Reliability-Based Moment Capacity Assessment of Reinforced Concrete Beams in Fire

Reliability-based moment capacity assessment of reinforced concrete (RC) beam sections exposed to different fire durations was performed in this study. A numerical model of RC sections was developed, taking into consideration the temperature distribution and temperature-dependent mechanical properties of materials. The model was verified and then used for parametric and reliability studies. The studied variables included the steel strength, concrete strength, cover thickness, and loads; these variables were applied in Monte Carlo simulations in which the fire duration varied from 0 to 80 min. Results showed that the coefficients of variation (COV) of yield moments due to variations of material strengths and cover thickness were lower than 0.042 and then increased to 0.059 when variations of loads were considered. However, these variations resulted in similar failure probability. In contrast, the failure probability of RC beams increased significantly up to 0.98 as the fire duration increased because the mechanical properties of materials were degraded in fire. Therefore, the fire duration is the most important parameter which determines the failure probability, whereas the probabilistic variations of materials and loads can be ignored in designing RC beams in fire.