Civil Engineering Reference
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those risks, as well as the costs and benefi ts of mitigation, in concise, cred-
ible, meaningful terms. Keller
et al.
(2006) have shown that when problems
are formulated in terms of frequencies rather than probabilities, the per-
ceived threat of the risk is increased.
The probabilistic approach described in the previous paragraph is com-
prehensive and general, but the information provided to the public (deci-
sion makers, politicians, etc.) should be deterministic (scenario basis or
event), because it is simpler and easier to understand. In communicating
risk effectively, public has diffi culty in interpreting probabilistic information
(Patt and Schrag, 2003). In fact, according to Kahneman and Tversky (2000),
small probabilities (which are frequently associated with natural hazard
events) are often underestimated. 'By eliminating probability, which is a
confusing concept for a lot of people, the [risk] becomes way more impact-
ful for an average person'. Many authors believe the scenario approach may
also impact the emotions associated with an event.
11.3.8 Defi nitions of resilience performance levels
The objective of PBEE is to design, construct and maintain facilities with
enhanced damage control. A comprehensive document was prepared by the
SEAOC (1995) Vision 2000 Committee (2000) that includes interim recom-
mendations. The performance design objectives couple expected or desired
performance levels with levels of seismic hazard as illustrated by the per-
formance design objective matrix shown in Fig. 11.11. According to the ATC
58 (2011), the performance assessment types can be classifi ed into: (i) inten-
sity-based; (ii) scenario-based; or (iii) time-based. PBD levels focus on the
performances a building can achieve during the shaking, and are associated
with engineering demand parameters such as deformation. More recently,
SPUR (Maffei, 2009), which is the San Francisco Planning and Urban
Research Association, introduced other defi nitions of performance levels
for physical infrastructure based on recovery target states which take into
account the safety as well as the recovery time. Five performance measures
for buildings have been identifi ed: (i)
Safe and operational
; (ii)
Safe and
usable during repair
; (iii)
Safe and usable after repair
; (iv)
Safe but not
repairable
; (v)
Unsafe
. However, no clear quantifi cation of these perfor-
mance levels has been provided so far. In Japan, using public interviews, the
accepted downtime and performance goals for bridges have been evaluated
(Fig. 11.12), attempting to fi nd what are the desired performance goals
expected by citizens after an extreme event like an earthquake. This infor-
mation is very useful to defi ne the boundaries of different resilience per-
formance levels.
The newly proposed resilience performance levels (RPL) focus on
building performance after the ground shaking stops, and recognize the
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