Inelastic buckling of pin-ended steel columns under longitudinal non-uniform temperature distribution

Columns under natural fire conditions are usually exposed to non-uniform temperature distribution in the longitudinal direction. The motivation for this study stems from zone modeling of a compartment fire where the gas layers are artificially divided into two zones, viz. the hotter upper zone and the cooler lower zone. However, for field modeling of a compartment fire, more detailed information of temperature distribution can be obtained. The difference in temperature between the top and bottom ends of a column can be quite significant, particularly prior to flashover condition. Depending on the required accuracy, one example due to piece-wise step distribution in the longitudinal direction is analyzed in this paper and compared with experimental results. This represents more realistically the thermal response of a column which experiences greater temperature variation with increasing height. In this paper, the inelastic stability of a pin-ended steel column under non-uniform temperature distribution is studied analytically. Across a column section, the temperature is assumed to be uniform. Two linear elastic springs connected to the column ends simulate axial restraints from adjoining unheated structures.