Circular and square steel tubes are two of the most commonly used members in the construction industry in China. Material damage and its accumulation cannot be neglected when structures undergo obvious deformation and material plasticity during severe earthquakes. In another published paper, a material damage constitutive model for Q235 steel was derived, and some of its parameters were defined based on a cyclic test. This article focuses on developing a normalized constitutive model at the material level and a damage model at the component level for square steel tubes based on experimentally derived results. First, the material damage behavior of 10 square steel tubes under five cyclic load schemes was investigated. The material damage and its accumulation at the material level were defined using a userdefined material sub-routine (UMAT) in the finite element software Abaqus. Next, the parameters in the constitutive model were calibrated by the fitting degree between the test result and numerical result. Furthermore, based on the experimental and numerical data, a damage model combined with deformation and energy was developed at the component level to evaluate the overall damage behavior of the specimens. Finally, the parameters in the damage model were calibrated based on the responses of the specimens at the time of collapse. The effect of material damage behavior and the accumulation of damage were found to significantly reduce the collapse load of specimens, which must be considered in the theoretical analysis and design process. The constitutive model and damage model developed in this article can be used to quantify the degree of damage of the material and components of structures under earthquake loads.

The large-span spatial structure is a complex structural type with large number of elements, which makes health monitoring difficult. A time domain global substructural identification method was proposed in this paper to identify the local damage for the large-span spatial structure. The proposed method was an improvement method based on the time domain substructural identification method, which can identify the damage with a reduced structural model, and explicit force identification method, which can give convergent force identification result with incomplete response measurements, and it can assess one or more target substructures without knowing the conditions of the other parts of the structure. The application of the new method to large-span spatial structure was presented, and then an improved global method was proposed to further reduce the computation time and promote it in practice. Two orthogonal spatial square pyramid grid structure models are constructed to validate the time domain global substructural method and the improved global method. The results show that the time domain global substructural damage identification method identifies the small local damage in multiple members with satisfactory accuracy and the improved global method effectively shortens identification time.