Section 9 Additional requirements for container ships

9.1.1 The minimum scantlings of structural members of single and double bottoms are to comply with the requirements of Pt 4, Ch 1, 6 Single bottom structure and Pt 4, Ch 1, 7 Double bottom structure, as applicable, but are to be confirmed by direct calculations in accordance with this Section.

9.1.2 A minimum container mass of 15 tonnes should be taken into account for either 20 ft or 40 ft containers. This figure is to be multiplied with the number of tiers of containers intended to be carried. Where it is intended to carry more than 4 tiers, the upper tier may be assumed empty. As an example, in case of a ship designed to carry 4 tiers of containers, a minimum stack load of 60 tonnes will need to be used. The bottom structure may be designed for higher stack loads as desired. The values of allowable container stack loadings are to be supplied to the ship.

9.1.3 The requirements given in this Section are based on the assumption that continuous girders are fitted under the container corners.

9.1.4 Local stiffening will be required under container corners, and the locations of the corners are to be clearly marked in the inner bottom plating or hold ceiling when no permanent container corner seatings are provided on the inner bottom.

9.1.5 Additional requirements regarding the double bottom structure are given in Pt 4, Ch 1, 9.3 Girders in the double bottom, Pt 4, Ch 1, 9.4 Double bottom floors and transverses and Pt 4, Ch 1, 9.5 Assessment of bottom structure by direct calculation.

9.2.1 The mass of the containers is to be evenly distributed over the width of the ship, thus preventing high torsional moments being imposed. If high torsional moments are foreseen or are to be incorporated in the design the values of these torsional moments are to be indicated on the structural plans of the cargo part and on the midship section plan. In such cases, the torsional strength of the ship will be specially considered.

9.3.1 Where no centreline girder is fitted, adequate support on the centreline must generally be provided for docking purposes.

9.3.2 Partial girders may be required close to the bottom girders to spread the container loads locally over the bottom structure. The partial girders in way of the container corners as indicated in Figure 1.9.1 Schematic bottom structure and Figure 1.9.2 Schematic bottom structure (longitudinal framing) are to have the same thickness as the continuous girders.

Figure 1.9.1 Schematic bottom structure

9.3.3 In single bottoms, in way of the container corner fittings, gusset plates are to be fitted connecting the floors or transverses to the longitudinal girders. The gusset plates are to extend over at least three floors or transverses and are to be tapered off in the fore and aft direction. See Figure 1.9.3 Gusset plate arrangements.

9.4.1 In a longitudinal framing system, floors or transverses are to be fitted at a spacing not exceeding 2,0 m. Special attention is to be paid to the distribution of shear loads and resulting shear stresses in floors and longitudinal girders directly loaded by containers, and this aspect is to be verified by direct calculations. Where necessary, additional panel stiffeners or web plating of increased thickness may need to be fitted in order to prevent local plate buckling.

9.4.2 Special attention should be paid to the shear strength of floors under container fittings in way of the connection with the side shell structure. For this purpose, the web thickness may require to be locally increased.

9.4.3 Where a double hull has been provided, the inner bottom plating in way of the floors is to be suitably scarfed into the double hull structure by means of horizontal gusset plates or equivalent.

Figure 1.9.2 Schematic bottom structure (longitudinal framing)

Figure 1.9.3 Gusset plate arrangements

9.5.1 The scantlings of the bottom structure are to be determined by direct calculations in accordance with this sub- Section, together with procedures and criteria as outlined in Pt 4, Ch 1, 13 Direct calculation procedures.

9.5.2 The calculation is to be carried out as a finite element analysis of the bottom structure, generally covering the bottom structure extending over one container length. Smaller extents, i.e. half container lengths may be used depending on the degree of uniformity of the bottom structure.

9.5.3 The analysis of the bottom structure is to be carried out for the bottom loaded by container point loads (for 20 ft and 40 ft containers as applicable) whereby the draught of the ship is to be taken not greater than 0,4T for ships with loading sequence notation LS’O’ and 0,6T for ships with notations LS’T’ or LS’D’.

9.6.1 Attention is drawn to the intact stability requirements as contained in the European Standard laying down Technical Requirements for Inland Navigation vessels (ES-TRIN).