Resilience and Sustainability of Civil Infrastructure: Toward a Unified Approach

In recent years, the concepts of resilience and sustainability have become very topical and popular. The concept of sustainability rose to prominence in the late 1980s and became a central issue in world politics, when the construction industry began to generate the first sustainable building assessment systems with more or less equally weighted environmental, economic, and social aspects for office buildings over their life cycles. On the other hand, resilience is usually connected to the occurrence of extreme events during the life cycle of structures and infrastructures. In the last decade, it has been used to minimize specifically direct and indirect losses from hazards through enhanced resistance and robustness to extreme events, as well as more effective recovery strategies. A detailed comparison of the studies dealing with either infrastructure sustainability or resilience presented in this paper leads to the conclusion that they have a vast number of similarities and common characteristics. For instance, they both combine structural analyses with social and economic aspects; they both rely on techniques for the life-cycle analysis and decision making; they both are in an early stage, where the academic world is trying to find the best way to promote the application of the scientific results among professional engineers and the industry. Indeed, both approaches try to optimize a system, such as a civil infrastructure system, with respect to structural design, utilized material, maintenance plans, management strategies, and impacts on the society. However, for the most part, researchers and practitioners focusing on either resilience or sustainability operate without a mutual consideration of the findings, which leads to a severe inefficiency. Therefore, this paper suggests that resilience and sustainability are complementary and should be used in an integrated perspective. In particular, the proposed approach is rooted in the well-established framework of risk assessment. The impact of the infrastructure and its service states on the society in normal operational conditions (assessed by sustainability analysis) and after exceptional events (assessed by resilience analysis) should be weighted by the associated probabilities of occurrence and combined in a global impact assessment. The proposed perspective and assessment technique is applicable to various types of civil infrastructure systems, but the case of transportation networks and bridge systems is emphasized herein. A numerical application dealing with the comparative analysis of two possible bridge layouts is presented to exemplify the approach. The results show that both resilience and sustainability analyses assess a relevant amount of the impact of the bridge on the community where it is built, so neither one can be neglected.