Dottorato in INGEGNERIA STRUTTURALE E GEOTECNICA

Titolo della tesi: Muli-Scale Natural Hazard Risk and Resilience

The growing toll of natural hazards represents a pressing call to action to address the inherent vulnerabilities of our built environment. With climate change influencing both the frequency and intensity of future extreme events, the already critical situation is expected to worsen. Addressing natural risks and the vulnerabilities of our cities is therefore of utmost importance to prevent societies from becoming trapped in a recurrent disaster–recovery cycle. Enhancing the resilience of society requires urgent investment in nationwide systematic strategies for natural hazard risk mitigation. A major step toward achieving resilience lies in the risk assessment phase. Assessing risk means understanding risk, which is a fundamental prerequisite for the development of effective mitigation strategies. A clear comprehension of risk empowers stakeholders and decision-makers to make informed choices and to design policies that strengthen community resilience. Among all natural hazards, three have been identified as the main contributors to losses: earthquakes, floods, and windstorms. Within this context, over the past decades, significant efforts have been devoted to developing methodologies for the assessment of these three hazards. These methodologies have been implemented at varying levels of detail, balancing accuracy and computational efficiency. However, most existing approaches are designed either for nationwide analyses or for individual assets, resulting in a gap at intermediate scales, such as urban or regional levels, where communities are best positioned to take direct action. National-scale models often lack the spatial resolution needed to inform local decision-making, highlighting the need for a methodology that bridges the gap between national-scale and asset-specific assessments. Considering this background, this Thesis aims to (1) investigate and propose methodologies for the assessment of seismic, flood, and windstorm risk at the single-building scale, and (2) develop adaptive and scalable frameworks for the assessment and prioritization of interventions for multi-hazard risk at both urban and national scales. The Thesis first provides the background and motivation for the research, including an overview of observed building damage due to the considered hazards, and a review of existing risk assessment methodologies from building codes, guidelines, and scientific literature. The primary focus is on ordinary reinforced concrete (RC) buildings, which represent the majority of the Italian and European building stock. For seismic risk, the study includes a review of historical construction practices, observed vulnerabilities, and existing portfolio assessment approaches. Similar discussions are presented for flood and windstorm hazards, covering the governing phenomena, observed damage mechanisms, and assessment methodologies at multiple scales. The first contribution of this Thesis concerns seismic risk assessment. Building upon existing methodologies, a unified framework for the assessment and classification of buildings in urban areas was proposed, based on safety, economic losses, and downtime. The framework operates on a building-by-building scale, employing a simulated design procedure and a mechanical-analytical approach using the SLaMA (Simple Lateral Mechanism Analysis) method. The simplicity and codified nature of SLaMA ensure a fast, scalable, and reliable assessment suitable for large-scale applications. The approach also enables the consideration of retrofit solutions and the evaluation of cost–benefit analyses. The methodology was applied to two case study neighborhoods, where the effects, cost-effectiveness, and prioritization of mitigation strategies were evaluated. The second contribution introduces a novel methodology for windstorm risk assessment, focusing on dynamically rigid buildings (i.e., structures whose dynamic response does not significantly influence the surrounding wind field). The approach adopts a component-based loss assessment, incorporating Fault Tree Analysis (FTA) to model cascading effects of water ingress resulting from envelope damage. The methodology allows for the estimation of vulnerability functions in terms of repair costs and downtime, within a fully probabilistic framework that quantifies associated uncertainties. An illustrative case study on a residential building demonstrates the applicability of the method. Finally, the third contribution integrates the developed and collected methodologies into a unified, multi-hazard framework for the assessment of seismic, flood, and windstorm risks at the urban scale. For each building, a component-based loss assessment is performed to derive vulnerability functions for both repair costs and downtime under all hazards. Results are integrated within a harmonized framework and visualized through a user-friendly interface to effectively communicate findings to non-technical stakeholders and decision-makers. The framework was applied to a case study neighborhood, where the multi-hazard prioritization of buildings was assessed, yielding estimates of direct and indirect losses and downtime across the urban area.