Fire in Railway Tunnels Dynamic Simulation. Structural Assessment and Effects Mitigation

Fire safety in tunnels is a key issue for railway safety. Various approaches are usable to assess the concerned risks and to assess how to manage them. Large-scale experiments are not economically affordable to recreate a significant variety of configurations, reason why Computational Fluid Dynamic (CFD) is nowadays the prevalent method to address such topics. This paper discusses the simulation of a very typical fire-scenario for lines with relevant freight traffic carried out with the Fire Dynamics Simulator (FDS). The scenario includes a 150 MW fire caused by an accidental spillage of liquid octane from a tanker inside an artificial railway tunnel. The main goal is to study how the geometric peculiarities of the tunnel can significantly influence the temperature field within the tunnel, to an extent that is not easy to predict through simplified conventional methods. The applied method bases on a sensitivity analysis on obtained results to the variation of specific parameters. The structural checks performed in this scenario show that prolonged exposure to fire plays a key role in reducing the load bearing capacity of the system. This result is more relevant for the structural elements inherently sensitive to spalling phenomena, triggered by high temperatures (e.g. beams or columns characterized by low concrete cover). These elements need appropriate mitigation measures to prevent the onset of spalling phenomena. In particular, the case study shows how the installation of insulating plaster is able to protect the pre-stressed concrete roof beams and to safeguard the required safety level for the structure.