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Development of a Blast and Fire-Resistant Structural Tunnel Liner
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2020-04-01
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[PDF-11.98 MB]
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Edition:Final Report (Sept. 2016 to Oct. 2018)
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Abstract:A comprehensive study was conducted on the design and performance of concrete tunnel liners subjected to blast and fire events. The effort initiated with a study to assess the impact of fire and blast events on the structural performance of the concrete liner. The effort is divided into three phases. The first phase focuses on the implications of blast events on the tunnel liner. The second phase examines the implications of fire events on the tunnel liner. The third phase consists of a preliminary study on the performance of the concrete liner subject to fire demands. In a contact or near filed blast event, the reflected tensile wave near boundaries is the primary reason for concrete spallation damage. Appropriate concrete model (RHT model) can be selected in finite element software LS-DYNA to simulate the behavior of concrete slab as well as concrete tunnel lining subjected to blast. The spalling of supported tunnel model is alleviated via changing the property of backfill. By increasing the backfill impedance, the tensile stress in concrete will gradually become compression thus reducing the amount of damage to the concrete substrate. The numerical study shows that the damage to tunnel liners will be localized and do not represent a significant threat to concrete lined tunnels. Experimental testing would be of use to validate the numerical results. Due to the fact that the benefits gained through modification of the substrate are minimal, the cost implications of substrate modification are high, and that minimal performance improvements will be achieved for a low likelihood threat, the blast testing is not recommended. The numerical tool for fire evaluation is discussed. The model consists of a confined discretized solid flame and is verified in comparison to computational fluid dynamic numerical results which were calibrated from experimental tests. The model indicates significant thermal exposure of the tunnel surface due to fire events. To address this threat a fire testing simulation fixture was developed. The experimental setup for the fire effects is presented and preliminary test results are provided showing spall and fire induced damage to tunnel liners.
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