Optimum retrofit of long-span bridges under conflicting objectives

Aerodynamic performance of old long-span bridges can be improved by retrofitting cross-sectional shapes, as was implemented for the retrofit of Bronx-Whitestone Bridge, Lions' Gate Bridge, and Strorebaelt Suspension Bridge. The goals of the retrofit typically have conflicting objectives, such as, to reduce the maximum displacement of the bridge and to minimize the cost of the retrofit. We propose a method based on multi-objective optimization to assist the decision-making process under conflicting objectives. Due to the conflict of different objectives, multiple optimal solutions are obtained, which are called Pareto-optimal solutions. Any optimal solution cannot be said to be strictly better than the rest of the optimal solutions. The entire solutions must be considered before making a decision. The Pareto-optimal solutions enable us to make a performance-based decision. The method is demonstrated using a hypothetical long-span bridge under vortex-induced vibrations.