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Vulnerability of failure scenario
8.6
Structural risk as a function of vulnerability and likelihood of
failure scenarios.
sideration of context is also required. For example, for a building to be used
as a theatre, an acceptable risk level will be lower than when it to be used
as a warehouse.
With the distinction between damage due to an action and consequence
of damage, risk assessment requires a slightly different approach. For the
latter, it is necessary to defi ne the probability of damage due to an action
(or a combination of actions) and then the probability of that damage
leading to the consequences. In other words, the latter depends upon the
actions present after the damage. For example, if stress levels of structural
members were already high before damage, self-weight of the members
alone may lead to failure. The former is rather complicated because of many
uncertainties and perhaps best captured using an evidence-based approach
(for example, Interval Probability Theory discussed above). Figure 8.6 helps
to illustrate the risk as a function of vulnerability of failure scenarios and
their likelihood.
8.4.2 Example 2
Figure 8.7 shows a slightly more complicated ball-jointed structure than the
previous example, but again with uniform member properties. A careful
common sense study of this structure reveals that damage to a member in
any storey will also damage the upper storey(s) and that damage to member
m1, for example, is one of the most obvious choice for total collapse of the
structure. However, it is not easy to predict other vulnerable failure sce-
narios. Figure 8.7 also shows the clustering hierarchy for this example and
the results of unzipping are summarized in Table 8.1. The minimum damage
demand is the same for members m2, m4, and m6. Each of these three
members forms a minimum demand failure scenario. Members m19, m20,
and m21 result in the least loss of form and each of them produces a
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