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Assessing and Improving the Resilience of Highway and Railway Tunnels to Fire and Blast
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2020-06-01
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Edition:Final Report (Sept. 2016 to Oct. 2018)
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Abstract:Tunnels are a critical component of the transportation infrastructure, and unexpected damage to a tunnel can significantly and adversely impact the functionality of a transportation network. 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. They are also vulnerable to potential threats of intentional and accidental blast that can lead to local damage (spalling and breach) and progressive collapse. This report outlines approaches for assessing fire-induced thermal demands and blast-induced damage to the concrete tunnel liner. First, a rapid assessment approach is developed to evaluate thermal demands using models that are calibrated using computationally intensive numerical assessment, experimental data, and semi-empirical relationships. These fast-running approaches are useful for calculating appropriate design limit states and to better understand risk potential in a multitude of underground environments. Utilizing Rhino and Grasshopper, the discretized solid flame model is adapted to account for confinement within 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. Second, an approach is presented to predict and map the damage to the reinforced concrete liner of a roadway tunnel for various explosive threat sizes and tunnel geometries. The proposed fast-running approach is an alternative to either high-fidelity computational models that require massive computational effort or simplified design expressions that cannot accurately capture spatial distributions of damage. A literature review of existing evaluation methods is conducted, and potential blast event scenarios are examined with varying charge position and size. Rectangular, horseshoe, and circular tunnel geometries, each with the same traffic throughput, are evaluated. The proposed approach shows good agreement with high-fidelity numerical models analyzed in LS-DYNA and is then used to examine the relationship between increasing blast hazard intensity and the extent of spall and breach damage. Inflection points in this relationship can be used to identify hazard levels at which a progressive collapse evaluation would be warranted.
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Content Notes:Zenodo Data Archive: https://zenodo.org/communities/utc-uti
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[PDF-7.22 MB]
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