Section 4 Hull envelope framing

4.1.1 Bottom, side and deck transverses are to be connected in such a manner as to ensure continuity of the transverse ring system, and longitudinals are to be attached to transverses. In way of deck and bottom transverses, a deep web frame may be required to be fitted.

4.1.2 End connections of longitudinals at bulkheads are to provide adequate fixity and continuity of longitudinal strength.

4.1.3 Brackets at the top and bottom of side frames are to extend to the deck and bottom longitudinals to which they are to be attached.

4.1.4 In pontoons where truss arrangements, comprising top and bottom girders in association with pillars and diagonal bracing, are used in the support of the deck loads, the diagonal members are generally to have angles of inclination with the horizontal of about 45° and cross-sectional area of at least 50 per cent of the adjacent pillar in accordance with Pt 3, Ch 4, 6 Pillars.

4.1.5 Adequate support is to be provided for the loads imposed on the structure when the pontoon is in dry-dock.

4.2.1 The scantlings of bottom, side and deck longitudinals are to comply with the requirements of Table 4.4.1 Longitudinal framing.

4.2.2 In addition, the following requirements for depth to thickness ratios of longitudinals are to be met:

1. Flat bar longitudinal:

   1. when continuous at bulkheads

      

   2. when non-continuous at bulkheads

      

2. Built sections

   1. 
   2. 
   3. 

4.3.1 The scantlings of bottom and side frames and deck beams are to comply with the requirements of Table 4.4.2 Transverse framing.

4.4.1 Primary supporting members are to comply with the requirements of Table 4.4.3 Primary supporting structure

4.5.1 The section modulus, Z, of deck beams or longitudinals is to be not less than that required to satisfy the most severe arrangement of print wheel loads on the stiffener in association with a bending stress of:

4.6.1 Where the load on deck girders and transverses is uniformly distributed, the section modulus is to be not less than:

where

h is defined in Pt 3, Ch 4, 1.3 Symbols and definitions 1.3.5

4.6.2 Where the member supports point loads, with or without the addition of uniformly distributed load, the section modulus is to be based on a stress of

4.6.3 Where it is proposed to carry tracked vehicles, the total weight of the vehicle is to be taken when determining the section modulus of the transverse at the top of a ramp or at other changes of gradient.

4.7.1 As an alternative to Pt 3, Ch 4, 4.5 Deck beams and longitudinals subject to vehicle loadingand Pt 3, Ch 4, 4.6 Deck girders and transverses subject to vehicle loading, permissible deck load capacity may be determined by direct calculation.

4.8.1 The deck plating and underdeck stiffening are to be considered for any loads imposed by ship ramps, where appropriate.

4.9.1 Decks for the transport of railway rolling stock on fixed rails will be specially considered.

4.10.1 Where heavy or special loads, such as machinery transporters are proposed to be carried, the scantlings and arrangements of the deck structure will be individually considered.