Civil Engineering Reference
In-Depth Information
man-made disturbances, shows contrary evidence. Just to mention an
example close to the authors, on 28 September 2003, 56 million people in
Italy experienced the most serious blackout in 70 years, which lasted almost
12 hours. It was caused by storm-induced damage to a single line supplying
power from Switzerland to Italy. According to reports, the blackout spread
to the entire country in less than 4 seconds.
One distinguishing feature of these failures is that in many cases the
size of the triggering event was minor, certainly not commensurate with
that of the consequences. This disproportion between causes and effects
highlights an emergent chaotic behaviour of the infrastructure. The causes
of this behaviour are due to the complexity and level of interconnectedness
that characterise the SOS: the sheer number of different systems and
of different components within them (themselves in turn, being quite
often part of a complex system), as well as the dependencies among
them, infl ate the possible states to large numbers, and pose a challenge to
modelling.
It can be argued whether trying to make quantitative predictions on the
performance of the infrastructure makes any sense. As Macaulay (2008) put
it, 'if [infrastructure] analysis reaches the level of forecasting accuracy
obtained by weather forecasting, we might be doing well!' Taking this opti-
mistic view, the following sections will outline a general object-oriented
framework for the modelling and simulation of an infrastructure. Before
introducing the model, the next two sections defi ne its scope and goal within
their possible ranges, and the type of model, analysis, and interactions,
respectively.
18.2 Time, space and stakeholder dimensions of
the problem
The assessment of the capability of a system to reliably carry out its
function(s) under normal as well as disturbed operating conditions is termed
its performance assessment. This task requires a model and metrics defi ned
on its response. With specifi c reference to the infrastructure, the formula-
tions of the models as well as metrics are not unique and depend at least
upon the spatial extent of the study region, the time horizon of the observa-
tion window, the purpose of the assessment and its end-user(s).
As far as the time dimension is concerned, three aspects are of interest:
the fi rst two are associated with the analysis time-frame and the analyst's
position on the time axis. With reference to the time-frame, typically, three
situations are considered:
Short term (hours, days, weeks): in the immediate aftermath of the event
the damaged infrastructure operates in a
state
of
emergency
.
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