Clasification Society Rulefinder 2020 - Version 9.33 - Fix
Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 6 Hull Local Scantling - Section 5 Stiffeners - 1 Stiffeners Subject to Lateral Pressure

1 Stiffeners Subject to Lateral Pressure

1.1 Yielding check

1.1.1 Web plating

The minimum net web thickness, tw in mm, is not to be taken less than the greatest value calculated for all applicable design load sets as defined in Ch 6, Sec 2, [2], given by:

with χ Ct not to be taken greater than 1.0.

where:

fshr : Shear force distribution factor taken as:
  • For continuous stiffeners with fixed ends, fshr is not to be taken less than:
    • fshr = 0.5 for horizontal stiffeners and upper end of vertical stiffeners.
    • fshr = 0.7 for lower end of vertical stiffeners.
  • For stiffeners with reduced end fixity, variable load or being part of grillage, the requirement in [1.2] applies.
Ct : Permissible shear stress coefficient for the design load set being considered, taken as:
  • Ct = 0.75 for acceptance criteria set AC-S.
  • Ct = 0.90 for acceptance criteria set AC-SD.

1.1.2 Section modulus

The minimum net section modulus, Z in cm3, is not to be taken less than the greatest value calculated for all applicable design load sets as defined in Ch 6, Sec 2, [2.1.3], given by:

  • with χ Cs not to be taken greater than 1.0.

where:

fbdg : Bending moment factor taken as:
  • For continuous stiffeners with fixed ends, fbdg is not to be taken higher than:
    • fbdg = 12 for horizontal stiffeners and upper end of vertical stiffeners.
    • fbdg = 10 for lower end of vertical stiffeners.
  • For stiffeners with reduced end fixity, variable load or being part of grillage, the requirement in [1.2] applies.

Cs : Permissible bending stress coefficient as defined in Table 1 for the design load set being considered.

σhg : Hull girder bending stress, in N/mm2, as defined in Ch 6, Sec 2, [1.1], calculated at the load calculation point as defined in Ch 3, Sec 7, [3.2].

βs : Coefficient as defined in Table 2.

αs : Coefficient as defined in Table 2.

Cs-max : Coefficient as defined in Table 2.

Table 1 : Definition of Cs

Sign of hull girder bending stress, σhg Lateral pressure acting on

Coefficient Cs
Tension (positive) Stiffener side

but not to be taken greater than Cs-max

Compression (negative)

Plate side
Tension (positive) Plate side Cs = Cs-max

Compression (negative)

Stiffener side

Table 2 : Definition of βs, αs and Cs-max

Acceptance criteria set Structural member βs αs Cs-max
AC-S Longitudinal strength member 0.85 1.0 0.75
Transverse or vertical member 0.75 0 0.75
AC-SD Longitudinal strength member 1.0 1.0 0.9
Transverse or vertical member 0.9 0 0.9

1.1.3 Group of stiffeners

Scantlings of stiffeners based on requirements in [1.1.1] and [1.1.2] may be decided based on the concept of grouping designated sequentially placed stiffeners of equal scantlings on a single stiffened panel between primary supporting members. The scantling of the group is to be taken as the greater of the following:
  • The average of the required scantling of all stiffeners within a group.
  • 90% of the maximum scantling required for any one stiffener within the group.

1.1.4 Plate and stiffener of different materials

When the minimum specified yield stress of a stiffener exceeds the minimum specified yield stress of the attached plate by more than 35%, the following criterion is to be satisfied:

where:

ReH-S : Minimum specified yield stress of the material of the stiffener, in N/mm2.

ReH-P : Minimum specified yield stress of the material of the attached plate, in N/mm2.

σhg : Hull girder bending stress, in N/mm2, as defined in Ch 6, Sec 2, [1.1] with |σhg| not to be taken less than 0.4 ReH-P.

Z : Net section modulus, in way of face plate/free edge of the stiffener, in cm3.

ZP : Net section modulus, in way of the attached plate of stiffener, in cm3.

αs , βs : Coefficients defined in Table 2.

1.2 Beam analysis

1.2.1 Direct analysis

The maximum normal bending stress, σ and shear stress, τ in a stiffener using net properties with reduced end fixity, variable load or being part of grillage are to be determined by direct calculations taking into account:
  • The distribution of static and dynamic pressures and forces, if any.
  • The number and position of intermediate supports (e.g. decks, girders, etc).
  • The condition of fixity at the ends of the stiffener and at intermediate supports.
  • The geometrical characteristics of the stiffener on the intermediate spans.

1.2.2 Stress criteria

The stress is to comply with the following criteria where the coefficients Ct and Cs, are defined in [1.1.1] and [1.1.2].
  • τ ≤ χ Ct τeH
  • σ ≤ χ Cs ReH
Parent topic: Section 5 Stiffeners
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