Simplified multi-scale simulation investigation of 3D composite floor substructures under different column-removal scenarios

The robustness of structures to withstand progressive collapse is a significant theme. However, owing to the restricted experimental conditions, some issues regarding 3D composite floor substructures under a column -removal scenario remain unclear, such as different column-removal scenarios, boundary constraints, loading schemes, floor numbers, reinforced concrete (RC) floors, and structural or nonstructural components. To un-derstand these issues, a progressive collapse study on 3D composite floor substructures subjected to uniformly distributed load (UDL) is carried out based on simplified multi-scale simulation. A 2 x 1-bay concrete-filled steel tubular (CFST) column-steel beam-RC floor substructure is employed to investigate the structural robustness under the corner column-, penultimate-edge column-, and middle-edge column-removal scenarios. It is found that the vertical resistance for the corner column-removal scenario is reduced by approximately 10-20% compared to the other two scenarios. The 3D substructure resists progressive collapse via the flexural action (FA), the catenary action (CA), and the RC floor. Compared with the real boundary constraints, the fixed and hinged supports at the beam ends can overestimate the CA, and disregarding boundary constraints can overestimate deformation performance. Moreover, the concentrated vertical load (CVD) severely underestimates the robust-ness of 3D substructures. The floor number, RC floor, shear wall, and steel brace significantly influence the progressive collapse performance of 3D substructures.