RESEARCH ON PROGRESSIVE COLLAPSE RESISTANCE CAPACITY OF COMPOSITE FRAME WITH CFST COLUMNS UNDER CORNER COLUMN REMOVAL SCENARIO

To study the progressive collapse performance of the composite frame with CFST columns under the corner column removal scenario, a 1/4-scale two-story-two-bay composite frame specimen was designed and tested. By the monotonic static loading of the residual structure after the corner column was damaged, the tests obtained the load-displacement relationship curves of the composite frame, the global/local failure modes of the structure and the strain developments of critical locations. The energy equivalence principle was used to analyze the progressive collapse dynamic effects. The resistance to progressive collapse of the composite CFST frame was evaluated. The experimental results show that the progressive collapse loading process of composite frame with CFST columns mainly includes four stages in the corner column removal scenario, i.e., elastic stage, elastic-plastic stage, internal force redistribution stage and damage stage. The damage of the specimen is mainly concentrated in the failure span. The failure characteristics are mainly on the fracture and distortion of steel beams, and the steel beams on the second floor are damaged before that on the first floor. It is also found that the composite slabs with profiled sheeting and concrete are separated from the steel beam and the shear studs are pulled off. When the flange of the steel beam on the second-floor is cracked, the internal force is transferred to the first-floor steel beam through the adjacent column. Based on the test results and the energy equivalence principle, it is found that the composite frame has 15.3% residual capacity to resist the progressive collapse in the corner column removal scenario.