Numerical analysis on axially-and-rotationally restrained cold-formed steel beams subjected to fire

• Numerical investigation on the fire behaviour of cold-formed steel beams presented.
• Influence of section geometry, load level, slenderness, axial and rotational restraints studied.
• Critical temperature of axially restrained beams may drop significantly.
• Fire resistance not change beyond a certain value of axial or rotational restraint.
• EN1993-1.2:2004 models are not appropriate for the fire design of these beams.

A numerical parametric investigation into the response of axially and rotationally restrained compound cold-formed steel beams in fire has been carried out. A suitable finite element model was validated against experimental fire tests. Some parameters that could have influence on the behaviour of these beams were evaluated, such as the section geometry, initial applied load, slenderness and influence of the axial and rotational restraints. The results showed that the critical temperature of axially restrained beams may drop significantly (reaching a 50% reduction) and, beyond a certain value of axial or rotational restraint it may be no longer possible to change its fire resistance. Furthermore, it was still concluded that the methods established in EN1993-1.2:2004 are not appropriate for the fire design of these beams (reaching relative differences in the order of 20% and some predictions can be unsafe).