Modified procedure for buckling of steel columns at elevated temperatures

• Buckling of steel columns at elevated temperatures is studied.
• Alternative analytical methods for buckling resistance are proposed.
• Nonlinear bending stiffness dependence on stress state in fire situation is shown.
• Analytical methods are validated by numerous fem results.

Buckling capacity of axially loaded steel columns with hot-rolled I-sections, circular and rectangular hollow sections in fire is studied. The current Eurocode method for checking the stability at elevated temperatures has been derived on the same basis as in ambient conditions. Due to significant nonlinearities in the behaviour in fire the standard method appears to be not fully appropriate in certain ranges of parameters. In the present work the behaviour of columns is studied by comprehensive numerical simulation at a wide range of temperatures and slenderness values. Based on the results two alternative analytical procedures have been proposed and validated for evaluation of buckling strength. One of them needs numerical determination of a number of parameters beforehand. The other is based on the modification of the nonlinear material model and despite some limitations, it is convenient to use with common design procedures and applicable for an appreciable range of typical sections.