Experimental And Theoretical Research On Seismic Behavior Of Strengthened Concrete-filled Square Tubular Frame

The structure of concrete-filled square steel tubular (CFST) has been increasingly used in high-rise and super high-rise buildings. The main researches dwell on beams, columns and joints, while few researches focus on the frame consisting with CFST columns and steel beams. Based on the former research on seismic safety about one CFST frame by pseudo static test, seismic safety of the strengthened damaged CFST frame is studied by the pseudo static test and nonlinear finite element analysis. Three aspects of work were done as follows :1. By studying CFST columns'hysteretic behavior under low cyclic loading, the cumulative dissipated hysteretic energy was utilized. Moreover, a two-parameter earthquake damage model based on CFST column has been set up by regression analysis.2. According to the demolishing characteristics of CFST frame damaged by earthquake, the compound design of axillary plates,cover-plate reinforcement and dog-bone joints was adopted to the damaged frame's nodes. Seismic safety of the strengthened damaged CFST frame was then studied by the pseudo static test.3. Having established the nonlinear finite element model of CFST frame, the calculated hysteretic curves were obtained under low cyclic loading. In order to analyze the dog-bone joints'strengthening effect, the nonlinear finite element model was built for comparison .Research results: the two-parameter earthquake damage model column accords with the CFST structures, which is helpful in evaluating the seismic damage possibilities of such structures. Besides, the repaired frame under low cyclic loading takes on good states: its bearing capacity, ductility, and energy dissipation capability energy dissipation are improved, is similar to the undamaged one. Thirdly, the joints have good turning capacity; the nonlinear finite element analytical results are consistent with experiment results, and the calculation results show that the dog-bone joints have significant effect on reducing the stiffness degradation's speed and increasing the structure's ductility.