A Method of Simulating Creep Buckling Behaviour of Steel Columns at Elevated Temperatures

When subjected to a constant applied load and elevated temperature, structural steel columns may buckle after a certain duration due to increasing creep-induced deformation, and such mode of failure is referred to as creep buckling. This paper presents an analytical method to simulate the creep buckling behaviour of steel columns at elevated temperatures by incorporating the Fields-and-Fields creep model and a nonlinear constitutive model of steel at elevated temperatures. Fire and creep buckling tests on Q690 high-strength steel columns are selected to validate the proposed method, and a good agreement between the experimental and analytical results is achieved. This demonstrates that the proposed method can provide an accurate assessment of the lateral deflection of steel columns at elevated temperatures accounting for the creep effect. Time- and strain-hardening formulations are separately incorporated into the analysis. The obtained results indicate that the strain-hardening formulation is more suitable for cases with stress variations. The study also unveils the failure mechanism of creep buckling, which indicates that the creep-induced lateral deflection of an axially loaded steel column at elevated temperatures is initiated by the gradient of stress and strain distributions on the cross-section of the column triggered by the initial imperfection. The parametric study results show that the creep buckling time of the steel column decreases as the load ratio, elevated temperature, and initial imperfection increase; however, the creep buckling time increases as the slenderness ratio increases.