Experimental analysis on cold-formed steel beams subjected to fire

• Behaviour of cold formed steel (CFS) beams at high temperature was studied.
• Flexural tests at high temperatures were carried out and results presented.
• Influence of cross-section, axial and rotational restraint on beam′s structural behaviour.
• CFS beams are very sensitive to local, distortional and global buckling.
• Critical temperature of CFS beams might be strongly affected by axial restraint.

The great majority of the studies in this area emphasise further the structural behaviour of cold-formed steel members by means of analytical approximation and purely numerical methods. In addition, they generally only take into account the structural behaviour of members with just one profile. On the contrary, this paper reports a series of flexural tests under fire conditions focused on cold-formed galvanised steel beams consisting on compound cold-formed steel profiles which are often used in floors and roofs of warehouses and industrial buildings. The main objective of this research was to assess the failure modes, the critical temperature and the critical time of the studied beams. Other important goals of this research work were also to investigate the influence of the cross-sections, the axial restraint to the thermal elongation of the beam and the rotational stiffness of the beam supports. Finally, the results showed above all that the critical temperature of a cold-formed steel beam might be strongly affected by the axial restraint to the thermal elongation of the beam.