Revealing the phase transition of steel frames with CFST columns during progressive collapse process from a thermodynamic perspective

Progressive collapse is a standard failure pattern of steel frames, which researchers expect to analyze quantitatively. However, the existing resist progressive collapse analysis methods based on empirical or reliability theories make it challenging to give quantitative results. Based on the stressing state theory, this work attempts to reveal the phase transition loads during the progressive collapse process from a thermodynamic perspective. Firstly, a 1/3-scale 4-bay steel frame with CFST columns is selected as a case study and equated to a thermodynamic/complex system, and its deformation distribution is transformed into state variables. Matrices (Modes) and Hamiltonians (Characteristic parameters) are constructed to describe the steel frame's stressing state in part or overall. The approximate phase transition loads can be detected by applying the clustering analysis criterion. Further, the phase transition loads can be verified from the renormalization perspective by comparing the Test-based and FEM-based phase transition loads. The EPB points can be directly used as a design reference. In summary, this work reveals the stable phase transition loads of steel frames from the thermodynamic perspective for a case study. Also, it enriches the theory and methodology of thermodynamic-based structural failure studies.