Energies 2021, 14, 7575. https://doi.org/10.3390/en14227575 www.mdpi.com/journal/energies Article Resilience Assessment: A Performance‐Based Importance Measure Ali Nouri Qarahasanlou 1 , Ali Zamani 2 , Abbas Barabadi 3, * and Mahdi Mokhberdoran 4 1 Faculty of Technical and Engineering, Imam Khomeini International University, Qazvin 3414896818, Iran; Ali_Nouri@eng.ikiu.ac.ir 2 College of Engineering, University of Tehran, Tehran 9813, Iran; Ali.Arabshah@alumni.ut.ac.ir 3 Department of Technology and Safety, UiT the Arctic University of Norway, 6050 Tromsø, Norway 4 Branch Manager of SGS, Tabriz 51368, Iran; Mahdi.Mokhberdoran@sgs.com * Correspondence: abbas.b.abadi@uit.no Abstract: The resilience of a system can be considered as a function of its reliability and recovera‐ bility. Hence, for effective resilience management, the reliability and recoverability of all compo‐ nents which build up the system need to be identified. After that, their importance should be iden‐ tified using an appropriate model for future resource allocation. The critical infrastructures are un‐ der dynamic stress due to operational conditions. Such stress can significantly affect the recovera‐ bility and reliability of a system‘s components, the system configuration, and consequently, the im‐ portance of components. Hence, their effect on the developed importance measure needs to be iden‐ tified and then quantified appropriately. The dynamic operational condition can be modeled using the risk factors. However, in most of the available importance measures, the effect of risk factors has not been addressed properly. In this paper, a reliability importance measure has been used to de‐ termine the critical components considering the effect of risk factors. The application of the model has been shown through a case study. Keywords: reliability; importance measure; operational condition; frailty model; fleet of loading system 1. Introduction Critical infrastructures are complex systems whose high performance requires proper interaction between hardware, software, and wetware (humans being involved in the design and operation of these systems). External and internal working of infrastruc‐ tures is dynamic, which constantly can change the performance characteristics of these systems. For example, dynamic operational conditions can affect equipment reliability and recoverability, two characteristics of infrastructure resilience (see Figure 1). Changing the reliability can cause an unexpected breakdown. For example, ambient temperature effects on the reliability and recoverability of power distribution have a dynamic nature, and a sudden low temperature will cause an unexpected power outage. Such unexpected stoppages need to be considered in any contingency plan. Moreover, it is important to clearly understand each component’s importance in building critical infrastructures and their sensitivity to any change in operational conditions. Recently, different resilience metrics have been developed to assess the resilience of systems in different sectors. Figure 1 shows some of the concepts of resilience and some key concepts, which have been used to represent the system statement pre‐disruption, during disruption, and post‐disruption. Resilience is a technical system that can be de‐ fined as the ability to withstand a major disruption within acceptable degradation param‐ eters and recover within an acceptable time and composite costs and risks [1,2]. Citation: Nouri Qarahasanlou, A.; Zamani, A.; Barabadi, A.; Mokhberdoran, M. Resilience Assessment: A Performance‐Based Importance Measure. Energies 2021, 14, 7575. https://doi.org/10.3390/ en14227575 Academic Editor: Athanasios Kolios Received: 31 October 2021 Accepted: 10 November 2021 Published: 12 November 2021 Publisher’s Note: MDPI stays neu‐ tral with regard to jurisdictional claims in published maps and institu‐ tional affiliations. Copyright: © 2021 by the authors. Li‐ censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con‐ ditions of the Creative Commons At‐ tribution (CC BY) license (http://crea‐ tivecommons.org/licenses/by/4.0/).