Influence of Damage and Degradation Index on Steel Frame under Severe Earthquakes

In order to quantitatively describe the effect of strength and stiffness degradation on seismic behaviors of steel frame, numerical models (the equivalent constitutive model considering damage and steel hysteretic constitutive model without considering damage) for predicting seismic behaviors of steel frame structures were described. Three frame models of five-floor, ten-floor and fifteen-floor frames were analyzed. Eight earthquake records were selected for time history analysis. The differences of inter-story drift ratio distribution calculated by two constitutive models were compared. The influencing laws and degrees of damage and degradation on seismic behaviors were also obtained. Finally, a prediction curve of degradation index was proposed, which could be used for damage control. Preliminary evaluation methods for seismic performance of steel frames considering damage and degradation were discussed. The analysis of the results showed that: the inter-story drift ratios of the three frames calculated by damage model were obviously larger than the results of non-damage model, showing that damage and degradation amplified the structural deformations. With the increasing of floors, the differences of inter-story drift ratio between damage model and non-damage model were gradually reduced. The weak stories of three models were located at 0.4 to 0.5 times of structural height, which should be paid more attention in design process.