Effect of Rotational Restraint on Inelastic Buckling of Steel Column at Elevated Temperatures

When a fire develops within the fire compartment of a building, the columns in the compartment are heated, whereas the beams and columns outside the compartment remain cold. Hence, the relative stiffness ratio between the cold members and heated column increases. Consequently, the end-rotational restraint on the heated column is increased, and the effective buckling length of the heated column becomes shorter compared with the ambient temperature condition. However, studies regarding the effect of increased end rotational restraint on heated columns are rare. Although some recommendations to consider this effect are available in representative design standards, they are suggested under limited or ideal conditions and hence not applicable under general conditions. In this study, a procedure for calculating the effective length factor of non-sway steel columns with general end restraints at elevated temperatures is proposed based on the classical Euler column theory and tangent modulus concept. The proposed procedure is validated based on a test-backed nonlinear finite element analysis. It is shown that the proposed equations can be combined with the existing column buckling curve to predict the column buckling strength with significantly increased accuracy compared with the methods suggested by representative design standards.