Knowing the relative slenderness ratio, the value of kcrit x characteristic bending strength can be derived by calculation or, for the softwood species of timber listed in BS EN338:2003 (E) [2], can be obtained from Table 4.4.

In Table 4.4, values of kcrit x characteristic bending strength are given for beams with relative slenderness ratios between 0.75 and 3.0, which should cover the range likely to be used in practical designs. For a strength class of timber, the reduced bending strength at a particular relative slenderness ratio is the value given in the column containing the material strength class, e.g. for a strength class C18 rectangular timber beam with a relative slenderness ratio of 2, the value of kcritx characteristic bending strength is 4.5 N/mm2. At intermediate values of relative slenderness ratio, the result is obtained

Table 4.4 The value of kcrit x characteristic bending strength tabulated against the relative slenderness ratio for bending, Xrel m, for all of the strength classes of softwood given in BS EN 338:2003 [E]

Strength class

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