A Multi-Hazard Framework for Optimum Life-Cycle Cost Design of Reinforced Concrete Bridges - Structural Seismic Design Optimization and Earthquake Engineering - page 87

Figure 5. Spectral acceleration plots developed
for three sets of 20 ground motions with differ-
ent seismic hazard levels: (a) 50% probability
of occurrence in 50 years; (b) 10% probability
of occurrence in 50 years; (c) 2% probability of
occurrence in 50 years

estimated log-standard deviations are very close to
each other (ranging from 0.50 to 0.70), the median
value of log-standard deviations (equal to 0.60) is
selected as the identical log-standard deviation.
To evaluate the effects of chloride-induced
corrosion on the seismic damageability of RC
bridges, the fragility curves are generated for the
case-study bridges at different time steps during
their life-cycle. Considering the extent of struc-
tural degradation (as discussed in Section 3), the
median and log-standard deviation of fragility
curves are estimated for the corroded bridges
following the procedure described for the intact
bridges. The change in the median values of fra-
gility curves is shown in Figure 8 for all the
bridges with the column height of 10.0 m. This
figure indicates that after 50 years, the overall
average of median values obtained for the four
damage states drops by 38%. For further illustra-
tion, the time-dependent fragility curves of the
bridges with medium span length and column
height of 10.0 m are depicted in Figure 9. It can
be understood from this figure that for a specific
PGA value, the probability of exceeding any
damage state increases over the time due to the
corrosion process. This increases the seismic
damageability of bridge and makes it more vul-
nerable to natural hazards. The time-dependent
fragility curves developed in this section will also
be used to predict the life-cycle cost of bridges
in a multi-hazard framework.

6. LIFE-CYCLE COST ANALYSIS OF
DEGRADED BRIDGES

The life-cycle cost (LCC) of a structure is defined
as the total cost of the structure from the begin-
ning of planning for construction to the end of
its service life time. The LCC analysis provides
a framework that helps to allocate appropriate