Section 4 Hull envelope framing – Transversely framed ships

4.1.1 This Section covers the arrangements and requirements for the transverse hull framing of the midship region of flush deck and trunk deck tankers. The scantlings of floors, bottom girders, frames, stringers and web frames, deck beams, deck girders and pillars are to be in accordance with Table 6.4.1 Hull framing - Transversely framed ships.

Table 6.4.1 Hull framing - Transversely framed ships

Item	Parameter	Requirement
Floors	Modulus	Z = 6,6ksl f2hb cm3
		df ≥ 30B mm
	Web thickness	t = (0,01df + 2) mm
Centre girder	Web depth	d = df mm
	Web and face plate thickness	t = (0,01d f + 2) mm
	Face plate width	w = 140s mm
Side girders	Scantlings	As centre girder
Side frames in cargo tanks (single skin)	Modulus	Z = 7ksle2hg cm3
Side frames in double skin	Modulus	Z = 6,6ksl e 2 hf cm3
Deck beams	Modulus	Z = 6,6ksle2hg cm3
Deck girders	Modulus	Z = (0,7 + 0,132L1) ksle2 hg cm3
		See Note 1
Deck beams on trunk deck	Modulus	Ztdb= 6,6ksle2 hg cm3
Trunk side stiffeners and deck beams abreast trunk	Modulus	Z = Ztdb cm3
Pillars	Cross-sectional area	A = 4,5 + 0,9P cm2
Stringers in cargo tanks (single skin)	Modulus	Z = 6,6kls2Shg cm3
Stringers in double skin	Modulus	Z = 6,6kls2Shf cm3
Webs, supporting stringers and girders	Modulus	Z to be determined from calculations using a stress of 103,0 N/mm2 (10,5 kgf/mm2) assuming fixed ends, in association with the head, h g
Plate webs in double skin	Thickness	The greater of:
		t = 7 mm
		t = 9s d
Symbols
L, B, D, T, S, s, le, h d, Z, I, ρ, k and t as defined in Pt 4, Ch 6, 1.12 Symbols and definitions 1.12.1 df = depth of floor, in mm h = the vertical distance from the middle of the effective length of the stiffening member under consideration to the top of the tank, excluding hatchways, in metres hb = the greater of: the depth, D, but need not to 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 h g – 0,4T m hf = h de + h s, but not less than 2 m hde = the vertical distance at mid-span of the stiffening member under consideration to the deck at side hs = 0 for void spaces or 0,5 m for deeptanks but not less than the actual distance of the top of the overflow above deck hg = hρ + h d + 0,2 m ht = test head as defined in Table 1.7.2 Testing requirements in Pt 3, Ch 1, in metres le = span of floor being 0,5B in ships with a centreline bulkhead and in ships with two longitudinal bulkheads the spacing of the bulkheads or 0,4B, whichever is the greater, in metres ls = span of stringer, in metres D2 = 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 K = 1 for Category ‘O’ ships K = 0,75 for Category ‘T’ ships L1 = L, but is to be not less than 50 m, nor more than 100 m P = load supported by the pillar, in tonne-f sd = stiffener spacing or width of double skin whichever is the smaller Zb = section modulus of trunk deck transverses, in cm3 Ztdb = section modulus of trunk deck beams, in cm3
Note 1. 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 6, 12 Direct calculation procedures. Note 2. The minimum compartment thickness of the tank structure is not to be less than as required by Pt 4, Ch 6, 1.10 Compartment minimum thickness.

4.1.2 Scantlings given in Table 6.4.1 Hull framing - Transversely framed ships 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 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.

4.1.3 Outside the midship region the structure is to be scarfed into the fore end and aft end structure as provided for in Pt 3, Ch 5 Fore End and Aft End Structure and Pt 3, Ch 6 Machinery Spaces so far as applicable.

4.1.4 It is recommended that the bottom of ships regularly resting aground be additionally strengthened to withstand the stresses to which it may be subjected. In such ships scallops or openings (unless reinforced) are not to be made in the lower region of the bottom framing.

4.2.1 Plate floors are to be fitted at every frame. The upper edge of the floors is to be suitably stiffened whilst adequate anti-tripping arrangements are to be provided.

4.2.2 The floors are to be provided with sufficient openings to obtain a good flow of cargo to the suction pipes in the tank. In way of large openings additional stiffening may be required. If floors are of scalloped construction, scallops are not to be made in way of the bilge, near longitudinal bulkheads, centre or side girders, or in way of pillars.

4.3.1 When the spacing between longitudinal bulkheads in ships without a centreline bulkhead exceeds 5 m, a centreline girder is to be fitted. When the spacing between the longitudinal bulkheads is 5 m or less, an intercostal docking bar is to be fitted at the centreline.

4.4.1 In ships with a centreline bulkhead only and a breadth, B, exceeding 12 m, a side girder is to be fitted port and starboard at about B from the centreline bulkhead. In ships with two longitudinal bulkheads, where the spacing between the centreline of the girder and the longitudinal bulkheads exceeds 6 m, a side girder is to be fitted port and starboard.

4.5.1 Side frames are to be fitted at every frame and are to be connected top and bottom, see Pt 4, Ch 6, 4.1 General 4.1.2.

4.5.2 Stringers may be taken into account into the calculation of the frames provided the stringers are fully effective and properly connected to the supporting webframes.

4.6.1 Deck beams are to be fitted at every frame and are to be connected at their ends, see Pt 4, Ch 6, 4.1 General 4.1.2.

4.6.2 A deck beam which is cut in way of an opening in the deck, is to be connected to efficient carlings.

4.6.3 For support of deck beams, deck girders may be fitted in conjunction with widely spaced pillars or web beams.

4.6.4 Tubular pillars or other hollow pillars are not to be used. The pillars are to be bracketed top and bottom. The sizes of brackets and welding are to take account of the maximum tensile force in the pillar when the tank is under internal pressure. The floor in way of the pillar heel is to be connected to the adjacent floors by an intercostal girder if not already in line with a Rule side girder.

4.7.1 Trunk deck beams, trunk side stiffeners and deck beams are to be fitted at every frame and are to be connected at their ends, see Pt 4, Ch 6, 4.1 General 4.1.2.

4.7.2 Where beams are cut in way of openings, the requirements of Pt 4, Ch 6, 4.6 Deck support – Flush deck tankers 4.6.2 are to be complied with.

4.7.3 Arrangements for support of deck beams are to comply with the requirements of Pt 4, Ch 6, 4.6 Deck support – Flush deck tankers 4.6.3 and Pt 4, Ch 6, 4.6 Deck support – Flush deck tankers 4.6.4.

4.8.1 The scantlings of the structure in the double skin are to be in accordance with Table 6.4.1 Hull framing - Transversely framed ships.

4.8.2 Where the inner skin forms the boundary of cargo tanks, the scantlings of stiffening members are to comply with the requirements of Pt 4, Ch 6, 7 Longitudinal and transverse bulkheads of integral cargo tanks. Otherwise, the scantlings of stiffening members of the inner skin are to comply with the requirements for deep tanks or watertight bulkheads, as applicable, see Pt 3, Ch 7 Bulkheads.

4.8.3 For details regarding the accessibility and the standard required width of the double skin on Type C tankers, reference is made to Pt 4, Ch 4, 3.6 Special requirements for Type C tankers. Requirements are also given for strengthening the double skin in cases where the width is reduced to the minimum value as allowed by the ADN(R). In that case the requirements for reinforcing the sideshell structure by means of additional stringers is also to be complied with.

4.8.4 For details regarding the accessibility and the standard required width of the double skin on Type N tankers, reference is made to Pt 4, Ch 6, 3.7 Trunk deck plating, trunk side plating and plating of deck abreast trunk of transversely framed trunk deck tankers.

4.8.5 On type C tankers, profiles or struts connecting structural members of the sideshell with structural members on the longitudinal bulkhead are not allowed.

4.9.1 The scantlings of the structure in the double bottom are to be in accordance with Table 6.4.2 Double bottom (transverse framing).

Table 6.4.2 Double bottom (transverse framing)

Item	Parameter	Requirement
(1) Double bottom at centreline	Minimum	df = 650 mm
	depth
(2) Centre girder and side girder	Thickness	t = (0,01df + 1) mm
(3) Floors	Thickness	t = (0,009df + 1) mm
(4) Watertight floors and floors in line with web frames	Thickness	t = (0,009df + 1) mm
For Symbols, see Table 6.4.1 Hull framing - Transversely framed ships.

4.9.2 All parts of double bottom tanks are to be accessible for cleaning and inspection. The tanks are to be well ventilated. Reference is made toPt 4, Ch 4, 3 Ship Arrangements with regard to general requirements concerning the minimum double bottom height, accessibility, the minimum size of openings and minimum free distances between structural members for passage and inspection.

4.9.3 Plate floors are to be fitted at every frame and are to be suitably stiffened, especially in way of manholes. Centre and side girders are to be arranged as required by Pt 4, Ch 6, 4.3 Centreline girder and Pt 4, Ch 6, 4.4 Side girder.

4.9.4 On type C tankers, profiles or struts connecting structural members of the bottomshell with structural members on the bottom of the cargo tank are not allowed.