Incorporating resilience in infrastructure investment decisions: Developed framework, specifications, estimations, and evaluation

Resilience strategies are important considerations to decision-makers responsible for planning, designing, maintaining, and operating critical infrastructure systems where the consequences of failure in the presence of low-probability extreme events are high. Numerous studies have sought to define and measure resilience as a characteristic of a system; represent performance of systems prior to, during, and after extreme events; and quantify a system's resilience, typically in the form of a score or an index. However, limited progress has been made towards making effective resilience decisions that take into account key tradeoffs.This study seeks to provide infrastructure decision-makers with comprehensive and operationally useful information regarding the resilience of their infrastructure by incorporating the probability of failure of facilities due to extreme events and the corresponding expected losses into a lifecycle cost function that can be optimized to determine the most beneficial balance between resilience to extreme events on the one hand and the cost of resilience strategies on the other. By incorporating both the cost and benefit of implementing resilience improving strategies within an infrastructure system planning, design, and management decision framework, resilience informed decisions can be made by exploring lifecycle cost tradeoffs.The developed framework is operationalized to investigate the facility hardening and system dispersal resilience improving strategies in the contexts of a natural disaster and, separately, an intentional threat aplications. Facility characteristic and damage data from a US Air Force base in Florida hit by a category 5 hurricane in 2018 along with US Department of Defense facility design guidelines in the presence of explosive threats are used to estimate construction cost, operating cost, and probability of failure models. These models are employed in an evaluation designed to illustrate the developed framework's feasibility; demonstrate its value to decision makers; understand the sensitivity of the solution to geographic constriants, likelihood of extreme events, and economic and social impacts of disruptions and failures that could result from such events; and gain insights into the nature of key resiliency tradeoffs at play.Results show that statistically significant cost and probability of failure models can indeed be estimated and that the resulting relationships can be used to build a expected lifecycle cost objective function that leads to determining optimal resilience improving decisions as well as quantifying the cost associated with sub-optimal decisions. Operationalizability, adaptability, and generalizability considering two real world grounded situations are clealry demonstrated. Meaningful results are arrived at where the optimal levels and combinations of resilience improving investments are identified considering key resiliency tradeoffs and geographical constraints that decision makers often face. Incorporating resilience strategies into infrastructure planning and design is shown to be beneficial. Only under limited conditions the implementation of all available resilience improving strategies or not implementing any are found to be optimal. These numerical results indicate that resilience related tradeoffs are important and that the developed framework and approach are effective in capturing these tradeoffs to determine optimal resileince investments. The results also provide insight into the aspects of the framework to which optimal solutions are most sensitive, namely the likelihood of extreme events and the their possible economic and social impacts, allowing decision makers to prioritize data collection and estimation efforts to target areas where the consequence of accurate information is at a premium.