Section 4 Primary members supporting oiltight bulkheads

4.1.1 These requirements are applicable to ships having two longitudinal bulkheads, and to ships not exceeding 75 m in length having one longitudinal bulkhead located on the centreline of the ship.

4.1.2 The minimum thickness and construction detail requirements of Pt 4, Ch 10, 7 Construction details and minimum thickness are to be complied with. Particular attention is to be paid to the design of end connections between primary members and buttresses. Where considered necessary, the shear and combined stresses in the connections may require to be examined and the scantlings and stiffening increased.

4.2.1 The symbols used in this Section are defined as follows:

4.2.2 Other symbols are defined in Pt 4, Ch 9, 1.6 Information required for CSR Double Hull Oil Tankers.

4.3.1 Where horizontal girders and vertical webs do not form part of a ring structure, they are to be arranged with substantial end brackets forming a buttress extending to the adjacent vertical web or transverse.

4.3.2 Where the cross-ties are omitted from the transverse ring in the wing tank adjacent to the bulkhead, the design of the horizontal girder, of the end buttress and of the transverse is to take account of the loads imposed and the deflection of the structure.

4.3.3 The spacing of transverses on longitudinal bulkheads is not to exceed 3,6 m.

4.3.4 Where, on ships with transverse side framing, transverses are required by Pt 4, Ch 10, 3 Primary members supporting transverse side framing, vertical webs are also to be fitted in line on the longitudinal bulkhead. Where such vertical webs are not required the lower horizontal girder on the bulkhead is to be suitably buttressed from the bottom transverses.

4.4.1 The scantlings of vertical webs on longitudinal bulkheads are to be as required for side transverses by Pt 4, Ch 10, 2 Primary members supporting longitudinal framing.

4.4.2 The section modulus of vertical webs on transverse bulkheads and of horizontal girders is to be not less than:

4.4.3 The net sectional area of the web at any section is to be not less than:

where Q _x is the shear force at the section. For the horizontal girders on ships with two longitudinal bulkheads, Q _x is calculated from shear force diagrams as shown in Figure 10.4.1 Horizontal girders. For end connections, Q _x is to be determined by projection of the shear force diagrams as indicated.

4.4.4 The moment of inertia of vertical webs and horizontal girders is to be not less than:

4.4.5 For the calculation of section modulus, the minimum span of horizontal girders on longitudinal bulkheads is to be taken as not less than the lesser of (1,2 + 0,02L) m or 3 m.

Figure 10.4.1 Horizontal girders

4.4.6 Where a trunk is fitted, the scantlings of primary members are to be modified as required by Pt 4, Ch 10, 6 Trunked construction.