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Figure 6.6 shows the relative magnitude of the actions and effects, as the combination factors are applied to characteristic actions and partial factors to the effects of actions. If the calculation model is linear, then the resultant design effects will be identical to those shown in Figure 6.5; if the model is nonlinear (which is invariably the case in geotechnical engineering), then the resultant design effects will differ. A further complication with this formulation is that permanent and variable effects of actions must be calculated separately to allow different partial factors to be applied to them. Existing computer software is unlikely to have been programmed to do this and hence will need amending to accommodate Eurocode 7.

Figure 6.6. Hierarchy of actions and effects when partial factors are applied to action effects

6.2.2 Material strength and resistance

The calculation of design resistance follows the route shown in the right hand channel of Figure 6.4:

Characteristic material strengths ^ Design strengths ^ Design resistance

Design material properties Xd are obtained from characteristic material properties Xk by dividing by partial factors ym $ 1.0: X,

The design resistance is then obtained from:

Yr Yr where the partial factor yr $ 1.0.

It is usual for one of the partial factors ym or yr to be equal to 1.0 and so the equation above typically reduces to one of two formats, either:

Figure 6.7 shows the relative magnitude of material strengths, assuming the first format, as the appropriate partial factors (y9 and Ycu) are applied to them. The diagram assumes arbitrary contributions to resistance from a coarse soil with characteristic angle of shearing resistance and from a fine soil with characteristic undrained shear strength cuk. The arrow denotes the insertion of design material strengths into the calculation model.

Resistance Material strength

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