Seismic risk and possible maximum loss (PML) analysis of reinforced concrete structures - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 746

0.05

0.04

NEL; event risk curve
PML; event risk curve

0.03

0.02

Risk curve

0.01

1/475=0.0021

0.00

0.00 0.10 0.20 0.30 0.40 0.50

Ratio of seismic loss to replacement cost

27.7 Seismic risk curves for NEL and PML.

Figure 27.7 shows the results for P019-Class I; in the fi gure, the probability
level corresponding to 475-year return period is highlighted. The PML 475
(i.e. PML at the return period of 475 years) is adopted as the seismic risk
measure in this case study.
Finally, to assess the seismic performance of different bridge piers in
relation to PML, the capacity and demand of the piers are estimated. The
horizontal maximum strength P u of the piers (referred to as capacity) and
the required horizontal seismic load k hc W (referred as demand) are
appraised according to the Japanese specifi cations for highway bridges
(JRA, 2002). The capacity level of each pier varies depending on the
designed load-carrying strength P u , while the demand (actually seismic
load) is almost the same among six piers. Figure.27.8 shows a relationship
between PML 475 (as a fraction of to the replacement cost of the piers) and
capacity/demand ratios for two ground conditions. The capacity/demand
ratio indicates that:

Capacity
Demand

> 1 code approved

[27.6]

Capacity
Demand

< 1 non-approved

Figure 27.8 demonstrates that the risk values are high for piers with low-
strength (P019, P043), whereas those for P141 and P184, having a capacity/
demand ratio greater than 1.0, are suffi ciently low. It is important to note
that the PML values can be used as a surrogate measure for seismic design
level. Because the PML values are expressed in monetary terms, various
non-expert stakeholders can comprehend the extent of the seismic risk