TIME-VARYING SEISMIC DAMAGE OF STEEL FRAME JOINTS CONSIDERING ATMOSPHERIC ENVIRONMENT

Due to environmental effects, mechanical properties of structures deteriorate with time. Based on low cycle tests of 12 steel frames with varying degrees of corrosion, the deterioration of mechanical properties of steel frame joints was analyzed. Considering that the deformation of steel frame joints is less than the deformation limit, it is not suitable to evaluate the degree of damage of the steel frame. The stiffness index can reflect two performance indexes of the bearing capacity and the deformation of the member, and the deformation of the member is inversely proportional to its stiffness. A two-parameter seismic damage model based on component stiffness and energy dissipation was established to consider the initial damage caused by environmental factors. The stiffness of the component and the cumulative energy dissipation capacity were linearly related to the corrosion rate. The computational accuracy of the damage model was checked by the regression of the experimental data. The results showed that the damage model had high computational accuracy and was easy to calculate, and it was suitable for damage description of steel frame joints under earthquake actions. Based on the damage model, it was assumed that the annual corrosion rate of the components was the same, and the time-varying damage model considering the environmental action was established.