Environmental Engineering Reference
In-Depth Information
Table 15.2
(Continued)
Step
Description
.
Knowledge uncertainty (epistemic uncertainty)
-
Uncertainties that come from basic lack of knowledge of
fundamental or measurable phenomena
Perhaps most critically, it is important to record the assumptions made regarding the uncertainty in the variables
and parameters and the associated supporting evidence for these choices. This provides a vehicle for peer review
and audit (Hall and Solomatine 2008)
7. Undertake reliability
analysis and display
results
Once the above inputs have been established the reliability analyses can be undertaken. For each hydraulic loading
condition a series of simulations (across the uncertainty bands for each input parameter) are resolved. Failure
arises in a particular case when the combinations of parameter values in the limit state function (Z) yield a value
for Z that is less than or equal to zero. The probability of failure for that given loading condition is then the
number of times when the simulation gives Z as less than or equal to zero divided by the total number of
simulations. Repeat for all hydraulic loads (Kortenhaus and Oumeraci 2002; Lassing et al. 2003; Simm
et al. 2006; van Gelder et al. 2008)
8. Display results
Present the results of interest (annual probability of failure, fragility curve, etc.)
To support a detailed analysis of reliability, a
flexible software tool (RELIABLE) has been devel-
oped based on a Level III reliability method. The
basic building blocks of a Level III analysis and the
way in which these have been enacted within
RELIABLE are shown in Figure 15.7. In particular,
RELIABLE contains:
.
A fault tree drawing tool (OpenFTA) - enabling
the user to construct an asset-specific fault tree
using failuremechanisms (andmodes) linkedwith
standard operators (AND, OR, NOT, etc.).
.
A library of limit state equations - limit state
equations (LSEs) are made available to the user
(currently describing 72 failure modes). These can
Structure-specific
parameters, probability
distribution functions
and ranges
Structure-specific
Fault tree
Limit state equation
Failure mode 1
Numerical
Integration
(Monte Carlo)
Limit state equation
Failure mode 2
Limit state equation
Failure mode 3
Structure-specific
annual probability of
failure or fragility curve
Limit state equation
Failure mode ..n
Fig. 15.7
Building blocks of a structured Level III reliability analysis (as implemented within the RELIABLE software).
