7.1.2　Sandwich construction

　

In general the outer and inner skins shall be similar in lay-up and in strength and elastic properties, each with similar tensile and compressive strengths and moduli. Special consideration has to be given where this is not the case.

In general the sandwich area of the hull forward of 0.5 ・ L_wl shall be supported by one longitudinal stringer or an alternative arrangement.

　

7.1.2.1　Section moduli

　

　

where

b is the shorter edge of plate panel, in millimetres;

l is the longer edge of plate panel, in millimetres;

P_r is the applicable design pressure, kN/m².

k₁ see 6.1, table 5;

k₂ is the coefficient, panel aspect ratio, for bending strength (see 7.1 .1 , table 6);

k₃ is the coefficient, panel aspect ratio, for bending stiffness (see 7.1 .1 , Table 6):

E_F is the flexural modulus, FRP single skin laminate;

σ_at is the design stress, outer skin, for FRP (see clause 6). N/mm².

σ_ac is the design stress, for FRP (see clause 6), N/mm2.

E_TC is the mean of tensile and compressive moduli for inner and outer skins of sandwich, N/mm²

f_k correction factor for curvature (see table 7)

　

7.1.2.2　Core shear strength

　

　

where

d_o is the overall thickness of sandwich excluding gel coat, in millimetres;

d_c is the thickness of core, in millimetres;

ν is the coefficient varying with plate panel aspect ratio. Where the elastic properties of the skins are different in the principal axes, v is to be taken not less than 0,5;

P is the design pressure, kN/m², as given in Clause 5, except that A_d shall be taken not less than b² and kar not less than 0,4;

τa is the design shear stress (see 6.1.3), N/mm² ;

b is the smaller side of the panel, in millimetres.

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