Section 4 Shell envelope framing

4.1.1 Requirements are given in this Section for both longitudinal and transverse framing systems. Where longitudinal framing is adopted in the midship region it is to be carried as far forward as practicable. In the case of oil tankers (see Pt 3, Ch 5, 1.1 Application 1.1.4), longitudinal framing is to be continued at least to the fore end of the cargo tanks.

4.1.2 End connections of longitudinals to bulkheads are to provide adequate fixity, lateral support and, so far as practicable, direct continuity of longitudinal strength, see also Pt 3, Ch 10, 3 Secondary member end connections. Where L exceeds 215 m, the bottom longitudinals are to be continuous in way of both watertight and non-watertight floors, but alternative arrangements will be considered. Higher tensile steel longitudinals within 10 per cent of the ship's depth at the bottom and deck are to be continuous irrespective of the ship length.

4.1.3 Stiffeners and brackets on side transverses, 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 it is 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 direct calculations.

4.1.4 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 aft side of the connection between the upper turn of bilge and 0,8D above the base line. Particular attention is to be given to ensuring the alignment of these brackets. Alternative arrangements will be considered if supported by appropriate direct calculations.

4.1.5 For ships intended to load or unload while aground, see Pt 3, Ch 9, 7 Bottom strengthening for loading and unloading aground.

4.2.1 The scantlings of bottom and side shell longitudinals in the forward region are to comply with the requirements given in Pt 3, Ch 5, 4.2 Shell longitudinals 4.2.1. For the scantlings of bottom shell longitudinals where additional bottom strengthening is required, see Pt 3, Ch 5, 1.5 Strengthening of bottom forward.

Table 5.4.1 Shell framing (longitudinal) forward

Location	Modulus, in cm3
(1) Side longitudinals in forecastle	Z = 0,0075s k e 2(0,6 + 0,167D 1)
(2) Side longitudinals in way of dry spaces including double skin construction:
(a) Forward of the collision bulkhead	Z = 0,007s k h T1 e 2 F s but not to be less than as required by (1)
(b) Between the collision bulkhead and 0,2L from the F.P.	As (a) above or as required in the midship region for the particular type of ship concerned, whichever is the greater. However, not to be taken less than as required by (1).
(c) Aft of 0,2L from the F.P.	As required in the midship region for the particular type of ship concerned.
(3) Side longitudinals in way of double skin tanks or deep tanks	The greater of the following: Z as from (2) As required by Pt 4, Ch 1, 9 Bulkheads for deep tanks.
(4) Bottom and bilge longitudinals	The greater of the following: As required in the midship region for the particular type of ship concerned. As required by Pt 3, Ch 5, 1.5 Strengthening of bottom forward, strengthening of bottom forward, where applicable.
Symbols
L, D, T, s, k, as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1
e = as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1, but is to be taken not less than 1,5m
L 1 = L but need not be taken greater than 190 m
F s is a fatigue factor to be taken as follows: (a) For built sections and rolled angle bars: F s = at 0,6D 1 above the base line = 1,0 at D 1and above, and F sb at the base line intermediate values by linear interpolation
F sb is a fatigue factor for bottom longitudinals = 0,5 (1 + F s at 0,6D 1) (b) For flat bars and bulb plates may be taken as 0,5
where b f1 = the minimum distance, in mm, from the edge of the face plate of the side longitudinal under consideration to the centre of the web plate, see Fig. 9.5.1 in Pt 4, Ch 9
b f = the width of the face plate, in mm, of the side longitudinal under consideration, see Fig. 9.5.1 in Pt 4, Ch 9
T 1 = T but not to be taken less than 0,65D 1
D 1 = T + H b metres, where H bis the minimum bow height, in metres, obtained from Pt 3, Ch 1, 6.1 Principal particulars 6.1.11
h T1 = F λ, in metres, for longitudinals above the waterline at draught T 1 where is not to be taken less than 0,7 = , in metres, for longitudinals below the waterline at draught T 1
where f w = 1,0 at 0,2L from the F.P. and 1,71 at, and forward of, 0,15L from the F.P. Intermediate positions by interpolation
h 6 = vertical distance, in metres, from the waterline at draught T 1, to the longitudinal under consideration
F λ = 1,0 for L ≤ 200 m = [1,0 + 0,0023 (L - 200)] for L > 200 m
C w = a wave head, in metres = 7,71 × 10-2 Le -0,0044L
where e = base of natural logarithms 2,7183
NOTE Where struts are fitted midway between transverses in double skin construction, the modulus of the side longitudinals may be reduced by 50k per cent from that obtained for locations (2) and (3) as applicable.

4.2.2 End connections of longitudinals to bulkheads are to provide adequate fixity, lateral support and so far as practicable, direct continuity of longitudinal strength, see also Pt 3, Ch 10, 3 Secondary member end connections.

4.3.1 The scantlings of side frames in the forward region are to comply with the requirements given in Pt 3, Ch 5, 4.4 Panting stringers in way of transverse framing 4.4.3.

4.3.2 The scantlings of main frames are normally to be based on Rule standard brackets at top and bottom, whilst the scantlings of 'tween deck frames are normally to be based on a Rule standard bracket at the top only.

4.3.3 End connections of transverse main and 'tween deck frames are to be in accordance with Pt 3, Ch 10, 3 Secondary member end connections. For bulk carriers the end connections of main frames in cargo holds are to be in accordance with Pt 4, Ch 7, 6.2 Transverse stiffening 6.2.5 to Pt 4, Ch 7, 6.2 Transverse stiffening 6.2.12. Where brackets are omitted at the foot of main frames in cargo spaces, small easing brackets are to be fitted forward of 0,15L from the F.P.

4.4.1 In lower hold or deep tank spaces panting stringers are generally to be fitted in line with each stringer or flat in the fore peak space and extending back to 0,15L from the F.P. These stringers may be omitted if the shell plating is increased in thickness as required by Pt 3, Ch 5, 3.5 Side shell and sheerstrake 3.5.2. Where the span of the main frames exceeds 9 m, panting stringers are to be fitted irrespective of whether the shell plating is increased in thickness or not. These stringers are to be arranged in line with alternate stringers or flats in the fore peak and are to extend back to 0,2L from the F.P.

4.4.2 In 'tween deck spaces in the region forward of 0,15L from the F.P., where the unsupported length of frame exceeds 2,6 m in a lower 'tween deck or 3,0 m in an upper 'tween deck, intermediate panting stringers are generally to be fitted. These stringers may be omitted if the shell plating is increased in thickness as required by Pt 3, Ch 5, 3.5 Side shell and sheerstrake 3.5.2.

4.4.3 The scantlings of panting stringers are to be determined from Pt 3, Ch 5, 4.4 Panting stringers in way of transverse framing 4.4.3.

Table 5.4.2 Shell framing (transverse) forward

Location	Modulus, in cm3	Inertia, in cm4
(1)Frames in fore peak spaces and lower 'tween decks over, see Note 1	Z = K 1 s k T D 2 S 1 x 10-3
(2) Frames in upper 'tween decks and forecastles forward of the collision bulkhead, see Notes 1, 2 and 8	The greater of the following: Z = C s k h T1 H 2 x 10-3 Z = 9,1 s k D 1 x 10-3
(3) Main and 'tween deck frames (including forecastle) between the collision bulkhead and 0,15L from the F.P., see Notes 1 to 4 and 8	The greater of the following: Z = C s k h T1 H 2 x 10-3 Z = 9,1 s k D 1 x 10-3
(4)Main and 'tween deck frames between 0,15L and 0,2L from the F.P. in dry cargo spaces, see Notes 1 to 4 and 8	The greater of the following: Z = C s k h T1 H 2 x 10-3 Z = 9,1 s k D 1 x 10-3
(5) Panting stringers, see Note 5	Web depth, d w, same depth as frames Web thickness, t = 6 + 0,025L 2 mm Face area, A =kS 2 (H + 1) cm2
(6) Main and 'tween deck frames elsewhere, see Notes 1 to 4	As required in the midship region for the particular type of ship concerned
Symbols
L, D, T, s, k as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1
L 2 = L, but need not be taken greater than 215 m
D 1 = T + H b, in metres, where H b is defined in Pt 3, Ch 1, 6.1 Principal particulars 6.1.11
D 2 = D 1, but is to be taken not greater than 16 m, nor less than 6,0 m
H = H MF or H TF as applicable, see Note 7
H MF = vertical framing depth, in metres, of main frames as shown in Fig. 5.4.1 but is to be taken not less than 3,5 m, see Note 6
H TF = vertical framing depth, in metres, of 'tween deck frames as shown in Fig. 5.4.1 but is to be taken not less than 2,5 m
K 1 = 2,3 for peak tanks = 1,87 for 'tween decks over peak tanks
S 1 = vertical spacing of peak stringers or height of lower 'tween deck above the peak, in metres, as applicable
S 2 = vertical spacing of panting stringers, in metres
C = end connection factor = 3,4 where two Rule standard brackets fitted = 3,4 (1,8 - 0,8( a/)) where one Rule standard bracket and one reduced bracket is fitted = 3,4 (2,15 - 1,15 ( amean/)) where two reduced brackets are fitted = 6,1 where one Rule standard bracket is fitted = 6,1 (1,2 - 0,2 ( a/)) where one reduced bracket is fitted. = 7,3 where no brackets are fitted = The requirements for frames where brackets larger than Rule standard are fitted will be specially considered
= length, in mm, as derived from Pt 3, Ch 10, 3.4 Scantlings of end brackets 3.4.1
a = equivalent arm length, in mm, as derived from Pt 3, Ch 10, 3.4 Scantlings of end brackets 3.4.1
amean = mean equivalent arm length, in mm, for both brackets
T 1 = T but not to be taken less than 0,65D 1
h T1 = head, in metres, at mid-length of H = , in metres for frames where the mid-length of frame is above the waterline, at draught T 1 where is not to be taken less than 0,7 = , in metres for frames where the mid-length of frame is below the waterline at draught T 1
where f W = 1,0 at 0,2L from F.P. and 1,71 at, and forward of, 0,15L from F.P. Intermediate positions by interpolation
h 6 = vertical distance, in metres, from the waterline at draught T 1 to the mid-length of H
F λ = 1,0 for L ≤ 200 m = [1,0 + 0,0023 (L - 200)] for L > 200 m
C W = a wave head, in metres = 7,71 x 10-2 Le -0,0044L where e = base of natural logarithms 2,7183
NOTES
1. For framing in the fore end of fishing vessels, see Pt 4, Ch 6, 6 Shell envelope framing
2. In offshore supply ships the moduli of main and 'tween deck frames are to be 25 per cent greater than given in (2), (3) and (4).
3. In way of the cargo tanks of oil tankers or ore carriers, the scantlings of frames are also to comply with the requirements for frames in the midship region of such ships, see Pt 4, Ch 9 Double Hull Oil Tankers, Pt 4, Ch 10 Single Hull Oil Tankers or Pt 4, Ch 11 Ore Carriers, as applicable.
4. In bulk carriers the scantlings of frames are also to comply with the requirements of Pt 4, Ch 7, 6 Shell envelope framing in which the requirements of Table 7.6.1 location (1) are to be multiplied by the following factor: Between 0,15L and 0,2L from the F.P., C 1 = (0,018D 2 + 0,82), but not to be taken less than 1,0. Between collision bulkhead and 0,15L from the F.P., C 1 = (0,021D 2+ 0,96).
5. Panting stringers are not required in tugs less than 46 m in length, see Pt 4, Ch 3, 4 Panting and strengthening of bottom forward.
6. Where the frames are supported by fully effective horizontal stringers, these may be considered as decks for the purpose of determining H MF.
7. Where frames are inclined at more than 15° to the vertical, H MF or H TF is to be measured along a chord between span points of the frame.
8. Except for main frames the modulus for these members need not exceed that derived from (1) using H TF in place of S 1.

4.5.1 For the arrangement of primary structure in peak tanks and deep tanks forward, see also Pt 3, Ch 5, 6 Fore peak structure and Pt 3, Ch 5, 7 Forward deep tank structure.

4.5.2 The spacing of side transverses and web frames is generally not to exceed the values given in Table 5.4.3 Spacing of side transverses and web frames forward.

4.5.3 The scantlings of side transverses supporting longitudinal framing and stringers and webs supporting transverse framing in the forward region are to be determined from Table 5.4.4 Primary structure forward.

Table 5.4.4 Primary structure forward

Item and location		Modulus, in cm3	Inertia, in cm4
Longitudinal framing system
(1)	Side transverses in dry spaces forward of 0,2L from the F.P., see Note 5:		—
	Holds 'tween decks
(2)	Side transverses in peak and deep tanks forward of 0,2L from the F.P., see Notes 1 and 4:
	where no struts fitted where struts fitted	or as (1) above, whichever is the greater As in Pt 4, Ch 9, 9 Primary members supporting longitudinal framing
(3)	Side transverses in dry spaces and deep tanks aft of 0,2L from the F.P.	As in Pt 4, Ch 1, 6 Shell envelope framing, see Notes 1 and 2
Transverse framing system
(4)	Side stringers supported by webs in dry spaces forward of 0,2L from the F.P., see Note 3 or as (4) above, whichever is the greater		—
(5)	Side stringers supported by webs in peak or deep tanks forward of 0,2L from the F.P., see Notes 1 and 3	or as (4) above, whichever is the greater
(6)	Web frames supporting side stringers forward of 0,2L from the F.P., see Notes 1, 2 and 3	Z to be determined from the calculations based on the following assumptions: Fixed ends Point loadings from stringers Head γh 4 or γh T1 as applicable Bending stress Shear stress	In deep tanks
(7)	Web frames in 'tween decks, not supporting side stringers, forward of 0,2L from the F.P.		—
(8)	Side stringers and web frames in dry spaces and deep tanks aft of 0,2L from the F.P.	As in Pt 4, Ch 1, 6 Shell envelope framing, see Notes 1 and 2
Symbols
D, T, S, le, k, ρ as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1
B f = bow fullness factor determined from Fig 5.4.3 to be taken as 1,0 for framing members located at and abaft 0,2L from the forward perpendicular
h 4 = tank head, in metres, as defined in Pt 3, Ch 3, 5 Design loading
h T1 = head, in metres, at mid-length of span = , in metres, where the mid-length of span is above the waterline at draught T 1 where is not to be taken less than 0,7 = , in metres, where the mid-length of span is below the waterline at draught T 1
where f W = 1,0 at 0,2L from F.P. and 1,71 at, and forward of, 0,15L from F.P. Intermediate positions by interpolation
h 6 = vertical distance, in metres, from the waterline at draught T 1 to the mid-length of span
F λ = 1,0 for L ≤ 200 m = [1,0 + 0,0023 (L -200)] for L > 200 m
C W = a wave head, in metres = 7,71 x 10-2 L e -0,0044 L where e = base of natural logarithms 2,7183
D 1 = T + H b, in metres, where H b is defined in Pt 3, Ch 1, 6.1 Principal particulars 6.1.11
T 1 = T but not to be taken less than 0,65D 1
C 2,C 3 = factors obtained from Figure 5.4.2 Framing factors for primary members
H TF = vertical height of `tween decks, in metres, as shown in Pt 3, Ch 5, 4.5 Primary structure at sides 4.5.4
γ is to be measured at the mid-span of the member as follows: γ 1 = 1,0 at base line γ 2 = bow fullness factor (B f) at 0,6D above base γ 3 = + 1,0 at depth D above base
Intermediate values are to be determined by interpolation. Minimum value = 1,0
Note 1. In way of the cargo tanks, fore peak tanks and dry spaces of oil tankers or ore carriers the scantlings of primary structure are to comply with the requirements of Pt 4, Ch 9 Double Hull Oil Tankers, Pt 4, Ch 10 Single Hull Oil Tankers or Pt 4, Ch 11 Ore Carriers, as appropriate.
Note 2. For bulk carriers see Pt 4, Ch 7, 6.2 Transverse stiffening.
Note 3. For stringers and webs in fore peaks or deep tanks, see also Pt 3, Ch 5, 6.3 Side structure − Transverse framing and Pt 3, Ch 5, 7.3 Side structure − Transverse framing.
Note 4. In the fore peak, the breadth S should be measured along the line of shell. The effective length e of the vertical webs should be measured along the line of shell from horizontal flat to horizontal flat, except that it may be taken to the underside of a transverse or strut where fitted.
Note 5. The web depth of side transverses forward of 0,2L from the F.P. is to be not less than 2,5 times the depth of the longitudinals supported. The web depth of stringers forward of 0,2L is to be not less than 2,2 times the depth of the frames supported.
Note 6. For the primary structure at sides in dredgers with restricted service notations, see Table 12.5.2 Primary supporting structure at sides.

4.5.4 The web thickness, stiffening arrangements and end connections of primary supporting members are to be in accordance with the requirements of Pt 3, Ch 10, 4 Construction details for primary members.

Figure 5.4.1 Framing depths for transverse frames

Figure 5.4.2 Framing factors for primary members

Figure 5.4.3 Illustration of bow fullness factor determination