Civil Engineering Reference
In-Depth Information
This is the approach adopted in the current model, and computed values of
each metric are stored in the corresponding object. Further, since the system
is affected by signifi cant uncertainty, probabilistic metrics are also employed.
These are usually defi ned based on the deterministic counterparts, and take
the form of their statistical moments and/or distributions. The next sections
describe briefl y some of the implemented performance metrics.
18.6.1 Component-level metrics
The infrastructure has been subdivided into three component classes,
InhabitedArea
,
Network
and
CriticalFacility
, and metrics can be grouped
accordingly. For networks, at the component-level, they usually take the
form of:
a Boolean variable indicating the existence of a connection of the node
with a node or set of nodes of interest;
a ratio of post-earthquake to pre-earthquake value of a network-depen-
dent quantity at a node, usually associated with a fl ow evaluation.
While the former type is basically network-independent, the second is obvi-
ously network specifi c. Examples include the voltage ratio
VR
i
V
i,s
/
V
i
,0
for
an EPN, ratio of the voltage in the
i
th bus in the seismically damaged
network to the reference value for non-seismic, normal conditions, and the
head ratio
HR
i
=
H
i,s
/
H
i
,0
for a WSS, ratio of the water head in the
i
th node
in the seismically damaged network to the reference value for non-seismic,
normal operation conditions. It is well worth noting how, since voltage or
water head computations require a fl ow analysis on the whole network,
these metrics express functional consequences in the
i
th component of the
physical damage to all system components (and, possibly, to other system
components when interactions are accounted for).
For the
InhabitedArea
class, component-level metrics (i.e. per grid cell)
include the percentage of damaged buildings (per category), and the number
of casualties, fatalities, or displaced people. For the
CriticalFacility
class,
metrics include the number of available beds and functional operating
theatres in health care facilities. For the VR and HR measures,
quantities, such as displaced people or operating theatres, are defi ned at
component-level but refl ect much wider system-level behaviour through
their evaluation.
=
18.6.2 System-level metrics
For networks, system-level metrics can take the form of:
Connectivity-related measures, such as the Simple or Weighted Con-
nectivity Loss, which express the average reduction in connectivity
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