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

Stochastic Thermal Demand and Resulting Capacity Loss of Concrete Tunnel Liners Subjected to Vehicle Fires

“…The two test programs involve different tunnel geometries, fire sizes, and wind speedsthe range of parameters provided robust validation of the FDS modeling approach. Conservative consistency was achieved between the FDS results and test data; details for this comparison have been reported previously by the authors (7). The validated FDS modeling approach was subsequently used to develop several benchmark fire scenarios for multiple tunnel cross-sectional shapes that are typical of the current U.S. tunnel inventory.…”

“…However, intermediate complexity tools like the aforementioned CDSF model can more rapidly predict the distribution of steady-state incident heat flux (i.e., the combination of radiative and convective effects) on the interior surface of the concrete tunnel liner based on a fire event size and location within the tunnel. In the CDSF model, radiation is emitted directly from the fire using discretized solid flame calculations, and convection from smoke is applied as a tapering layer (i.e., with the greatest intensity above the fire and decreasing downward and longitudinally away from that location) ( 7 ). The first step in analyzing the heat flux contour on tunnel liners from vehicle fires is to convert the vehicle footprint to an equivalent pool surface area of diesel fuel that emits the same HRR.…”

“…The equivalent diesel pool fire is adopted as a representation of the thermal energy released by an actual vehicle fire. The conversion simplifies the analysis by maintaining the most important parameter (i.e., HRR) of the vehicle fire, while avoiding the definition of the numerous material types that comprise a vehicle and its cargo ( 7 ). An elliptical rather than rectangular diesel pool footprint is used to avoid creating corners in a vertically extruded solid flame model.…”

“…A confined flame is implemented by shortening the flame height to remain within the tunnel while increasing the emissive power in the tapering (i.e., domed) top surface of the confined solid flame shape to ensure conservation of energy. Further details on this approach and the associated experimental and numerical validation can be found in the authors’ previous work ( 7 ).…”

“…Latin hypercube sampling (LHS) ( 6 ) is used to generate input variables that include uncertainty—LHS has higher representation capability for stochastic parameters with less computational demand than the common Monte Carlo method. A rapid thermal demand mapping tool called the confined discretized solid flame (CDSF) model ( 7 ) is utilized for fire hazard analysis in this proposed framework. The CDSF is a semi-empirical solid flame model that was previously developed by the authors to calculate the spatial contour of steady-state total heat flux (including both radiative and convective effects) on a tunnel liner from a defined enclosed fire.…”