Section 5 Hull framing

5.1.1 In the cargo tank region, the scantlings of deck, bottom and side longitudinals, and of transverse side framing, where fitted, are to be in accordance with the requirements of this Section.

5.1.2 Longitudinal and transverse framing members outside the cargo tank region are to comply with the requirements of Pt 3, Ch 5, 4 Shell envelope framing, Pt 3, Ch 6, 4 Shell envelope framing and Pt 3, Ch 7 Machinery Spaces, as appropriate to their location.

5.1.3 Outside the cargo tank region the structure is to be scarfed into the end structure as provided for in Pt 3, Ch 5 Fore End Structure, Pt 3, Ch 6 Aft End Structure and Pt 3, Ch 7 Machinery Spaces.

5.2.1 The symbols used in this Section are defined as follows:

Other symbols are defined in Pt 4, Ch 9, 1.5 General definitions and symbols

5.3.1 The modulus of longitudinals within the cargo tank region, except as provided for in Pt 4, Ch 9, 5.3 Deck, side and bottom longitudinals 5.3.2 and Pt 4, Ch 9, 5.5 Deck longitudinals outside 0,4L amidships is to be not less than the greater of the following:

1. Z = 0,056s kh ₁ l _e ² F ₁ F _s cm³, or

2. Z = 0,0051s kh ₃ l _e ² F ₂ cm³

where F ₁ and F ₂ values are as given in Table 9.5.1 Values of F1 and Table 9.5.2 Values of F2 and F _s is a fatigue factor to be taken as follows:

For flat bars and bulb plates may be taken as 0,5

The modulus of side longitudinals need not exceed that of a bottom longitudinal having the same spacing and configuration.

5.3.2 The modulus of bottom longitudinals is to satisfy the requirements of Pt 4, Ch 9, 5.3 Deck, side and bottom longitudinals 5.3.1 or Table 1.6.1 Shell framing (longitudinal)(3) in Pt 4, Ch 1 General Cargo Ships, whichever is the greater.

5.3.3 The section modulus given is that of the longitudinal and associated plating, for the extent of the associated plating, see Pt 3, Ch 3, 3.2 Geometric properties of section 3.2.3. The webs and flanges are to comply with the minimum thickness requirements of Pt 4, Ch 9, 10 Construction details and minimum thickness.

5.3.4 Where the spacing of transverses exceeds 5,5 m, the scantlings of side and bottom longitudinals in way of bulkheads and primary members, including end connections, are to be verified by direct calculation.

5.3.5 The side and bottom longitudinal scantlings derived from Pt 4, Ch 9, 5.3 Deck, side and bottom longitudinals 5.3.1 and Pt 4, Ch 9, 5.3 Deck, side and bottom longitudinals 5.3.2, using the midship thickness of plating, are to extend throughout the cargo tanks. Where the shell plating is inclined at an angle to the horizontal longitudinal axis of greater than 10°, the span of the longitudinals is to be measured along the member. Where the shell plating is inclined at an angle to the vertical axis of greater than 10°, the spacing of longitudinals is to be measured along the chord between members. Where the angle of attachment of side longitudinals clear of amidships varies by 20° or more from a line normal to the plane of the shell, the properties of the section are to be determined about an axis parallel to the attached plating. Angles of slope greater than 40° are to be avoided.

5.3.6 Fabricated longitudinals having the face plate welded to the underside of the web, leaving the edge of the web exposed, are not recommended for shell, inner hull or longitudinal bulkhead longitudinals. Where it is proposed to fit such sections, a symmetrical arrangement of connection to transverse members is to be incorporated. This can be achieved by fitting backing brackets on the opposite side of the transverse web or bulkhead. The primary member web stiffener and backing bracket are to be lapped to the longitudinal. Recommended examples of such backing structure can be seen in the ShipRight FDA Procedure, Structural Detail Design Guide (SDDG).

5.3.7 Where partial filling of the tanks is also contemplated the deck longitudinals are to comply with the requirements of Pt 4, Ch 9, 6.1 General 6.1.2.

5.3.8 Stiffeners and brackets on vertical webs in wing ballast tanks, where fitted on one side and connected to higher tensile steel longitudinals between the base line and 0,8D above the base line, are to have their heels well radiused to reduce stress concentrations. Where a symmetrical arrangement is fitted, i.e. bracket or stiffening on both sides, and they are connected to higher tensile steel longitudinals, the toes of the stiffeners or brackets are to be well radiused. Alternative arrangements will be considered if supported by appropriate fatigue life assessment calculations.

5.3.9 Where higher tensile steel side longitudinals pass through transverse bulkheads in the cargo area, well radiused brackets of the same material are to be fitted on both the fore and after side of the connection between the upper turn of bilge and 0,8D above the base line. Particular attention should be given to ensuring the alignment of these brackets. Alternative arrangements will be considered if supported by appropriate fatigue life assessment calculations.

5.4.1 The scantlings of bilge longitudinals are to be graduated between those required for the bottom and lowest side longitudinals.

5.4.2 Where bilge longitudinals are omitted, the spacing of transverses or equivalent bilge brackets must not exceed:

Where no intermediate brackets are fitted between transverses, the spacing between the two outermost bottom longitudinals and between the two lowest side longitudinals is not to exceed one-third of the bilge radius or 40 times the local shell thickness, whichever is the greater.

5.4.3 Attention is drawn to Pt 4, Ch 9, 4.6 Bilge plating 4.6.2 and Pt 4, Ch 9, 4.6 Bilge plating 4.6.3 concerning bilge plating thickness where longitudinals are omitted.

5.5.1 Within the cargo tank region, deck longitudinals may be gradually tapered outside 0,4L amidships in association with the deck plating, on the basis of area and modulus. For the requirements, see Pt 3, Ch 3, 2.5 Taper requirements for hull envelope and Table 3.2.1 Taper requirements for hull envelope, see also Pt 4, Ch 9, 5.3 Deck, side and bottom longitudinals 5.3.5.

5.5.2 The midship spacing of longitudinals is, in general, to be maintained throughout the cargo tank region. The plating thickness and longitudinal depth and thickness are not to be increased at any point in the direction of the taper of area towards the ends of the ship, other than as may be required for compensation for openings. Changes of longitudinal section are, in general, to be avoided.

5.5.3 Attention is also drawn to Pt 4, Ch 9, 5.3 Deck, side and bottom longitudinals 5.3.3, which is to be complied with, where necessary, by maintaining a constant deck plating thickness in way of the ends of the cargo tank region.

5.5.4 Where the spacing of transverses in cargo tanks is not constant and variations in longitudinal scantlings are contemplated to suit differing spans, individual consideration will be given to the taper arrangements.

5.6.1 The lateral and torsional stability of longitudinals together with web and flange buckling criteria are to be verified in accordance with Pt 3, Ch 4, 7 Hull buckling strength.

5.6.2 In addition, the following requirements are to be satisfied:

1. Flat bar longitudinal

   1. when continuous at bulkheads

      

   2. when non-continuous at bulkheads

      

2. Built sections

   1. 

   2. 15 for asymmetric sections

   3. 30 for symmetric sections.

5.7.1 Connections of longitudinals to bulkheads are to provide adequate fixity and continuity of longitudinal strength. See also the ShipRight FDA Procedure, Structural Detail Design Guide (SDDG), for recommended design details in critical areas.

5.7.2 Where the length of the ship exceeds 150 m, the longitudinals within 0,1D of the bottom and deck are to be continuous through the transverse bulkheads. Higher tensile steel longitudinals are to be continuous irrespective of ship length. Alternative arrangements will be individually considered.

5.7.3 Longitudinals are to be connected to transverse primary members as required by Pt 3, Ch 10, 5.2 Arrangements at intersections of continuous secondary and primary members.

5.8.1 In general, closely spaced scallops are not permitted in longitudinals within the range of cargo tanks except in way of ballast pipe suctions, reinforcement in these areas will be specially considered.

5.8.2 Small air and drain holes, cut-outs at erection butts and similar widely spaced openings are, in general, to be not less than 200 mm clear of the toes of end brackets, intersections with primary supporting members and other areas of high stress. All openings are to be well rounded with smooth edges.

5.8.3 Drain holes in higher tensile steel longitudinals attached to higher tensile steel plating are to be elliptical in shape or of equivalent design to minimise stress concentrations. The opening is generally to be located clear of the welded connection to the plating, but where a flush opening is essential for drainage the weld connection is to end in a soft toe.

5.8.4 Small circular air holes may be arranged in higher tensile steel deck longitudinals.

5.8.5 Isolated openings spaced greater than 1 metre apart need not be taken into account in calculating the section modulus of the longitudinal, provided that the depth does not exceed 10 per cent of the web depth, or 75 mm, whichever is the greater, but in no case more than 25 per cent of the depth of the longitudinal.

5.8.6 Where the depths given in Pt 4, Ch 9, 5.8 Openings in longitudinals 5.8.5 are exceeded, the arrangements are to be such as will minimise resultant stress concentration.

5.9.1 For limits of application of transverse side framing, see Pt 4, Ch 9, 1.3 Class notation and applicable Rules for CSR Double Hull Oil Tankers.

5.9.2 The section modulus of transverse side frames is to be not less than:

Z = 0,01025ksh ₂ l _e ² cm³, where side webs are fitted;

or

Z = 0,012ksh ₂ l _e ² cm³, where side webs are not fitted.

5.9.3 The size of the frame is to be governed by the maximum modulus derived from the appropriate formula in Pt 4, Ch 9, 5.9 Transverse side frames 5.9.2, and is to be maintained for the full depth of the ship.

5.9.4 The section modulus given is that of the frame and associated side shell plating. The frame is to comply with the minimum thickness requirements of Pt 4, Ch 9, 10 Construction details and minimum thickness.

5.9.5 The inertia of transverse side frames is to be not less than:

In the forward 0,15L: = 3,5l_e Z cm⁴

Elsewhere: = 3,2l_e Z cm⁴.