Verification by the partial factor method Partial factors on actions

Representative actions (Frep) are converted into design values (Fd) by multiplying by an appropriate partial factor (yf):

d F rep where yf takes account of uncertainties in the magnitude of the action, model uncertainties, and dimensional variations. For unfavourable actions, yf $ 1, whereas for favourable actions yf # 1 and the previous equation is qualified as follows (see Figure 2.18):

Weak And Partial Structural Models
Figure 2.18. Factors on actions

Values of yf and YF,fav for persistent and transient design situations are given in EN 1990 and vary between 0.9 and 1.5, depending on the duration of the action (see the table below).

For limit state EQU, the factors on permanent actions are fairly small, with Yg = 1.1 increasing the adverse effects of unfavourable permanent actions and YG,fav = 0.9 reducing the beneficial effects of favourable ones. Unfavourable variable actions are increased by 50% (yq = 1.5), but favourable variable actions are ignored (Yafav = 0).

For limit state STR, significant factors are applied to unfavourable permanent and variable actions (yg = 1.35 and yq = 1.5); favourable permanent and unfavourable accidental actions are taken at their representative values (YG,fav = ya = 1.0) ; and favourable variable and accidental actions are ignored (YQ,fav = YAfav = 0). In geotechnical design, these partial factors also depend on the Design Approach adopted (see Chapter 6).

EN 1990 also allows limit states EQU and STR to be checked simultaneously by the application of partial factors from the last column of the table.

Action and symbol

Partial factor

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