Titolo della tesi: Assessment and management of earthquake NaTech risk in Major Hazard industrial Plants: a case study on cylindrical tank with floating roof
Industrial plants, which include a wide variety of equipment and structures, exhibit elevated vulnerability to earthquakes. The risk of accidents with severe consequences for health, environment, and economy, as substance releases, fires and explosions, increases when dealing with hazardous substances, which classifies facilities as Major-Hazard industrial Plants (MHPs), as petrochemical plants. The European Seveso III Directive underlines the urgency of assessing and managing seismic risks in MHPs, in the context of NaTech, where natural and technological events intersect. Despite the availability of numerous techniques for seismic risk assessment, the absence of a standardised methodology presents challenges in integrating seismic risks into these processes. Fragility curves, commonly used for vulnerability assessment, are not applicable to all equipment, especially to non-structural elements, which are often neglected in risk analyses. Also, seismic risk mitigation remains an open issue, whit proposed intervention measures frequently left unimplemented. Among industrial components, large storage tanks with floating roof are particularly prone to seismic failures. To ensure comprehensive risk assessment and mitigation, predicting the seismic behavior of tanks due to fluid dynamics is essential. In particular, the convective motion of the fluid can induce hydrodynamic overpressures on the floating roof, leading to damage, excessive inclination, sinking, and fluid overtopping. Additionally, pounding between the bumper bars and the tank wall may occur due to the in-plane oscillation of the roof. Damage to the roof seal could potentially lead to sparks and rim fires. While extensive research has focused on the transverse motion of floating roofs, the in-plane response remains largely unexplored in the literature. This study aims to address this gap by clarifying the methodology of seismic risk analysis for MHPs through its application to a floating roof tank. Vulnerability assessment and fragility curves require simple structural models in order to carry out analyses without relying on a comprehensive model, as already exists in the literature. Therefore, a simplified and reduced model for the in-plane dynamics of the floating roof is proposed, accounting for roof-to-wall pounding. To obtain simplified models, a complete finite element model of the tank with fluid, roof, sealing system and bumper bars has been developed. This simplification is achieved through the validated hypothesis of decoupling between transversal and in-plane components of roof motion. The study also evaluates the influence of seal and impact parameters on the roof dynamics. Seismic damage probability assessment is conducted using simplified models, and potential solutions for seismic risk management of floating roof tanks are proposed, including the use of deformable and dissipative bumpers to mitigate roof impacts, as well as the implementation of fiber optic sensors for tank monitoring.