Simulation methodology for the assessment of the structural safety of concrete tunnel linings based on CFD fire – FE thermo-mechanical analysis: a case study

ABSTRACT This work aims to provide a comprehensive procedure for the assessment of structural safety of tunnel linings exposed to fire. To this purpose, numerical simulations that model the three fundamental features influencing tunnel fire safety design, namely fire dynamics, thermal behavior and structural response, are performed. Fire development within tunnel is simulated by applying advanced Computational Fluid Dynamics (CFD) techniques under a Fire Safety Engineering (FSE) approach. CFD fire simulation is carried out first, and then the results are transferred into a thermo-mechanical Finite Element (FE) model. A “sequentially coupled thermo-mechanical analysis” is then performed by linking a heat-transfer analysis that provides the temperature distribution within the lining with a refined non-linear mechanical simulation. A proper non-linear constitutive model for concrete subjected to high temperature, able to account the main features governing concrete behavior (i.e. cracking and crushing), is applied to the purpose. Comparisons in terms of structural results obtained by applying this coupled procedure and those obtained through a thermo-mechanical analysis adopting a standard time-dependent fire curve are provided. The importance of considering a refined simulation of the fire scenario is proved: from a structural point of view, significant differences concerning stress distribution and cracking development in the lining are indeed observed. Therefore, the use of a realistic model to describe fire development appears crucial to understand the behavior of unreinforced concrete linings subjected to fire and to control their possible weaknesses, such as the appearance of cracks.