Seismic retrofit decision-making of bridges based on life-cycle cost criteria

In a decision-making framework within the context of performance-based design, life-cycle cost can be regarded as a suitable benchmark performance variable to quantify and measure performance objectives for a set of (discrete) limit states. Life-cycle cost criteria is identified as an economic term expressed in monetary units; it accounts for the initial construction costs, the repair costs taking into account also the loss of revenue due to down time, and finally the maintenance cost. The expected life-cycle cost is used for retrofit design of an existing reinforced concrete bridge infrastructure that is located in south of Italy. The retrofit design involves decision-making between a set of viable rehabilitation schemes, which mainly isolate the simply-supported bridge deck from the pier cap or force the deck to have a uniform displacement along its longitudinal direction. The proposed methodology for life-cycle cost assessment takes the advantage of a closed- and analytic-form approximation in order to take into account the time-varying profile of the probability of exceeding a set of structural limit states. The presented procedure can be effectively used for screening among alternative proposed upgrading strategies while satisfying prescribed reliability-based criteria. The optimal solution is highlighted based on the minimization of the life-cycle cost.