Section 3 Topside structure and deck structure
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Inland Waterways Ships, July 2022 - Part 4 Ship Structures (Ship Types) - Chapter 2 Ferries and Roll on-Roll off Ships - Section 3 Topside structure and deck structure

Section 3 Topside structure and deck structure

Parent topic: Chapter 2 Ferries and Roll on-Roll off Ships

3.1 General

3.1.1 The topside structure for ships of a structural configuration according to Figure 2.1.2 Configuration of a single deck hull with a long wide hatch opening, a double bottom and double skin side construction is to comply with Pt 4, Ch 1, 4 Deck plating and continuous longitudinal hatch side coamings .

3.1.2 Where a ship has a structural configuration according to Figure 2.1.1 Configuration with single flush deck or a multi-deck hull with a single or double bottom arrangement and a single skin side construction, the deck plating and deck supporting structure is to comply with the requirements of Table 2.3.1 Deck plating and sheerstrake and Table 2.3.2 Deck supporting structure respectively, but in ships over 65 m in length, the thickness of deck plating may require to be increased to obtain the midship section modulus as required in Pt 3, Ch 4 Longitudinal Strength.

Table 2.3.1 Deck plating and sheerstrake

Item and Parameter Longitudinal framing Transverse framing
(1) Deck plating Thickness The greater of:

mm

mm

See Note 2 in Table 2.3.2 Deck supporting structure

The greater of:

mm

mm

See Note 2 in Table 2.3.2 Deck supporting structure

(2) Sheerstrake thickness and width As required by Table 1.5.1 Shell envelope plating in Ch 1,1, see Note

Note For ships having a length L less than 40 m the sheerstrake may be replaced by the normal side shell plating, provided a suitable doubler plate or half round pipe is fitted in way.

Table 2.3.2 Deck supporting structure

Item Parameter Requirements
(1) Deck beams Modulus Z = 4,3h1 ksle 2 + 4 cm3
(2) Deck longitudinals Modulus Z = (1,45 + 0,07L1)h1 ksSle 2 cm3
(3) Deck girders Modulus Z = (1,35 + 0,085L 1) h 1kS le 2 cm3
Inertia I = le Z cm4
(4) Deck transverses Modulus Z = 4,75h1 kSle 2 cm3
(5) Pillars Cross- sectional area A p =
Minimal wall thickness of hollow pillars

The greater of:

(a) t = 0,033d p mm for tubular pillars

t = 0,056b mm for square pillars

(b) t = 5 mm

Symbols applying to Table 2.3.1 Deck plating and sheerstrake and Table 2.3.2 Deck supporting structure
L, B, D, S, s, le, Z, I, k and t are as defined in Pt 4, Ch 2, 1.5 Symbols and definitions 1.5.1
a 1 = total area of deck longitudinals, in cm2
b = breadth of side of a hollow rectangular pillar, in mm
d p = mean diameter of tubular pillars, in mm
h 1 = head on deck, in metres, as defined in Pt 3, Ch 3, 4 Design loading
l = overall length of pillar, in metres
r = least radius of gyration of pillar cross-section, in mm, and may be taken as:
r =
A p = cross-sectional area of pillar, in cm2
C 1 = where is the ratio of the unstiffened deck panel under consideration
Ip = least moment of inertia of cross-section, in cm4
L 1 = L, but is to be not less than 40 m, nor more than 100 m
M = the greater of MS and MH
MH = maximum design hogging moment, in tm, see Pt 3, Ch 4 Longitudinal Strength
MS = maximum design hogging moment, in tm, see Pt 3, Ch 4 Longitudinal Strength
P = load supported by the pillar, in tonne-f

Note 1 The deck structure is also to comply with the requirements of Pt 3, Ch 9, 2 Decks loaded by wheeled vehicles for the parts of the deck used by wheeled vehicles.

Note 2 Where the head, in metres, h 1, exceeds 3,5 m this thickness is to be increased by the factor:

3.1.3 The parts of the deck used by wheeled vehicles are also to comply with the requirements of Pt 3, Ch 9, 2 Decks loaded by wheeled vehicles.

3.2 Deck plating

3.2.1 Where hatch openings are made in the deck plating, compensation will be required for the material cut out. However, no compensation need be fitted if the loss of sectional area has already been taken into consideration in calculating the actual midship hull section modulus. Plate panels, in which openings are cut, are where necessary, to be adequately stiffened against compression.

3.3 Deck supporting structure

3.3.1 Scantlings given in Table 2.3.2 Deck supporting structure are based on end connections in accordance with Pt 3, Ch 10, 3 Secondary member end connections. Where brackets having arm lengths differing from the standard are fitted, the modulus of the stiffening member is to be corrected in accordance with Pt 3, Ch 10, 3.7 Correction of stiffening member modulus in relation to end connections.

3.3.2 Deck girders and transverses may be fitted in conjunction with load-bearing bulkheads or pillars for support of deck beams and deck longitudinals. Where tracked vehicles are proposed, girders are to be fitted under the trackways.

3.3.3 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.

3.4 Sheerstrakes

3.4.1 The sheerstrake is to comply with the requirements of Table 2.3.1 Deck plating and sheerstrake.

3.5 Truss arrangements

3.5.1 Truss arrangements comprising top and bottom girders or transverses in association with pillars and diagonal bracing, may be fitted to support the bottom and deck structure. The diagonal members are generally to have angles of inclination with the horizontal of 45° and a cross-sectional area of not less than 50 per cent of the adjacent pillar.

3.6 Vehicle ramps

3.6.1 The strength of ramps forming an integral part of the ship’s structure, and of ramps used as watertight means of closing, is to be equivalent to the surrounding ship’s structure. The strength of the ramps is also to be verified for vehicle loading and to comply with Pt 3, Ch 9, 2 Decks loaded by wheeled vehicles.

3.6.2 Where hinges are provided for support of ramps, the ship’s structure in way is to be suitably reinforced.

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