Framework for rapid prediction of fire-induced heat flux on concrete tunnel liners with curved ceilings

Abstract

Recent vehicular fires in concrete-lined tunnels have demonstrated the vulnerability of the liner to heat-induced spalling and cracking damage. To evaluate the structural fire resistance of either existing or newly designed tunnel structures, there is a need for fast-running tools that can accurately predict the distribution and severity of fire-induced heat exposure over the interior surface of the liner. This study proposes an analytical prediction framework which is more realistic than current design fire curves and yet less computationally intensive than high-fidelity numerical solutions. The Confined Discretized Solid Flame (CDSF) model is proposed for calculating the spatial contour of total heat flux imparted to the tunnel liner due to an enclosed fire. The CDSF computation includes both radiation heat transfer via a 3D discretized solid flame and a convective region representing the ceiling jet of smoke and hot gas. CDSF heat flux results show strong agreement with experimentally validated computational models at a fraction of the computational cost over a matrix of four large vehicle fire sizes and three tunnel prototypes with curved ceilings (i.e. horseshoe or circular cross-sections). The fast-running CDSF approach is conducive to parametric thermal analysis and stochastic damage evaluation for concrete tunnel liners exposed to fire.