4.1 Introduction
Traditionally the term risk assessment is associated with the framework, procedures,
techniques and tools required to manage the risks associated with a given engineering activity
or facility. Risks are here normally understood as the expected value of adverse consequences
associated with all possible events to which the activity or facility may be subject to. As
outlined in the lecture on decision analysis in engineering, risk assessments play an important
role in engineering decision making as the risk measure enters directly into the utility function
or in more normal engineering terms, into the benefit function. Hence, if by risk also all gains
are considered, i.e. not only all possible events associated with negative consequences but
also all possible events associated with positive consequences, then the evaluated risk may be
used directly as a benefit function on the basis of which a decision analysis may be performed.
In the following, risk assessment will at first be introduced following a framework for risk
assessment in engineering developed within the Joint Committee on Structural Safety (JCSS).
Thereafter a procedure for risk assessment in accordance with present best practice in codified
risk assessment will be shortly outlined. Finally, a set of traditional techniques and tools for
the support of risk assessments are introduced.
4.2 The JCSS Framework for Risk Assessment in Engineering
The development and management of the societal infrastructure is a central task for the
continued success of society. The decision processes involved in this task concern all aspects
of managing and performing the planning, investigations, designing, manufacturing,
execution, operations, maintenance and decommissioning of objects of societal infrastructure,
such as traffic infrastructure, housing, power distribution systems and water distribution
systems. The main objective from a societal perspective of such activities is to improve the
quality of life of the individuals of society both for the present and the future generations.
From the perspective of individual projects the objective may simply be to obtain a maximal
positive economical return of investments.
If all aspects of the decision problem would be known with certainty the identification of
optimal decisions would be straightforward by means of traditional cost-benefit analysis.
However, due to the fact that the understanding of the problems involved in the decision
problems often is far less than perfect and that it is only possible to model the involved
processes of physical phenomena as well as human interactions in rather uncertain terms the
decision problems in engineering is subject to significant uncertainty. Due to this it is not
possible to assess the result of decisions in certain terms. There is no way to assess with
certainty the consequences resulting from the decisions made. However, what can be assessed
are the risks associated with the different decision alternatives. Based on risk assessments
decision alternatives may thereby be consistently ranked. If the concept of risk as the simple
product between probability of occurrence of an event with consequences and the
consequence of the event is widened to include also the aspects of the benefit achieved from
the decisions then risk may be related directly to the concept of utility from the economical
decision theory and a whole methodical framework is made available for the consistent