Figure 1.4: Risk contributions from different service life phases to be considered at the planning stage.
It is important to recognize that different things may go wrong during the different phases of
the service life including events such as mistakes and errors during design and failures and
accidents during construction, operation and decommissioning. The potential causes of errors,
mistakes, failures and accidents may be numerous, including human errors, failures of
structural components, extreme load situations and not least natural hazards. Careful planning
during the very first phase of a project is the only way to control the risks associated with
such events.
As an illustration the dam structures must be designed such that the safety of the dam is
ensured in all phases of the service life, taking into account yet another factor of uncertainty,
namely the future deterioration, but also taking into account the quality of workmanship, the
degree of quality control implemented during construction and not least the foreseen
strategies for the inspection and maintenance of the structures and mechanical equipment
during the operation of the power plant. As a final aspect concerning the structures these
should at the end of the service life be in such a condition that the work to be performed
during the decommissioning of the power plant can be performed safely for both the persons
involved and the environment.
A final fundamental problem arises in regard to the question – what are the acceptable risks? -
what are people prepared to invest and/or pay for the purpose of getting a potential benefit?
The decision problem of whether or not to establish the hydraulic power plant is thus seen to
be a decision problem involving a significant element of uncertainty.
The mathematical basis for the treatment of such decision problems is the decision theory.
Important aspects of decision theory are the assessment of consequences and probabilities and
in a very simplified manner one can say that risk and reliability analysis in civil engineering is
concerned with the problem of decision making subject to uncertainty.
1.3 Definition of Risk
In daily conversation risk is a rather common notion used interchangeably with words like
chance, likelihood and probability to indicate that there is uncertainty about the state of the
activity, item or issue under discussion. For example talks are made about the risk of getting