Life-cycle considerations in risk-informed decisions for design of civil infrastructures

Civil structures and infrastructures, such as buildings, bridges, and other facilities, are constructed and built for long service lives; many for over 50 or 100 years. In this light, the performance of an engineered system over its useful life span is naturally of major concern. The concern must include the assurance of a minimum level of reliability of performance, which will necessarily require inspections, repair, and maybe even retrofitting or replacement. The whole-life cost associated with this life-cycle performance, therefore, is the pertinent cost that ought to be the basis for determining the cost during the design stage (in terms of present value); this must include the maintenance and potential damage costs, besides the initial cost, over the life of a system. In this regard, significant technical and economic uncertainties can be expected and are unavoidable; therefore, decisions required in the design of such systems must consider risk associated with the probability of non-performance and serious damage or failure, as well as of the financial risk. The importance of these factors in the decision process at the design stage is emphasised and a practical approach for life-cycle consideration in formulating risk-informed decisions in the planning and design of infrastructure systems is described. The approach is illustrated with specific applications in the optimal design of civil infrastructure systems.