Performance-based evaluation of exposed electrical conduit for severe fires in roadway tunnels

Abstract

This paper numerically investigates the thermal impact of vehicle fire hazards on exposed electrical conduits in roadway tunnels. By modeling the fire and subsequent heat transfer to the conduit, the analysis results provide performance-based design guidance for allowable temperature increases before the conduit and its contents fail. The computationally efficient Confined Discretized Solid Flame (CDSF) model (previously developed by the authors) is used to calculate the heat flux imparted to the tunnel conduit from the enclosed fire. A simplified finite element model is used to calculate the subsequent thermal response of the conduit piping. Envelopes of conduit temperature increase, as well as exposure duration, are developed for a range of vehicle fire intensities that are enclosed in two- and three-lane circular tunnels. By accounting for overall traffic volume and truck traffic percentage, the limiting criteria for conduit temperature increase during standard experimental testing can be associated with a return period or a probability of exceeding an expected temperature. Sensitivity analyses are performed to examine the influence of conduit size and material, conduit location, tunnel ventilation conditions, average annual daily traffic, and traffic composition.