E

G mean

where Emean fin is the final mean value of the modulus of elasticity, Emean is the mean value of elasticity, Gmean,fin is the final mean value of the shear modulus, Gmean is the mean value of the shear modulus, K^,fin is the final slip modulus, Kser is the slip modulus, defined in EC5, 7.1, and kdef is the deformation factor for timber and wood-based products and, for connections, it will be as defined in 2.3.2. Values for kdef for timber and some wood-related products are given in Table 2.10.

The design value of stiffness properties used in the analysis will therefore be

where Ed,sLs is the design value of the final mean value of the modulus of elasticity at the SLS, Gd,sLs is the design value of the final mean value of the shear modulus at the SLS, and Kd,sLs is the design value of the final slip modulus at the SLS.

2.3.4.2 ULS analyses

At the ULS, analyses are undertaken to validate strength and stability behaviour, and the loading to be used will be that producing the greatest design effect, selected from the action combinations referred to in 2.2.24:

(a) When undertaking a first-order linear elastic analysis (see 2.2.16.1) on a structure and the stiffness distribution within the structure does not affect the distribution of internal stress resultants, in accordance with the requirements of EC5,2.2.2(1)P, the mean values of the appropriate modulus of elasticity, shear modulus and slip modulus shall be used to derive stiffness properties. This condition will apply where all members have the same time-dependent properties and the relevant stiffness related properties will be Emean, Gmean and Kser.

(b) When undertaking a first-order linear elastic analysis of a structure and the stiffness distribution within the structure does affect the distribution of internal stress resultants, for the instantaneous condition, the stiffness related properties given in 2.3.4.2(a) will still apply. This will be the case for structures where the members, including connections, have different time-dependent properties, or with composite members where the materials being used have different time-dependent properties. For the final condition, in accordance with the requirements of EC5, 2.2.2(1)P, the properties must be derived using the final mean value of the appropriate modulus of elasticity, shear modulus and slip modulus given in EC5, 2.3.2.2(2). The final mean values are adjusted to the load component causing the largest stress in relation to strength and are as follows:

Emean

Emean,fin = -—mea" (EC5, equation (2.10)) (2.38)

G mean

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