Section
9 Primary members supporting longitudinal framing
9.1 General
9.2 Symbols
9.2.1 The
symbols used in this Section are defined as follows:
|
d
DB
|
= |
Rule depth of centre girder, in mm |
|
h
c
|
= |
vertical distance from the centre of the cross-ties to deck
at side amidships, in metres |
|
h
s
|
= |
distance between the lower span point of the vertical web and
the moulded deck line at centreline, in metres |
|
lb
|
= |
the
distance, in metres, between the transverse bulkheads (oiltight or
non-oiltight) adjacent to the bulkhead under consideration |
|
lc
|
= |
one-half
the vertical distance, in metres, between the centres of the adjacent
cross-ties or between the centre of the adjacent cross-tie and the
centre of the adjacent bottom or deck transverse, or double bottom, see
Figure 9.9.1 Wing tank construction
|
|
s
|
= |
spacing
of transverses, in metres |
|
A
c
|
= |
cross sectional area of the cross-tie material which is continuous
over the span of the cross-tie in cm2
|
 c
|
= |
least
moment of inertia of the cross-tie in cm4
|
|
S
c
|
= |
length of cross-tie, in metres, measured as follows: |
- (a) For centre tank cross-ties: S
c is the distance between the face plates of the vertical webs on the
longitudinal bulkheads.
- (b) For wing tank cross-ties: S
c is the distance between the face plate of the vertical web on the
longitudinal bulkhead and the inner hull
Other symbols are defined in Pt 4, Ch 9, 1.5 General definitions and symbols.
9.3 Girders and floors in double bottom
9.3.1 Girders
are to be arranged at the centreline or duct keel, at the hopper side
and in way of longitudinal bulkheads and bulkhead stools. Plate floors
are to be arranged in way of transverse bulkheads and bulkhead stools.
9.3.2 In way
of vertically corrugated transverse bulkheads supported by stools,
additional girders are to be arranged extending at least to the first
plate floor adjacent to the bulkhead each side and spaced not more
than 3,8 m apart, see
Pt 4, Ch 9, 7.4 Bulkheads supported by stools 7.4.5.
9.3.4 Thickness
of floors and girders is to be confirmed by means of a direct calculation.
Due account is to be taken of access and other openings. The minimum
thickness however, is to be not less than that given by:
-
Centre girder
or duct keel:
t = (0,008d
DB + 1,0)  mm
-
Floors and side
girders:
t = (0,007d
DB + 1,0)  mm but need not exceed 12,0  mm.
9.3.5 The
scantlings of plating and stiffeners of longitudinal girders are not
to be less than necessary to comply with the buckling requirements
of Pt 3, Ch 4, 7 Hull buckling strength.
9.3.6 Floors
and girders forming the boundaries of tanks are also to satisfy the
requirements of tank bulkheads given in Pt 4, Ch 1, 9 Bulkheads.
9.3.7 Provision
is to be made for the free passage of air and water from all parts
of the tanks to the air pipes and suctions, account being taken of
the pumping rates required. Adequate access is also to be provided
to all parts of the double bottom. The edges of all openings are to
be smooth. The size of the opening should not, in general, exceed
50 per cent of the double bottom depth, unless edge reinforcement
is provided. In way of ends of floors and fore and aft girders at
transverse bulkheads, the number and size of openings are to be kept
to a minimum, and the openings are to be circular or elliptical. Edge
stiffening may be required in these positions.
9.4 Vertical webs and horizontal girders in wing ballast tanks and
hopper spaces
9.4.2 Vertical
webs are to be arranged in line with the floors in the double bottom
to ensure continuity of transverse strength.
9.4.3 A horizontal
girder is to be arranged at the top of the hopper space and is to
be located close to the knuckle between the hopper and inner hull.
Where additional longitudinal girders are provided to satisfy access
requirements in accordance with Pt 4, Ch 9, 13.2 Access to spaces in the cargo area 13.2.8,
these are to be arranged in line with horizontal girders on the transverse
bulkhead and wing tank cross-ties where these are fitted.
9.4.4 The
scantlings of vertical webs and horizontal girders are to be determined
by means of direct calculations and due account is to be taken of
openings in the structure, see also the buckling requirements
in Pt 3, Ch 4, 7 Hull buckling strength for horizontal
girders.
9.4.5 Access
openings are to be kept clear of other small openings and are to have
smooth edges. Edge stiffening is also to be arranged in regions of
high shear stress.
9.5 Deck transverses and girders
9.5.1 Deck
transverses are to be arranged in line with the vertical webs at the
side and vertical transverses at longitudinal bulkheads, where fitted,
to ensure continuity of transverse structure.
9.5.2 Deck
girders are to be supported at transverse bulkheads by vertical webs
or equivalent.
9.6 Cross-ties
9.6.1 Cross-ties,
where fitted, may be of plate or sectional material and are to have
an area and least moment of inertia to satisfy the following:
where
|
r
|
= |
 cm.
|
(As a first approximation the area and inertia of the cross-tie
may be calculated in accordance with Pt 4, Ch 10, 2.10 Cross-ties 2.10.1.)
9.6.2 The
scantlings of the webs and flanges of cross-ties are also to be confirmed
by means of direct calculation.
9.6.3 Design
of end connections is to be such that the area of the welding, including
vertical brackets, where fitted, is to be not less than the minimum
cross-sectional area of the cross-tie derived from Pt 4, Ch 9, 9.6 Cross-ties 9.6.1. To achieve this, full penetration
welding may be required and thickness of brackets may require further
consideration. Attention is to be given to the full continuity of
area of the backing structure on the vertical webs and within the
wing ballast tank. Particular attention is also to be paid to the
welding at the toes of all vertical end brackets on the cross-tie.
9.7 Primary members supporting oiltight bulkheads
9.7.3 Where
longitudinal oiltight bulkheads are fitted, vertical webs are to be
arranged in line with the deck transverses and the double bottom floors.
Particular attention is to be paid to the alignment of the bulkhead
web end brackets with the double bottom floors.
9.7.4 The
section modulus of vertical webs on longitudinal bulkheads in ships
with one or two longitudinal bulkheads is to be not less than:
Z = K
3
sh
s
S
s
2
k cm3
where K
3 is given in Table 9.9.1 Vertical web on longitudinal
bulkhead coefficient.
Table 9.9.1 Vertical web on longitudinal
bulkhead coefficient
| Number of cross-
ties
|
K
3
|
K
4
|
K
5
|
Range of
application
|
| 1
|
2,16
|
0,455-0,316φ
|
0,103
|
0,5≤φ≤0,7
|
| 2
|
1,88
|
0,441-0,267φ1
|
0,498φ2-0,249
|
0,4≤φ1≤0,5
0,65≤φ2≤0,8
|
9.7.6 The
moment of inertia of vertical webs on longitudinal bulkheads is to
be not less than:
9.7.7 Where
horizontal girders and vertical webs on transverse bulkheads do not
form part of a ring structure, they are to be arranged with substantial
end brackets forming a buttress extending to the adjacent vertical
web or transverse. The shear and combined stresses in the buttress
arrangements are to be examined.
9.7.8 Where
the cross-ties are omitted from the transverse ring in the wing or
centre tanks adjacent to the transverse bulkhead, the design of the
horizontal girder, end buttress and vertical webs is to take account
of the loads imposed and the deflection of the structure.
9.7.9 Where,
in ships exceeding 150 m in length, the longitudinal bulkhead is corrugated,
the transverses are generally to be symmetrical on both sides of the
bulkhead, and the scantlings may require to be increased to limit
deflection.
9.8 Primary members supporting non-oiltight bulkheads
9.8.1 These
requirements are applicable to primary members supporting non-oiltight
transverse bulkheads. Where non-oiltight longitudinal bulkheads are
proposed, the requirements for primary members will be individually
considered.
9.8.2 Direct
calculation procedures will generally be required where non-oiltight
bulkhead primary members will interact with, or tend to support, the
primary bottom, longitudinal bulkhead or side structure, and in other
cases where warranted by structural design features. In general the
section modulus of horizontal girders is to be not less than:
9.8.3 When
determining the width of plating supported and the effective breadth
for calculating the section modulus, no deduction is to be made on
account of perforations.
|