Predicting Formula for Critical Axial Restraint Stiffness Ratio of Hinged Box‐Section Steel Columns Under Fire

Fire‐induced column failure can lead to collapse of the entire structure, and the failure type of the column, that is, quasi‐static or dynamic failure, can significantly impacts overall structural performance. Accurately predicting column failure types under fire conditions is of practical engineering importance. This study investigates the classification of failure types in hinged box‐section steel columns under fire, characterized by the critical axial restraint stiffness ratio ( β l ,cr ), using a validated explicit dynamic finite element model. The influence of key parameters, including load ratio (), slenderness ratio ( λ ), sectional length‐to‐width ratio ( D / B ), sectional width‐to‐thickness ratio ( b / t ), and sectional size ( B ), is examined. The analyses reveal that β l ,cr generally increases as rises. In addition, with the rise of D / B , b / t , and B , both β l ,cr and column dynamic effects under fire conditions intensify. Based on these findings, a predictive formula for β l ,cr is proposed for hinged box‐section steel columns. Finally, the accuracy of the proposed formula is validated using independent numerical simulations.