Strategies of investment in the management of urban bridges: a life-cycle approach illustrated for Paris

Abstract

As demonstrated in past research, decisions regarding maintenance and rehabilitation strategies for a portfolio of bridges should be based on the analysis of both costs and benefits over their life cycle. Such decisions involve the priority and timing of expenditure. This is particularly important in the current era that is characterised by limited funding for infrastructure preservation in most countries. This article presents a probabilistic life-cycle-based investment framework to develop decisions for bridge maintenance and rehabilitation. The framework ranks different projects by priority, using the savings-to-investment ratio (SIR) as a measure of cost-effectiveness. The SIR computation includes the initial investment; annual operation, maintenance and repair/rehabilitation costs; and failure costs. These future costs are linked to probable events, such as natural hazards, vehicle and boat crashes, and user time delay. Since life-cycle analysis is sensitive to the analysis period, this article introduces the concept of infinite lifetime or perpetuity. A case study involving 37 bridges across the Seine River in the City of Paris is used to illustrate the framework application. The application considers pile protections and avoidance of traffic disturbance, and it is especially interesting because the examined bridges have a wide variation with regard to their dates of construction, material type and dimensions. Results of the study prove that this approach enables the decision maker to select the most cost-effective project, and to convey it to the public by incorporating social and political issues that represent practical considerations. In addition, the results seem to be relatively insensitive to the analysis period and the discount rate.