2 Plates

2.1 Idealisation of EPP

2.1.1 EPP

An elementary plate panel (EPP) is the unstiffened part of the plating between stiffeners and/or primary supporting members. The plate panel length, a, and breadth, b, of the EPP are defined respectively as the longest and shortest plate edges, as shown in Figure 17.

Figure 17 : Elementary Plate Panel (EPP) definition

2.1.2 Strake required thickness

The required thickness of a plate strake is to be taken as the greatest value required for each EPP within that strake. The requirements given in Table 3 are to be applied for the selection of strakes to be considered as shown in Figure 18.

The maximum corrosion addition within a strake is to be applied according to Ch 3, Sec 3, [1.2.4].

Table 3 : Strake considered in a given EPP

	a ⁄ b > 2	a ⁄ b ≤ 2
a₁ > b ⁄ 2	All strakes (St1, St2, St3, St4)	All strakes (St1, St2, St3, St4)
a₁ ≤ b ⁄ 2	Strakes St2 and St4	All strakes (St1, St2, St3, St4)

Figure 18 : Strake considered in a given EPP

where:

a₁ : Distance, in mm, measured inside the considered strake in the direction of the long edge of the EPP, between the strake boundary weld seam and the EPP edge.

2.1.3 For direct strength assessment, the EPP is idealised with the mesh arrangement in the finite element model.

2.2 Load calculation point

2.2.1 Yielding

For the yielding check, the local pressure and hull girder stress, used for the calculation of the local scantling requirements are to be taken at the Load Calculation Point (LCP) having coordinates x, y and z as defined in Table 4.

Table 4 : LCP coordinates for yielding

LCP coordinates	General ⁽¹⁾		Horizontal plating		Vertical transverse structure and transverse stool plating
	Longitudinal framing (Figure 19)	Transverse framing (Figure 20)	Longitudinal framing	Transverse framing	Horizontal framing (Figure 21)	Vertical framing (Figure 22)
x coordinate	Mid-length of the EPP		Mid-length of the EPP		Corresponding to y and z values
y coordinate	Corresponding to x and z coordinates		Outboard y value of the EPP		Outboard y value of the EPP, taken at z level⁽²⁾
z coordinate	Lower edge of the EPP	The greater of lower edge of the EPP or lower edge of the strake	Corresponding to x and y values		Lower edge of the EPP	The greater of lower edge of the EPP or lower edge of the strake
(1) All structures other than horizontal platings or vertical transverse structures.
(2) For transom plate, the y coordinate of the load calculation point is to be taken corresponding to y value at side shell at z level of the load calculation point, for the external dynamic pressure calculation.

Figure 19 : Load calculation point (LCP) for longitudinal framing

Figure 20 : Load calculation point for transverse framing

Figure 21 : Load calculation point for horizontal framing on transverse vertical structure

Figure 22 : Load calculation point for vertical framing on transverse vertical structure

2.2.2 Buckling

For the prescriptive buckling check of the EPP according to Ch 8, Sec 3, the LCP for the pressure and for the hull girder stresses are defined in Table 5.

For the FE buckling check, Ch 8, Sec 4 is applicable.

Table 5 : LCP coordinates for plate buckling

LCP coordinates	LCP for pressure	LCP for hull girder stresses (Figure 23)
		Bending stresses ⁽¹⁾		Shear stresses
		Non horizontal plate	Horizontal plate
x coordinate	Same coordinates as LCP for yielding See Table 4	Mid-length of the EPP
y coordinate		Corresponding to x and z values	Outboard and inboard ends of the EPP (points A1 and A2)	Mid-point of EPP (point B)
z coordinate		Both upper and lower ends of the EPP (points A1 and A2)	Corresponding to x and y values
(1) The bending stress for curved plate panel is the mean value of the stresses calculated at points A1 and A2.

Figure 23 : LCP for plate buckling – hull girder stresses