Section 7 Longitudinal and transverse bulkheads of integral cargo tanks

7.1.1 This Section covers the arrangements and requirements for plane and corrugated longitudinal and transverse bulkheads. The thickness of plating and the scantlings of vertical and horizontal stiffeners, stringers, webs and transverses and of corrugated bulkheads are to be in accordance with Table 6.7.1 Scantlings of plane and corrugated transverse and longitudinal bulkheads of integral cargo tanks.

Table 6.7.1 Scantlings of plane and corrugated transverse and longitudinal bulkheads of integral cargo tanks

Item	Parameter	Requirement
Plating	Thickness	Plane bulkheads
		Corrugated bulkheads
Stiffeners	Modulus	Z = 6ks le 2 h g
Corrugations	Modulus	Z = 7,5ks le 2 h g
See Note 2
	Inertia	I = 3,2le Z cm4
Stringers and webs supporting stiffeners	Modulus	Z = 8,5kSle2hg
Webs supporting stringers	Modulus	Z is to be determined by direct calculations using a stress of assuming fixed ends, in association with the head, h g
Symbols
Z, I, S, t, s, le, ρ, k and hd are as defined in Pt 4, Ch 6, 1.12 Symbols and definitions 1.12.1 f = 1,1 – h = load height, in metres, measured vertically as follows: = (a) for vertically stiffened plating, the distance from a point 0,5 m above the lower edge of the plate to the top of the tank = (b) for horizontally stiffened plating, the distance from the middle of the first panel above the lower edge of the plate to the top of the tank = (c) for vertically corrugated bulkheads, the distance from a point 0,5 m above the lower edge of the corrugation to the top of the tank = (d) for horizontally corrugated bulkheads, the distance from the middle of the panel of the corrugation to the top of the tank = (e) for stiffening members, the distance from the middle of the effective length to the top of the tank hg = hρ +h d + 0,2 m w = width of flange (b) or web (c), in metres, whichever is the greater, see Figure 3.3.3 Dimensions and symbols for corrugated bulkheads in Pt 3, Ch 3,3 Kc = The lesser of 1,5 or dt in Pt 3, Ch 4, 7.3 Corrosion additionsfor mild steel. See Pt 3, Ch 4, 7.3 Corrosion additions 7.3.7 for solid stainless steel
Note 1. 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.
Note 2. The required section modulus of corrugations is based on a fully clamped connection at the lower end and a simple support at the upper end of the bulkhead. Other arrangements will receive special consideration.
Note 3. The basic requirements for the use of higher tensile steels and the associated reduction in required thicknesses and scantlings are, in principle, restricted to transverse bulkheads or longitudinal bulkheads of independent tanks. Structural elements taking part in the global strength of the hull such as integrated longitudinal bulkheads are to be be specially considered for compliance with buckling and/or global stress criteria by which the scantlings may need to be increased.
Note 4. The proof of satisfactory buckling capabilities of corrugated bulkheads executed in higher tensile steel is to be proven by direct calculations.

7.1.2 The scantlings given in Table 6.7.1 Scantlings of plane and corrugated transverse and longitudinal bulkheads of integral cargo tanks 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 as indicated in Pt 3, Ch 10, 3.7 Correction of stiffening member modulus in relation to end connections. In tankers of types C and N Closed, all bulkhead stiffeners are to have at least Type I end connections.

7.1.3 Longitudinals may either be carried through transverse bulkheads, or may stop in way. In case longitudinals terminate at transverse bulkheads brackets are to be fitted interconnecting the longitudinals. These are to be arranged such that the cross-sectional area of the longitudinals is maintained, see Pt 3, Ch 10, 3.3 Basis for calculation of bracket connections 3.3.1.(c).

7.1.4 When the ship is longitudinally framed in deck and bottom, the vertical stiffeners on transverse bulkheads are to be in line with the deck and bottom longitudinals.

7.1.5 Where, in accordance with Table 6.7.1 Scantlings of plane and corrugated transverse and longitudinal bulkheads of integral cargo tanks, higher tensile steels are used in the construction of plane or corrugated bulkheads, structural items forming the supporting structure in double bottoms or within the double hull may require to be made of equivalent materials depending on the maximum stress levels in way.

7.1.6 Scallops in stiffeners may not be fitted in way of end connections, crossings with primary members and tripping brackets.

7.1.7 The depth of primary members is generally to be not less than twice the depth of the slots for the stiffening members.

7.2.1 The material is to comply with the requirements of Pt 4, Ch 6, 1.9 Stainless steel.

7.2.2 The thickness of plating forming boundaries of cargo tanks is to be in accordance with the requirements given in Pt 4, Ch 6, 7.1 General.

7.2.3 Where tank boundary plating may be subjected to primary buckling stresses, or is required to form an effective flange of a primary member, it may be necessary to increase the plating thickness for compliance with general buckling aspects.

7.2.4 The thickness of plating is not to be less than the minimum compartment thickness, see Pt 4, Ch 6, 1.10 Compartment minimum thickness.

7.2.5 The section modulus of mild steel stiffeners attached to stainless steel plating is to be based on the actual plating thickness.

7.3.1 Requirements for the location, arrangement and testing of cofferdams are given in Pt 4, Ch 4, 3 Ship Arrangements.

7.3.2 The scantlings of cofferdam bulkheads are to comply with the requirements of Pt 4, Ch 6, 7.1 General and Pt 4, Ch 6, 7.2 Stainless steel, as applicable.

7.3.3 Cofferdam bulkheads not bounding the cargo tank are to comply with the requirements of Table 6.7.1 Scantlings of plane and corrugated transverse and longitudinal bulkheads of integral cargo tanks using ρ =1,0 and h _d = 1,0 m.

7.4.1 Vertical stiffeners may be supported by an effective system of stringers and webs. The stringers are to be in line with the stringers of the ship’s sides, if fitted.

7.4.2 Horizontal stiffeners of longitudinal bulkheads are to be supported by webs which are to form part of the ring system of transverses required by Pt 4, Ch 6, 5.4 Primary structure 5.4.1.

7.4.3 Webs 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.