Section 9 Superstructures and deck-houses

9.1 General

9.1.1 The term ‘erection’ is used in this Section to include both superstructures and deckhouses.

9.1.2 Erections are to comply with

Pt 4, Ch 4 Structural Unit Types for surface-type units other than ship units.
This Section for other unit types.

9.1.3 The scantlings of exposed bulkheads and decks of deckhouses are generally to comply with the requirements of this Section, but increased scantlings may be required where the structure is subjected to local loadings greater than those defined in the Rules, see also Pt 4, Ch 6, 9.1 General 9.1.6. Where there is no access from inside the house to below the freeboard deck or into buoyant spaces included in stability calculations, or where a bulkhead is in a particularly sheltered location, the scantlings may be specially considered.

9.1.4 The scantlings of superstructures which form an extension of the side shell or which form an integral part of the unit’s hull and contribute to the overall strength of the unit will be specially considered. The upper hull structure of column-stabilised units are to comply with Pt 4, Ch 6, 3 Watertight shell boundaries.

9.1.5 Any exposed part of an erection which may be subject to immersion in damage stability conditions and which could result in down flooding is to have scantlings not less than required for watertight bulkheads given in Pt 4, Ch 6, 7 Bulkheads.

9.1.6 The boundary bulkheads of accommodation spaces which may be subjected to blast loading are to comply with Pt 4, Ch 3, 4 Structural design loads and permissible stress levels are to satisfy the factors of safety given in Table 5.2.1 Factors of safety for the combined load cases – load case (d) in Pt 4, Ch 5, 2 Permissible stresses.

9.1.7 The scantlings of erections used for helicopter landing areas are also to comply with Pt 4, Ch 6, 5 Helicopter landing areas.

9.1.8 For requirements relating to companionways, doors and hatches, see Pt 4, Ch 7 Watertight and Weathertight Integrity and Load Lines.

9.2 Symbols

9.2.1 The following symbols and definitions are applicable to this Chapter, unless otherwise stated:

L, B, and as defined in Pt 4, Ch 1, 5.1 General.

breadth of deckhouse, at the positions under consideration, in metres

higher tensile steel factor, see Pt 4, Ch 2, 1.2 Steel

effective length, in metres, of the stiffening member, deck beam or longitudinal measured between span points, see Pt 4, Ch 3, 3.3 Determination of span point

span, in metres, of erection stiffeners and is to be taken as the ‘tween deck or house height but in no case less than 2,0 m

spacing of stiffeners, beams or longitudinals, in mm

standard spacing, in mm, of stiffeners, beams or longitudinals, and is to be taken as:

for 0,05L from the ends:
= 610 mm or that required by Pt 4, Ch 6, 9.2 Symbols 9.2.1.(b), whichever is the lesser
elsewhere:
= 470 + 1,67mm but forward of 0,2L from the forward perpendicular is not to exceed 700 mm

actual breadth of unit at the section under consideration, measured at the weather deck, in metres

Rule length, L, but need not be taken greater than 250 m

Rule length, L, but need not be taken greater than 300 m

moulded depth of unit, in metres, to the uppermost continuous deck

distance, in metres, between the after perpendicular and the bulkhead under consideration. When determining the scantlings of deckhouse sides, the deckhouse is to be subdivided into parts of approximately equal length not exceeding 0,15L each, and X is to be measured to the mid-length of each part

a coefficient given in Table 6.9.1 Values of α

β	=	1,0 + for ≤ 0,45
β	=	1,0 + 1,5 for ≤ 0,45

is to be taken not less than 0,6 nor greater than 0,8. Where the aft end of an erection is forward of amidships, the value of used for determining β for the aft end bulkhead is to be taken as 0,8

vertical distance, in metres, from the maximum transit waterline to the mid-point of span of the bulkhead stiffener, or the mid-point of the plate panel, as appropriate

1,0 for exposed machinery casings and

elsewhere, but in no case to

be taken less than 0,475

a coefficient given in Pt 4, Ch 6, 9.2 Symbols 9.2.1.

Table 6.9.1 Values of α

Position	α
Lowest tier – unprotected front	2,0 + 0,0083
Second tier – unprotected front	1,0 + 0,0083
Third tier and above – unprotected front	0,5 + 0,0067
All tiers – protected fronts
All tiers – sides
All tiers – aft end where aft of amidships	0,7 + 0,001 – 0,8
All tiers – aft end where forward of amidships	0,5 + 0,001 – 0,4

Table 6.9.2 Values of λ

Length L in metres	λ	Expression for λ
20	0,89	L ≤ 150 m
30	1,76
40	2,57
50	3,34
60	4,07
70	4,76
80	5,41
90	6,03
110	7,16
130	8,18
150	9,10
150	9,10	150 m ≤ L ≤ 300 m
170	9,65
190	10,08
210	10,43
230	10,69
250	10,86
270	10,98
290	11,03
300	11,03
300		L ≥ 300 m
and above	11,03	λ = 11,03

9.3 Definition of tiers

9.3.1 The first, or the lowest tier, is an erection situated on the deck to which D is measured. The second tier is the next tier above the lowest tier, and so on.

9.3.2 For ship units and self-elevating units where the freeboard corresponding to the required summer moulded draught for the unit can be obtained by considering the unit to have a virtual moulded depth of at least one standard superstructure height less than the Rule depth, D, measured to the uppermost continuous deck, proposals to treat the first tier erection as a second tier, and so on, will be specially considered. The standard height of superstructure is the height defined in the International Convention on Load Lines, 1966.

9.4 Design pressure head

9.4.1 The design pressure head, h, to be used in the determination of erection scantlings is to be taken as:

α δ (β λ – γ) m

9.4.2 In no case is the design pressure head to be taken as less than the following:

Lowest tier of unprotected fronts:
minimum h = 2,5 + 0,01 m
All other locations:
minimum h = 1,25 + 0,005 m

9.5 Bulkhead plating and stiffeners

9.5.1 The plating thickness, t, of fronts, sides and aft ends of all erections other than the sides of the superstructures where these are an extension of the side shell, is not to be less than:

0,003s

mm,

but in no case is the thickness to be less than:

for the lowest tier:
t = (5,0 + 0,01) mm,

but t + t_c not less than 5,0 mm.
for the upper tiers:
t = (4,0 + 0,01) mm,

but t + t_c not less than 5,0 mm.

9.5.2 The thickness of sides of forecastles, bridges and poops is to be as required by Pt 4, Ch 4, 4 Surface type units.

9.5.3 The modulus of stiffeners, Z, on fronts, sides and end bulkheads of all erections, other than the sides of superstructures where these are an extension of the side shell, is to be not less than:

0,0035h s

k cm³

9.5.4 The end connections of stiffeners are to be as given in Table 6.9.3 Stiffener end connections.

9.5.5 The section modulus of side frames of forecastles, bridges and poops is to be as required by Pt 4, Ch 4, 4 Surface type units.

Table 6.9.3 Stiffener end connections

Position	Attachment at top and bottom
1. Front stiffeners of lower tiers and of upper tiers when L is 160 m or greater	See Pt 4, Ch 8 Welding and Structural Details See Note
2. Front stiffeners of upper tiers when L is less than 160 m	May be unattached
3. Side stiffeners of lower tiers where two or more tiers are fitted	Bracketed, unless stiffener modulus is increased by 20 per cent and ends are welded to the deck all round
4. Side stiffeners if only one tier is fitted, and aft end stiffeners of after deckhouses on deck to which D is measured	See Pt 4, Ch 8 Welding and Structural Details
5. Side stiffeners of upper tiers where L is 160 m or greater	See Pt 4, Ch 8 Welding and Structural Details
6. Side stiffeners of upper tiers when L is less than 160 m	May be unattached
7. Aft end stiffeners except as covered by item 4	May be unattached
8. Exposed machinery and pump-room casings. Front sitffeners on amid-ship casings and all stiffeners on aft end casings which are situated on the deck to which D is measured	Bracketed
9. All other stiffeners on exposed machinery and pump-room casings	6,5 cm² of weld
NOTE
Front stiffeners of lower tiers on self-elevating units are to be bracketed.

9.6 Erections on self-elevating units

9.6.1 The scantlings of exposed ends and sides of erections are to comply with 9,5, but the additional requirements of this sub-Section are to be complied with.

9.6.2 The plating thickness, t, of exposed lower tier fronts is to be not less than:

0,0036s

but in no case is the gross thickness t + t_c to be less than 7,0 mm.

9.6.3 The modulus of stiffeners, Z, on exposed lowest tier fronts is to be not less than:

0,0044h s

k cm³

9.6.4 Where the exposed side of an erection is close to the side shell of the unit, the scantlings may be required to conform to the requirements for exposed bulkheads of unprotected house fronts.

9.6.5 The scantlings of jackhouses will be specially considered, but are not to be less than the scantlings that would be required for an erection at the same location.

9.6.6 The end connections of stiffeners are to be as given in Table 6.9.3 Stiffener end connections .

9.7 Erections on other unit types

9.7.1 Where the erection can be subjected to wave forces, the scantlings of exposed ends and sides of erections are to comply with Pt 4, Ch 6, 9.5 Bulkhead plating and stiffeners.

9.7.2 When the erection is not subjected to wave forces in any condition then the structure is to be suitable for the maximum design loadings but the minimum scantlings of exposed sides and ends of all erections is to be not less than:

for the lowest tier:
t = (5,0 + 0,01L) mm, but not t + t_c less than 5,0 mm.
for the upper tiers:
t = (4,0 + 0,01L) mm, but not t + t_c less than 5,0 mm.

9.7.3 The modulus of stiffeners, Z, of exposed sides and ends of all erections is to be not less than:

0,0035h s

k cm³

where

1,25 + 0,005L m.

9.7.4 The end connections of stiffeners not subjected to wave loadings are to be as given in Table 6.9.4 Other unit types stiffener end connections.

Table 6.9.4 Other unit types stiffener end connections

Position	Attachment at top and bottom
1. Side stiffeners of lower tiers where two or more tiers are fitted	Bracketed unless stiffener modulus is increased by 20 per cent and ends are welded to the deck all around
2. Side stiffeners if only one tier is fitted	See Pt 4, Ch 8 Welding and Structural Details
3. All other stiffeners	May be unattached

9.8 Deck plating

9.8.1 In general, the thickness of erection deck plating is to be not less than that required by Table 6.9.5 Thickness of deck plating.

9.8.2 For erections not subjected to wave forces in any condition, the thickness of erection deck plating for all tiers need not exceed the requirements given in Table 6.9.5 Thickness of deck plating for third tier erections, using:

470 + 1,67

Table 6.9.5 Thickness of deck plating

Position	Thickness of deck plating, in mm
	L ≤ 100 m		L > 100 m
Top of first tier erection	(5,5 + 0,02L)	but not less than 5,0 mm	7,5
Top of second tier erection	(5,0 + 0,02L)		7,0
Top of third tier and above	(4,5 + 0,02L)		6,5
NOTE
For units not subjected to wave loading, see Pt 4, Ch 6, 9.8 Deck plating 9.8.2.

9.8.3 When decks are fitted with approved sheathing, the net thickness derived from Table 6.9.5 Thickness of deck plating may be reduced by 10 per cent for a 50 mm sheathing thickness, or five per cent for 25 mm, with intermediate values in proportion. The steel deck is to be coated with a suitable material in order to prevent corrosive action, and the sheathing or composition is to be effectively secured to the deck. Inside erections the net thickness may be reduced by a further 10 per cent. In no case is the deck gross thickness to be less than 5,0 mm.

9.8.4 The thickness, t, of forecastle deck plating is to be not less than:

(6 + 0,017L)

mm.

9.9 Deck stiffening

9.9.1 The requirements for deck stiffeners in this sub- Section are applicable to both beams and longitudinals.

9.9.2 Deck stiffeners on deckhouses are to have a section modulus, Z, not less than:

0,0048

k cm³, but in no case less than:

0,025s cm³

where the load head, h6, is to be taken as not less than:

on first tier decks	0,9 m
on second tier	0,6 m
on third tier decks and above	0,45 m

but where the deck can be subjected to weather loading, the load, h₆ , is to be increased in accordance with the requirements given in Pt 4, Ch 6, 2.3 Stowage rate and design heads 2.3.2.

9.9.3 When deckhouses are subjected to specified deck loadings greater than the heads defined in Pt 4, Ch 6, 9.9 Deck stiffening 9.9.2 or are subjected to concentrated loads, equivalent load heads are to be used, see Pt 4, Ch 6, 9.9 Deck stiffening 9.9.2 or Pt 4, Ch 6, 9.9 Deck stiffening 9.9.3.

9.9.4 The section modulus of deck stiffeners on forecastles, bridges and poops is to be as required by Pt 4, Ch 4, 4 Surface type units.

9.10 Deck girders and transverse

9.10.1 The scantlings of deck girders and transverses on erection decks are to be in accordance with the requirements of Table 6.2.1 Design heads and permissible deck loadings (SI units), using the appropriate load head, , determined from Pt 4, Ch 6, 9.9 Deck stiffening 9.9.2 or Pt 4, Ch 6, 9.9 Deck stiffening 9.9.3.

9.11 Strengthening at ends and sides of erections

9.11.1 Web frames or equivalent strengthening are to be arranged to support the sides and ends of large erections.

9.11.2 These web frames should be spaced about 9 m apart and are to be arranged, where practicable, in line with watertight bulkheads below. Webs are also to be arranged in way of large openings, boats davits and other points of high loading.

9.11.3 Arrangements are to be made to minimise the effect of discontinuities in erections. All openings cut in the sides are to be substantially framed and have well rounded corners. Continuous coamings or girders are to be fitted below and above doors and similar openings. Erections are to be strengthened in way of davits.

9.11.4 Adequate support under the ends of erections is to be provided in the form of webs, pillars, diaphragms or bulkheads in conjunction with reinforced deck beams.

9.11.5 At the corners of deckhouses and in way of supporting structures, attention is to be given to the connection to the deck, and doublers or equivalent arrangements should generally be fitted.

9.12 Unusual designs

9.12.1 Where superstructures or deckhouses are of unusual design, the strength is to be not less than that required by this Section for a conventional design.

9.13 Aluminium erections

9.13.1 Where an aluminium alloy complying with Ch 8 Aluminium Alloys of the Rules for Materials is used in the construction of erections, the scantlings of these erections are to be increased (relative to those required for steel construction) by the percentages given in Table 6.9.6 Percentage increase of scantlings.

9.13.2 The thickness, t, of aluminium alloy members is to be not less than:

2,5 + 0,022

mm but t + t_c need not exceed 10 mm

where

depth of the section, in mm.

9.13.3 The minimum moment of inertia, I, of aluminium alloy stiffening members is to be not less than:

5,25Z l cm⁴

where l is the effective length of the member

, in metres, as defined in Pt 4, Ch 6, 9.2 Symbols and Z is the section modulus of the stiffener and attached plating in accordance with Pt 4, Ch 6, 9.4 Design pressure head and Pt 4, Ch 6, 9.9 Deck stiffening, taking k as 1.

Table 6.9.6 Percentage increase of scantlings

Item	Percentage increase
Fronts, sides, aft ends, unsheathed deck plating	20
Decks sheathed in accordance with Pt 4, Ch 6, 9.8 Deck plating 9.8.3	10
Deck sheathed with wood, and on which the plating is fixed to the wood sheathing at the centre of each beam space	Nil
Stiffeners and beams	70
Scantlings of small isolated houses	Nil

9.13.4 Where aluminium erections are arranged above a steel hull, details of the arrangements in way of the bimetallic connections are to be submitted.

9.13.5 For aluminium alloy helicopter decks, see Pt 4, Ch 6, 6 Decks loaded by wheeled vehicles.

9.14 Fire protection

9.14.1 Fire protection of aluminium alloy erections is to be in accordance with the fire safety Regulations of the appropriate National Administration, see Pt 7, Ch 3 Fire Safety.

9.14.2 Where it is proposed to use aluminium alloy for items or equipment in hazardous areas, incendive sparking may constitute a risk and full details are to be submitted for consideration.