Cardellino, Enrico (2024) Fire behaviour of underground structures: damage states and spalling modelling. [Tesi di dottorato]

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Abstract

The thesis explores the critical issue of fire resistance in tunnels and underground infrastructures, which are becoming increasingly crucial in modern society for overcoming significant physical obstacles and advancing technological capabilities. Historically, tunnel excavation relied on manual labour and rudimentary mechanical aids until the mechanization of the mid-1800s, leading to modern advanced construction techniques using Tunnel Boring Machines (TBMs). Ensuring the safety of these structures, particularly their fire resistance, is fundamental due to the highrisk activities often associated with them. Recently, the EU has established directives to standardize safety requirements for road tunnels, highlighting the importance of structural integrity during fires to ensure safe evacuation and postincident functionality. The main aim of this thesis is to contribute with a new methodology, to the structural fire assessment of tunnels, by using performance-based approaches. In the scientific literature, the fire resistance of tunnel linings is a widely discussed topic, particularly focusing on two main aspects: fire modelling and thermomechanical modelling of structures. In this work, the definition and quantification of damage states and performance levels of underground infrastructures subjected to fire were proposed, in deep understanding and model-ling the very common concrete spalling phenomenon due to fires. In started with studying the existing literature, analysing both prescriptive and performancebased approaches to fire safety. Next, it addresses the definition of damage levels, performance levels and especially their qualitative and quantitative specification. Within this framework, significant importance is given to spalling, which was find very frequent event in tunnel fires. The theory of the phenomenon and modelling are considered to simulate its effects and accurately predict the resulting damage on the structural elements. The result of this work phase is a new spalling model integrated with a probabilistic correction based on experimental data, useful to predict the concrete spalling in case of fire, linked also to the proposed damage levels and their quantifica-tion. The final part of the thesis is dedicated to apply the developed methodologies to a specific case study: an underground structure used for nuclear physics research, at CERN in Geneva, Switzerland. Advanced fire models and thermomechanical analyses were conducted to evaluate the structure's performance under fire conditions, optimizing the simulation of structural behaviour with the application of the proposed methodologies, by including also the spalling phenomenon. In conclusion, the thesis contributes to the field of fire resistance in underground infrastructures by offering new models and methodologies for evaluat-ing structural performances and the spalling effect. The practical application of these models to real scenarios demonstrates their effectiveness and potential to enhance the safety and resilience of underground structures against fire incidents.

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