed for liquid filling Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Light load
Deep load
Pin Pin Flooded Pin Pin Watertight boundaries/void space Light load
Deep load
Pin Pin Flooded Pin Pin Dry spaces Flooded Pin Pin NOTES 1. When the unit’s configuration cannot be described by Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, the applicable Design Load Sets to determine the scantling requirements of structural boundaries are to be selected so as to specify a full tank on one side with the adjacent tank or space empty. The boundary is to be evaluated for loading from both sides. Design Load Sets are to be selected based on the tank or space contents, and are to maximise the pressure on the structural boundary. The applicable draught is to be taken in accordance with the Design Load Set and this Table. Design Load Sets covering the S and S+D design load combinations are to be selected.
2. Load cases for exposed decks are to consider any other distributed or concentrated loads, whereby simultaneously occurring green sea pressure may be ignored. Load cases for internal decks are to consider any other distributed or concentrated loads when green sea pressure is not applicable.
3. Ship motion parameters of GM and kr are to be selected according to the loading condition.
4. Light load draught to be taken as the minimum for the load scenario under consideration (Operation, Inspection/maintenance, Transit). The minimum draught may vary between load scenarios.
5. Deep load draught to be taken as the maximum for the load scenario under consideration (Operation, Inspection/maintenance, Transit). The maximum draught may vary between load scenarios.
6. Draughts for flooded conditions to be taken as the deepest flooded draught in way of compartment under assessment.
7. Under the assumption that the ship unit is at sea, external sea pressure will always be present. Therefore, the design load set to assess the external shell envelope when the dominant load direction is from inside the hull outwards may be taken as Pin -Pex .
- The depth of the corrugation,
dcg
, is not to be less than:
where
lcg = length of corrugation, defined as the distance between the lower stool (or inner bottom if no lower stool is fitted) and the upper stool (or upper end if no upper stool is fitted), in metres, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6. - Where a lower stool is fitted, the net
thickness of the lower two thirds of the flanges of corrugated bulkheads,
tf-net
, is to be taken as the greatest value calculated for all applicable design
load sets, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7.
where
σbdg-max = maximum vertical bending stress in the flange. The bending stress is to be calculated at the lower end and at the midspan of the corrugation length = 
N/mm2
Mcg = as defined in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 Zcg-act-net = actual net section modulus at the lower end and at the mid length of the corrugation, in cm3 bf = breadth of flange plating, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 bw = breadth of web plating, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 - Where a lower stool is fitted, the net section
modulus at the lower and upper ends and at the mid length of the corrugation,
Zcg-net
, is to be taken as the greatest value calculated for all applicable design
load sets, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7.
where
scg = spacing of corrugation, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 lo = effective bending span of the corrugation, measured from the mid depth of the lower stool to the mid depth of the upper stool, or upper end where no upper stool is fitted, in metres, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 lcg = length of corrugation, defined as the distance between the lower stool and the upper stool, or the upper end where no upper stool is fitted, in metres, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 Ci = the relevant bending moment coefficients, as given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 bf = breadth of flange plating, in mm, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 Table 3.2.7 Values of Ci
Bulkhead At lower end of lcg At mid length of lcg At upper end of lcg Transverse bulkhead C1 Cm1 0,80Cm1 Longitudinal bulkhead C3 Cm3 0,65Cm3 where bav-t = average width of transverse bulkhead lower stool, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 bav-1 = average width of longitudinal bulkhead lower stool, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 hst = height of transverse bulkhead lower stool, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 hsl = height of longitudinal bulkhead lower stool, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 bib = breadth of cargo tank at the inner bottom level between hopper tanks, or between the hopper tank and centreline lower stool, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 bdk = breadth of cargo tank at the deck level between upper wing tanks, or between the upper wing tank and centreline deck box or between the corrugation flanges if no upper stool is fitted, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 lib = length of cargo tank at the inner bottom level between transverse lower stools, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 ldk = length of cargo tank at the deck level between transverse upper stools or between the corrugation flanges if no upper stool is fitted, in metres. See Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 - For tanks with effective sloshing breadth, bslh , greater than 0,56B or effective sloshing length lslh , greater than 0,13L, additional sloshing analysis is to be carried out to assess the section modulus of the unit corrugation.
- For ship units with a moulded depth equal to or greater than 16
m, a lower stool is to be fitted in compliance with the following
requirements:
- general:
- the height and depth are not to be less than the depth of the corrugation;
- the lower stool is to be fitted in line with the double bottom floors or girders;
- the side stiffeners and vertical webs (diaphragms) within the stool structure are to align with the structure below, as far as is practicable, to provide appropriate load transmission to structures within the double bottom.
- stool top plating:
- the net thickness of the stool top plate is not to be less than that required for the attached corrugated bulkhead and is to be of at least the same material yield strength as the attached corrugation;
- the extension of the top plate beyond the corrugation is not to be less than the as-built flange thickness of the corrugation.
- stool side plating and internal structure:
- within the region of the corrugation depth from the stool top plate, the net thickness of the stool side plate is not to be less than 90 per cent of that required by Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 for the corrugated bulkhead flange at the lower end and is to be of at least the same material yield strength;
- the net thickness of the stool side plating and the net section modulus of the stool side stiffeners is not to be less than that required by Pt 10, Ch 3, 2.6 Bulkheads 2.6.2, Pt 10, Ch 3, 2.6 Bulkheads 2.6.4 and Pt 10, Ch 3, 2.6 Bulkheads 2.6.5for transverse or longitudinal bulkhead plating and stiffeners;
- the ends of stool side vertical stiffeners are to be attached to brackets at the upper and lower ends of the stool;
- continuity is to be maintained, as far as practicable, between the corrugation web and supporting brackets inside the stool. The bracket net thickness is not to be less than 80 per cent of the required thickness of the corrugation webs and is to be of at least the same material yield strength;
- scallops in the diaphragms in way of the connections of the stool sides to the inner bottom and to the stool top plate are not permitted.
- general:
- For ship units with a moulded depth less than 16 m, the lower
stool may be eliminated, provided the following requirements are complied
with:
- general:
- Double bottom floors or girders are to be fitted in line with the corrugation flanges for transverse or longitudinal bulkheads, respectively;
- brackets/carlings are to be fitted below the inner bottom and hopper tank in line with corrugation webs. Where this is not practicable, gusset plates with shedder plates are to be fitted, see Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 below and Pt 10, Ch 3, 2.6 Bulkheads 2.6.6;
- the corrugated bulkhead and its supporting structure are to be assessed by Finite Element (FE) analysis, in accordance with the LR ShipRight Procedure for Ship Units. In addition, the local scantlings requirements of Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 and Pt 10, Ch 3, 2.6 Bulkheads 2.6.6 and the minimum corrugation depth requirement of Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 are to be applied.
- Inner bottom and hopper tank plating:
- The inner bottom and hopper tank in way of the corrugation are to be of at least the same material yield strength as the attached corrugation.
- Supporting structure:
- Within the region of the corrugation depth below the inner bottom, the net thickness of the supporting double bottom floors or girders is not to be less than the net thickness of the corrugated bulkhead flange at the lower end, and is to be of at least the same material yield strength;
- the upper ends of vertical stiffeners on supporting double bottom floors or girders are to be bracketed to adjacent structure;
- brackets/carlings arranged in line with the corrugation web are to have a depth of not less than 0,5 times the corrugation depth and a net thickness not less than 80 per cent of the net thickness of the corrugation webs and are to be of at least the same material yield strength;
- cut-outs for stiffeners in way of supporting double bottom floors and girders in line with corrugation flanges are to be fitted with full collar plates;
- where support is provided by gussets with shedder plates, the height of the gusset plate, see hg in Pt 10, Ch 3, 2.6 Bulkheads 2.6.6, is to be at least equal to the corrugation depth, and gussets with shedder plates are to be arranged in every corrugation. The gusset plates are to be fitted in line with and between the corrugation flanges. The net thickness of the gusset and shedder plates are not to be less than 100 per cent and 80 per cent, respectively, of the net thickness of the corrugation flanges and are to be of at least the same material yield strength. See also Pt 10, Ch 3, 2.6 Bulkheads 2.6.7;
- scallops in brackets, gusset plates and shedder plates in way of the connections to the inner bottom or corrugation flange and web are not permitted.
- general:
- In general, an upper stool is to be fitted in compliance with the
following requirements:
- General:
- where no upper stool is fitted, finite element analysis is to be carried out in accordance with the LR ShipRight Procedure for Ship Units to demonstrate the adequacy of the details and arrangements of the bulkhead support structure to the upper deck structure;
- side stiffeners and vertical webs (diaphragms) within the stool structure are to align with adjoining structure to provide for appropriate load transmission;
- brackets are to be arranged in the intersections between the upper stool and the structure on deck.
- Stool bottom plating:
- the net thickness of the stool bottom plate is not to be less than that required for the attached corrugated bulkhead, and is to be of at least the same material yield strength as the attached corrugation;
- the extension of the bottom plate beyond the corrugation is not to be less than the attached as-built flange thickness of the corrugation.
- Stool side plating and internal structure:
- within the region of the corrugation depth above the stool bottom plate, the net thickness of the stool side plate is to be not less than 80 per cent of that required by Pt 10, Ch 3, 2.6 Bulkheads 2.6.7 for the corrugated bulkhead flange at the upper end, where the same material is used. If material of different yield strength is used, the required thickness is to be adjusted by the ratio of the two material factors (k);
- the net thickness of the stool side plating and the net section modulus of the stool side stiffeners are not to be less than that required by Pt 10, Ch 3, 2.6 Bulkheads 2.6.2, Pt 10, Ch 3, 2.6 Bulkheads 2.6.4 and Pt 10, Ch 3, 2.6 Bulkheads 2.6.5 for the transverse or longitudinal bulkhead plating and stiffeners;
- the ends of stool side vertical stiffeners are to be attached to brackets at the upper and lower ends of the stool;
- scallops in the diaphragms in way of the connections of the stool sides to the deck and to the stool bottom plate are not permitted.
- General:
- Where gussets with shedder plates, or shedder plates (slanting plates), are fitted at the end connection of the corrugation to the lower stool or the inner bottom, appropriate means are to be provided to prevent the possibility of gas pockets being formed by these plates.
- Non-tight bulkheads (wash bulkheads) are to be in line with transverse webs, bulkheads or similar structures. They are to be of plane construction, horizontally or vertically stiffened, and are to comply with the sloshing requirements given in the LR ShipRight Procedure for Ship Units. In general, openings in the non-tight bulkheads are to have generous radii and their aggregate area is not to be less than 10 per cent of the area of the bulkhead.
2.7 Primary support members
- The scantlings of a primary support member are to comply with the minimum requirements of Pt 10, Ch 3, 2.2 General 2.2.5.
- The shear area of a primary support member is, in general, to comply with the requirements of Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3 when idealised as a simple beam.
- The scantlings of all primary support members are to be verified by the Finite Element (FE) cargo tank structural analysis defined in the LR ShipRight Procedure for Ship Units.
- Primary support members are to be provided with adequate end fixity and in general be arranged in one plane to form continuous transverse rings.
- Primary support members are to have adequate lateral stability and the webs stiffened in accordance with buckling requirements from Pt 10, Ch 1, 18 Buckling.
- Primary support members that have open slots for stiffeners are to have a depth not less than 2,5 times the depth of the slots.
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