Seismic vulnerability analysis of a complex interconnected civil infrastructure - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 469

the component located at the site of the node is vulnerable to seismic
hazard. More appropriately, it determines if a vulnerability model for the
component exists and can be adopted in the model. When the component
is vulnerable, its fragility model is a function of a scalar or vector IM that
needs to be specifi ed, and is infl uenced by site amplifi cation (see Section
18.5.4). The latter is described by a model that will take as an input a V s30
value (a proxy for site class) stored in the corresponding node object as an
attribute of the class. Classes describing edges in each network store the
edge connectivity , its centroid (computed from the connected nodes' posi-
tions), and parameters related to seismic vulnerability of the edge (pipe,
line, road segment, etc.). The next sections provide more details on two
specifi c networks, in terms of the implemented functional model and the
vulnerability models of the components.
Model of a WSS
Water supply systems are networks whose edges and nodes are pressure
pipes and either pipe junctions, water sources or end-users, respectively.
Their function is to provide end-users with potable water with a suffi cient
pressure level. A WSS can be decomposed into hierarchically arranged tiers.
The fi rst layer collects all pipes in the main distribution which (within urban
areas) follow the main roads and convey the main water fl ow. This is usually
designed with a redundant grid-like topology to ensure reliable connection
of the sub-components. The latter follows lower-order roads and have a
more vulnerable tree-like topology (but are made of more easily repairable
smaller diameter pipes and serve smaller demands, thus limiting the impact
of service interruption).
The class diagram for a WSS is shown in Fig. 18.5 together with that of
an EPN. Both WSSedge and WSSnode are abstract classes. Edges can be
either pipes or tunnels. Nodes can be demand nodes, pumping stations, or
water sources. The latter can be either constant head sources (such as a river
or a dam) or variable head sources (such as a tank). The distinction has an
infl uence on the solution of the fl ow equations.
Examples of the main attributes and methods include, for instance, at the
WSS level, the waterEquipment attribute, that stores the water daily equip-
ment per person in the study region, a parameter employed by the compute-
Demand method to estimate demands in the demand nodes starting from
the population in the tributary cells. Two more methods are the compute-
Flow and the discretiseEdge , which assemble and solve the fl ow equations
in the functional model, and automatically subdivide edges in smaller length
segments to ensure a predefi ned maximum segment length, respectively.
As discussed also in Section 18.7, vulnerable components in a system can
be of two types: point-like and line-like components. The former usually