Construction of Time-Varying Boundary Conditions: Hybrid Testing of Steel Frame Structures against Progressive Collapse

To precisely evaluate the collapse resistance of structures, this paper introduces a hybrid testing technique that establishes time-varying boundary conditions. Traditional and hybrid tests were executed under scenarios involving internal column failure, and a detailed comparative analysis was conducted on deformation, internal forces, collapse resistance mechanisms, and load-bearing capacity reserves of traditional and hybrid tests. Compared to the hybrid test, the traditional test significantly overestimated the horizontal constraints of the substructure. The traditional test failed to consider additional vertical forces transferred from the upper structure to the column during internal force redistribution. Moreover, the hinged constraint applied at the inflection point restricted potential lateral deformations of the column, thereby hindering an accurate representation of the column’s true stress state during tests. These factors substantially affect the reliability of the structure’s collapse resistance assessment. The hybrid testing technique, integrated with a triple evaluation criterion encompassing resistance, deformation, and stability, effectively mitigates these challenges. Under various load ratios, the performance indicators derived from the hybrid test exhibited robust consistency across all three criteria, making it a more accurate reflection of the structural system’s collapse resistance through substructure performance testing.