Performance-based Seismic Design Method Of CFST Frame With BRBs

Concrete filled steel tube(CFST) frame has been widely used because of its advantage of high vertical bearing capacity, fast speed of construction and high economic efficiency.But the low lateral stiffness, and the little energy dissipation of the structure under rare earthquake makes the seismic performance need to be improved. To improve the lateral stiffness of CFST frame, the buckling restrained braces(BRBs) were installed in CFST frame structrure and “the CFST frame structure with dissipation devices” was established, and then a series of experimental and theoretical studies were carried on. Based on the above study, the research on the performance based seismic design of this kind of structure system is carried out in this paper. The main research work is showed as below:1) The performance indexes in the theory of performance-based seismic design were studied about the concrete filled steel tube columns. Five performance levels were adopted to give the corresponding failure state and macroscopic description. Horizontal drift ratio was selected as performance level quantitative index. The seismic test data were collected including 68 concrete filled circular steel tube columns and 82 concrete filled square steel tube columns, based on normal distribution statistical methods the limit of horizontal drift ratio was determined under different performance levels.2) Based on the limits of performance index of buckling-restrained brace(BRB) in American code(ASCE41-13), a numerical study was carried out using ABAQUS software capable of nonlinear analysis to investigate the mechanical performance and damage degree of BRB at different performance levels, and the reasonableness and feasibility of the limits of performance index in American code were verified. Combined with engineering example, the significance in performance evaluation of structural members and the application in performance-based seismic design were finally discussed.3) Based on a large number of elasto-plastic time-history analysis of buckling restrained braces frames(BRBF) examples, the relationship between maximum story drift and lateral stiffness ratio k is established for BRBF subjected to rare earthquakes. And according to the analysis of the structure performance under rare earthquake, a reasonable range of lateral stiffness ratio k is recommended.4) Referring to literature at home and abroad, and the Chinese code for the description of structure in each performance level, the structure seismic performance is divided into five levels in the paper. A kind of qualitality method is proposed to classify structure performance level describing the relationship between structure performance level and component performance level. According to the current code, the author designed buckling restrained braces frames models with different seismic fortification intensity and different height, and used PERFROM-3D to analyze the above models carrying on Push-over analysis, then use the above qualititative method to find out the structure story drift limit of each performance level.