Incorporating Life-Cycle Costs in Highway-Bridge Planning and Design

Life-cycle cost analysis has been stressed by various state departments of transportation and applied to a highway bridge-management system (BMS) as a decision-making strategy in maintenance, rehabilitation, or replacement (MR & R). In essence, life-cycle cost analysis is based on the concept of discounted cash-flow analysis. A brief review of related current methods in the area of life-cycle cost-analysis implementation is presented. Based on this review, key factors that impose a significant effect on life-cycle cost analysis are identified. A new method called the VI model is developed; it considering bridge age, condition rating, and cost, which are believed to be the most important factors in the decision-making process. A parameter, referred to as the value index ( VI), is introduced to incorporate these variables for the optimization strategy. This enables rational decisions to be made regarding the type of work to be performed that best suits a bridge's needs within the appropriate constraints. The “objective function,” the function to be optimized, is written in terms of the key factors that control the decision-making process. The method is applied to several case studies for highway bridges in Illinois. Finally, the significance of certain limits imposed on the key factors in the optimization process and the various alternatives that can be selected within these limits are discussed. The proposed model is for project-level analysis. The model can also be extended for use in a network-level analysis. However, such an application requires development of a separate allocation-of-fund process that in turn needs input from the bridge engineer and information on the individual bridges in the network in terms of their needs and priorities for rehabilitation, repair, or replacement.