Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 10 Other Structures - Section 1 Fore Part - 2 Structural Arrangement
2 Structural Arrangement
2.1 Floors and bottom girders
2.1.1 Floors
In case of transverse framing, solid floors are to be fitted at each web frame location.
In case of longitudinal framing, the spacing of solid floors is not to be greater than 3.5 m or four transverse frame spaces, whichever is smaller.
The minimum depth of the floor at the centreline is not to be less than the required depth of the double bottom of the foremost cargo hold. See Ch 2, Sec 3, [2.3].
2.1.2 Bottom girders
A supporting structure is to be provided at the centreline either by extending the centreline girder to the stem or by providing a deep girder or centreline bulkhead.
Where a centreline girder is fitted, the minimum depth and thickness is not to be less than that required for the depth of the double bottom in the neighbouring cargo hold region, and the upper edge is to be stiffened.
In case of transverse framing, the spacing of bottom girders is not to exceed 2.5 m.
In case of longitudinal framing, the spacing of bottom girders is not to exceed 3.5 m.
2.1.3 Alternative design verification
This spacing, defined in [2.1.1] and [2.1.2] may be increased, if the designer performs a verification of the bottom structure by means of grillage analysis or FE analysis and provides their full documentation. The acceptance criteria to be applied are defined in Ch 6, Sec 6, [3]. A FE analysis is to be performed under consideration of the requirements provided in Ch 7.
2.2 Wash bulkheads
2.2.1
Where a centreline wash bulkhead is fitted, the lowest strake is to have thickness not less than required for a centreline girder.
Where a longitudinal wash bulkhead supports bottom transverses, the details and arrangements of openings in the bulkhead are to be configured to avoid areas of high stresses in way of the connection of the wash bulkhead with bottom transverses.
2.3 Side shell supporting structure
2.3.1 Web frames
The spacing of web frames, S, in m as defined in Ch 1, Sec 4, Table 5, is to be taken as:
S = 2.6 + 0.005 L, but not to be taken greater than 3.5 m.
Perforated flats are to be fitted to limit the effective span of web frames to not greater than 10 m.
2.3.2 Stringers
The transverse framing forward of the collision bulkhead stringers are to be spaced approximately 3.5 m apart. Stringers are to have an effective span not greater than 10 m, and are to be adequately supported by web frame structures.
2.3.3 Alternative design verification
The spacing of web frames and stringers may be increased, if the designer performs a verification of the side shell supporting structure by means of beam analysis or FE analysis and provides their full documentation. The acceptance criteria to be applied are defined in Ch 6, Sec 6, [3]. A FE analysis is to be performed under consideration of the requirements provided in Ch 7.
2.4 Tripping brackets
2.4.1
For side shell and tank walls, located forward of the collision bulkhead and vertically framed, tripping brackets spaced not more than 2.6 m are to be fitted, according to Figure 1, between primary supporting members, decks and/or platforms.
The as-built thickness of the tripping brackets is not to be less than the as-built thickness of the side frame webs to which they are connected.
Figure 1 : Tripping brackets
2.5 Bulbous bow
2.5.1 General
Where a bulbous bow is fitted, the structural arrangements are to be such that the bulb is adequately supported and integrated into the fore peak structure.
2.5.2 Diaphragm plates
At the forward end of the bulb the structure is generally to be supported by horizontal diaphragm plates spaced about 1m apart in conjunction with a deep centreline web. In general, vertical transverse diaphragm plates are to be arranged in way of the transition from the peak framing to the bulb framing.
2.5.3 Special bulbous bow designs
In way of a wide bulb, additional strengthening in the form of a centreline wash bulkhead is generally to be fitted. In way of a long bulb, additional strengthening in the form of transverse wash bulkheads or substantial web frames is to be fitted.
2.5.4 Strengthening for anchor and chain cable contact
The shell plating is to be increased in thickness at the forward end of the bulb and also in areas likely to be subjected to contact with anchors and chain cables during anchor handling. The increased plate thickness is to be the same as that required for plated stems given in [4.1.1].
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