| The structures of concrete-filled steel tubular(CFST)is widely used in high-rise buildings because of its excellent seismic performance.How to assess the damage of structures accurately is a key problem to for the application of the design of CFST based on the seismic design theory.The current code of”Seismic Design Code”(GB 50011-2010)is mainly based on the research of reinforced concrete structures.The evaluation indexes of seismic performance of structures are the inter-story drift.Based on the limitation of inter-story drift of reinforced concrete structure and steel structure,“Technical code ofr concrete filled steel tubular structures”(GB 50936-2014)provide the the limitation of inter-story drift of CFST structures.However,studies have shown that,there is a risk of evaluation failurethe when inter-story drift as a performance index can not consider the impact of seismic cumulative damage on the the structure after the earthquke.In order to ensure the safety of concrete-filled steel tubular structures,this paper chooses the performance index parameters based on stiffness degradation,then carry out the stiffness degradation performace index limits for concrete filled circular steel tubular and rectangular steel tubular.The purpose of the index limits tha based ”Seismic Design Code” is to supplement the current codes.The main research contents are as follows:(1)The results of quasi-static test of 111 concrete-filled steel tubular columns were collected and analyzed,then to evaluate the result of the accessing to the damage of concrete-filled steel tubular column.Compared with the inter-story drift,this paper verifies the validity of the stiffness degradation index.(2)According to the classification method of structural performance level in ”Seismic Design Code”(GB 50011-2010),this paper divides the performance level of concrete-filled steel tubular column into basically complete,slightly broken,medium broken,severe broken and collapse.Then the paper puts forward the criterion of the corresponding performance level according to the damage of the steel pipe and the concrete.(3)Based on the finite element analysis software platform of ABAQUS,this paper developed material subroutines of concrete filled circular steel tubular and rectangular steel tubular.Then the finite element model of two kinds of concrete-filled steel tubular columns is established,and the reliability of the finite element model is verified by comparing the finite element simulation results with the experimental results.(4)In this paper,144 concrete-filled circular steel tubular columns and 144 concrete-filled rectangular steel tubular columns were designed by changing the parameters such as axial compression ratio,slenderness ratio,diameter-thickness ratio(width-thickness ratio),height-width(only for rectangular section),concrete strength and steel strength.Then ABAQUS software was used to analyze the finite element analysis of two types of concrete-filled steel tubular columns,taking into account the influence of different parameters on the seismic performance of the members.And the influence of different parameters on the performance limit of stiffness degradation is further analyzed.(5)Based on the finite element analysis results of concrete-filled circular steel tubular columns and rectangular steel tubular columns,the correlation between performance level and above parameters is analyzed statistically,and the key parameters are selected by T test.On this basis,the regession formulas about stiffness degradation limit are created to connect performance levels of concrete-filled steel tubular columns.Finally,the limits of stiffness degradation of five performance levels are proposed. |
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