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Fire hazards can cause severe and irrecoverable damage to reinforced concrete tunnel linings. Historically, major fire events have led to months of downtime and millions of dollars of losses due to repair costs and affected operations. Advanced modeling can be used during the design process or for post-fire assessment to evaluate the level of damage and repairability of tunnel liners subjected to fire. Proper material properties, both at elevated temperatures and post-fire, are needed as inputs to these models. This paper provides a comprehensive review of experimental investigations on the residual compressive strength of concrete after exposure to high temperatures up to 1000 °C. The existing data are analysed to identify attributes that could affect the dispersion in residual strength. The refined datasets are used to develop probabilistic models for the normalized residual compressive strength of concrete. Also, the stiffness of soil or rock that is supporting the tunnel liner impacts the response of the structure. Thus, the paper provides the results of experiments to characterize the elastic modulus of three rock samples, including limestone, mudstone, and gypsum at temperatures ranging from 20 to 80°C. Experimental data in the literature show a larger variation in the stiffness of clay could be expected when compared to rock. The analyses indicate that the vertical crown displacement of a tunnel liner could be underestimated by 26% if the temperature-dependent elastic modulus of clay is not considered in the structural analysis of the tunnel.

The paper describes the outcomes of the analysis of a steel braced frame subjected to fires following earthquake (FFE). Nonlinear time-history analyses were performed in order to evaluate the seismic response. Then, based on the damage suffered by the structure, which was estimated according to the inter-storey drift ratio (IDR) and floor acceleration, the post-earthquake fire ignitions within selected compartments were considered. Natural fire curves were determined by means of zone models. Thus, compartmentation and opening characteristics were included in the analysis. Finally, thermomechanical analyses were run and failure criteria based on the column and beam displacement and rate of displacement were applied. The results of the probabilistic analyses were used to produce fragility functions to evaluate the probability of exceeding a limit state conditioned on an intensity measure in the context of FFE.

Evaluating reliability of structures requires consideration of the uncertainties in demand and capacity. While material strengths exhibit a significant scatter at high temperature, no probabilistic model is available to quantify these uncertainties. To fill this gap, this work has compiled a database of test data on strength retention factors for steel and concrete, formulated a set of temperature-dependent probabilistic models based on these data, and applied the models in FE analyses of columns in fire. The proposed material models yield an average response similar to well-established deterministic models (Eurocode), but allow an explicit evaluation of the variability in structural fire response due to experimentally observed variability in material strength.