Section 7 Application of scantling requirements to other structure
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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 7 Application of scantling requirements to other structure

Section 7 Application of scantling requirements to other structure

Parent topic: Chapter 3 Scantling Requirements

7.1 Symbols

7.1.1 The symbols used in this Chapter are defined as follows:
σyd = specified minimum yield stress of the material, in N/mm2
τyd = N/mm2
s = stiffener spacing, in mm
S = primary support member spacing, in metres
F = point load for the design load set being considered, in kN
P = design pressure for the design load set being considered, in kN/m2.

7.2 General

7.2.1  Application.
  1. The requirements of this Section apply to plating, local and primary support members where the basic structural configurations or strength models assumed in Pt 10, Ch 3, 2 Cargo tank region to Pt 10, Ch 3, 5 Aft end are not appropriate. These are general-purpose strength requirements to cover various load assumptions and end support conditions.
  2. The requirements for local and primary support members are to be specially considered when the member is:
    1. part of a grillage structure;
    2. subject to large relative deflection between end supports;
    3. where the load model or end support condition is not given in Table 3.7.2 Values of fbdg and fshr.
  3. The application of alternative or more advanced calculation methods will be specially considered.

7.3 Scantling requirements

7.3.1  General.
  1. The design load sets to be applied to the structural requirements for the local and primary support members are given in Table 3.2.6 Design load sets for plating and local support members (see continuation), as applicable for the particular structure under consideration. The static and dynamic load components are to be combined in accordance with Table 2.6.1 Design load combinations and the requirements given in Pt 10, Ch 2 Loads and Load Combinations.
7.3.2  Plating and local support members.
  1. For plating subjected to lateral pressure, the net thickness, tnet , is to be taken as the greatest value for all applicable design load sets, and given by:
    tnet = mm

    where

    αp = correction factor for the panel aspect ratio
    =
    lp = length of plate panel, to be taken as the spacing of primary support members, S, unless carlings are fitted, in metres
    Ca = permissible bending stress coefficient for the design load set being considered, as given in Table 3.2.3 Thickness requirements for plating, Table 3.3.2 Permissible bending stress coefficient for plating or Table 3.4.2 Permissible bending stress coefficient for plating, as applicable for the individual member being considered.
  2. For stiffeners subjected to lateral pressure, point loads, or some combination thereof, the net section modulus requirement, Znet , is to be taken as the greatest value for all applicable design load sets, and given by:
    Znet = cm3, for lateral pressure loads
    Znet = cm3, for point loads
    Znet = cm3, for a combination of loads

    where

    lbdg = effective bending span, in metres
    fbdg = bending moment factor

    for continuous stiffeners and where end connections are fitted consistent with idealisation of the stiffener as having fixed ends:

    = 12 for horizontal stiffeners
    = 10 for vertical stiffeners

    for other configurations the bending moment factor may be taken as in Table 3.7.2 Values of fbdg and fshr
    Cs = permissible bending stress coefficient for the design load set being considered as given in Table 3.2.4 Section modulus requirements for stiffeners, Table 3.3.3 Permissible bending stress coefficient for stiffeners or Table 3.4.3 Permissible bending stress coefficient for stiffeners, as applicable for the individual member being considered
    I = indices for load component i
    j = indices for load component j.
  3. For stiffeners subjected to lateral pressure, point loads, or some combination thereof, the net web thickness, tw-net , based on shear area requirements is to be taken as the greatest value for all applicable design load sets, and given by:
    tw-net = mm, for lateral pressure loads
    tw-net = mm, for point loads
    tw-net = mm, for a combination of loads

    where

    fshr = shear force factor

    for continuous stiffeners with end connections consistent with the idealisation of the stiffener as having fixed ends:

    = 0,5 for horizontal stiffeners
    = 0,7 for vertical stiffeners

    for other configurations the shear force factor may be taken as in Table 3.7.2 Values of fbdg and fshr
    lshr = effective shear span, in metres
    dshr = effective shear depth, in mm
    Ct = permissible shear stress coefficient for design load set, as given in Table 3.2.5 Web thickness requirements for stiffeners or Table 3.3.3 Permissible bending stress coefficient for stiffeners, for the individual member being considered
    I = indices for load component i
    j = indices for load component j.
7.3.3  Primary support members.
  1. The requirements in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3 are applicable where the primary support member is idealised as a simple beam. More advanced calculation methods may be required to ensure that nominal stress levels for all primary support members are less than the permissible stresses and stress coefficients given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3.(d) and Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3.(e), when subjected to the applicable design load sets. See also 7.1.1.4.
  2. The section modulus and web thickness of the local support members apply to the areas clear of the end brackets. The section modulus and cross-sectional shear areas of the primary support member are to be applied as required in the notes of Table 3.7.2 Values of fbdg and fshr.
  3. For primary support members intersecting with or in way of curved hull sections, the effectiveness of end brackets is to include an allowance for the curvature of the hull.
  4. For primary support members, the net section modulus requirement, Znet50 , is to be taken as the greatest value for all applicable design load sets, and given by:
    Znet50 = cm3, for lateral pressure loads
    Znet50 = cm3, for point loads
    Znet50 = cm3, for a combination of loads

    where

    lbdg = effective bending span, in metres
    fbdg = bending moment factor, as given in Table 3.7.2 Values of fbdg and fshr
    Cs-pr = permissible bending stress coefficient as given in Table 3.7.1 Permissible stress coefficients, Cs-pr for primary support members for design load set given in , for the individual member being considered
    I = indices for load component i
    j = indices for load component j.

    Table 3.7.1 Permissible stress coefficients, Cs-pr for primary support members

    Acceptance criteria set

    Permissible bending stress coefficient,

    Cs-pr

    Permissible shear stress coefficient,

    Ct-pr

    AC1 0,70 0,70
    AC2 0,85 0,85
    AC3 0,9 0,9

    Table 3.7.2 Values of fbdg and fshr

    Load and boundary conditions Bending moment and shear force factor (based on load at mid span where load varies) Application
    Load model   Position, see Note 1   1 2 3  

    1

    Support

    2

    Field

    3

    Support

    fbdg1

    fshr1

    fbdg2

    -

    fbdg3

    fshr3

     

    12,0

    0,50

    24,0

    -

    12,0

    0,50

    Built-in at both ends

    Uniform pressure distribution
     

    —

    0,38

    14,2

    —

    8,0

    0,63

    Built-in at one end plus simply supported one end

    Uniform pressure distribution
     

    —

    0,50

    8,0

    —

    —

    0,50

    Simply supported, (both ends are free to rotate)

    Uniform pressure distribution
     

    15,0

    0,30

    23,3

    —

    10,0

    0,70

    Built-in at both ends

    Linearly varying pressure distribution

     

    —

    0,20

    16,8

    —

    7,5

    0,80

    Built-in at one end plus simply supported one end

    Linearly varying pressure distribution

     

    —

    —

    —

    —

    2,0

    1,0

    Cantilevered beam

    Uniform pressure distribution
     

    8,0

    0,5

    8,0

    —

    8,0

    0,5

    Built-in at both ends

    Single point load in the centre of the span

     

    —

    Built-in at both ends

    Single point load, with load anywhere in the span

     

    —

    0,5

    4

    —

    —

    0,5

    Simply supported

    Single point load in the centre of the span

      — —

    Simply supported

    Single point load, load anywhere along the span

    Symbols
    l = effective span, lbdg and lshr , as applicable
    lbdg = effective span in bending, for local or primary support members, in metres
    lshr = effective span in shear, for local or primary support members, in metres
    NOTES

    1. The bending moment factor, fbdg , for the support positions is applicable for a distance of 0,2lbdg from the end of the effective bending span for both local and primary support members.

    2. The shear force factor, fshr , for the support positions is applicable for a distance of 0,2lshr from the end of the effective shear span for both local and primary support members.

    3. Application of fbdg and fshr for local support members:

    (a) the section modulus requirement of local support members is to be determined using the lowest value of fbdg1 , fbdg2 and fbdg3 ;   

    (b) the shear area requirement of local support members is to be determined using the greatest value of fshr1 and fshr3 .

    4. Application of fbdg and fshr for primary support members:    

    (a) the section modulus requirement within 0,2lbdg from the end of the effective span is generally to be determined using the applicable fbdg1 and fbdg3 ; however, fbdg is not to be taken greater than 12;  

    (b) the section modulus of mid span area is to be determined using fbdg = 24, or fbdg2 from the Table if lesser;

    (c) the shear area requirement of end connections within 0,2lshr from the end of the effective span is to be determined using fshr = 0,5 or the applicable fshr1 or fshr3 , whichever is greater;   

     (d) for models A to F, the value of fshr may be gradually reduced outside of 0,2lshr towards 0,5fshr at mid span, where fshr is the greater value of fshr1 and fshr3 .

  5. For primary support members, the net shear area of the web, Ashr-net50 , is to be taken as the greatest value for all applicable design load sets, and given by:
    Ashr-net50 = cm2, for lateral pressure loads
    Ashr-net50 = cm2, for point loads
    Ashr-net50 = cm2, for a combination of loads

    where

    lshr = effective shear span, in metres
    fshr = shear force factor, as given in Table 3.7.2 Values of fbdg and fshr
    Ct-pr = permissible shear stress coefficient as given in Table 3.7.1 Permissible stress coefficients, Cs-pr for primary support members for design load set given in Table 3.2.6 Design load sets for plating and local support members (see continuation), for the individual member being considered
    I = indices for load component i
    j = indices for load component j.
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