Fire-induced concrete spalling: development and validation of a novel and practical numerical approach incorporating a stress-strain-based criterion

Fire-induced concrete spalling is a severe and complex phenomenon that affects the safety of reinforced concrete structures in fire. A major obstacle in simulating fire response of concrete structures is the lack of effective numerical models for fire-induced concrete spalling, a problem complicated by its multi-scale nature. As a consequence, the spalling theories cannot be extensively validated. This research developed a practical numerical approach using user-defined subroutine VUSDFLD in ABAQUS to simulate fire-induced concrete spalling. A spalling criterion was proposed based on both stress and strain indicators. The proposed numerical approach and spalling criterion were verified against experimental results of a concrete beam and a concrete column, subjected to fire exposure. The numerical study successfully reproduced the experimentally observed spalling patterns, deformation responses, and fire resistance of the reinforced concrete beam and column. It also demonstrated the capability of the proposed approach to capture the progressive development of fire-induced spalling under the combined effects of pore pressure and thermo-mechanical actions. Good comparisons were achieved in terms of spalling patterns, deformations, and fire rates, which prove the reliability of the proposed spalling criterion and the numerical approach. Stress evolution process was analyzed to further reveal the failure mechanism of concrete beam and column due to fire-induced spalling.