Risk-based life-cycle optimization of deteriorating steel bridges: Investigation on the use of novel corrosion resistant steel

Corrosion-induced material loss can reduce the load-carrying capacity of structures, resulting in an increase of the probability and risk of failure. Currently, carbon steel is predominantly used in steel bridges due to its relatively low material cost, ease of fabrication at large scale and excellent material strength. However, low corrosion resistance of carbon steel can result in severe deterioration of bridges. As a result, a very high maintenance cost may be incurred during the service life of carbon steel bridges. A new type of corrosion-resistant steel, A709-50CR, has been recently developed for bridge construction. Despite its relatively high material cost, A709-50CR has the potential to reduce the life-cycle maintenance cost and mitigate the increasing failure risk due to structural deterioration. To further reduce the cost of using A709-50CR steel, this paper explores the prospect of using it for major bridge maintenance actions. Bi-objective optimization is conducted to determine when and which carbon steel girders should be replaced using A709-50CR during the life-cycle of a bridge. The two objectives in the optimization problem are to minimize life-cycle risk and life-cycle maintenance cost. The results indicate that using A709-50CR in major maintenance actions can achieve considerable economic benefits.