Fire Risk Assessment of Subway Tunnel Linings with Different Exposed Surface Areas

Abstract

The impact of fire on underground tunnels can vary significantly with differing patterns of heat exposure, potentially leading to structural failure. Using a circular tunnel case study, a framework for fire risk assessment of the tunnel lining with different exposed surface areas has been established. A critical reduction factor is proposed for modifying the moment-axial force interaction diagrams derived for a pre-specified fire exposure duration to quantify the risk of structural failure. The results show that the worst-case scenario is when the internal surface area of the tunnel lining is partially exposed to fire above its mid-height, as opposed to a complete exposure of the internal surface area. Moreover, this study underscores the critical impact of fire through a combined effect of axial forces and bending moments within the lining section, as compared to its load-bearing capacity. The proposed technique has shown merit in assessing fire risk, particularly when the time to failure of the lining structure is not known before analyzing the impact of fire.