AbstractEvaluating the performance of postfire RC beams is a crucially important step to provide information for structural engineers on the next step of retrofitting design. Appropriate evaluation methods should be placed in the context of very limited information obtained from a real fire event. In this direction, this paper presents an experimental and theoretical investigation on the flexural performance of postfire RC beams. Experiments were performed on 15 RC beams, which were classified into 5 groups exposed to 0, 30, 45, 60, and 75 min of fire. These beams were then loaded to failure and different mechanical properties were analyzed, followed by theoretical analyses. The results showed that postfire specimens experienced flexural-shear failure, which was different from flexural failure of control specimens. Compared with control specimens, the yield stiffness and strength of postfire specimens were reduced by 47.5% and 13.1%, respectively, while yield deflection was increased by 42.6%−91.6%. The ductility of postfire specimens was decreased by up to 61.1%, resulting in moderately ductile behavior. Significant changes in yield stiffness, yield deflection, and ductility confirmed these high-priority parameters in evaluating postfire RC beams. The proposed simple method, which combined the temperature-distribution model and the reduced 500°C isotherm method, provided conservative bending moment capacities compared with the test results. The simplicity and reasonable safety of the model can be useful for structural engineers.

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