Multi-level damage index of RC structures based on material damage

In past seismic events, earthquakes have often caused significant damage to buildings. It is noteworthy that most of the existing buildings are reinforced concrete structures. Therefore, in order to mitigate the damage caused by earthquakes, it is important to conduct damage assessment of reinforced concrete structures. Considering that damage at the material level is the fundamental cause of component and structural performance degradation, indices based on material damage often have advantages in reflecting and evaluating component and structural damage. This paper proposes a damage constitutive model for concrete based on existing research results. Then, aiming at the shortcomings of current research on steel bar damage constitutive models, a steel bar damage constitutive model under cyclic loading is proposed, reflecting various failure modes of steel bars under seismic actions. Based on this, a multi-level damage index system from materials to components to structures is established. Through multi-level experimental simulations and finite element analysis, the accuracy of the proposed damage indices is validated, and performance indices for components and structures are provided. These indices can effectively reflect the damaged state of components and entire structures and can be used to guide seismic design, damage assessment, and strengthening design.