Section 6 Single bottom structure in way of cargo compartment space

6.1.1 This Section covers the arrangements and requirements for transversely and longitudinally framed single bottoms in way of the cargo compartment space.

6.1.2 The scantlings are based on end connections in accordance with Pt 3, Ch 10, 3 Secondary member end connections. Where brackets having arm lengths differing from the standard are fitted, the modulus of the stiffening member is to be corrected in accordance with Pt 3, Ch 10, 3.7 Correction of stiffening member modulus in relation to end connections.

6.1.3 A side girder is to be fitted port and starboard between the centreline and the shell or longitudinal bulkhead near the shell and is to comply with Table 5.6.1.

Table 5.6.1 Single bottom structure in way of cargo compartment space

Item	Parameter	Requirements
Transverse framing system
(1) Centreline girder, side girders and partial side girders	Web and face plate thickness	t = (0,01d w + 2,5) mm
	Width of face plate	b f = 140s mm
(2) Floors	Web depth	d w= 40B mm
	Web thickness	t w = (0,01d w + 2,5) mm
	Face plate thickness	t = ≥ t w mm
	Face plate width	The greater of:
		b f = 16l f mm
		b f = 100 mm
	Minimum modulus	Z = 7Tslf 2 cm3
(3) Bottom structure supporting cargo tanks (combination of floors with top and bottom plating)	Minimum modulus	Z = 8,5klf (W – 0,3lf 2 T) cm3
Longitudinal framing system
(4) Centreline girder, side girders and partial side girders	Web and face plate thickness	t = (0,01d w + 3) mm
	Width of face plate	b f = 100 mm
(5) Transverses	Web depth at centreline	d w= 40B mm
	Web thickness	t = (0,01d w + 3) mm
	Modulus	Z = 7kTSlf 2 cm3
(6) Bottom structure supporting cargo tanks (combination of floors/transverses with top and bottom plating)	Minimum modulus	Z = 8,5klf (W – 0,3lf2 T) cm3
(7) Bottom longitudinals	Modulus	Z = (3,95 + 0,04L 1)kD1sle 2 cm3
Symbols
L, B, D, T, S, s, le, k, Z and t are as defined in Pt 4, Ch 5, 1.10 Symbols and definitions 1.10.1 dw = web depth of girder or floor, in mm lf = span of floor or transverse, in metres, measured at the top of floor or transverse between side shell or between the longitudinal bulkheads according to Pt 4, Ch 5, 1.2 Ship arrangement 1.2.4.(b) D1 = D but need not be taken greater than T + 0,4 m for Zone 3, T + 0,7 m for Zone 2, T + 1,0 m for Zone 1 L1 = L but is to be taken not less than 40 m, nor more than 100 m W = weight of tanks with maximum weight of cargo supported by the combination of floors or transverses, in tonnes

6.1.4 Where no centreline bulkhead is fitted, a centreline girder is to be arranged having the same depth as the floors or transverses in way and the scantlings are to comply with Table 5.6.1 Single bottom structure in way of cargo compartment space. Where the spacing between side girders required by Pt 4, Ch 5, 6.1 General 6.1.3 does not exceed 5 m, the centreline girder may be omitted, but efficient support at the centreline is to be arranged for docking purposes.

6.1.5 For ADN related structural requirements regarding cargo tank supports, seePt 4, Ch 4, 3.5 Special requirements for Type G tankers

6.2.1 Plate floors are to be fitted at every frame and are to comply with the requirements of Table 5.6.1 Single bottom structure in way of cargo compartment space. Floors may be cut at the centreline, with the centre girder web plate continuous, provided the transverse strength of the floors is maintained.

6.2.2 The bottom structure supporting the cargo tanks is to comply with the requirements of Table 5.6.1 Single bottom structure in way of cargo compartment space.

6.2.3 For the purpose of these Rules, the structure is assumed to consist of three to five successive plate floors with a continuous top plate from side to side or between the longitudinal bulkheads according to Pt 4, Ch 5, 1.2 Ship arrangement 1.2.4.(b) in association with continuous side girders according to Pt 4, Ch 5, 6.1 General 6.1.3 and at least two partial girders port and starboard, each extending over a length of six to ten frame spaces, see Figure 5.6.1 Single bottom structure in way of cargo tank support.

Figure 5.6.1 Single bottom structure in way of cargo tank support

6.2.4 The actual arrangement required depends on the total weight of cargo tanks with maximum cargo load. Verification of the structure by direct calculation may be required.

6.2.5 Bottom structures with an arrangement differing from that assumed in Pt 4, Ch 5, 6.2 Single bottom structure – Transversely framed ships 6.2.3, will, in general, be required to be assessed by direct calculations.

6.3.1 Transverses are to be fitted at a spacing not exceeding 3,5 m and are to comply with the requirements of Table 5.6.1 Single bottom structure in way of cargo compartment space. Vertical stiffeners having a depth of not less than 50 mm are to be fitted to the transverses at every fourth longitudinal.

6.3.2 The bottom structure supporting the cargo tanks is to comply with the requirements of Table 5.6.1 Single bottom structure in way of cargo compartment space.

6.3.3 For the purpose of these Rules, the structure is assumed to consist of three to five floors or transverses, having a spacing of about 0,6 m, with a continuous top plate from side to side or between the longitudinal bulkheads according to Pt 4, Ch 5, 1.2 Ship arrangement 1.2.4.(b), in association with continuous side girders according to Pt 4, Ch 5, 6.1 General 6.1.3 and at least two partial girders port and starboard, each extending forward and aft of the support structure over a full bay and in line with bottom longitudinals (see Figure 5.6.1 Single bottom structure in way of cargo tank support).

6.3.4 The actual arrangement required depends on the total weight of cargo tanks with maximum cargo load. Verification of the structure by direct calculation may be required.

6.3.5 Bottom structures with an arrangement differing from that assumed in Pt 4, Ch 5, 6.3 Single bottom structure – Longitudinally framed ships 6.3.3, will in general be required to be assessed by direct calculation.