Section
4 Shell envelope framing
4.1 General
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 aft as practicable.
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.
4.2 Shell longitudinals
4.3 Shell framing
4.3.1 The
scantlings of side frames in the aft region are to comply with the
requirements given in Table 6.4.2 Shell framing (transverse)
aft.
Table 6.4.1 Shell framing (longitudinal)
aft
| Location
|
Modulus, in
cm3
|
| (1) Side longitudinals in
poop
|
Z = 0,0065sk
e
2(0,6 + 0,167D
2)
|
| (2) Side longitudinals in way
of dry spaces including double skin construction:
|
|
| (a) Aft of the after peak
bulkhead
|
Z = 0,0085skh
T1
e
2
F
s but not to be less than as required by (1)
|
| (b) Between the after peak
bulkhead and 0,2L from the A.P.
|
Z = 0,007skh
T1
e
2
F
s
|
|
|
or as required in the midship region
for the particular type of ship concerned, whichever is the greater
|
| (c) Forward of 0,2L
from the A.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:
|
| (a)
Z as from (2)
|
| (b) As required by Pt 4, Ch 1, 9 Bulkheads for deep tanks
|
| (4) Bottom and bilge
longitudinals
|
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 6, 1.4 Symbols and definitions 1.4.1
|
| le as defined in Pt 3, Ch 6, 1.4 Symbols and definitions 1.4.1, but is to be taken not less than 1,5m
|
|
D
2
|
= |
D
1 but need not be taken greater than 20 m |
|
|
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
|
|
|
|
|
|
|
|
T
1
|
= |
T but not to be taken less than 0,65D
1
|
|
|
h
T1
|
= |
 , in metres, for longitudinals above the
waterline at draught T
1 where  is not to be less than 0,7 |
| = |
 , in metres, for longitudinals below the
waterline at draught T
1
|
|
where
|
f
w
|
= |
1,0 at 0,2L from A.P. and 1,32 at and aft of
aft peak bulkhead. Intermediate positions by interpolation. |
|
|
h
6
|
= |
vertical distance, in metres, from the waterline at
draught T
1, to the longitudinal under consideration |
|
|
C
w
|
= |
a wave head, in metres = 7,71 × 10-2
L
e
-0,0044L
|
|
where
|
e |
= |
base of natural logarithm 2,7183 |
|
|
F
λ
|
= |
1,0 for L ≤ 200 m |
| = |
[1,0 + 0,0023 (L - 200)] for L > 200
m |
|
Note
1. 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.
|
|
|
Table 6.4.2 Shell framing (transverse)
aft
| Location
|
Modulus, in cm3
|
Inertia, in cm4
|
| (1) Frames in after peak
spaces and lower 'tween decks over
|
Z = 1,85s k T D
2
S
1 x 10-3
|
|
| (2) Frames in upper 'tween
decks and poops aft of the after peak bulkhead, see Notes 1, 2 and 6
|
The
greater of the following:
- Z = C s k h
T1
H
2 x 10-3
- Z = 9,1s k D
1 x 10-3
|
|
| (3) Main and 'tween deck
frames (including poop) between the after peak bulkhead and 0,2L from
the A.P., see Notes 1, 2 and 3
|
The
greater of the following:
- Z = C s k h
T1
H
2 x 10-3
- Z = 9,1s k D
1 x 10-3
|
|
| (4) Main and 'tween deck
frames elsewhere, see Notes 1, 2 and 3
|
As
required in the midship region for the particular type of ship
concerned
|
| (5) Panting
stringers, see Note 4
|
Web
depth, d
w, same depth as frames
|
| Web
thickness, t = t
W as in Pt 3, Ch 10, 4.4 Geometric properties and proportions
|
| Face
area, A =k S
2 (H + 1) cm2
|
| Symbols
|
| L, D, T, s,
k as defined in Pt 3, Ch 6, 1.4 Symbols and definitions 1.4.1
|
|
|
|
D
2
|
= |
D
1 but is to be taken not greater than 16 m nor less than
6 m |
|
|
H
|
= |
H
MF or H
TF as applicable, see Note 3 |
|
|
H
MF
|
= |
vertical framing depth, in metres, of main frames as
shown in Figure 6.4.1 Framing depths but is not to be taken
less than 3,5 m, see Note 5 |
|
|
H
TF
|
= |
vertical framing depth, in metres, of 'tween deck
frames as shown in Figure 6.4.1 Framing depths, but is not to be taken
less than 2,5 m |
|
|
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 fitted |
| = |
3,4 (2,15 - 1,15(
amean/ )) where two reduced brackets fitted |
| = |
6,1 where one Rule standard bracket fitted |
| = |
6,1 (1,2 - 0,2 (
a/ )) where one reduced bracket fitted |
| = |
7,3 where no brackets fitted |
|
| The requirements for frames where brackets
larger than Rule standard are fitted will be specially considered
|
|
|
|
|
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
 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 A.P. and 1,32 at and aft of
aft peak bulkhead 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
-0,0044
L
|
|
| where e = base of natural
logarithm 2,7183
|
Note
1. In fishing vessels the modulus of main
and 'tween deck frames need not be greater than 80 % of that given in
(2).
Note
2. In offshore supply ships the moduli of
main and 'tween deck frames are to be 25 % greater than those given in
(2), (3) and (4).
Note
3. 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.
Note
5. Where the frames are supported by
fully effective horizontal stringers, these may be considered as decks
for the purpose of determining H
MF.
Note
6. Except for main frames the modulus for
these members need not exceed that derived from (1) using H
TF in place of S
1.
|
4.3.2 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.
4.4 Panting stringers in way of transverse framing
4.5 Primary structure at sides
4.5.3 Where
the shape of the after sections is such that there are large sloped
flat areas, particularly in the vicinity of the propellers, additional
primary supports for the secondary stiffening may be required. Their
extent and scantlings will be specially considered.
4.5.4 The
web thickness, stiffening arrangements and connections of primary
supporting members are to be in accordance with the requirements of Pt 3, Ch 10, 4 Construction details for primary members.
Table 6.4.3 Spacing of side transverses and
web frames aft
| Location
|
Maximum spacing
|
| Web
frames in association with transverse framing system
|
Side
transverses in association with longitudinal framing system
|
| (1) Aft of the
after peak bulkhead
|
4 frame spaces
|
2,5 m where L ≤
100 m
3,5 m where L ≥ 300
m
Intermediate values by interpolation
|
| (2) Elsewhere in
way of dry cargo spaces or deep tanks, see Note
|
—
|
3,8 m where L ≤
100 m
(0,006L + 3,2) m
where L
> 100 m
|
| (3) In way of
cargo tanks of oil tankers, chemical tankers or ore or oil carriers
|
—
|
3,6 m where L ≤
180 m
0,02L where L > 180 m
|
|
|
Table 6.4.4 Primary structure aft
| Item and location
|
Modulus, in cm3
|
Inertia, in cm4
|
| Longitudinal framing system
|
| (1) Side transverses in dry spaces aft of
the after peak bulkhead, see Note 4:
|
|
—
|
| (a) Lower space
|
Z = 10 k
S
h
T1
e
2
|
| (b) 'Tween deck
|
Z = C
2
k
ST H
TF
|
| (2) Side transverses in tanks aft of the
after peak bulkhead, see Note 4:
|
|
|
| (a) Lower space
|
Z = 11,7ρ k
S
h
4
e
2
|
| (b) 'Tween decks
|
Z = 14,1ρ k
S
h
4
e
2
or as (1) above, whichever is the greater
|
| (3) Side transverses in dry spaces and deep tanks
forward of the after peak bulkhead
|
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 after peak
dry space, see Note 3
|
Z = 7,75 k
S
h
T1
e
2
|
—
|
| (5) Side stringers supported by webs in after peak
tank, see Note 3
|
Z = 11,7 ρk
S
h
4
e
2
or as (4) above, whichever is the greater
|
|
| (6) Web frames supporting side stringers in after
peak, see Note 3
|
Z is to be determined from calculations based on the
following assumptions:
- Fixed ends
- Point loadings from stringers
- Head h
4 or h
T1 as applicable
- Bending stress
- Shear stress
|
In deep
tanks:
|
|
(7)Web frames in 'tween decks aft of the after peak
bulkhead not supporting side stringers
|
Z = C
3
k S T H
TF
|
—
|
|
(8)Side stringers and web frames in dry spaces and
deep tanks forward of the after peak bulkhead
|
As in Pt 4, Ch 1, 6 Shell envelope framing, see Notes 1 and 2
|
| Symbols
|
D, T,
S, 
e, k, ρ as defined in Pt 3, Ch 6, 1.4 Symbols and definitions 1.4.1
|
|
|
|
|
|
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 A.P. and 1,32 at and aft of
aft peak bulkhead. 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 |
|
|
|
|
T
1
|
= |
T but not to be taken less than 0,65D
1
|
|
|
|
Note
4. The web depth of side transverses aft
of the after peak bulkhead is to be not less than 2,5 times the depth
of the longitudinals supported. The web depth of stringers is to be
not less than 2,2 times the depth of frames supported.
|
|