A LIFE SPAN OF AT LEAST 100 YEARS - The Westerschelde Tunnel: Approaching Limits - page 66

The life span requirement of 100 years particularly has major consequences for
sections that cannot be inspected or maintained.The various performances -
such as the bearing capacity, usability and limiting the maintenance - must
have a life span spread as such, that the combined requirements in respect
of the reference period and the dependability can be complied with.
With regard to the functional aspects such as water tightness, it has been
assumed that when leakages lead to unsafe situations in which the tunnel
must be placed out of order, this concurs with the exceeding of an ultimate limit
state. If as a result of leakages emergency measures must be taken to keep
the tunnel in use, this concurs with the exceeding of a service limit state.

Probability

Fig. 6.3
Chance P acc on the
exceeding of a limit
state function
Z R S 0

S

R

R, S

0

P acc

- the limit state function
- is a function which describes the bearing capacity of the construction
- a function for the influence of the load
- acceptable chance of exceeding the limit state function Z.

Z
R
P acc

Fig. 6.4
Sustainability
formulated by means
of R and S functions
and as a life span
function

R, S

(R)

(S)

X X1 100 years

Life span

Fig. 6.5
Calculation of the
failure rate in the
year X

R, S

(R)

Chance of
failure
in year X

(S)

X X 1

100 years
Life span