PEC possesses outstanding expertise and experience in the protective design of transportation infrastructure subject to explosive, impact, and fire threats. Our team has conducted transportation security projects on four continents and will shortly chair the ASCE Technical Committee for Bridge & Tunnel Security. PEC has been central to much of the seminal R&D and testing work pertaining to bridge security over the last decade, including the development of NCHRP Report 645 Blast Resistant Highway Bridges: Design and Detailing Guidelines. Recent work has included the development of the U.S. Department of Homeland Security’s (DHS) Anti-Terrorism Planner for Bridges (ATP-Bridge) software and the U.S. Federal Highway Administration (FHWA) Bridge Security Design Manual, scheduled for publication in late 2017.
(Left) Interstate 85 bridge fire and subsequent collapse [March 2017]
(Right) Tanker truck catches fire on Harbor Bridge in Corpus Christi [April 2017]
The threat posed by fire/thermal effects to bridges can be seen with events like the recent Interstate 85 collapse in Atlanta, GA and the massive hydrocarbon pool fire that shut down the Harbor Bridge in Corpus Christi, TX. These types of incidents demonstrate the potential severity of accidents and malicious acts involving fire and bridge structures. PEC is committed to supporting bridge designers, builders, and operators in the identification, characterization, and mitigation of potential fire/thermal hazards.
Where appropriate, PEC utilizes recognized empirical methods and closed-form solutions to quantify potential consequences of a fire/thermal threat scenario. However, the scale, complexity, and criticality of many bridges require the use of higher-fidelity methods to effectively quantify thermal loads arising from fire events, as well as associated material damage and structural response.
Connecting the thermal output (including convection and fluid flow through complex geometries, or under variable environmental conditions, e.g., wind) of a given fire to a system response is achieved via the method of conjugate heat transfer. Leveraging our extensive experience using and extending the OpenFOAM C++ library and the NIST Fire Dynamics Simulator (FDS), PEC provides detailed computational fluid dynamics (CFD) modeling, including combustion and coupled heat transfer. Where required, thermal loads can be mapped to additional finite element thermal solvers for detailed evaluation of transient heat transfer and degradation of structural performance.
Analysis of Fuel Truck Fire Under Highway Overpass using NIST FDS
Modeling rapid evaporation and combustion of liquid fuels is essential for analyzing liquid pool fires, including fuel transport (potentially through drainage systems). This requires explicit (volume-of-fluid-based) approaches to capture the dynamics of liquid fuel transport and drainage, combined with accurate combustion modeling.
Consideration of hot gas transport and combustion products (species) is essential for analyzing scenarios such as a fire on a bridge deck and the calculation of thermal loads imparted to above-deck supporting components (e.g., bridge towers, stay cables, and suspenders). Simplified models that only consider radiation can yield specious results for such scenarios, and therefore the use of higher-fidelity methods is necessary.