Argyroudis, Sotirios

Integrating diverse expert opinions in hazard and risk projects is essential to managing subjective decisions and quantifying uncertainty to produce stable and trustworthy results. A structured procedure is necessary to organize the gathering of experts' opinions while ensuring transparency, accountability, and independence in judgements. We propose a novel Multiple-Expert management Protocol (MEP) to address this challenge, providing procedural guidelines for conducting single to multi-hazard risk analyses. MEP establishes a workflow to manage subjectivity rooted in (i) moderated and staged group interactions, (ii) trackable blind advice through written elicitations with mathematical aggregation, (iii) participatory independent review, (iv) close cooperation between scientific and managerial coordination, and (v) proper and comprehensive documentation. Originally developed for stress testing critical infrastructure, MEP is designed as a single, flexible, technology-neutral procedural workflow applicable to various sectors. Moreover, its scalability allows it to adapt from high to low-budget projects and from complex probabilistic multi-hazard risk assessments to standard single-hazard analyses, with different experts' degree and type of involvement depending on available funding and emerging controversies. We present two compelling case studies to showcase MEP's practical applicability: a multi-hazard risk analysis for a port infrastructure and a single-hazard regional tsunami hazard assessment.

Recent natural disasters that seriously affected critical infrastructure (CI) with significant socio-economic losses and impact revealed the need for the development of reliable meth- odologies for vulnerability and risk assessment. In this paper, a risk-based multi-level stress test method that has been recently proposed, aimed at enhancing procedures for evaluation of the risk of critical non-nuclear infrastructure systems against natural hazards, is speci- fied and applied to six key representative CIs in Europe, exposed to variant hazards. The following CIs are considered: an oil refinery and petrochemical plant in Milazzo, Italy, a conceptual alpine earth-fill dam in Switzerland, the Baku–Tbilisi–Ceyhan pipeline in Tur- key, part of the Gasunie national gas storage and distribution network in the Netherlands, the port infrastructure of Thessaloniki, Greece, and an industrial district in the region of Tuscany, Italy. The six case studies are presented following the workflow of the stress test framework comprised of four phases: pre-assessment phase, assessment phase, decision phase and report phase. First, the goals, the method, the time frame and the appropriate stress test level to apply are defined. Then, the stress test is performed at component and system levels and the outcomes are checked and compared to risk acceptance criteria. A stress test grade is assigned, and the global outcome is determined by employing a grading system. Finally, critical components and events and risk mitigation strategies are formu- lated and reported to stakeholders and authorities.

An engineering risk-based methodology for stress testing critical infrastructures is introduced and applied to the port of Thessaloniki in Greece exposed to seismic, geotechnical and tsunami hazards. The methodology workflow consists of four phases: Pre-Assessment, Assessment, Decision and Report phase. In the pre-assessment phase, all the necessary information is collected and archived. For the pilot study, the inventory includes the main port components namely buildings, waterfronts, cranes and the electric power system. Generic or site-specific fra- gility models are used for all exposed elements and considered hazards. Risk metrics and objectives are defined related to the functionality of the system and the structural losses. In the first level of the assessment phase, the performance of each component is evaluated using a risk-based approach. Then, a system level probabilistic risk analysis is conducted separately for earthquake and tsunami hazards. A complementary scenario-based risk analysis is carried out aiming to investigate the impact of site-specific response and extreme seismic events to the performance of the port. In the Decision phase, the results are compared with predefined objectives to decide whether the infrastructure passes, partly passes or fails the test. Guidelines and strategies to improve the per- formance and resilience of the port are summarized.

This article presents an integrated approach for the probabilistic systemic risk analysis of a road network considering spatial seismic hazard with correlation of ground motion intensities, vulnerability of the network components, and the effect of interactions within the network, as well as, between roadway components and built environment to the network functionality. The system performance is evaluated at the system level through a global connectivity performance indicator, which depends on both physical damages to its components and induced functionality losses due to interactions with other systems. An object-oriented modeling paradigm is used, where the complex problem of several interacting systems is decomposed in a number of interacting objects, accounting for intra- and interdependencies between and within systems. Each system is specified with its components, solving algorithms, performance indicators and interactions with other systems. The proposed approach is implemented for the analysis of the road network in the city of Thessaloniki (Greece) to demonstrate its applicability. In particular, the risk for the road network in the area is calculated, specifically focusing on the short-term impact of seismic events (just after the earthquake). The potential of road blockages due to collapses of adjacent buildings and overpass bridges is analyzed, trying to individuate possible criticalities related to specific components/subsystems. The application can be extended based on the proposed approach, to account for other interactions such as failure of pipelines beneath the road segments, collapse of adjacent electric poles, or malfunction of lighting and signaling systems due to damage in the electric power network.

Fragility curves (FCs) constitute an emerging tool for the seismic risk assessment of all elements at risk. They express the probability of a structure being damaged beyond a specific damage state for a given seismic input motion parameter, incorporating the most important sources of uncertainties, that is, seismic demand, capacity and definition of damage states. Nevertheless, the implementation of FCs in loss/risk assessments introduces other important sources of uncertainty, related to the usually limited knowledge about the elements at risk (e.g., inventory, typology). In this paper, within a Bayesian framework, it is developed a general methodology to combine into a single model (Bayesian combined model, BCM) the information provided by multiple FC models, weighting them according to their credibility/ applicability, and independent past data. This combination enables to efficiently capture inter-model variability (IMV) and to propagate it into risk/loss assessments, allowing the treatment of a large spectrum of vulnerability-related uncertainties, usually neglected. As case study, FCs for shallow tunnels in alluvial deposits, when subjected to transversal seismic loading, are developed with two conventional procedures, based on a quasi-static numerical approach. Noteworthy, loss/risk assessments resulting from such conventional methods show significant unexpected differences. Conventional fragilities are then combined in a Bayesian framework, in which also probability values are treated as random variables, characterized by their probability density functions. The results show that BCM efficiently projects the whole variability of input models into risk/loss estimations. This demonstrates that BCM is a suitable framework to treat IMV in vulnerability assessments, in a straightforward and explicit manner.