A precise 3D numerical method of dynamic and static behaviors in corroded RC beams exposed to fire: Considering multi-damaged cracks

This paper presents a precise 3D numerical simulation method for analyzing the behavior of corroded reinforced concrete (RC) beams exposed to fire. Multiple damage factors, including corrosion cracking, load-induced cracking, and spalling of the concrete cover were considered. Specifically, cohesive elements, the concrete damaged plasticity model, and birth-death elements are employed to effectively simulate corrosion cracking, load-induced cracking, and cover layer spalling in corroded RC beams, respectively. These damage mechanisms are incorporated into the heat transfer model to obtain accurate temperature field. Subsequently, the temperature severed as the predefined filed was introduced into the static loading model. Moreover, 3D springs were also employed into the model to represent the corrosion-induced bonding degradation between reinforcement and concrete. Following this, the effects of fire exposure time, corrosion level, and cover layer thickness on the thermal and static behavior of corroded RC beams was systematically investigated through analysis of temperature field and static loading results. Furthermore, modal analysis was conducted on corroded RC beams through numerical simulation. It was observed that the first-order natural frequency variation of corroded RC beams after fire exposure correlates closely with residual moment capacity. Based on this correlation, a novel prediction equation derived from dynamic analysis was proposed to evaluate residual moment capacity. It demonstrates a high-level accuracy within 10 % error compared to experimental values. In conclusion, this study provides a method for predicting the residual moment capacity of corroded RC beams after fire exposure based on the structure's vibrational natural frequency, without causing any damage to the structure.