Development and Verification of a Confined Discretized Solid Flame Model for Calculating Heat Flux on Concrete Tunnel Liners

Road tunnels are susceptible to severe fire-induced heat flux due to the constant presence of vehicular traffic combined with the likelihood of accidents and subsequent combustion. Rapid assessment of thermal demands is a necessity to calculate appropriate design limit states and to better understand risk potential in a multitude of underground environments. A proposed approach is developed which allows for rapid assessment of thermal demands using models that are validated and informed through computationally intensive numerical assessment, experimental data, and semi-empirical relationships based on first principles. Utilizing Rhino and Grasshopper, the discretized solid flame model is adapted to account for the confinement present in tunnel structures and development of a convective zone under the tunnel ceiling. The confined discretized solid flame model (CDSF) accurately captures the spatial distribution of heat flux in circular tunnels as compared to experimentally-validated, high fidelity numerical solutions. Potential for cracking, spalling, breach, and other adverse structural consequences can be evaluated based on contour maps of total heat flux over the tunnel liner.