2.4.6 Design values

2.4.6.1 Design values of actions

(1)P The design value of an action shall be determined in accordance with EN 1990:2002.

(2)P The design value of an action (F_d) shall either be assessed directly or shall be derived from representative values using the following equation:

with

(3)P Appropriate values of ψ shall be taken from EN 1990:2002.

(4)P The partial factor γ_F for persistent and transient situations defined in Annex A shall be used in equation (2.1a).

NOTE 1 The values of the partial factors may be set by the National annex.

NOTE 2 The recommended values in Annex A indicate the appropriate level of safety for conventional designs.

(5) If design values of geotechnical actions are assessed directly, the values of the partial factors recommended in Annex A should be used as a guide to the required level of safety.

(6)P When dealing with ground-water pressures for limit states with severe consequences (generally ultimate limit states), design values shall represent the most unfavourable values that could occur during the design lifetime of the structure. For limit states with less severe consequences (generally serviceability limit states), design values shall be the most unfavourable values which could occur in normal circumstances.

(7) In some cases extreme water pressures complying with 1.5.3.5 of EN 1990:2002, may be treated as accidental actions.

(8) Design values of ground-water pressures may be derived either by applying partial factors to characteristic water pressures or by applying a safety margin to the characteristic water level in accordance with 2.4.4 (1)P and 2.4.5.3 (1)P.

(9) The following features, which may affect the water pressures should be considered:

• the level of the free water surface or the ground-water table;
• the favourable or unfavourable effects of drainage, both natural and artificial, taking account of its future maintenance;
• the supply of water by rain, flood, burst water mains or other means;
• changes of water pressures due to the growth or removal of vegetation.

(10) Consideration should be given to unfavourable water levels that may be caused by changes in the water catchment and reduced drainage due to blockage, freezing or other causes.

(11) Unless the adequacy of the drainage system can be demonstrated and its maintenance ensured, the design ground-water table should be taken as the maximum possible level, which may be the ground surface.

2.4.6.2 Design values of geotechnical parameters

(1)P Design values of geotechnical parameters (X_d) shall either be derived from characteristic

values using the following equation:

or shall be assessed directly.

(2)P The partial factor γ_M for persistent and transient situations defined in Annex A shall be used in equation (2.2).

NOTE 1 The values of the partial factors may be set by the National annex.

NOTE 2 The recommended values in Annex A indicate the minimum level of safety for conventional designs.

(3) If design values of geotechnical parameters are assessed directly, the values of the partial factors recommended in Annex A should be used as a guide to the required level of safety.

2.4.6.3 Design values of geometrical data

(1) The partial action and material factors (γ_F and γ_M) include an allowance for minor variations in geometrical data and, in such cases, no further safety margin on the geometrical data should be required.

(2)P In cases where deviations in the geometrical data have a significant effect on the reliability of a structure, design values of geometrical data (a_d) shall either be assessed directly or be derived from nominal values using the following equation (see 6.3.4 of EN 1990:2002):

for which values of Δa are given in 6.5.4 (2) and 9.3.2.2

2.4.6.4 Design values of structural properties

(1)P The design strength properties of structural materials and the design resistances of structural elements shall be calculated in accordance with EN 1992 to EN 1996 and EN 1999.