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UBC Theses and Dissertations

Risk-based retofit decision model for bridges Nishimura, Kim S.


A risk-based methodology for making bridge retrofit decisions is demonstrated through a case study of two reinforced concrete highway bridges which were damaged in the Northridge earthquake. An expected value decision model is constructed in order to select the optimal retrofit option for each bridge. The decision alternative which minimizes the total cost of the structure over its life is sought. The total cost includes the initial retrofit cost and the probabilistically predicted future damage cost. Seismic assessments of the Fairfax-Washington and La Cienega-Venice bridges were performed. The seismic hazard at the bridge sites, estimated in terms of intensity and annual probability, was established. The probability of damage was linked to the probability of occurrence of different levels of strong ground motion for a specific site. Inelastic dynamic analyses of the vulnerable bridge components produced estimates of the seismic structural damage for different earthquake intensity levels. These estimates were in the form of damage indices. The damage estimates were then interpreted in terms of dollar losses. Using the hazard information and the damage costs, an expected annual cost of future damages was calculated. Adding the estimated cost of retrofit and the present value of future damages, the total expected cost for each decision alternative was determined. Finally, the sensitivity of the decision model to the input values was investigated. The methodology presented demonstrates rational decision making in the face of inexact or approximate information.

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