26 Damage to concrete structures
period (e.g. 100 years). The failure probability P f or the reliability index
β is then calculated considering the time-dependency of resistance R and
load-action  S. In a further simplification of the durability design, an
approach based on partial safety factors can be defined analogous with
structural design codes, avoiding the need to perform detailed statistical
calculations based on complete distribution functions. For more details on
a probabilistic durability design, reference is made to literature (Sarja and
Vesikari 1996).
An often cited probabilistic durability design model is the Duracrete
Model, developed within a European Research Project (Brite-EuRam
1998, 1999). With this model, the service life of a structure is studied by
F L
F L
r
F L
F L
r
F L
F L
r
t
t
(a)
(b)
(c)
t
t
t
t
t
t
t
Figure 1.15 Different service life distribution types.
1
st period
2
nd period
3
rd period
Time
r
Figure 1.16 Example of a hazard function for a real structure.