Whole-process analytical model on progressive collapse response of reinforced concrete structures under middle column loss

Since progressive collapse is essentially a dynamic process, the whole-process resistance evolution path is critical for a structure against progressive collapse. Previous analytical studies focus primarily on one particular phase of a single load transfer mechanism, such as compressive arch action (CAA) or catenary action (CA) capacity. This study develops a unified analytical model to evaluate the whole resistance-displacement curve of reinforced concrete (RC) structures. In the analytical model, compatibility, equilibrium condition, constitutive laws of concrete and reinforcing bars, and fracture of reinforcing bars are considered. To avoid complex iterations, curvature equations and combination schemes of cross-sectional forces are also established. The analytical model is verified against experimental resistances and axial forces of RC beam-column substructures measured in 24 tests, and it is subsequently utilized to illustrate the evolution of cross-sectional forces throughout the loading process. Furthermore, a sensitivity analysis based on the K-L entropy index is conducted to quantify the effects of different parameters on the progressive collapse resistance. The results show that the yield strength and diameter of reinforcing bars are vital to the whole resistance curves. The axial stiffness and beam depth primarily affect CAA capacity, while having a less significant impact on the CA capacity. Fracture displacement of reinforcing bars is the most influential parameter for CA capacity, suggesting the importance of considering the fracture of reinforcing bars in the analytical model.