Section
4 Decks
4.1 General
4.1.3 The minimum scantlings of deck structures on column-stabilised units,
self-elevating units, tension-leg units, buoys and deep draught caissons are to
comply with this Section.
4.1.4 The scantlings of deck structures are also to satisfy the overall
strength requirements in Pt 4, Ch 4 Structural Unit Types and be sufficient to withstand the actual local
loadings plus any additional loadings superimposed due to overall frame action. The
permissible stress levels are to comply with Pt 4, Ch 5 Primary Hull Strength.
4.1.5 Where decks form watertight boundaries in damage stability conditions,
the minimum scantlings are not to be less than required for watertight bulkheads
given in Pt 4, Ch 6, 7 Bulkheads.
4.1.6 For units fitted with a pipe-laying system, process plant facility
and/or drilling equipment, the support stools and integrated hull support structure
to the pipe-laying system, process plant and other equipment supporting structures
to drilling derricks and flare structures, etc. are considered to be classification
items regardless of whether or not the pipe-laying system, process/drilling plant
facility is classed and the loadings are to be determined in accordance with Pt 3, Ch 8, 2 Structure. Permissible stress levels
are to comply with Pt 4, Ch 5 Primary Hull Strength.
4.2 Deck plating
4.2.1 The requirements are in general applicable to strength/weather deck
plating with stiffeners fitted parallel to the hull bending compressive stress. When
other stiffening arrangements are proposed, the scantlings will be specially
considered, but the minimum requirements of Table 6.4.1 Deck plating are to be complied with.
4.2.3 The thickness of strength/weather deck plating is also to be that
necessary to satisfy the overall strength requirements of:
4.2.4 The deck plating thickness and supporting structure in way of towing
brackets, winches, masts, crane pedestals, davits and machinery items, etc., is to
be suitably reinforced, see also
Pt 4, Ch 6, 1 General requirements.
4.2.5 Where plated decks are sheathed with wood or approved compositions,
consideration will be given to allowing a reduction in the minimum plating thickness
given in Table 6.4.1 Deck plating.
4.3 Deck stiffening
4.3.1 The scantlings of deck stiffeners are to comply with the requirements of
Pt 4, Ch 6, 4.4 Deck supporting structure 4.4.2. Stiffeners fitted in way of
concentrated loads and heavy machinery items, etc., will be specially considered.
4.3.3 End connection of stiffeners to bulkheads are to provide adequate fixity
and, so far as practicable, direct continuity of primary strength. In general deck
stiffeners are to be continuous through primary support structure, including
bulkheads but alternative arrangements will be considered. The end connections of
stiffeners are in general to be in accordance with the requirements of Pt 4, Ch 8 Welding and Structural Details.
Table 6.4.1 Deck plating
Symbols
|
Location
|
Thickness, in mm,
see also
Pt 4, Ch 6, 4.2 Deck plating
|
b = breadth of increased plating, in mm
|
(1) Strength/weather
deck
|
t = 0,00083
but not less than (2)
|
f = 1,1 – but not to be taken greater than 1,0
|
See Notes 1 and 2
|
|
k = steel factor as defined in 2.1.2
|
|
s = spacing of deck stiffeners, in mm
|
(2) Lower decks
|
t = 0,012
but t + tc not less
than 7,0 mm
|
= s but is to be taken not less than
the smaller of:
|
|
470 + mm or 700 mm
|
(3) Platform decks
|
t = 0,01
but t + tc not less than
6,5 mm
|
= cross sectional area of girder face plate,
in cm2
|
L = length of unit, in metres, as defined in Pt 4, Ch 1, 5.1 General
|
(4) In way of
the crown or bottom of tanks
|
t = 0,004sf
|
S = spacing of primary members, in metres
|
or as (1),
(2) or (3) whichever is the greater but t +
tc not less than 7,5 mm
|
ρ, as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
(5) Plating
forming the upper flange of underdeck girders
|
t =
|
|
but not less
than required by (1), (2), (3) or (4) as appropriate to the
location of the plating Minimum breadth, b = 760 mm
|
NOTES
|
1. The thickness derived in accordance with (1) is
also to satisfy the buckling requirements of Pt 4, Ch 5 Primary Hull Strength.
|
2. On column-stabilised units when the primary deck
structure consists of box girders or equivalent structure and
the deck plating is considered as secondary structure only the
thickness of the plating will be specially considered but in no
case is the thickness to be less than 6,5 mm.
|
3. Where
the local deck loading exceeds 43,2 kN/m2(4,4
tonne-f/m2) the thickness of plating will be
specially considered.
|
4.4 Deck supporting structure
4.4.2 Transverses supporting deck longitudinals are, in general, to be spaced
not more than 3,8 m apart when the length, L, is 100 m or less, and
(0,006L + 3,2) m apart where L is greater than 100 m.
Table 6.4.2 Deck Stiffeners
Symbols
|
Location
|
Modulus, in
cm3
|
Inertia,
in cm4
|
= depth of stiffener, in mm, see Note 2
|
(1) Weather decks
|
Z = 4,5s k
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e1196.png)
2 x 10–3
|
––
|
= weather head, in metres
|
= work area head, in metres
|
(2) Work areas
|
Z = 4,5s k
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e1343.png)
2 x 10–3
|
––
|
= storage head, in metres
|
= tank head, in metres, as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
(3) Storage areas
|
Z = 4,5s k
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e1495.png)
2 x 10–3
|
––
|
= accommodation head, in metres
|
k = steel factor defined in Pt 4, Ch 2, 1.2 Steel
|
(4) Accommodation decks and
crew spaces
|
Z = 4,5s k
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e1620.png)
2 x 10–3
|
––
|
= span point, in metres as defined in Pt 4, Ch 3, 3.3 Determination of span point but not less than 1,5 m
|
s = spacing of stiffeners, in mm
|
(5) In way of the crown or
bottom of tanks
|
As (1), (2), (3) or (4)
as
applicable, or
whichever is the
greater
|
|
γ = 1,4 for rolled or built
sections
|
= 1,6 for flat bars
|
ρ as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
NOTES
|
1.
The load heads , , and are to be determined from the maximum design
uniform loadings and are not to be less than the minimum design load
heads given in Table 6.2.1 Design heads and permissible
deck loadings (SI units).
|
2. The web depth, , of stiffeners is to be not less than 60 mm.
|
Table 6.4.3 Deck girders, transversers and
deep beams
Location
and arrangements
|
Modulus,
in cm3
|
Inertia,
in cm4
|
(1) Girders and transverses in
way of dry spaces:
|
Z to be determined from calculations using stress
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e2169.png)
and assuming fixed ends
Z = 6,4 k S
|
|
(a) Supporting point
loads
|
(b) Supporting a uniformly
distributed load
|
(2) Deep beams supporting deck
girders in way of dry spaces:
|
Z to be determined from calculations using stress
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e2476.png)
and assuming fixed ends
Z = 6,4 k S
|
|
(a) Supporting point
loads
|
(b) Supporting a uniformly
distributed load
|
(3) Girders and transverses in way of the
crown or bottom of tanks
|
Z = 6,3ρk
|
|
Symbols
|
= tank head, in metres, as defined in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
k = steel factor as defined in Pt 4, Ch 2, 1.2 Steel
|
= span point, in metres, defined in Pt 4, Ch 3, 3.3 Determination of span point
|
= weather head or work area head or storage head or accommodation head , in metres, as defined in Table 6.2.1 Design heads and permissible
deck loadings (SI units) whichever
is applicable
|
S = spacing of primary members, in metres
|
ρ as defined
in Table 6.7.1 Watertight and deep tank
bulkhead scantlings
|
4.4.4 Where a girder is subject to concentrated loads, such as pillars out of
line, the scantlings are to be suitably increased. Also, where concentrations of
loading on one side of the girder may occur, the girder is to be adequately
stiffened against torsion.
4.4.6 Pillars are to be fitted in the same vertical line wherever possible,
and effective arrangements are to be made to distribute the load at the heads and
heels of all pillars. Where pillars support eccentric loads, they are to be
strengthened for the additional bending moment imposed upon them.
Table 6.4.4 Pillars
Symbols
|
Parameter
|
Requirement
|
b = breadth of side of a hollow rectangular pillar or breadth
of flange or web of a built or rolled section, in mm
|
(1) Cross-sectional area of
all types of pillar
|
|
= mean diameter of tubular pillars, in mm
|
See Note
|
k = local scantling higher tensile steel factor, see
Pt 4, Ch 2, 1.2 Steel 1.2.1, but not less than 0,72
|
(2) Minimum wall thickness of
tubular pillars
|
The greatest of the
following:
|
l = overall length of pillar, in metres
|
(a)
|
= effective length of pillar, in metres, and is
taken as 0,80l
|
(b) t = mm
|
(c) t = 5,5 mm where L < 90 m,
or
= 7,5 mm where L ≥ 90 m
|
r = least radius of gyration of pillar cross-section, in mm,
and may be taken as:
|
(3) Minimum wall
thickness of hollow rectangular pillars or web plate thickness of I
or channel sections
|
The lesser of the
following:
|
|
(a) t = mm
|
= cross-sectional area of pillar, in
cm2
|
(b) t = mm
|
but to be not less than
t = 5,5 mm where L < 90 m,
or
= 7,5 mm where L ≥ 90 m
|
as defined in Table 6.4.3 Deck girders, transversers and
deep beams
|
(4) Minimum
thickness of flanges of angle or channel sections
|
The lesser of the
following:
|
I = least moment of inertia of cross-section, in
cm4
|
(a) = mm
|
P = load, in kN (tonne-f), supported by the pillar and is to
be taken as: but not less than 19,62 kN (2 tonne-f)
|
(b) = mm
|
= load, in kN (tonne-f), from pillar or pillars
above (zero if no pillars over)
|
(5) Minimum
thickness of flanges of built or rolled I sections
|
The lesser of the
following:
|
= load, in kN (tonne-f), supported by pillar based
on
|
(a) = mm
|
(b) = mm
|
NOTE
|
As
a first approximation, may be taken as and the radius of gyration estimated for a
suitable section having this area.
|
If the area calculated using this radius of gyration
differs by more than 10 per cent from the first approximation, a
further calculation using the radius of gyration corresponding to
the mean area of the first and second approximation is to be
made.
|
4.4.7 Tubular and hollow square pillars are to be attached at their heads to
plates supported by efficient brackets, in order to transmit the load effectively.
Doubling or insert plates are to be fitted to decks under the heels of tubular or
hollow square pillars. The pillars are to have a bearing fit and are to be attached
to the head and heel plates by continuous welding. At the heads and heels of pillars
built of rolled sections, the load is to be well distributed by means of
longitudinal and transverse brackets.
4.4.8 Where pillars are not fitted directly above the intersection of
bulkheads, equivalent arrangements are to be provided.
4.4.9 In double bottoms where pillars are not directly above the intersection
of the plate floors and girders, partial floors and intercostals are to be fitted as
necessary to support the pillars. Manholes are not to be cut in floors and girders
below the heels of pillars.
4.4.10 Where pillars are fitted inside tanks or under watertight flats, the
tensile stress in the pillar and its end connections is not to exceed 108
N/mm2 (11,0 kgf/mm2) at the test heads. In general, such
pillars should be of built sections, and end brackets may be required.
4.4.11 Pillars or equivalent structures are to be fitted below deckhouses,
machinery items, winches, etc., and elsewhere where considered necessary.
4.4.12 The thickness of primary longitudinal and transverse bulkheads supporting
decks is to satisfy the requirements for the overall strength of the unit in
accordance with:
When the bulkheads are to be watertight the scantlings are also to
comply with the requirements of Pt 4, Ch 6, 7 Bulkheads.
4.4.14 When openings are cut in the primary longitudinal and transverse
bulkheads the openings are to have well rounded corners and full compensation is to
be provided. All openings are to be adequately framed.
4.5 Deck openings
4.5.2 All openings are to be adequately framed. Attention is to be paid to
structural continuity, and abrupt changes of shape, section or plate thickness are
to be avoided.
4.5.3 Arrangements in way of corners and openings are to be such as to minimise
the creation of stress concentrations. Openings in highly stressed areas of decks,
having a stress concentration factor in excess of 2,4, will require edge
reinforcements in the form of a spigot of adequate dimensions, but alternative
arrangements will be considered. The area of any edge reinforcement which may be
required is not to be taken into account in determining the required sectional area
of compensation for the opening
4.5.4 When large openings are cut in highly stressed areas of decks, the
corners of the openings are to be elliptical, parabolic or rounded, with a radius
generally not less than 1/24 of the breadth of the opening. The minimum radius for
large openings is to be 150 mm, provided the inner edge of the plating is stiffened
by means of a coaming or spigot. Where the inner edge is unstiffened, the minimum
radius is to be 300 mm.
4.5.5 Where the corners of large openings are rounded, the deck plating
thickness is to be increased at the corners of the openings.
4.5.6 Compensation will be required for deck openings cut in highly stressed
areas.
4.5.7 All openings which are required to be made watertight or weathertight are
to have closing appliances in accordance with the requirements of Chapter 7.
Table 6.4.5 Non-watertight pillar
bulkheads
Symbols
|
Parameter
|
Requiremet
|
, , b, c as defined in Pt 4, Ch 3, 3.2 Geometric properties of section
r = radius of gyration, in mm, of
stiffener and attached plating
= 10 mm for rolled, built
or swedged stiffeners
= for symmetrical corrugation
s = spacing of stiffeners, in mm
I = moment of inertia, in cm4,
of stiffener and attached plating
A = cross-sectional area, in
cm2, of stiffener and attached plating
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e5351.png)
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e5479.png)
As a first approximation may be taken as
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e5646.png)
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e5718.png)
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e5840.png)
As a first approximation may be taken as
![](svgobject/965F-4D2C-850C-8D7B1D70602D.xml_d2401021e6000.png)
P, as defined in Pt 4, Ch 6, 4.4 Deck supporting structure 4.4.6
λ =
|
(1) Minimum thickness of bulkhead
plating
|
5,5 mm
|
(2) Maximum stiffener spacing
|
1500 mm
|
(3) Minimum depth of stiffeners or
corrugations
|
75 mm
|
(4) Cross-sectional area
(including plating) for rolled, built or swedged stiffeners
supporting beams, longitudinals, girders or transverses
|
(a) Where ≤ 80
|
A =
|
|
(b) When ≥ 120
|
A =
|
|
(c) Where 80 < < 120
|
A is obtained by interpolation between and
|
(5) Cross-sectional area
(including plating) for symmetrical corrugation
|
(a) Where ≤
|
A =
|
|
(b) Where >
|
A =
|
|