4 Primary Supporting Members

4.1 Proportions and stiffness

4.1.1 Proportions of web plate and flange

The net thicknesses of the web plates and flanges of primary supporting members are to satisfy the following criteria:

a) Web plate:
b) Flange:

where:

s_w : Plate breadth, in mm, taken as the spacing of the web stiffeners.

C_w : Slenderness coefficient for the web plate taken as:

C_w = 100

C_f : Slenderness coefficient for the flange taken as:

C_f = 12

4.1.2 Deck transverse primary supporting members

The net moment of inertia for deck transverse primary supporting members, I_psm-n50, in cm⁴, supporting deck longitudinals subject to axial compressive hull girder stress, is to comply, within its central half of the bending span, with the following criterion:

where:

I_psm-n50 : Net moment of inertia, in cm⁴, of deck transverse primary supporting member, with effective width of attached plate equal to 0.8S.

: Effective bending span of deck transverse primary supporting member, in m, as defined in Ch 3, Sec 7.

S : Spacing of deck transverse primary supporting members, in m, as defined in Ch 3, Sec 7.

I_st : Moment of inertia of deck stiffeners within the central half of the bending span, in cm⁴, as given in [3.1.3].

4.2 Web stiffeners of primary supporting members

4.2.1 Proportions of web stiffeners

The net thickness of web and flange of web stiffeners fitted on primary supporting members is to satisfy the requirements specified in [3.1.1] and [3.1.2].

4.2.2 Bending stiffness of web stiffeners

The net moment of inertia, in cm⁴, of web stiffener, I_st, fitted on primary supporting members, with effective attached plate, s_eff, is not to be less than the minimum moment of inertia defined in Table 2.

Table 2 : Stiffness criteria for web stiffeners

Stiffener arrangement		Minimum moment of inertia of web stiffeners, in cm⁴
A	Web stiffeners fitted along the PSM span
B	Web stiffeners fitted normal to the PSM span
where: C : Slenderness coefficient to be taken as: C = 1.43 for longitudinal stiffeners including sniped stiffeners. C = 0.72 for other stiffeners. : Length of web stiffener, in m. For web stiffeners welded to local supporting members, the length is to be measured between the flanges of the local support members. For sniped web stiffeners, the length is to be measured between the lateral supports, e.g. the total distance between the flanges of the primary supporting member as shown for stiffener arrangement B. A_eff : Net section area of web stiffener including effective attached plate, s_eff, in cm². t_w : Net web thickness of the primary supporting member, in mm. R_eH : Specified minimum yield stress of the material of the web plate of the primary supporting member, in N/mm2.