Section 4 Panel scantling requirements

4.1.1 The requirements of this Section are applicable to steel sandwich panel construction, except for bulkheads and decks loaded by wheeled vehicles where Ch 3, 2 Panel scantling requirements – bulkheads and Ch 3, 3 Panel scantling requirements – decks loaded by wheeled vehicles is applicable respectively.

4.2.1 In this Section the scantling requirements for the top and bottom plates and core of steel sandwich panels are given.

4.2.2 The thickness of the top and bottom plates of the steel sandwich panels may, in addition, need to be increased to meet the hull girder requirements.

4.3.1 The scantlings of the steel sandwich panels are to taper gradually from the midship region to the fore and aft ends, see Pt 3, Ch 3, 2.5 Taper requirements for hull envelope of the Rules and Regulations for the Classification of Ships, July 2022. Where it is proposed to taper from steel sandwich panel construction to single steel construction the rule thickness should be used as the basis for the tapering (t_c = t_rule ), see Ch 3, 4.4 Thickness of sandwich panel 4.4.3 for the calculation of t_rule.

4.3.2 Changes in steel sandwich thickness are to be made using a gradual taper.

4.3.3 Where the construction changes from steel sandwich panel to a single steel plate construction a taper of not less than 4:1 is to be adopted and additional stiffening may be required.

4.4.1 The thickness of the top and bottom plates and core of the steel sandwich panel is to be determined, as shown in Figure 3.4.1 Determination of equivalent scantlings t_rule and Z_rule and in the following paragraphs, on the basis of the equivalent scantlings given in the Rules and Regulations for the Classification of Ships, July 2022 (t_rule and Z_rule).

Figure 3.4.1 Determination of equivalent scantlings t_rule and Z_rule

4.4.2 The top and bottom plate thickness, t₁ and t₂, of the steel sandwich are to be determined as shown in Figure 3.4.2 Determination of top and bottom plate thickness and core thickness. In no case are the thickness of the top and bottom plating and the core thickness to be less than the minimum values given in Ch 3, 6 Minimum thickness.

Figure 3.4.2 Determination of top and bottom plate thickness and core thickness

4.4.3 The equivalent rule thickness, t_rule, is to be calculated in accordance with the appropriate chapter for the particular ship type. For example, the equivalent rule thickness t_rule, for the bottom shell of a general cargo ship is to be calculated from Table 1.5.2 Bottom shell and bilge plating of the Rules and Regulations for the Classification of Ships, July 2022.

1. The equivalent rule thickness of the inner bottom plating is to be calculated from Pt 4, Ch 1, 8.4 Inner bottom plating and stiffening 8.4.1 or Table 7.8.1 Strengthening for heavy cargo requirements Item (3)(b) as appropriate and does not include the additions for the protection of steelwork.

4.4.4 The equivalent section modulus, Z_rule, of secondary member is to be calculated in accordance with the appropriate chapter for the particular ship type. For example, the equivalent section modulus for the bottom shell longitudinals of a general cargo ship is to be calculated from Table 1.6.1 Shell framing (longitudinal) in Pt 4, Ch 1, 6 Shell envelope framing of the Rules and Regulations for the Classification of Ships, July 2022.

4.4.5 In the calculation of t_rule and Z_rule the material factor is always to be taken as k = 1 and the spacing is always to be taken as s = 700 mm.

4.5.1 The steel sandwich panel is to be dimensioned in accordance with the strength index, R, given below. This will ensure that the steel sandwich panel is equivalent to a conventional steel construction:

where

AR	=
Peq,R	=	0,0017 in N/mm2
l	=	length of panel, in metres
Zrule	=	equivalent section modulus, in cm3, see Ch 3, 4.4 Thickness of sandwich panel 4.4.4
tc	=	selected core thickness, in mm
a, b, d	=	see Ch 1, 7.2 Symbols 7.2.1
t1, t2	=	thicknesses of the top and bottom plating, in mm, see Figure 3.4.2 Determination of top and bottom plate thickness and core thickness
k	=	see Pt 3, Ch 2, 1.2 Steel 1.2.3 of the Rules and Regulations for the Classification of Ships, July 2022.

4.5.2 The strength index for steel sandwich panel is to be such that:

1. R ≤ 1

4.6.1 The local thickness allowances for individual structural members are given in Table 3.4.1 Thickness allowance. Structural elements not listed in the table, and ships having non-typical structural configurations will be subjected to special consideration.

4.6.2 The thickness allowance is to be applied to the plate thickness in direct contact with the application in Table 3.4.1 Thickness allowance. For example the crown of a deep tank which also forms a vehicle deck would have t_a = 2,0 for the top plate and t_a = 2,5 for the bottom plate.

4.6.3 For the protection of steelwork, in addition to the requirements specified in Ch 3, 5 Overlay scantling requirements, any ship which is regularly to be discharged by grabs the thickness of the top plating is to be increased by the allowances given below. Inner bottom and hopper plating:

• Continuous wooden ceiling: 2,0 mm
• No continuous wooden ceiling: 3,7 mm