Section 7 Topside tank structure

7.1.1 Requirements are given in this Section for longitudinal or transverse framing in the topside tank, but, in general, the deck is to be longitudinally framed. The sloped bulkhead is to be of plane construction with the associated stiffening arranged inside or outside the tank.

7.1.2 The buckling requirements of Pt 3, Ch 4, 7 Hull buckling strength are also to be satisfied.

7.1.3 Recommended examples of structural design configurations around the transverse ring web of the topside tank can be seen in the ShipRight FDA Procedure, Structural Detail Design Guide (SDDG).

7.2.1 The thickness of the sloped bulkhead, tank end bulkhead, and diaphragm, if fitted, is to be the greater of the following:

1. For watertight bulkheads, the thickness, t, as derived from Table 1.9.1 Watertight and deep tank bulkhead scantlings in Pt 4, Ch 1 General Cargo Ships for a deep tank bulkhead using a head, h ₄, in metres, determined as follows:

   h 4	=	h o cosθ + Rb 1 or
   	=	the greater of the distance from a point one-third of the height of the plate above its lower edge to the top of the tank, or half the distance to the top of the overflow

   whichever is the greater, or

2. 

   In no case, however, is the thickness of the sloped bulkhead and diaphragm to be taken less than:

   1. 

      whichever is the greater

      where

      k D	=	the higher tensile steel factor equal to k L value for deck material
      F D	=	as defined in Pt 3, Ch 4, 5.7 Local reduction factors
      R	=	as defined in Pt 4, Ch 7, 1.8 Symbols and definitions 1.8.1
      h o	=	the vertical distance, in metres, from a point one third of the height of the plate from the lower edge to the highest point of the tank excluding hatchway
      b 1	=	the larger horizontal distance, in metres, from the tank corner at top of tank either side to point of plate under consideration.

7.2.2 The thickness of the top strake of the sloped bulkhead, including the vertical plate attached to deck, may be required to be increased to form an effective girder below the deck. In general, this plate is to be not less in thickness than 60 per cent of the thickness of the deck plate outside the line of openings nor less than:

1. whichever is the greater.

7.2.3 The thickness of the transverse wash bulkhead, where fitted, is to be not less than:

7.3.1 The section modulus of longitudinal or transverse stiffeners on the sloped bulkhead or watertight diaphragms, if fitted, is to be not less than:

7.3.2 Where the bulkhead stiffening is fitted on the hold side of the sloped bulkhead, suitable arrangements are to be made to prevent tripping.

7.3.3 The scantlings of stiffeners on tank end bulkheads are to be not less than those given in Table 1.9.1 Watertight and deep tank bulkhead scantlings of Pt 4, Ch 1 General Cargo Ships for deep tanks, using h as defined in Pt 4, Ch 7, 7.3 Bulkhead stiffeners 7.3.1.

7.3.4 The section modulus of stiffeners of non-watertight fore and aft diaphragms, or transverse wash bulkheads is to be not less than 50 per cent of that required by Pt 4, Ch 7, 7.3 Bulkhead stiffeners 7.3.3. The stiffeners are to be bracketed at both ends.

7.3.5 Tank end bulkheads are generally to be in line with the main hold bulkheads.

7.4.1 The scantlings of shell and deck longitudinals are to comply with Pt 4, Ch 7, 7.3 Bulkhead stiffeners 7.3.1. The scantlings must also satisfy the requirements of Pt 4, Ch 1 General Cargo Ships, see also Pt 4, Ch 7, 7.6 Structural details 7.6.1.

7.4.2 The scantlings of side shell frames are to comply with Pt 4, Ch 7, 6.2 Transverse stiffening.

7.5.1 The section modulus and inertia of deck, shell and bulkhead transverses or stringers are to be not less than:

using h as defined in Pt 4, Ch 7, 7.3 Bulkhead stiffeners 7.3.1. The scantlings of shell and deck members must also satisfy the requirements of Pt 4, Ch 1 General Cargo Ships for dry cargo holds.

7.5.2 Primary transverse members are, in general, to be spaced not more than 3,8 m apart where the length, L, is 100 m or less, and (0,006L + 3,2) m apart for lengths greater than 100 m.

7.5.3 Transverses are to be arranged in line with the primary structure at ends of hatchways, or equivalent scarfing arranged. Where the sloped bulkhead or side shell is transversely framed, arrangements are to be made to ensure effective continuity at the ends of the deck transverse.

7.5.4 Where non-watertight transverse diaphragms are arranged instead of open transverses, the thickness of plating is to be in accordance with Pt 4, Ch 7, 7.2 Bulkhead plating 7.2.3. The diaphragms are to be efficiently stiffened.

7.6.1 Bracket/diaphragm connections at the bottom of the topside tank are to be of sufficient size and thickness to provide effective rigidity, and care is to be taken to ensure alignment with brackets at the heads of the side frames in the holds, see also Pt 4, Ch 7, 6.2 Transverse stiffening 6.2.12. The shell and sloped bulkhead longitudinals supporting the diaphragms are to be derived using the span taken between transverses.

7.6.2 For ships where L ≥ 300 m a fore and aft diaphragm extending vertically from the deck to the sloping plating of the topside tank is to be arranged at about the half-width of the tank.

7.6.3 Where longitudinal framing is fitted to the side shell, a bracket may be required in way of a rounded gunwale, approximately halfway between transverses and extending to the adjacent shell and deck longitudinal.