Section 4 Hull envelope framing (longitudinal or transverse framing)

4.1.1 The requirements of Pt 4, Ch 1, 11 Double skin structure are to be applied together with the requirements of this Section. The scantlings of the hull structural members are to comply with Table 3.4.1 Hull envelope framing .

Table 3.4.1 Hull envelope framing

Item	Parameter	Requirements
(1) Floors	Modulus	Z = 6,6 x k x D1 x s x le 2 cm3
	Web depth	dw ≥ 30B mm
	Web thickness	t = (0,01d w + 2) mm
(2) Bottom longitudinals	Modulus	Z = (2 + 0,1L1) x D1 x k x s x le 2 cm3
	Inertia	I = x le x Z cm4
(3) Bottom transverses	Modulus	Z = 7 x D1 x k x S x le 2 cm3
(4) Bottom centre girder	Web and face plate thickness	t = (0,01d w + 3) mm
	Minimum flange width	bf = 100 mm
(5) Bottom side girders	Scantlings	As centre girders
(6) Side frames	Modulus	Z = 7 x hf x k x s x le 2 cm3
		See Note 1
(7) Side longitudinals	Modulus	Z = (4,6 + 0,0342L1) x hf x k x s x le 2 cm3
(8) Side transverses	Modulus	Z = 10 x hf x k x S x le 2 cm3
		See Note 1
(9) Stringers	Modulus	Z = 6,6 x hf x k x S x le 2 cm3
(10) Web supporting stringers and girders	Modulus	Z is to be determined from calculations using a stress of 98/k N/mm2, assuming fixed ends, in association with a head, hf
		See Note 1
(11) Deck beams	Modulus	Z = 4,3 x h1 x k x s x le 2 + 4 cm3
(12) Deck longitudinals	Modulus	Z = (1,45 + 0,07L1) x h1 x k x s x le 2 cm3
	Inertia	I = x le x Z cm4
(13) Deck girders	Modulus	Z = (1,35 + 0,085L 1) x k x S x h1 x le 2 cm3
	Inertia	I = x le x Z cm4
(14) Deck transverses	Modulus	Z = 4,75 x h1 x k x S x le 2 cm3
(15) Pillars	Cross-sectional area
	Minimum wall thickness of hollow	The greater of:
	pillars	(a) t = 0,033d p mm for tubular pillars
		t = 0,056b mm for square pillars
		(b)t = 5 mm
Symbol
L, B, D, T, S, s, le, Z, I, k and t are as defined in Pt 4, Ch 3, 1.5 Symbols and definitions 1.5.1
b = breadth of side of a hollow square pillar, in mm
bf = minimum flange width of the bottom centre girder or bottom side girders as applicable
dp = mean diameter of tubular pillars, in mm
dw = depth of web plate, in mm
hf = the vertical distance, in metres, from the middle of the effective length of the stiffening member under consideration to the deck at side or to a line at T + 0,4 m, whichever is the lesser, but is to be taken as not less than 0,25D m
h1 = head on deck, in metres, as defined in Pt 3, Ch 3, 4 Design loading, but is to be taken as not less than 1,5 m
l = overall length of pillar, in metres
r = least radius of gyration of pillar cross-section, in mm, and may be taken as:
r =
Ap = cross-sectional area of pillar, in cm2
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
Ip = least moment of inertia of cross-section, in cm4
L1 = L but is to be not less than 40 m, nor more than 100 m
P = load supported by the pillar, in tonne-f
Note 1. The section modulus of side transverses and frames connecting deck and bottom transverses at top and bottom is to be not less than half the section modulus of the bottom and deck transverse whereto connected. Note 2. In case the scantlings of longitudinal members result in an appreciable excess in the hull midship section modulus as required by Pt 3, Ch 4 Longitudinal Strength for the ship type concerned, a reduction in the modulus of the relevant members may be applied provided the permissible combined bending stress and the permissible local bending stress are not exceeded. For permissible stresses, see Pt 4, Ch 3, 5 Direct calculation procedures.

4.1.2 Scantlings given in Table 3.4.1 Hull envelope framing 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 inaccordance with Pt 3, Ch 10, 3.7 Correction of stiffening member modulus in relation to end connections.

4.2.1 A centreline girder is generally required in ships with a breadth, B, of more than 6 m. Alternatively, side girders may be fitted under pillars supporting the deck structure, but generally adequate support for docking purposes is to be provided on the centreline. Girders are to have the same depth as transverses.

4.2.2 Longitudinal stiffening members are to be supported by transverses arranged to form ring systems. Their spacing is not to exceed 3,5 m.

4.2.3 The depth of transverses is generally to be not less than twice the depth of the slot for the longitudinals.

4.2.4 Transverses fitted on the inboard face of longitudinals are to comply with the requirements of Pt 3, Ch 3, 3 Structural idealisation and associated Figure 3.3.4 Rolled or built sections fitted on top of supported stiffening members .

4.2.5 Longitudinals are generally to be carried through transverse bulkheads. If they stop at transverse bulkheads, brackets are to be fitted inter-connecting the longitudinals. See also Pt 3, Ch 10, 3.3 Basis for calculation of bracket connections 3.3.1.(c).

4.2.6 Scallops in longitudinals may not be fitted in way of end connections, crossings with transverses or tripping brackets.

4.3.1 Floors, frames and deck beams are to be fitted at every frame. Girders may be fitted to reduce the unsupported span of floors and deck beams.

4.3.2 When side frames are supported by an effective system of stringers and web frames, the Rule section modulus of the frames (ignoring the stringers) may be reduced by 30 per cent.

4.4.1 Where a combination framing system is adopted (shell transverse and bottom and deck longitudinal framing) a transverse ring system as indicated in Pt 4, Ch 3, 4.2 Longitudinal framing system 4.2.2 is to be fitted.

4.4.2 Brackets at the top and bottom of side frames are to extend to the adjacent deck or bottom longitudinal to which they are to be connected.

4.5.1 Deck girders and transverses may be fitted in conjunction with load-bearing bulkheads or pillars, for support of deck beams and deck longitudinals.

4.5.2 Effective arrangements are to be made to distribute the load at the heads and heels of all pillars. Tripping brackets or equivalent are to be fitted to the transverse or girder web plates in way of the pillar. Where pillars support eccentric loads, they are to be strengthened for the additional bending moment imposed upon them.

4.5.3 Areas of the deck used by wheeled vehicles are also to comply with the requirements of Pt 3, Ch 9, 2 Decks loaded by wheeled vehicles.

4.5.4 The scantlings of the deck supporting structure forward and aft of the midship region are to be based on the actual deck loading but the head on deck, h ₁, is to be taken as not less than 1,5 m.

4.6.1 Truss arrangements, comprising top and bottom girders or transverses in association with pillars and diagonal bracing, may be fitted to support the bottom and deck structure. The diagonal members are generally to have angles of inclination with the horizontal of 45° and a cross-sectional area of not less than 50 per cent of the adjacent pillar.