| Summary: | With our increased knowledge about seismicity and risks related to earthquakes,
there is a greater need for retrofitting deficient structures to ensure the functioning of a
transportation network and to minimize the life and economic loss associated with
catastrophic events. Given the scarcity of funds, the decision maker should try to
determine the optimal level of retrofit for a structure and the priorities among various
candidates. A decision analysis methodology is thus proposed and demonstrated through
two example bridges in order to determine the most preferable level of retrofit and the
retrofit order for the two candidates. The decision alternative minimizing the total cost of
the structure over its life is the best retrofit strategy while the bridge with the lower cost-to-
benefit ratio should be retrofitted first.
Seismic assessment o f the Colquitz river south structure was performed in terms
of three different levels of seismicity. Various earthquake records were scaled to match
the site-specific spectra corresponding to each level of seismicity. These records were
then used to drive the non-linear dynamic analysis of the bridge pier. Overall damage
states for the bridge were determined based on damage index values for the pier and
expert judgement for other bridge components corresponding to various pre-defined
levels of retrofit. The structural damage was then translated into dollar damage and this
information was used in the decision analysis algorithm as consequence costs. An
expected annual cost of future damage was then calculated and converted to present
worth for each retrofit level. The estimated retrofit costs and the present value of future
damages were then added to find the total expected cost for each decision alternative.
Sensitivity analyses were carried out to examine the variations in decision outcome due
to changes in different input parameters. Also, the effectiveness of decision analysis
techniques not employing probability and risk attributes was briefly examined.
For the Interurban overpass, it was assumed that the safety level retrofit would
be the optimal strategy. Cost-to-benefit ratios for the two structures were then calculated
corresponding to the optimal retrofit decision for each, thus determining the order of
retrofit. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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