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

Fire resistant design of both structural and non-structural components in road tunnels is predicated on the determination of fire demand intensity. Current practice typically uses a conservative, deterministic fire curve that does not necessarily provide a representative evaluation of the spatial and temporal distribution of thermal demands in tunnels that are caused by large vehicle fires. This paper proposes a tunnel-specific probabilistic framework for evaluating vehicle fire frequency and intensity based on tunnel geometry and traffic information. The framework leverages a fast-running computational tool that has been previously developed by the authors for calculating fire-induced heat flux exposure on tunnel liners because of enclosed vehicle fires. The likelihood of a vehicular fire and the associated fire size distribution are used to generate probabilistic distributions of total fire exposure for the reinforced concrete tunnel liner. Critical heat flux values according to these probabilistic distributions are then used to assess reductions in concrete material strength and resulting losses in the structural performance of the system. A case study of the Fort Pitt Tunnel in Pittsburgh, PA, is included for demonstration. The proposed framework enables decision making regarding design and renovation of tunnels for fire resistance as well as post-fire inspection by quantifying the risk of capacity reduction in the concrete liner because of a realistic range of fire hazard intensities.