Research on a macro joint model for progressive collapse analysis of L-CFST column frames

In this study, a macro joint model was developed to evaluate the progressive collapse resistance of L-shaped column composed of concrete-filled steel tubes (L-CFST column) frames, accounting for joint performance. The methods used to calculate the spring stiffness in each part of the macro joint model were derived using the component method and deformation coordination principle. Additionally, an L-CFST frame model consisting of fibre beam elements and macro joint models was created. For frame models with different parameters, the dynamic response of column removal was analysed. These parameters included the loading conditions, the connection types, the location of the failed columns, the height and number of floors, and the span-depth ratio of the steel beams. The results indicated that the macro joint model had high accuracy in predicting progressive collapse resistance. The L-CFST column frames with novel side-plate reinforced connections fully exploited the catenary mechanism and Vierendeel action. All the variables affected the vertical displacement at the position of the failed columns, with the span-depth ratio having the most significant impact.