New safety concept

The most fundamental change is the implementation of the semi-probabilistic safety concept.

The global factor of safety

Up to now the design or dimensioning of a structural component was carried out in a way that it was considered „safe“ as soon as the resistance (R) against the stress (effects of action, E) was given with a factor of safety (η).

R > η · E

In this case η is termed as the global factor of safety, as it is only put up after all necessary calculations are made, as a multiplier for the stresses. Only one factor is used to take into consideration all naturally given imponderables (dimensional inaccuracies, tolerances on geometry, design assumptions of stresses,...). 

The semi-probabilistic safety concept

According to the semi-probabilistic safety concept, the calculating operation is more detailed. The distribution of influencing parameters is immediately taken into account in the respective step of the analysis. This is made with the help of partial safety factors γ.

Should the properties of an influencing parameter be well known, e.g. the density of water, the partial safety factors γ are almost or equal to 1. When taking a dynamic action into consideration, of which the progression and the absolute magnitude can only be estimated, the partial factor of safety γ could be 2,5.

By

  • raising the nominal value (characteristic value) of an action (partial factor of safety γ higher than 1) resp.
  • attenuating the nominal value (characteristic value) of a components resistance (partial factor of safety γ smaller than 1)

design values are derived (Rd and Ed).

After accomplishing the necessary calculations it has to be proven that

Rd > Ed.

Should this requirement be met, a component or construction work is considered sufficiently dimensioned.