Analysis of seismic behavior of composite frame structures

There are great needs of simple but reliable mechanical nonlinear behavior analysis and performance evaluation method for frames constructed by steel and concrete composite beams or columns when the structures subjected extreme loads, such as earthquake loads. This paper describes an approach of simplified macro-modelling for composite frames consisting of steel-concrete composite beams and CFST columns, and presents the performance evaluation procedure based on the pushover nonlinear analysis results. A four-story two-bay composite frame underground is selected as a study case. The establishment of the macro-model of the composite frame is guided by the characterization of nonlinear behaviors of composite structural members. Pushover analysis is conducted to obtain the lateral force versus top displacement curve of the overall structure. The identification method of damage degree of composite frames has been proposed. The damage evolution and development of this composite frame in case study has been analyzed. The failure mode of this composite frame is estimated as that the bottom CFST columns damage substantially resulting in the failure of the bottom story. Finally, the seismic performance of the composite frame with high strength steel is analyzed and compared with the frame with ordinary strength steel, and the result shows that the employment of high strength steel in the steel tube of CFST columns and steel beam of composite beams benefits the lateral resistance and elasticity resuming performance of composite frames.