Holistic Framework to Determine Structural Fire Performance of Shield Tunnel: Mechanism, Models and Design

Fire safety is an increasingly important topic in the underground space. This study aims to contribute to this growing area of research by establishing a holistic framework for shield tunnels and provides new insights into the performance-based analysis. Results from experimental studies on the fire performance of the shield tunnel are presented under the combined effect of fire and structural loading. Test variables included fire exposure, load level, restraint conditions, etc. The experimental investigation has shown the basic failure mechanism of shield tunnel structure in fire. Data generated from fire tests is used to validate models developed for evaluating the fire response of the shield tunnel under any specified fire, loading, and restraint conditions. The multi-scale thermo-mechanical models accounts for critical factors governing structural fire response with fire exposure duration. Results from validation show that the models can capture the fire response of the shield tunnel structure with reasonable accuracy in both thermal and structural domains. Numerical analysis from single ring to multiple rings reveals that the entire structural failure occurs due to localized elevated temperatures. As far as the models concern, an alternative design methodology is introduced based on the concept of maximum allowable deformation, which is exemplified in multiple case studies. The methodology proposed aims at shield tunnels upon the knowledge of fire safety engineering to obtain more trustworthy performance-based designs, and therefore demonstrates adequate fire safety performance. This new understanding should help to improve predictions of the impact of the fire on the shield tunnel and have significant implications for design and maintenance.