Structural vulnerability analysis of civil infrastructure facing seismic hazards - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 212

3

3 3

4

4

1

1 2

1 2

2

Seed cluster Node 4 with two

members is included

Member 1-4 is
included

(a)

4

4 4

3

3

3

5

5 1

1

1

2

2

2

Seed cluster Node 5 with three

members is included

Member 1-5 is
included

(b)

3

3 3

1 1 1 1

or

2 2 2 4 2

Seed cluster Member 1-3 is

included

Depending upon
the structure

(c)

8.3 Typical clustering sequences: (a) pin-jointed structure; (b) ball-
jointed structure; and (c) rigid-jointed structure.

The description of damage scale is related to the change in the quality of
form (i.e. well-formedness). The loss in structural well-formedness is calcu-
lated as the difference between the structural well-formedness of intact
structure and that of a damaged structure. The ratio of this loss in structural
well-formedness to the well-formedness of the intact structure defi nes sep-
arateness. The ratio of separateness with respect to damage demand gives
vulnerability index.
A failure scenario is a set of deteriorating events that reduce the well-
formedness of a structure. Failure scenarios are identifi ed by exposing a
structure to deteriorating events while traversing down the hierarchy. A
deteriorating event could be a cut or formation of a pin. Complete failure
of a joint is the same as the failure of all members meeting at that joint.
Although a large number of failure scenarios are possible, fi ve types of
failure scenarios are important. The minimum demand scenario is the easiest
way to cause damage to the structure, no matter how small. It is identifi ed