Novel Approach to Calculate the Postfire Bending Capacity of Corroded Reinforced Concrete Beams: Incorporating Failure Mode Analysis

This paper proposed a method, combined with failure mode analysis, for calculating the flexural capacity of corroded reinforced concrete (RC) beams after a fire. The method took into account the degradation of the mechanical properties of steel and concrete due to corrosion and elevated temperatures as well as the reduction in the cross-sectional area of steel bars caused by corrosion. Further, it also considered the varying impacts of different cooling methods on the failure modes. By analyzing the stress and strain distribution across the normal cross-section of postfire corroded RC beams, four failure modes were identified, with corresponding calculation methods for bending capacity developed for each mode. The results show that, for initially underreinforced beams exposed to high temperatures, an increase in corrosion leads to a shift in the bending failure mode from Mode A or B to Mode D, accompanied by a gradual decrease in bending capacity until it aligns with that of a plain concrete beam. Experimental analysis was conducted to identify the conditions for the occurrence of failure Modes A and B, and the accuracy of the proposed method was validated. Further, a database was compiled from flexural experimental data in the literature, revealing that the calculated flexural capacity based on failure modes closely aligns with experimental results, further confirming the feasibility of the proposed approach. However, it is worth noting that Modes C and D have not yet been experimentally verified, which may be attributed to the fact that the corrosion degrees investigated in both the experiments and existing literature are limited to values within 0.144. Therefore, further research is required to verify the conditions under which Modes C and D occur and to assess the accuracy of the corresponding calculations. The calculation method introduced in this paper is expected to be valuable for assessing the performance of corroded RC beams in aging RC structures after accidental fire events.