3 Primary Supporting Members outside Cargo Hold Region

3.1 Application

3.1.1 The requirements of this article apply to primary supporting members, subjected to lateral pressure within the fore part, aft part and machinery space.

3.2 Scantling requirements

3.2.1 Net section modulus

The net section modulus, Z_n50 in cm³, of primary supporting members subjected to lateral pressure is not to be taken less than the greatest value for all applicable design load sets defined in Ch 6, Sec 2, [2], given by:

where:

f_bdg : Bending moment distribution factor, as given in Table 2.

C_s : Permissible bending stress coefficient for the acceptance criteria set, as given in Table 1.

3.2.2 Net shear area

The net shear area, A_shr-n50 in cm², of primary supporting members subjected to lateral pressure is not to be taken less than the greatest value for all applicable design load sets defined in Ch 6, Sec 2, [2], given by:

where:

f_shr : Shear force distribution factor, as given in Table 2.

C_t : Permissible shear stress coefficient for the acceptance criteria set being considered, as given in Table 1.

Table 1 : Permissible bending and shear stress coefficients for primary supporting members

Acceptance criteria set	Structure attached to primary supporting member	**C_s and C_t**
AC-S	All boundaries, including decks and flats	0.70
AC-SD	All boundaries, including decks and flats	0.85

Table 2 : Bending moment and shear force factors, f_bdg and f_shr

Load and boundary condition

Bending moment and shear force distribution factors (based on load at mid span, where load varies)

Position

f_bdg1

f_shr1

2f_bdg2-

f_bdg3

f_shr3

Load model

Support

Field

Support

12.0

0.50

24.0

12.0

0.50

0.38

14.2

8.0

0.63

0.50

8.0

0.50

15.0

0.30

23.3

10.0

0.70

0.20

16.8

7.5

0.80

2.0

1.0

Note 1: The bending moment distribution factor, f_bdg for the support positions is applicable for a distance of 0.2 from the end of the effective bending span of the primary supporting member.

Note 2: The shear force distribution factor, f_shr for the support positions is applicable for a distance of 0.2 from the end of the effective shear span of the primary supporting member.

Note 3: Application of f_bdg and f_shr:

The section modulus requirement within 0.2 from the end of the effective span is to be determined using the applicable f_bdg1 and f_bdg3, however f_bdg is not to be taken greater than 12.
The section modulus of mid-span area is to be determined using f_bdg = 24, or f_bdg2 from the table if lesser.
The shear area requirement of end connections within 0.2 from the end of the effective span is to be determined using f_shr = 0.5 or the applicable f_shr1 or f_shr3, whichever is greater.
For models A through F, the value of fshr may be gradually reduced outside of 0.2 towards 0.5 f_shr at mid-span, where f_shr is the greater value of f_shr1 and f_shr3.

3.3 Advanced calculation methods

3.3.1 Direct analysis

Where complex grillage structures are employed or cross ties are fitted in side shell primary supporting members, the scantlings are to be determined by direct calculation taking into account:

The distribution of still water and wave pressure 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 primary supporting members and at intermediate supports.
The geometrical characteristics of the primary supporting members on the intermediate spans.

3.3.2 Analysis criteria

The calculated stresses are to comply with the following criteria where the coefficients C_t and C_s, are defined in [3.2]:

σ ≤ χ C_s R_eH
τ ≤ χ C_t τ_eH

where:

τ : Shear stress in member, in N/mm², based on t_n50.

σ : Normal stress in member, in N/mm², based on t_n50.

3 Primary Supporting Members outside Cargo Hold Region

Table 1 : Permissible bending and shear stress coefficients for primary supporting members

Table 2 : Bending moment and shear force factors, fbdg and fshr

Table 2 : Bending moment and shear force factors, f_bdg and f_shr