Section 2 Primary members supporting longitudinal framing

2.1.1 These requirements are applicable to the following structural arrangements for ships with two longitudinal bulkheads:

1. Centre tank structure:

   1. Primary supporting centreline girder between oiltight transverse bulkheads, in association with up to five transverses.

   2. Bottom transverses spanning between longitudinal bulkheads in association with a non-primary centreline docking girder.

   3. Double bottom.

2. Wing tank structure:

   1. Transverse ring structure consisting of bottom, side shell, longitudinal bulkhead and deck transverses and incorporating one cross-tie or no cross-ties in tankers not exceeding 75 m in length.

   2. Double bottom.

2.1.2 The requirements are also applicable to structural arrangements incorporating a single longitudinal bulkhead located on the ship's centreline without cross-ties, for tankers not exceeding 75 m in length.

2.1.3 The minimum thickness and constructional 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. The shear and combined stress levels in these connections are to be examined and should be within the limits specified in ShipRight SDA Procedure - Guidance Notes on Direct Calculations.

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

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

2.3.1 The spacing of transverses is not to exceed 3,6 m.

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

2.4.1 Where a primary supporting bottom centreline girder is fitted, in a single bottom, the requirements for the girder and transverses may be derived using bending moment and shear force coefficients K ₁ and K ₂ determined from Table 10.2.1 Bottom structure coefficients. To obtain the coefficients, the following factors are required:

Initially, an estimated value of the ratio may be used, and an iterative process adopted to obtain the final required values.

2.4.2 Where bottom transverses are fitted in association with a non-primary centreline girder the coefficients for the transverse are to be taken as:

For the requirements for the non-primary girder, see Pt 4, Ch 10, 2.6 Bottom girders.

2.4.3 In ships with one longitudinal bulkhead, the coefficient for the bottom transverse is to be taken as:

1. K ₁ = 0,177.

2.5.1 The section modulus of bottom transverses is to be not less than:

2.5.2 In ships with two longitudinal bulkheads, the depth of the bottom transverse web plate is to be not less than 0,2S _T and the net sectional area of the web at any section, including vertical end connections, is to be not less than:

where Q _x is calculated from shear force diagrams constructed as shown in Figure 10.2.1 Bottom transverses. For end connections, Q_x is to be determined by projection of the shear force diagram as indicated.

2.5.3 The moment of inertia of bottom transverses is to be not less than:

2.6.1 The section modulus of the primary centreline bottom girder, where fitted, is to be not less than:

2.6.2 The net sectional area of the web at any section, including vertical end connections, is to be not less than:

where Q _x is calculated from a shear force diagram constructed as shown in Figure 10.2.2 Bottom centreline girder. For end connections, Q _x is to be determined by projection of the shear force diagram as indicated.

2.6.3 In a single bottom the section modulus and web area of a non-primary centreline docking girder are to be not less than:

The scantlings of this girder may, however, be required to be increased, depending upon the docking condition and support arrangements, details of which are to be submitted. Consideration may be required to be given to restricting the level of ballast tank filling for docking purposes. The loads are to be specially considered when wing tanks are ballasted for docking.

2.6.4 Consideration will be given to alternative methods of stiffening in way of the keel blocks when accompanied by supporting calculations.

2.6.5 In way of the vertical centreline web and centreline supports to horizontal girders of transverse bulkheads, the docking girder is to be increased in depth and scantlings as necessary to provide an effective support.

2.7.1 The section modulus of side transverses in ships with one or two longitudinal bulkheads is to be not less than:

where K ₃ is given in Table 10.2.2 Side transverse cofficients.

2.7.2 In ships with two longitudinal bulkheads, the net sectional area of the web at any section is to be not less than:

where Q _x is calculated from shear force diagrams constructed as shown in Figure 10.2.3 Wing tank construction. For this purpose the values of K ₄ and K ₅ and the range of application is given in Table 10.2.2 Side transverse cofficients.

2.7.3 The moment of inertia of side transverses is to be not less than:

2.8.1 The section modulus of deck transverses is to be not less than:

Where a continuous deck girder is fitted, the term S _T in the above formula is to be replaced by .

2.8.2 The net sectional area of the web is to satisfy the requirements of Pt 4, Ch 10, 2.5 Bottom transverses 2.5.2 using a head, m.

2.8.3 The moment of inertia of the transverses is to be not less than:

2.9.1 Where a continuous deck centreline girder supporting deck transverses is fitted, it is to have a section modulus not less than:

2.9.2 The net sectional area of the web is to satisfy the requirements of Pt 4, Ch 10, 2.6 Bottom girders 2.6.2 using a head, m.

2.9.3 In way of the vertical centreline web on transverse bulkheads, the continuous deck girder is to be increased in depth and scantlings as necessary to provide an effective support.

2.9.4 Where an intercostal deck girder is fitted, it is to have a depth not less than 50 per cent of the depth of the deck transverse and the area of the face flat is to be not less than that of the transverse.

2.9.5 In way of the vertical centreline web and centreline supports to horizontal girder on transverse bulkheads, the intercostal deck girder may be required to be increased in depth and scantlings to provide an effective support.

2.10.1 Cross-ties, where fitted, may be of plate or sectional material and are to have an area and least moment of inertia not less than:

2.10.2  Design of end connections is to be such that the area of the welding, including vertical brackets, where fitted, is to be not less than the minimum cross-sectional area of the cross tie derived from Pt 4, Ch 10, 2.10 Cross-ties 2.10.1. To achieve this full penetration may be required and thickness of brackets may require further consideration. Attention is to be given to the full continuity of area of the backing structure on the transverses. Particular attention is also to be paid to the welding at the toes of all vertical end brackets on the cross-tie.

2.11.1 The scantlings of girder and floors are to satisfy the requirements of Pt 4, Ch 1, 8.3 Girders and Pt 4, Ch 1, 8.5 Floors respectively for longitudinally framed ships.