Section 1 General

1.1.1 The guidance notes, information and formulae contained within this Chapter are to be used when calculating the global strength requirements (Vol 1, Pt 6, Ch 3 Global Strength Requirements) and the required scantlings due to local loads (Vol 1, Pt 6, Ch 4 Local Scantling Requirements).

1.2.1 Where plating thicknesses as determined by the Rules require to be rounded then this is to be carried out to the nearest full or half millimetre, with thicknesses 0,75 and 0,25 being rounded up.

1.3.1 The basic grade of steel used in the determination of the Rule scantling requirements is taken as mild steel with the following mechanical properties:

1. Yield strength (minimum), σ_yd = 235 N/mm²

2. Tensile strength, σ_u = 400 – 490 N/mm²

3. Modulus of elasticity, E = 200 x 10³ N/mm².

1.4.1 Steels having a yield stress not less than 265 N/mm² are to be regarded as higher tensile steels.

1.4.2 Where higher tensile steels are to be used, due allowance is given in the determination of the Rule requirement for plating thickness, stiffener section modulus, inertia and cross-sectional area by the use of higher tensile steel correction factors k _l and k _g or f _hts

where

k l	=
k g	=
f hts	=	is as follows:

σyd	fhts
235	1,00
265	0,964
315	0,956
355	0,919
>390	0,886

1.4.3 Normally, this allowance is included in the appropriate scantling requirements. Where this is not the case, the following correction factors may be applied:

1. Plating thickness factor

2. Plating thickness factorSection modulus and cross sectional area factor = k _l.

1.4.4 The designer should note that there is no increase in fatigue performance with the use of higher tensile steels.

1.4.5 Local scantlings which are to be calculated according to the Complementary Rules are to use the high tensile steel factor as defined in the Complementary Rules. This local factor, having the same values as in the Trimaran Rules, is named as follows in the Complementary Rules: