Section 1 Scantling requirements
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 10 Ship Units - Chapter 3 Scantling Requirements - Section 1 Scantling requirements

Section 1 Scantling requirements

Parent topic: Chapter 3 Scantling Requirements

1.1 Symbols

1.1.1 The symbols used in this Chapter are defined as follows:

L = Rule length, in metres, as defined in Pt 4, Ch 1, 5 Definitions
B = moulded breadth, in metres, as defined in Pt 4, Ch 1, 5 Definitions
D = moulded depth, as defined in Pt 4, Ch 1, 5 Definitions
= wave coefficient, as defined in Pt 10, Ch 2, 3.1 Symbols
= block coefficient, as defined in Pt 4, Ch 1, 5 Definitions, but is not to be taken as less than 0,7
ρ = density, tonnes/m3, not to be taken less than specified values defined in Table 2.1.1 Minimum density of liquid for strength and fatigue assessment in Pt 10, Ch 2 Loads and Load Combinations
g = acceleration due to gravity, 9,81 m/s2
k = higher strength steel factor, as defined in Pt 10, Ch 1, 3.1 General 3.1.7.

1.2 Loading guidance

1.2.1 All units are to be provided with loading guidance information containing sufficient information to enable the loading, unloading and ballasting operations and inspection/ maintenance of the unit within the stipulated operational limitations. The loading guidance information is to include an approved Loading Manual and Loading Computer System complying with the requirements given in Pt 3, Ch 4, 8 Loading guidance information of the Rules and Regulations for the Classification of Ships (hereinafter referred to as the Rules for Ships).

1.2.2 All relevant loading conditions and limitations are to be clearly stated in the loading manual. The loading computer system should be installed to monitor still water bending moments and shear forces and ensure they are maintained within the approved permissible levels.

1.3 Hull girder bending strength

1.3.1  General.
  1. The hull girder section modulus requirements in Pt 10, Ch 3, 1.3 Hull girder bending strength 1.3.3 apply along the full length of the hull girder, from AE to FE.
  2. Structural members included in the hull girder section modulus are to satisfy the buckling criteria given in Pt 10, Ch 3, 1.5 Hull girder buckling strength.
1.3.2  Minimum requirements.
  1. In order to limit the maximum permissible deflection, at the midship the net vertical hull girder section moment of inertia, ,a about the horizontal neutral axis is not to be less than the following:
    = m4

    where

    = net vertical hull girder section moment of inertia, in m4, to be calculated in accordance with Ch 1,13.4.2.
  2. Additional longitudinal strength and stiffness may be required to take account of the interaction between the hull structure and a liquefied gas cargo containment system if fitted.
1.3.3  Hull girder requirement on total design bending moment.
  1. The net vertical hull girder section modulus requirement as defined in Pt 10, Ch 3, 1.3 Hull girder bending strength 1.3.3.(b) is to be assessed for both hogging and sagging conditions.
  2. The hull girder net section modulus, , about the horizontal neutral axis is not to be less than the Rule required section modulus, based on the permissible still water and design wave bending moments as follows:
    = m3

    where

    = permissible hull girder hogging or sagging still water bending moment, in kNm, as given in Table 3.1.1 Loads and corresponding acceptance criteris for hull girder bending assessment
    = hogging or sagging vertical wave bending moment, in kNm, as given in Table 3.1.1 Loads and corresponding acceptance criteris for hull girder bending assessment
    = permissible hull girder bending stress as given in Table 3.1.1 Loads and corresponding acceptance criteris for hull girder bending assessment, in N/mm2
    = vertical hull girder net section modulus, in m3, to be calculated in accordance with Ch 1,13.4.2.

    Table 3.1.1 Loads and corresponding acceptance criteris for hull girder bending assessment

    Design load combination Still water bending moment, Vertical wave bending moment, Permissible hull girder bending stress, see Note 1
    (S) 0 143/k within 0,4L amidships
    105/k at and forward of 0,9L from AP and at and aft of 0,1L from AP
    (S + D) 190/k within 0,4L amidships
    140/k at and forward of 0,9L from AP and at and aft of 0,1L from AP
    Symbols
    = permissible hull girder hogging and sagging still water bending moment for Static (S) or Static + Dynamic (S+D) design load combination, as applicable from Pt 10, Ch 2, 6.1 Symbols 6.1.1 in Pt 10, Ch 2 Loads and Load Combinations, for the load case under consideration, in kNm
    = hogging and sagging vertical wave bending moments, in kNm, as defined in Pt 10, Ch 2, 3.7 Dynamic hull girder loads 3.7.1.(a)
      is to be taken as:
      for assessment with respect to hogging vertical wave bending moment
      for assessment with respect to sagging vertical wave bending moment
    NOTES
    1. is to be linearly interpolated between values given.
    2. For the flooded condition the permissible hull girder bending stress is to be taken as equal to the yield stress.
1.3.4 Hull girder section
  1. The following actual hull girder sectional properties are required to be verified:
    1. vertical hull girder moment of inertia, about the horizontal axis;
    2. hull girder section modulus about the horizontal axis – at deck-at-side;
    3. hull girder section modulus about the horizontal axis – at keel;
    4. hull girder section modulus about the vertical axis – at side;
    5. hull girder vertical shear area.
  2. The minimum allowable hull girder section properties are to be calculated with every member at a thickness equal to its required net minimum thickness plus half the applicable corrosion addition given in Pt 4, Ch 3, 7.3 Corrosion additions.

1.4 Hull girder shear strength

1.4.1  General.
  1. The hull girder shear strength requirements apply along the full length of the hull girder, from AE to FP.
  2. The following requirements are applicable to units with standard structural arrangements as shown in Table 3.1.2 Shear force distribution factors. Alternative configurations will be specially considered.
1.4.2  Assessment of hull girder shear strength.
  1. The net hull girder shear strength capacity, , is not to be less than the required vertical shear force, :
    = kN

    where

    = permissible hull girder positive or negative still water shear force as given in Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment, in kN
    = vertical wave positive or negative shear force as defined in Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment, in kN.
  2. The permissible positive and negative still water shear forces, , are to satisfy the following for each loading condition:

    ≤ — kN

    for maximum permissible positive shear force

    ≥ — kN

    for minimum permissible negative shear force

    where

    = net hull girder vertical shear strength to be taken as the minimum for all plate elements that contribute to the hull girder shear capacity
    = kN
    = permissible hull girder shear stress, , as given in Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment, in N/mm2, for plate ij
    = positive vertical wave shear force, in kN, as defined in Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment
    = negative vertical wave shear force, in kN, as defined in Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment
    = equivalent net thickness, , for plate ij, in mm. For longitudinal bulkheads between cargo tanks, is to be taken as and as appropriate, see Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(a) and Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.4.(a)
    = net thickness of plate, in mm
    = —
    = gross plate thickness, in mm. For corrugated bulkheads, to be taken as the minimum of and , in mm
    = gross thickness of the corrugation web, in mm
    = gross thickness of the corrugation flange, in mm
    = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions
    = unit shear flow per mm for the plate being considered and based on the net scantlings. Where direct calculation of the unit shear flow is not available, the unit shear flow may be taken equal to
    =
    = shear force distribution factor for the main longitudinal hull girder shear carrying members being considered. For standard structural configurations is as defined in Table 3.1.2 Shear force distribution factors.

Table 3.1.2 Shear force distribution factors

Hull configuration fi factors
Outside cargo region, no longitudinal bulkhead

Side shell
Outside cargo region, centreline bulkhead

 Side shell
Longitudinal bulkhead
Outside cargo region, two longitudinal bulkheads

 Side shell
Longitudinal bulkhead
Double hull, single cargo tank abreast

 Side shell
Inner hull
Double hull, one centreline bulkhead

 Side shell
Inner hull
Longitudinal bulkhead
Double hull, two centreline bulkheads

 Side shell
Inner hull
Longitudinal bulkhead
Double hull, two longitudinal bulkheads

 Side shell
Inner hull
Longitudinal bulkhead
Symbols
i = index for the structural member under consideration

1, for the side shell

2, for the inner hull

3, for the longitudinal bulkhead
Ai-net50 = net area based on deduction 0,5tc, of the structural member, i, at one side of the section under consideration. The area A3-net50 for the centreline bulkhead is not to be reduced for symmetry around the centreline
Note 1. The effective net hull girder vertical shear area includes the net plating area of the side shell including the bilge, the inner hull including the hopper side and the outboard girder under, the upper deck girder where applicable, and the longitudinal bulkheads including the double bottom girders in line.
Note 2. For longitudinal strength members forming the web of the hull girder which are inclined to the vertical, the area of the member to be included in the shear force calculation is to be based on the projected area onto the vertical plane.

Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment

Design load combination Still water shear force,Qsw-perm Vertical wave shear force,Qwv Permissible shear stress,τperm, see Note
(S) Qsw-perm 0 105/k for plate ij
(S + D) Qsw-perm Qwv 120/k for plate ij
Symbols
Qsw-perm = permissible positive or negative hull girder still water shear force for Static (S) or Static + Dynamic (S + D) design load combination, as applicable from Table 2.6.1 Design load combinations for the load case under consideration, in kN
Qwv = positive or negative vertical wave shear, in kN, as defined in Pt 10, Ch 2, 3.7 Dynamic hull girder loads 3.7.1.(a). Qvw is to be taken as:

Qwv-pos for assessment with respect to maximum positive permissible still water shear force

Qwv-neg for assessment with respect to minimum negative permissible still water shear force

plate ij = for each plate j, index i denotes the structural member of which the plate forms a component

NOTE

For the flooded condition the permissible hull girder shear stress is to be taken as equal to 0,58 yield stress.

q1-net50 = first moment of area, in cm3, about the horizontal neutral axis of the effective longitudinal members between the vertical level at which the shear stress is being determined and the vertical extremity, taken at the section being considered. The first moment of area is to be based on the net thickness, tnet50
Iv-net50 = net vertical hull girder section moment of inertia, in m4 to be calculated in accordance with Pt 10, Ch 3, 1.3 Hull girder bending strength 1.3.4.(b).
1.4.3  Shear force correction for longitudinal bulkheads between cargo tanks.
  1. For longitudinal bulkheads between cargo tanks, the effective net plating thickness of the plating above the inner bottom, tsfc-net50 for plate ij, used for calculation of hull girder shear strength, Q v-net50, may be corrected for local shear distribution and is given by:
    tsfc-net50 = tgrs – 0,5tc – tΔ mm

    where

    tgrs = gross plate thickness, in mm
    tc = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions
    tΔ = thickness deduction for plate ij, in mm, as defined in Pt 10, Ch 3, 1.3 Hull girder bending strength 1.3.4.(b).
  2. The vertical distribution of thickness reduction for shear force correction is assumed to be triangular, as indicated in Figure 3.1.1 Shear force correction for longitudinal bulkheads. The thickness deduction, tΔ, to account for shear force correction is to be taken as:
    tΔ = mm

    where

    δQ3 = shear force correction for longitudinal bulkhead as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(c) and Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(e) for ship units with one or two longitudinal bulkheads respectively, in kN
    ltk = length of cargo tank, in metres
    hblk = height of longitudinal bulkhead, in metres, defined as the distance from inner bottom to the deck at the top of the bulkhead, as shown in Figure 3.1.1 Shear force correction for longitudinal bulkheads
    xblk = the minimum longitudinal distance from section considered to the nearest cargo tank transverse bulkhead, in metres. To be taken positive and not greater than 0,5ltk
    zp = the vertical distance from the lower edge of plate ij to the base line, in metres. Not to be taken as less than hdb
    hdb = height of double bottom, in metres, as shown in Figure 3.1.1 Shear force correction for longitudinal bulkheads
    τ ij-perm = permissible hull girder shear stress, τperm, in N/mm2 for plate ij
    = 120/kij
    kij = higher strength steel factor, k, for plate ij as defined in Pt 10, Ch 3, 1.1 Symbols.
  3. For ship units with one or two centreline longitudinal bulkheads between the cargo tanks, the shear force correction in way of transverse bulkhead, δQ3, is to be taken as:
    δQ3 = 0,5K3 Fdb kN

    where

    K3 = correction factor, as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(d)
    Fdb = maximum resulting force on the double bottom in a tank, in kN, as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(h).
  4. For ship units with one or two centreline longitudinal bulkheads between the cargo tanks, the correction factor, K3 , in way of transverse bulkheads is to be taken as:
    K3 =

    where

    n = number of floors between transverse bulkheads
    f3 = shear force distribution factor, see Table 3.1.2 Shear force distribution factors.
  5. For ship units with two longitudinal bulkheads between the cargo tanks, the shear force correction, δQ3 , is to be taken as:
    δ Q3 = 0,5K3 Fdb kN

    where

    K3 = correction factor, as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(f)
    Fdb = maximum resulting force on the double bottom in a tank, in kN, as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(g).

    Figure 3.1.1 Shear force correction for longitudinal bulkheads

  6. For ship units with two longitudinal bulkheads between the cargo tanks, the correction factor, K3 , in way of transverse bulkheads is to be taken as:
    K3 =

    where

    n = number of floors between transverse bulkheads
    r = ratio of the part load carried by the wash bulkheads and floors from longitudinal bulkhead to the double side and is given by
    r =

    NOTE

    For preliminary calculations, r may be taken as 0,5

    ltk = length of cargo tank, between transverse bulkheads in the side cargo tank, in metres
    b80 = 80 per cent of the distance from longitudinal bulkhead to the inner hull longitudinal bulkhead, in metres, at tank mid length
    AT-net50 = net shear area of the transverse wash bulkhead, including the double bottom floor directly below, in the side cargo tank, in cm2, taken as the smallest area in a vertical section. AT-net50 is to be calculated with net thickness given by tgrs – 0,5tc
    A1-net50 = net area, as shown in Table 3.1.2 Shear force distribution factors, in m2
    A2-net50 = net area, as shown in Table 3.1.2 Shear force distribution factors, in m2
    A3-net50 = net area, as shown in Table 3.1.2 Shear force distribution factors, in m2
    f3 = shear force distribution factor, as shown in Table 3.1.2 Shear force distribution factors
    n5 = number of wash bulkheads in the side cargo tank
    R = total efficiency of the transverse primary support members in the side tank
    R = cm2
    γ =
    AQ-net50 = net shear area, in cm2, of a transverse primary support member in the wing cargo tank, taken as the sum of the net shear areas of floor, cross ties and deck transverse webs

    AQ-net50 is to be calculated using the net thickness given by tgrs – 0,5tc .The net shear area is to be calculated at the midspan of the members

    Ipsm–net50 = net moment of inertia for primary support members, in cm4, of a transverse primary support member in the wing cargo tank, taken as the sum of the moments of inertia of transverses and cross ties. It is to be calculated using the net thickness given by tgrs – 0,5tc . The net moment of inertia is to be calculated at the midspan of the member, including an attached plate width equal to the primary support member spacing
    tgrs = gross plate thickness, in mm
    tc = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions.
  7. The maximum resulting force on the double bottom in a tank, Fdb , is to be taken as:
    Fdb = g |WCT + WCWBT – ρsw b2 ltk Tmean | kN

    where

    WCT = weight of cargo, in tonnes, as defined in Table 3.1.4 Design conditions for double bottoms
    WCWBT = weight of ballast, in tonnes, as defined in Table 3.1.4 Design conditions for double bottoms
    b2 = breadth, in metres, as defined in Table 3.1.4 Design conditions for double bottoms
    ltk = length of cargo tank, between watertight transverse bulkheads in the wing cargo tank, in metres
    Tmean = draught at the mid length of the tank for the loading condition considered, in metres.

    Table 3.1.4 Design conditions for double bottoms

    Structural configuration WCT WCWBT b2
    Ship units with one longitudinal bulkhead Weight of cargo in cargo tanks, in tonnes, using a minimum specific gravity of 1,025 tonnes/m3 Weight of ballast between port and starboard inner sides, in tonnes Maximum breadth between port and starboard inner sides at mid length of tank, in metres, as shown in Figure 3.1.2 Tank breadth to be included for standard tank configuration
    Ship units with two cargo tanks abreast with a centreline cofferdam Weight of cargo in cargo tanks, in tonnes, using the specific gravity of the cargo as shown inTable 2.1.1 Minimum density of liquid for strength and fatigue assessment in Pt 10, Ch 2 Loads and Load Combinations for strength assessment Weight of ballast below the cargo tanks, in tonnes Total breadth of the portion of the ballast tanks below the cargo tanks, in metres as shown in Figure 3.1.2 Tank breadth to be included for standard tank configuration
    Ship units with two longitudinal bulkheads Weight of cargo in the centre tank, in tonnes, using a minimum specific gravity of 1,025 tonnes/m3 Weight of ballast below the centre cargo tank, in tonnes Maximum breadth of the centre cargo tank at mid length of tank, in metres, as shown in Figure 3.1.2 Tank breadth to be included for standard tank configuration
    Ship units with a single cargo tank abreast Weight of cargo in cargo tank, in tonnes, using the specific gravity of the cargo as shown in Table 2.1.1 Minimum density of liquid for strength and fatigue assessment for strength assessment Weight of ballast below the cargo tank, in tonnes Breadth of the ballast tanks below the cargo tank, in metres, as shown in Figure 3.1.2 Tank breadth to be included for standard tank configuration
  8. The maximum resulting force on the double bottom in a tank, Fdb , is in no case to be less than that given by the Rule minimum conditions given in Table 3.1.5 Rule minimum conditions for double bottoms. Where other tank configurations are proposed, the equivalent loading scenario is to be considered.

    Table 3.1.5 Rule minimum conditions for double bottoms

    Structural configuration Positive/negative force, Fdb Minimum condition
    Ship units with one longitudinal bulkhead Max. positive net vertical force, Fdb + 0,9TSC and empty cargo and ballast tanks
    Max. negative net vertical force, Fdb – 0,6TSC and full cargo tanks and empty ballast tanks
    Ship units with two longitudinal bulkheads Min. positive net vertical force, Fdb + 0,9TSC and empty cargo and ballast tanks
    Min. negative net vertical force, Fdb – 0,6TSC and full centre cargo tank and empty ballast tanks
  9. The effective net plating thickness of the plating, tsfc-net50, used for calculation of hull girder shear strength, Qv-net50, is to comply with the minimum thickness requirements for the cargo region given in Pt 10, Ch 3, 2.2 General 2.2.4 and Pt 10, Ch 3, 2.2 General 2.2.5.
  10. The structure is to be subsequently confirmed as compliant using direct calculations in terms of both stress and buckling.
1.4.4  Shear force correction due to loads from transverse bulkhead stringers.
  1. In way of transverse bulkhead stringer connections, within areas as specified in Figure 3.1.4 Region for stringer correction, tij, for a unit with three stringers, the equivalent net thickness of plate used for calculation of the hull girder shear strength, tstr-k , where the index k refers to the identification number of the stringer, is not to be taken greater than:
    tstr-k = mm

    τstr is not to be taken greater than τif-perm

    where

    tsfc-net50 = effective net plating thickness, in mm, as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.3.(a) and calculated at the transverse bulkhead for the height corresponding to the level of the stringer
    τij-perm = permissible hull girder shear stress, τperm , for plate ij
    = 120/kij N/mm2
    kij = higher strength steel factor, k, for plate ij, as defined in Pt 10, Ch 3, 1.1 Symbols
    τstr = N/mm2
    lstr = connection length of stringer, in metres, see Figure 3.1.3 Effective connection length of stringer
    Qstr-k = shear force on the longitudinal bulkhead from the stringer in loaded condition with tanks abreast full
    = kN
    Fstr-k = total stringer supporting force, in kN, as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.4.(b)
    hdb = the double bottom height, in metres, as shown in Figure 3.1.4 Region for stringer correction, tij, for a unit with three stringers
    hblk = height of bulkhead, in metres, defined as the distance from inner bottom to the deck at the top of the bulkhead, as shown in Figure 3.1.4 Region for stringer correction, tij, for a unit with three stringers
    zstr = the vertical distance from baseline to the considered stringer, in metres.

    Figure 3.1.2 Tank breadth to be included for standard tank configuration

    Figure 3.1.3 Effective connection length of stringer

    Figure 3.1.4 Region for stringer correction, tij, for a unit with three stringers

    Figure 3.1.5 Load breadth of stringers for units with a one or two centreline longitudinal bulkheads

  2. The total stringer supporting force, Fstr-k , in way of a longitudinal bulkhead is to be taken as:
    Fstr-k =

    where

    Pstr = pressure on stringer, in kN/m2, to be taken as ρgh tt
    htt = the height from the top of the tank to the midpoint of the load area between hk /2 below the stringer and hk-1 /2 above the stringer, in metres
    hk = the vertical distance from the considered stringer to the stringer below. For the lowermost stringer, it is to be taken as 80 per cent of the average vertical distance to the inner bottom, in metres
    hk-1 = the vertical distance from the considered stringer to the stringer above. For the uppermost stringer, it is to be taken as 80 per cent of the average vertical distance to the upper deck, in metres
    ρ =

    density, tonnes/m3, as defined in Pt 10, Ch 2, 1.2 Definitions 1.2.3
    g = acceleration due to gravity, 9,81 m/s2
  3. Where reinforcement is provided to meet the above requirement, the reinforced area based on tstr-k is to extend longitudinally for the full length of the stringer connection and a minimum of one frame spacing forward and aft of the bulkhead. The reinforced area shall extend vertically from above the stringer level and down to 0,5hk below the stringer, where hk , the vertical distance from the considered stringer to the stringer below, is as defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.4.(b). For the lowermost stringer, the plate thickness requirementtstr-k is to extend down to the inner bottom, see Figure 3.1.5 Load breadth of stringers for units with a one or two centreline longitudinal bulkheads.
  4. The equivalent net thickness of plate used for calculation of the hull girder shear strength, tstr-k, is to comply with the minimum thickness requirements for the cargo region given in Pt 10, Ch 3, 2.2 General 2.2.4 and Pt 10, Ch 3, 2.2 General 2.2.5.
  5. The structure is to be subsequently confirmed as compliant using direct calculations in terms of both stress and buckling.

1.5 Hull girder buckling strength

1.5.1  General.
  1. These requirements apply to plate panels and longitudinals subject to hull girder compression and shear stresses. These stresses are to be based on the permissible values for wave bending moments and shear forces given in Pt 10, Ch 2, 2.2 Static hull girder loads and Pt 10, Ch 2, 3.7 Dynamic hull girder loads.
  2. The hull girder buckling strength requirements apply along the full length of the ship unit, from AE to FE.
  3. For the purposes of assessing the hull girder buckling strength in this sub-Section, the following are to be considered separately:
    1. Axial hull girder compressive stress to satisfy requirements in Pt 10, Ch 3, 1.5 Hull girder buckling strength 1.5.2.(f) and Pt 10, Ch 3, 1.5 Hull girder buckling strength 1.5.2.(h).
    2. Hull girder shear stress to satisfy requirements in Pt 10, Ch 3, 1.5 Hull girder buckling strength 1.5.2.(g).
1.5.2  Buckling assessment.
  1. The buckling assessment of plate panels and longitudinals is to be determined according to Pt 10, Ch 1, 17 Buckling, with hull girder stresses calculated on net hull girder sectional properties.
  2. The buckling strength for the buckling assessment is to be derived using local net scantlings, tnet , as follows:
    tnet = tgrs – 1,0tc mm

    where

    tgrs = gross plate thickness, in mm
    tc = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions.
  3. The hull girder compressive stress due to bending, σhg-net50, for the buckling assessment is to be calculated using net hull girder sectional properties and is to be taken as the greater of the following:
    σ hg-net50 = N/mm2
    σ hg-net50 = N/mm2

    where

    Msw-perm = permissible still water bending moment for the Static + Dynamic (S+D) design load combination, as applicable from Table 2.6.1 Design load combinations for the load case under consideration, in kNm, with signs as given in Pt 10, Ch 2, 1.2 Definitions 1.2.2.(d)
    Mwv-v = hogging and sagging vertical wave bending moments, in kNm, as defined in Pt 10, Ch 2 Loads and Load Combinations, with signs as given in Pt 10, Ch 2, 1.2 Definitions 1.2.2.(d)

    Mwv-v is to be taken as:

    Mwv-hog for assessment with the hogging still water bending moment

    Mwv-sag for assessment with the sagging still water bending moment

    z = distance from the structural member under consideration to the baseline, in metres
    zNA-net50 = distance from the baseline to the horizontal neutral axis, in metres
    Iv-net50 = net vertical hull girder section moment of inertia, in m4.
  4. The sagging bending moment values of Msw-perm and Mwv-v , are to be taken for members above the neutral axis. The hogging bending moment values are to be taken for members below the neutral axis.
  5. The design hull girder shear stress for the buckling assessment, τhg-net50, is to be calculated based on net hull girder sectional properties and is to be taken as:
    τ hg-net50 = N/mm2

    where

    Qsw-perm = positive and negative still water permissible shear force for Static + Dynamic (S+D) design load combination, as applicable from Table 2.6.1 Design load combinations in Pt 10, Ch 2 Loads and Load Combinations for the load case under consideration, in kN
    Qwv = positive or negative vertical wave shear, in kN, as defined in Pt 10, Ch 2 Loads and Load Combinations

    Qwv is to be taken as:

    Qwv-pos for assessment with the positive permissible still water shear force

    Qwv-neg for assessment with the negative permissible still water shear force

    tij-net50 = net thickness for the plate ij, in mm
    = tij-grs − 0,5tc
    tij-grs = gross plate thickness of plate ij, in mm. The gross plate thickness for corrugated bulkheads is to be taken as the minimum of tw-grs and tf-grs , in mm
    tw-grs = gross thickness of the corrugation web, in mm
    tf-grs = gross thickness of the corrugation flange, in mm
    tc = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions
    qv = unit shear per mm for the plate being considered, defined in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.2.(a)

    NOTES

    1. Maximum of the positive shear (still water + vertical wave) and negative shear (still water + vertical wave) is to be used as the basis for calculation of design shear stress.

    2. All plate elements ij that contribute to the hull girder shear capacity are to be assessed. See also Table 3.1.3 Loads and corresponding acceptance criteria for hull girder shear assessment and Table 3.1.2 Shear force distribution factors.

  6. The compressive buckling strength of plate panels is to satisfy the following criteria:

    η ≥ ηallow

    where

    η = buckling utilisation factor
    =
    σ hg-net50 = hull girder compressive stress based on net hull girder sectional properties, in N/mm2, as defined in Pt 10, Ch 3, 1.5 Hull girder buckling strength 1.5.2.(c)
    σ cr = critical compressive buckling stress, σxcr or σycr as appropriate, in N/mm2, as specified in Pt 10, Ch 1, 17.2 Buckling of plates 17.2.1.(c). The critical compressive buckling stress is to be calculated for the effects of hull girder compressive stress only. The effects of other membrane stresses and lateral pressure are to be ignored. The net thickness given as tgrs – tc as described in Pt 10, Ch 1, 12 Corrosion additions is to be used for the calculation of σcr
    η allow = allowable buckling utilisation factor
    = 1,0 for plate panels at or above 0,5D
    = 0,90 for plate panels below 0,5D
    tgrs = gross plate thickness, in mm
    tc = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions.

    Figure 3.1.6 Load breadth of stringers for units with two inner longitudinal bulkheads

  7. The shear buckling strength of plate panels, is to satisfy the following criteria:

    η ≤ ηallow

    where

    η = buckling utilisation factor
    =
    τhg-net50 = design hull girder shear stress, in N/mm2, as defined in Pt 10, Ch 3, 1.5 Hull girder buckling strength 1.5.2.(c)
    τ cr = critical shear buckling stress, in N/mm2, specified in Pt 10, Ch 1, 17.2 Buckling of plates 17.2.1.(c). The critical shear buckling stress is to be calculated for the effects of hull girder shear stress only. The effects of other membrane stresses and lateral pressure are to be ignored. The net thickness tgrs – tc as described in Pt 10, Ch 1, 12 Corrosion additions is to be used for the calculation of τcr
    η allow = allowable buckling utilisation factor
    = 0,95
    tgrs = gross plate thickness, in mm
    tc = corrosion addition, in mm, as defined in Pt 10, Ch 1, 12 Corrosion additions.
  8. The compressive buckling strength of longitudinal stiffeners is to satisfy the following criteria:

    η ≤ ηallow

    where

    η = the greater of the buckling utilisation factors given in Pt 10, Ch 1, 17.3 Buckling of stiffeners 17.3.2.(a) and Pt 10, Ch 1, 17.3 Buckling of stiffeners 17.3.3.(a). The buckling utilisation factor is to be calculated for the effects of hull girder compressive stress only. The effects of other membrane stresses and lateral pressure are to be ignored
    η allow = allowable buckling utilisation factor
    = 1,0 for stiffeners at or above 0,5D
    = 0,90 for stiffeners below 0,5D.

1.6 Tapering and structural continuity of longitudinal hull girder elements

1.6.1  Tapering based on minimum hull girder section property requirements.
  1. Scantlings required by the Rule minimum moment of inertia and section modulus may be gradually reduced to the local requirements at the ends, provided the hull girder bending and buckling requirements, as given in Pt 10, Ch 3, 1.3 Hull girder bending strength 1.3.3 and Pt 10, Ch 3, 1.5 Hull girder buckling strength, are complied with along the full length of the ship unit.
1.6.2  Longitudinal extent of higher strength steel.
  1. Where used, the application of higher strength steel is to be continuous over the length of the ship unit up to locations where the longitudinal stress levels are within the allowable range for mild steel structure.
1.6.3  Vertical extent of higher strength steel.
  1. The vertical extent of higher strength steel, z hts, used in the deck or bottom and measured from the moulded deck line at side or keel is not to be taken less than the following, see also Figure 3.1.7 Vertical extent of higher strength steel.
    zhts =

    where

    z1 = distance from horizontal neutral axis to moulded deck line or keel respectively, in metres
    σ 1 = to be taken as σdk or σkl for the hull girder deck and keel respectively, in N/mm2
    σ dk = hull girder bending stress at moulded deck line given by

    N/mm2
    σ kl = hull girder bending stress at keel given by

    N/mm2

    Msw-perm = permissible hull girder still water bending moment for applicable static + dynamic condition, in kNm, as defined in Table 2.6.1 Design load combinations in Pt 10, Ch 2 Loads and Load Combinations
    Mwv-v = hogging and sagging vertical wave bending moments, in kNm, as defined in Pt 10, Ch 2, 1.2 Definitions 1.2.2.(d). Mwv-v is to be taken as:

    Mwv-hog for assessment with respect to hogging vertical wave bending moment

    Mwv-sag for assessment with respect to sagging vertical wave bending moment

    Iv-net50 = net vertical hull girder moment of inertia, in m4
    zdk-side = distance from baseline to moulded deck line at side, in metres
    zkl = vertical distance from the baseline to the keel, in metres
    zNA-net50 = distance from baseline to horizontal neutral axis, in metres
    ki = higher strength steel factor for the area i defined in Figure 3.1.7 Vertical extent of higher strength steel The factor, k, is defined in Pt 10, Ch 3, 1.1 Symbols.

    Figure 3.1.7 Vertical extent of higher strength steel

1.6.4  Tapering of plate thickness due to hull girder shear requirement.
  1. Longitudinal tapering of shear reinforcement is permitted, provided that the requirements given in Pt 10, Ch 3, 1.4 Hull girder shear strength 1.4.2 are complied with for any longitudinal position.
1.6.5  Structural continuity of longitudinal bulkheads.
  1. Suitable scarphing arrangements are to be made to ensure continuity of strength and the avoidance of abrupt structural changes. In particular, longitudinal bulkheads are to be terminated at an effective transverse bulkhead and large transition brackets shall be fitted in line with the longitudinal bulkhead.
1.6.6  Structural continuity of longitudinal stiffeners.
  1. Where longitudinal stiffeners terminate, and are replaced by a transverse system, adequate arrangements are to be made to avoid an abrupt changeover.
  2. Where a deck longitudinal stiffener is cut, in way of an opening, compensation is to be arranged to ensure structural continuity of the area. The compensation area is to extend well beyond the forward and aft ends of the opening and not be less than the area of the longitudinal that is cut. Stress concentration in way of the stiffener termination and the associated buckling strength of the plate and panel is to be considered.

1.7 Standard construction details

1.7.1 Details to be submitted:
  1. A booklet of standard construction details is to be submitted for review. It is to include the following:
    1. the proportions of built-up members to demonstrate compliance with established standards for structural stability.
    2. the design of structural details which reduce the harmful effects of stress concentrations, notches and material fatigue, such as:
      • details of the ends, at the intersections of members and associated brackets;
      • shape and location of air, drainage, and/or lightening holes;
      • shape and reinforcement of slots or cut-outs for internals;
      • elimination or closing of weld scallops in way of butts, ‘softening’ of bracket toes, reduction of abrupt changes of section or structural discontinuities;
      • proportion and thickness of structural members to reduce fatigue response due to machinery operational and/or wave induced cyclic stresses, particularly for higher strength steels.

1.8 Termination of local support members

1.8.1  General.
  1. In general, structural members are to be effectively connected to adjacent structures to avoid hard spots, notches and stress concentrations.
  2. Where a structural member is terminated, structural continuity is to be maintained by suitable back-up structure fitted in way of the end connection of frames, or the end connection is to be effectively extended with additional structure and integrated with an adjacent beam, stiffener, etc.
  3. All types of stiffeners (longitudinals, beams, frames, bulkhead stiffeners) are to be connected at their ends. However, in special cases, sniped ends may be permitted. Requirements for the various types of connections (bracketed, bracketless or sniped ends) are given in Pt 10, Ch 3, 1.8 Termination of local support members 1.8.3 to Pt 10, Ch 3, 1.8 Termination of local support members 1.8.5.
1.8.2  Longitudinal members.
  1. All longitudinals are to be kept continuous within the 0,4L amidships cargo tank region. In special cases, in way of large openings, foundations and partial girders, the longitudinals may be terminated, but end connection and welding are to be specially considered.
  2. Where continuity of strength of longitudinal members is provided by brackets, the correct alignment of the brackets on each side of the primary support member is to be ensured, and the scantlings of the brackets are to be such that the combined stiffener/bracket section modulus and effective cross-sectional area are not less than those of the member.
1.8.3  Bracketed connections.
  1. At bracketed end connections, continuity of strength is to be maintained at the stiffener connection to the bracket and at the connection of the bracket to the supporting member. The brackets are to have scantlings, sufficient to compensate for the non-continuous stiffener flange or noncontinuous stiffener.
  2. The arrangement of the connection between the stiffener and the bracket is to be such that at no point in the connection is the section modulus less than that required for the stiffener.
  3. Minimum net bracket thickness, tbkt-net, is to be taken as:
    tbkt-net = mm

    but is not to be less than 6 mm and need not be greater than 13,5 mm

    where:

    fbkt = 0,2 for brackets with flange or edge stiffener
    = 0,3 for brackets without flange or edge stiffener
    Zrl-net = net Rule section modulus, for the stiffener, in cm3.

    In the case of two stiffeners connected, it need not be taken as greater than that of the smallest connected stiffener

    σ yd-stf = specified minimum yield stress of the material of the stiffener, in N/mm2
    σ yd-bkt = specified minimum yield stress of the material of the bracket, in N/mm2.

    Figure 3.1.8 Bracket arm length

  4. Brackets to provide fixity of end rotation are to be fitted at the ends of discontinuous local support members, except as otherwise permitted by Pt 10, Ch 3, 1.8 Termination of local support members 1.8.4 The end brackets are to have arm lengths, lbkt , not less than:
    lbkt = mm, but is not to be less than:
    1. 1,8 times the depth of the stiffener web for connections where the end of the stiffener web is supported and the bracket is welded in line with the stiffener web or with offset necessary to enable welding, see Figure 3.1.8 Bracket arm length (c)
    2. 2,0 times for other cases, see Figure 3.1.8 Bracket arm length (a), (b) and (d)

    where

    cbkt = 65 for brackets with flange or edge stiffener
    = 70 for brackets without flange or edge stiffener
    Zrl-net = net Rule section modulus, for the stiffener, in cm3. In the case of two stiffeners connected, it need not be taken as greater than that of the smallest connected stiffener
    tbkt-net = minimum net bracket thickness, as defined in Pt 10, Ch 3, 1.8 Termination of local support members 1.8.3.(c).
  5. Where an edge stiffener is required, the depth of stiffener web, dw , is not to be less than:
    dw = mm,

    but is not to be less than 50 mm

    where

    Zrl-net = net Rule section modulus, for the stiffener, in cm3. In the case of two stiffeners connected, it need not be taken as greater than that of the smallest connected stiffener.
1.8.4  Bracketless connections.
  1. Local support members, for example, longitudinals, beams, frames and bulkhead stiffeners forming part of the hull structure, are generally to be connected at their ends, in accordance with the requirements of Pt 10, Ch 3, 1.8 Termination of local support members 1.8.2 and Pt 10, Ch 3, 1.8 Termination of local support members 1.8.3.
  2. Where alternative connections are adopted, the proposed arrangements will be specially considered.
  3. The design of end connections and their supporting structure is to be such as to provide adequate resistance to rotation and displacement of the joint.
1.8.5  Sniped ends.
  1. Stiffeners with sniped ends may be used where dynamic loads are small and where the incidence of vibration is considered to be small, i.e. structure not in the stern area and structure not in the vicinity of engines or generators, provided the net thickness of plating supported by the stiffener, tp-net, is not less than:
    tp-net = mm

    where

    l = stiffener span, in metres
    s = stiffener spacing, in mm
    P = design pressure for the stiffener for the design load set being considered, in kN/m2. The design load sets and method to derive the design pressure are to be taken in accordance with the following criteria, which define the acceptance criteria set to be used:
    1. Table 3.2.4 Section modulus requirements for stiffeners in the cargo tank region
    2. Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2.(b) in the area forward of the forward cargo tank, and in the aft end
    3. Pt 10, Ch 3, 4.9 Scantling requirements 4.9.1 in the machinery space
      k = higher strength steel factor, as defined in Pt 10, Ch 1, 3.1 General 3.1.7
      c1 = coefficient for the design load set being considered, to be taken as:
      = 1,2 for acceptance criteria set AC1
      = 1,1 for acceptance criteria set AC2
      = 1,0 for acceptance criteria set AC3.
  2. Bracket toes and sniped end members are, in general, to be kept within 25 mm of the adjacent member. The maximum distance is not to exceed 40 mm unless the bracket or member is supported by another member on the opposite side of the plating. Special attention is to be given to the end taper by using a sniped end of not more than 30 degrees. The depth of toe or sniped end is, generally, not to exceed the thickness of the bracket toe or sniped end member, but need not be less than 15 mm.
  3. The end attachments of non-load-bearing members may be snipe ended. The sniped end is to be not more than 30 degrees and is generally to be kept within 50 mm of the adjacent member, unless it is supported by a member on the opposite side of the plating. The depth of the toe is generally not to exceed 15 mm.
1.8.6  Air and drain holes and scallops.
  1. Air and drain holes and scallops are to be kept at least 200 mm clear of the toes of end brackets, end connections and other areas of high stress concentration measured along the length of the stiffener toward the midspan and 50 mm measured along the length in the opposite direction, see Figure 3.1.10 Location of air and drain holes. Openings that have been fitted with closing plates, such as scallops, may be permitted in way of block fabrication butts. In areas where the shear stress is less than 60 per cent of the allowable limit, alternative arrangements may be accepted. Openings are to be well-rounded. Figure 3.1.9 Examples of air and drain holes and scallops shows some examples of air and drain holes and scallops. In general, the ratio of a/b, as defined in Figure 3.1.9 Examples of air and drain holes and scallops, is to be between 0,5 and 1,0. In fatigue-sensitive areas, further consideration may be required with respect to the details and arrangements of openings and scallops.

    Figure 3.1.9 Examples of air and drain holes and scallops

    Figure 3.1.10 Location of air and drain holes

1.8.7  Special requirements.
  1. Closely spaced scallops or drain holes, i.e. where the distance between scallops/drain holes is less than twice the width b as shown in Figure 3.1.9 Examples of air and drain holes and scallops, are not permitted in longitudinal strength members or within 20 per cent of the stiffener span measured from the end of the stiffener. Widely spaced air or drain holes may be permitted, provided that they are of elliptical shape or equivalent to minimise stress concentration and are, in general, cut clear of the weld connection.

1.9 Termination of primary support members

1.9.1  General.
  1. Primary support members are to be arranged to ensure effective continuity of strength. Abrupt changes of depth or section are to be avoided. Primary support members in tanks are to form a continuous line of support and, wherever possible, a complete ring system.
  2. The members are to have adequate lateral stability and web stiffening, and the structure is to be arranged to minimise hard spots and other sources of stress concentration. Openings are to have well-rounded corners and are to be located considering the stress distribution and buckling strength of the panel.
1.9.2  End connection.
  1. Primary support members are to be provided with adequate end fixity by brackets or equivalent structure. The design of end connections and their supporting structure is to provide adequate resistance to rotation and displacement of the joint and effective distribution of the load from the member.
  2. The ends of brackets are generally to be soft-toed. The free edges of the brackets are to be stiffened. Scantlings and details are given in Pt 10, Ch 3, 1.9 Termination of primary support members 1.9.3.
  3. Where primary support members are subjected to concentrated loads, additional strengthening may be required, particularly if these are out of line with the member web.
  4. In general, ends of primary support members or connections between primary support members forming ring systems are to be provided with brackets. Bracketless connections may be applied, provided that there is adequate support of the adjoining face-plates.
1.9.3  Brackets.
  1. In general, the arm lengths of brackets connecting primary support members are not to be less than the web depth of the member, and need not be taken as greater than 1,5 times the web depth. The thickness of the bracket is, in general, not to be less than that of the girder web plate.
  2. For a ring system where the end bracket is integral with the webs of the members and the face-plate is carried continuously along the edges of the members and the bracket, the full area of the largest face-plate is to be maintained close to the mid point of the bracket and gradually tapered to the smaller face-plates. Butts in face-plates are to be kept well clear of the bracket toes.
  3. Where a wide face-plate abuts a narrower one, the taper is generally not to be greater than 1 in 4. Where a thick face-plate abuts against a thinner one and the difference in thickness is greater than 4 mm, the taper of the thickness is not to be greater than 1 in 3.
  4. Face-plates of brackets are to have a net cross-sectional area, Af-net , which is not to be less than:
    Af-net = lbkt-edge tbkt-net cm

    where

    lbkt-edge = length of free edge of bracket, in metres. For brackets that are curved, the length of the free edge may be taken as the length of the tangent at the mid point of the free edge. If lbkt-edge is greater than 1,5 m, 40 per cent of the face-plate area is to be in a stiffener fitted parallel to the free edge and a maximum 0,15 m from the edge
    tbkt-net = minimum net bracket thickness, in mm, as defined in Pt 10, Ch 3, 1.8 Termination of local support members 1.8.3.(c).
1.9.4  Bracket toes.
  1. The toes of brackets are not to land on unstiffened plating. Notch effects at the toes of brackets may be reduced by making the toe concave or otherwise tapering it off. In general, the toe height is not to be greater than the thickness of the bracket toe, but need not be less than 15 mm. The end brackets of large primary support members are to be soft-toed. Where any end bracket has a face-plate, it is to be sniped and tapered at an angle not greater than 30 degrees.
  2. Where primary support members are constructed of higher strength steel, particular attention is to be paid to the design of the end bracket toes in order to minimise stress concentrations. Sniped face-plates, which are welded onto the edge of primary support member brackets, are to be carried well around the radiused bracket toe and are to incorporate a taper not greater than 1 in 3. Where sniped face-plates are welded adjacent to the edge of primary support member brackets, an adequate cross-sectional area is to be provided through the bracket toe at the end of the snipe. In general, this area, measured perpendicular to the face-plate, is to be not less than 60 per cent of the full cross-sectional area of the face-plate, see Figure 3.1.11 Bracket toe construction.

    Figure 3.1.11 Bracket toe construction

1.10 Intersections of continuous local support members and primary support members

1.10.1  General.
  1. Cut-outs for the passage of stiffeners through the web of primary support members, and the related collaring arrangements, are to be designed to minimise stress concentrations around the perimeter of the opening and on the attached web stiffeners.
  2. Cut-outs in way of cross-tie ends and floors under bulkhead stools or in high stress areas are to be fitted with ‘full’ collar plates, see Figure 3.1.12 Collars for cut-outs in areas of high stress.

    Figure 3.1.12 Collars for cut-outs in areas of high stress

  3. Lug type collar plates are to be fitted in cut-outs where required for compliance with the requirements of Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3, and in areas of significant stress concentrations, e.g. in way of primary support member toes.
  4. When, in the following locations, the calculated direct stress, σw, in the primary support member web stiffener according to Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(e) exceeds 80 per cent of the permissible values, a soft heel is to be provided in way of the heel of primary support member web stiffeners:
    1. connection to shell envelope longitudinals below the deep load draught, Tsc ;
    2. connection to inner bottom longitudinals.

    A soft heel is not required at the intersection with watertight bulkheads, where a back bracket is fitted or where the primary support member web is welded to the stiffener faceplate. The soft heel is to have a keyhole, similar to that shown in Figure 3.1.14 Primary support member web stiffener details (c).

1.10.2  Details of cut-outs.
  1. In general, cut-outs are to have rounded corners and the corner radii, R, are to be as large as practicable, with a minimum of 20 per cent of the breadth, b, of the cut-out or 25 mm, whichever is greater, but need not be greater than 50 mm, see Figure 3.1.12 Collars for cut-outs in areas of high stress. Consideration will be given to other shapes on the basis of maintaining equivalent strength and minimising stress concentration.
1.10.3  Connection between primary support members and intersecting stiffeners (local support members).
  1. The cross-sectional areas of the connections are to be determined from the proportion of load transmitted through each component in association with its appropriate permissible stress.
  2. The total load, W, transmitted through the connection to the primary support member is given by:
    W =

    where

    P = design pressure for the stiffener for the design load set being considered, in kN/m2. The design load sets, method to derive the design pressure and applicable acceptance criteria set are to be taken in accordance with the following criteria, which define the acceptance criteria set to be used:
    S = primary support member spacing, in metres
    s = stiffener spacing, in mm

    For stiffeners having different primary support member spacing, S, and/or different pressure, P, at each side of the primary support member, the average load for the two sides is to be applied, e.g. vertical stiffeners at transverse bulkhead.

  3. The load, W1 , transmitted through the shear connection is to be taken as follows:

    If the web stiffener is connected to the intersecting stiffener:

    W1 = kN

    If the web stiffener is not connected to the intersecting stiffener:

    W1 = W

    where

    α a = panel aspect ratio, not to be taken greater than 0,25
    =
    S = primary support member spacing, in metres
    s = stiffener spacing, in mm
    A1-net = effective net shear area of the connection, to be taken as the sum of the components of the connection:

    Ald-net + Alc-net cm2

    in case of a slit type slot connections area, A1-net , is given by:

    Al-net = 2ld tw-net 10–2 cm2

    in case of a typical double lug or collar plate connection area, Al-net , is given by:

    Al-net = 2f1 lc tc-net 10–2 cm2
    A1d-net = net shear connection area excluding lug or collar plate, as given by the following and Figure 3.1.13 Symmetric and asymmetric cut-outs:

    Ald-net = ld tw-net 10–2 cm2

    ld = length of direct connection between stiffener and primary support member web, in mm
    tw-net = net web thickness of the primary support member, in mm
    A1c-net = net shear connection area with lug or collar plate, given by the following and Figure 3.1.13 Symmetric and asymmetric cut-outs:

    Alc-net = f1 lc tc-net 10–2 cm2
    lc = length of connection between lug or collar plate and primary support member, in mm
    tc-net = net thickness of lug or collar plate, not to be taken greater than the net thickness of the adjacent primary support member web, in mm
    f1 = shear stiffness coefficient:
    = 1,0 for stiffeners of symmetrical cross-section
    = for stiffeners of asymmetrical cross-section but is not to be taken as greater than 1,0
    w = the width of the cut-out for an asymmetrical stiffener, measured from the cut-out side of the stiffener web, in mm, as indicated in Figure 3.1.13 Symmetric and asymmetric cut-outs
    Aw-net = effective net cross-sectional area of the primary support member web stiffener in way of the connection, including backing bracket where fitted, as shown in Figure 3.1.14 Primary support member web stiffener details, in cm. If the primary support member web stiffener incorporates a soft heel ending or soft heel and soft toe ending, Aw-net is to be measured at the throat of the connection, as shown in Figure 3.1.14 Primary support member web stiffener details
    fc = the collar load factor defined as follows: for intersecting stiffeners of symmetrical cross-section:
    = 1,85 for Aw-net ≤ 14
    = 1,85 – 0,0441 (Aw-net – 14) for 14 < Aw-net ≤ 31
    = 1,1 – 0,013 (Aw-net – 31) for 31 < Aw-net ≤ 58
    = 0,75 for Aw-net > 58

    for intersecting stiffeners of asymmetrical cross-section:

    where

    ls = lc for a single lug or collar plate connection to the primary support member
    = ld for a single sided direct connection to the primary support member
    = mean of the connection length on both sides, i.e. in the case of a lug or collar plus a direct connection, ls = 0,5 (lc + ld )

    Figure 3.1.13 Symmetric and asymmetric cut-outs

    Figure 3.1.14 Primary support member web stiffener details

  4. The load, W2 , transmitted through the primary support member web stiffener is to be taken as follows: If the web stiffener is connected to the intersecting stiffener:
    W2 = kN

    If the web stiffener is not connected to the intersecting stiffener:

    W2 = 0

    where

    α a = panel aspect ratio
    S = primary support member spacing, in metres
    s = stiffener spacing, in mm
    A1-net = effective net shear area of the connection, in cm2, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c)
    Aw-net = effective net cross-sectional area of the primary support member web stiffener, in cm2, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c).
  5. The values of Aw-net , Awc-net and A1–net are to be such that the calculated stresses satisfy the following criteria: for the connection to the primary support member web stiffener away from the weld:

    σ w ≤ σperm

    for the connection to the primary support member web stiffener in way of the weld:

    σ wc ≤ σperm

    for the shear connection to the primary support member web:

    τ w ≤ τperm

    where

    σ w = direct stress in the primary support member web stiffener at the minimum bracket area away from the weld connection:
    = N/mm2
    σ wc = direct stress in the primary support member web stiffener in way of the weld connection:
    = N/mm2
    τ w = shear stress in the shear connection to the primary support member
    = N/mm2
    Aw-net = effective net cross-sectional area of the primary support member web stiffener, in cm2, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c)
    Awc-net = effective net area of the web stiffener in way of the weld as shown in Figure 3.1.14 Primary support member web stiffener details, in cm2
    A1-net = effective net shear area of the connection, in cm2, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c)
    W1 = load transmitted through the shear connection, in kN, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c)

    0,9W ≤ kN

    A1-net = effective net shear area in cm2 of the connection, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c)
    Aw-net = effective net cross-sectional area in cm2 of the primary support member web stiffener in way of the connection including backing bracket where fitted, as defined in Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(c)

    Table 3.1.6 Permissible stresses for connection between stiffeners and primary support members

    Item Direct stress, σperm, in N/mm2 Shear stress, τperm, in N/mm2
    Acceptance criteria set, see Pt 10, Ch 3, 3.4 Side structure 3.4.3.(b) Acceptance criteria set, see Pt 10, Ch 3, 3.4 Side structure 3.4.3.(b)
    AC1 AC2 AC3 AC1 AC2 AC3
    Primary support member web stiffener 0,83σyd, see Note 3 σyd σyd — — —
    Primary support member web stiffener to intersecting stiffener in way of weld connection:            
    double continuous fillet 0,58σyd see Note 3 0,7σyd see Note 3 σyd — — —
    partial penetration weld 0,83σyd see Notes 2 & 3 σyd see Note 2 σyd — — —
    Primary support member stiffener to intersecting stiffener in way of lapped welding 0,5σyd 0,6σyd σyd — — —
    Shear connection including lugs or collar plates:            
    single sided connection — — — 0,71τyd 0,85τyd τyd
    double sided connection — — — 0,83σyd τyd τyd
    Symbols
    τperm = permissible shear stress, in N/mm2
    σperm = permissible direct stress, in N/mm2
    σyd = minimum specified material yield stress, in N/mm2
    τyd = , in N/mm2

    NOTES

    1. The stress computation on plate type members is to be performed on the basis of net thicknesses, whereas gross values are to be used in weld strength assessments, see Pt 10, Ch 3, 1.10 Intersections of continuous local support members and primary support members 1.10.3.(k).

    2. The root face is not to be greater than one third of the gross thickness of the primary support member stiffener.

    3. Allowable stresses may be increased by 5 per cent where a soft heel is provided in way of the heel of the primary support member web stiffener.

  6. Where a backing bracket is fitted in addition to the primary support member web stiffener, it is to be arranged on the opposite side to, and in alignment with, the web stiffener. The arm length of the bracket is to be not less than the depth of the web stiffener and its net cross-sectional area through the throat of the bracket is to be included in the calculation of Aw-net as shown in Figure 3.1.14 Primary support member web stiffener details.
  7. Lapped connections of primary support member web stiffeners or tripping brackets to local support members are not permitted in the cargo tank region, e.g. lapped connections between transverse and longitudinal local support members.
  8. Fabricated stiffeners having their face-plate welded to the side of the web, leaving the edge of the web exposed, are not recommended for side shell and longitudinal bulkhead longitudinals. Where such sections are connected to the primary support member web stiffener, a symmetrical arrangement of connection to the transverse members is to be incorporated. This may be implemented by fitting backing brackets on the opposite side of the transverse web or bulkhead. In way of the cargo tank region, the primary support member web stiffener and backing brackets are to be butt welded to the intersecting stiffener web.
  9. Where the web stiffener of the primary support member is parallel to the web of the intersecting stiffener, but not connected to it, the offset primary support member web stiffener may be located as shown in Figure 3.1.15 Offset primary support member web stiffeners. The offset primary support member web stiffener is to be located in close proximity to the slot edge, see also Figure 3.1.15 Offset primary support member web stiffeners. The ends of the offset web stiffeners are to be suitably tapered and softened.

    Figure 3.1.15 Offset primary support member web stiffeners

  10. Alternative arrangements will be specially considered on the basis of their ability to transmit load with equivalent effectiveness. Details of calculations made and/or testing procedures and results are to be submitted.
  11. The size of the fillet welds is to be calculated according to Pt 4, Ch 8 Welding and Structural Details, based on the weld factors given in Table 3.1.7 Weld factors for connection between stiffeners and primary support members. For the welding in way of the shear connection, the size is not to be less than that required for the primary support member web plate for the location under consideration.

    Table 3.1.7 Weld factors for connection between stiffeners and primary support members

    Item Weld factor
    Primary support member stiffener to intersecting stiffener 0,44 σwc / σperm not to be less than 0,34
    Shear connection inclusive lug or collar plate 0,34
    Shear connection inclusive lug or collar plate, where the web stiffener of the primary support member is not connected to the intersection stiffener 0,44 τw / τperm not to be less than 0,38
    Symbol

1.11 Openings

1.11.1  General.
  1. Openings are to have well rounded corners.
  2. Manholes, lightening holes and other similar openings are to be avoided in way of concentrated loads and areas of high shear. In particular, manholes and similar openings are to be avoided in high stress areas unless the stresses in the plating and the panel buckling characteristics have been calculated and found satisfactory. Examples of high stress areas include:
    1. in vertical or horizontal diaphragm plates in narrow cofferdams/double plate bulkheads within one sixth of their length from either end;
    2. in floors or double bottom girders close to their span ends;
    3. above the heads and below the heels of pillars.

    Where larger openings than given by Pt 10, Ch 3, 1.11 Openings 1.11.2 or Pt 10, Ch 3, 1.11 Openings 1.11.3 are proposed, the arrangements and compensation required will be specially considered.

1.11.2  Manholes and lightening holes in single skin sections not requiring reinforcement.
  1. Openings cut in the web with depth of opening not exceeding 25 per cent of the web depth and located so that the edges are not less than 40 per cent of the web depth from the face-plate do not generally require reinforcement. The length of opening is not to be greater than the web depth or 60 per cent of the local support member spacing, whichever is greater. The ends of the openings are to be equidistant from the corners of cut-outs for local support members.
1.11.3  Manholes and lightening holes in double skin sections not requiring reinforcement.
  1. Where openings are cut in the web and are clear of high stress areas, reinforcement of these openings is not required, provided that the depth of the opening does not exceed 50 per cent of the web depth and is located so that the edges are well clear of cut-outs for the passage of local support members.
1.11.4  Manholes and lightening holes requiring reinforcement.
  1. Manholes and lightening holes are to be stiffened as required by Pt 10, Ch 3, 1.11 Openings 1.11.4.(b) and Pt 10, Ch 3, 1.11 Openings 1.11.4.(c).
  2. The web plate is to be stiffened at openings when the mean shear stress, as determined by application of the requirements of Pt 10, Ch 3 Scantling Requirements, is greater than 50 N/mm22 for acceptance criteria set AC1 or greater than 60 N/mm2 for acceptance criteria sets AC2 and AC3. The stiffening arrangement is to ensure buckling strength, as required by Pt 10, Ch 3 Scantling Requirements.
  3. On members contributing to longitudinal strength, stiffeners are to be fitted along the free edges of the openings parallel to the vertical and horizontal axis of the opening. Stiffeners may be omitted in one direction if the shorter axis is less than 400 mm, and in both directions if the length of both axes is less than 300 mm. Edge reinforcement may be used as an alternative to stiffeners, see Figure 3.1.16 Web plate with large openings

    Figure 3.1.16 Web plate with large openings

1.12 Local reinforcement

1.12.1  Reinforcement at knuckles.
  1. Whenever a knuckle in a main member (shell, longitudinal bulkhead, etc.) is arranged, adequate stiffening is to be fitted at the knuckle to transmit the transverse load. This stiffening, in the form of webs, brackets or profiles, is to be connected to the transverse members to which they are to transfer the load (in shear), see Figure 3.1.17 Example of reinforcement at knuckles.

    Figure 3.1.17 Example of reinforcement at knuckles

  2. In general, for longitudinal shallow knuckles, closely spaced carlings are to be fitted across the knuckle, between longitudinal members above and below the knuckle. Carlings or other types of reinforcement need not be fitted in way of shallow knuckles that are not subject to high lateral loads and/or high inplane loads across the knuckle, such as deck camber knuckles.
  3. Generally, the distance between the knuckle and the support stiffening described in Pt 10, Ch 3, 1.12 Local reinforcement 1.12.2.(a) is not to be greater than 50 mm.
1.12.2  Reinforcement for openings and attachments associated with means of access for inspection/ maintenance purposes.
  1. Local reinforcement is to be provided, taking into account proper location and strength of all attachments to the hull structure for access for inspection/maintenance purposes.
Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.