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(a) General

(b) When determining the yield moment of the screw, account is taken of the reduced flexural strength due to the threaded part of the screw by using an effective diameter as follows:

(i) Smooth shank screws - where the outer threaded diameter (d) equals the shank diameter and the smooth shank penetrates the pointside member by not less than 4d

(ii) Where the conditions in (i) are not met

(a) The screw diameter (the shank/outer threaded diameter)

(b) (i) The effective diameter, def is the shank diameter d

(b) (ii) The effective diameter, def is 1.1 times the threaded root diameter

the elastic modulus of the fastener. This gave a lower bound strength value and in the subsequent development of his theory by other researchers the elasto-plastic strength has been used. This takes account of the amount of rotation at the failure state for different types of fastener; the tensile strength of the fastener, including the effect of strain hardening where relevant and of variation in material strength.

From these investigations the characteristic yield moment, My Rk, for the different types of metal fasteners referred to in EC5 is summarised in Table 10.5.

10.3.3 Characteristic embedment strength (fh)

The embedment strength of timber or a wood-based product, fh, is the average com-pressive strength of the timber or wood-based product under the action of a stiff straight dowel loaded as shown in Figure 10.7. For a piece of timber t (mm) thick, loaded with a nail d (mm) in diameter, under the maximum load able to be taken, Fmax (N), the embedment strength is defined as:

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