United States Department of Transportation
i
Post-fire Damage Assessment of Concrete Tunnel Liners
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2022-07-01
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[PDF-7.45 MB]
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Edition:Final Report 02/01/2021 – 07/31/2022
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Abstract:Extreme fire events in tunnels may have catastrophic consequences, which include loss of life, structural damage, and major socioeconomic impacts due to service disruptions. This report focuses on post-fire damage assessment of reinforced concrete tunnel liners and provides recommendations on damage assessment procedures for application in practice. A review of experimental post-fire residual mechanical properties, primarily organized and sorted based on aggregate type and soak time, are presented. The normalized residual concrete strength results are compared to Eurocode. The reduction factors for siliceous aggregate are approximately equivalent to the median of the data, whereas the Eurocode reduction factors are likely unconservative for calcareous aggregate, although more data is needed to confirm. Two continuous temperature-dependent probabilistic models, for residual concrete strength with siliceous and calcareous aggregates are developed for use in numerical simulations. Further, this report describes a series of finite element analyses on realistic tunnel sections within soil or rock profiles. Four tunnel-soil combinations are presented: shallow and soft soil, moderate depth and soft soil, moderate depth and rock, and deep depth and rock. Post-fire residual deformations and stresses within concrete liner are studied. The model for soft soil captures temperature-dependent excess pore water generation and thermal hardening. Upper and lower bounds of modulus of elasticity for models containing temperature- dependent soils are presented, although more data is needed for other soil or rock types. Finally, this report details a framework for the damage assessment of concrete tunnels following a fire, considering ad-hoc processes, advanced modelling, data collected from stakeholders, and published classification and damage thresholds. The framework quantifies fire damage to tunnel linings in terms of surface discoloration, crack width, concrete spalling, sectional temperatures, strength loss of materials, and residual displacement. A case study is presented, and a damage classification system is proposed to systematically map damage metrics to repair strategies.
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