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^Provided yg = YG,fav = 1.0 is not more onerous

^Provided yg = YG,fav = 1.0 is not more onerous

For accidental design situations, values of yg, YG,fav, YQ and ya are 1.0 and the values of Yf and YA,fav are 0.

2.13.2 Partial factors on material properties

Characteristic material properties (Xk) are converted into design values (Xd) by dividing by an appropriate partial factor (Ym):

(see Figure 2.19) where ym takes account of uncertainties in the magnitude of the material property, model uncertainties, Figure 2.19. Factors on material and dimensional variations. properties

Values of ym for persistent and transient design situations are given in the resistance codes (ENs 1992 to 1999) and vary between 1.0 and 1.5, depending on the material type. In geotechnical design, these partial factors also depend on the Design Approach adopted for limit state STR (see Chapter 6).

For accidental design situations, values of ym are 1.0.

2.13.3 Tolerances on geometry

Nominal geometrical dimensions (anom) are converted into design values (ad) by adding or subtracting an appropriate safety margin or tolerance (Aa):

(see Figure 2.20) where Aa takes account of uncertainties in the magnitude of the geometrical dimension.

Values of Aa for persistent and transient design situations are given in the resistance codes (ENs 1992 to 1999) and depend on the sensitivity of the design situation to geometrical imperfections.

Values of Aa for accidental design situations are 0.

2.13.4 Verification of strength for limit state STR

Figure 2.21 combines the previous flow diagrams for limit state STR. Actions (characteristic ^ representative ^ design) are shown down the left-hand channel; geometrical parameters (nominal ^ design) down the central channel; and material properties (characteristic ^ design) down the right-hand channel. The introduction of combination factors partial factors y, and tolerances Aa at appropriate points in this process is shown.

Structural analysis uses design actions and design dimensions to determine design effects of actions; stress analysis employs design material properties and design dimensions to determine design resistance.

Limit state STR is verified when design effects are less than or equal to the design resistance.

Figure 2.20. Tolerances on geometrical parameters
0 0

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