Heating rate and boundary restraint effects on fire resistance of steel columns with creep

This paper presents a series of numerical studies conducted on thermally restrained steel columns subjected to predominantly axial loads. The parameters under investigation include the column slenderness ratio λ, axial restraint ratio β_l, rotational restraint ratio β_R, and axial load utilisation factor μ^N. For the heating scheme, only the cross-sectional uniform heating profile is investigated, as columns are normally exposed to fire on four faces. A finite element program FEMFAN2D is applied for the analyses and creep strain has been explicitly considered. The behaviour of thermally restrained steel columns is explained in terms of the development of cross-sectional stresses and strains. Extensive investigations are conducted to study the creep effect on the development of stress and strain, internal forces and critical temperature of a column. It shows that for some considered cases, the creep effect becomes significant for as low as 350 °C. Besides, the study also shows that the rotational restraints significantly reduce the column effective length under fire conditions and increase the column critical temperature through restoring moment. It is suggested that the effective length ratio for non-sway generally restrained columns can take the value of 0.55 for design purposes.