Section 4 Construction details for primary members

4.1.1 This Section includes the requirements for proportions, stiffening, end connections and construction details for primary members.

4.1.2 The requirements of this Section may be modified where direct calculation procedures are adopted to analyse the stress distribution in the primary structure.

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

4.3.1 Primary members are to be so arranged as to ensure effective continuity of strength and abrupt changes of depth or section are to be avoided. Where members abut on both sides of a bulkhead or on other members, arrangements are to be made to ensure that they are in alignment. Primary transverse members in a longitudinal framing system are to form a continuous line of support and wherever possible, a complete ring system.

4.3.2 Where a primary member ends at a structure which provides only a low degree of restraint against rotation, the member is generally to extend for at least two frame spaces, or equivalent, beyond the point of support.

4.3.3 Where primary members are subject to concentrated loads, particularly if these are out of line with the member web, additional strengthening may be required.

4.4.1 The geometric properties of the member are to be calculated in association with an effective width of attached plating determined in accordance with Pt 3, Ch 3, 3.2 Geometric properties of section.

4.4.2 The minimum thickness or area of material in each component part of the primary member is given in Table 10.4.1 Minimum thickness of primary structures.

4.5.1 Primary members are to be supported by tripping brackets. The tripping brackets supporting asymmetrical sections are to be spaced no more than two secondary frames apart. The tripping brackets supporting symmetrical sections are to be spaced no more than four secondary frames apart.

4.5.2 Tripping brackets are also to be fitted at the toes of end brackets and in way of heavy or concentrated loads such as the heels of pillars.

4.5.3 Intermediate secondary members may be welded directly to the web or connected by lugs.

4.5.4 Apart from the requirements of Table 10.4.1 Minimum thickness of primary structures, the web thickness of a longitudinal girder at the strength deck within 0,5L amidships is to be not less than 0,018S _w mm.

4.6.1 Where openings are cut in the web, the depth of opening is not to exceed 25 per cent of the web depth, and the opening is to be so located that the edges are not less than 40 per cent of the web depth from the face plate. The length of opening is not to exceed 60 per cent of the secondary member spacing. Where larger openings are proposed, the arrangement and compensation required will be considered. Openings are to have smooth edges and well rounded corners.

4.6.2 Cut-outs for the passage of secondary members are to have smooth edges and rounded corners and are to be kept as small as practicable. The connection of the web plating to the secondary member is to be sufficient for the load to be transmitted to the primary member.

4.7.1 End connections of primary members are generally to comply with the requirements of Pt 3, Ch 10, 3 Secondary member end connections, taking Z as the section modulus of the primary member.

4.7.2 The thickness of the bracket is to be not less than that of the primary member web. The free edge of the bracket is to be stiffened.

4.7.3 Continuity is to be maintained where primary members intersect and where the members are of the same depth, a suitable gusset plate is to be fitted.

4.7.4 Where a deck girder or transverse is connected to a vertical member on the shell or bulkhead, the scantlings of the latter may be required to be increased to provide adequate resistance to rotation and displacement of the joint.