REFINED FINITE ELEMENT ANALYSIS OF PROGRESSIVE COLLAPSE OF PLANAR FRAMES WITH CONCRETE-FILLED STEEL TUBULAR COLUMNS

The capacity of concrete filled steel tubular (CFST) structures against progressive collapse are determined by the beam mechanism and catenary action of the steel beams connected with the damaged key column which is destroyed by extreme loads. This paper presents a finite element (FE) model of a planar frame with CFST columns based on refined finite element analysis to study the progressive collapse resistance. The whole collapse failure modes and the stress distribution revealed the resistance mechanism of the planar frame during the process of progressive collapse. The relationship between the load-carrying capacity (P) versus vertical displacement (Δ) was analyzed in the FE model. The influence of different geometric and physical parameters on the collapse-resisting capacity of the frames were also studied. The results showed that the P-Δ relationship curves contain four stages during the whole collapse, i.e., beam mechanism, transformation mechanism, catenary action and failure phase. The steel beam flange thickness and the steel ratio of tube have significant influence on the collapse-resisting capacity of CFST structures based on the resistance index and displacement ductility index. Attentions should be paid in practical engineering designs and applications.