On the applicability and accuracy of fire design methods for open cold-formed steel beams

Abstract

This paper presents the results of an experimental and numerical investigation on the structural behaviour of cold-formed steel C and lipped-I beams subjected to uniform temperature distributions under standard fire conditions. A total of 18 specimens divided into four-point bending tests under fire conditions and under 3 different restraining conditions (including no restraints, partial axial restraint to the thermal elongation of the beam and both partial axial and rotational restraints at the beam supports) have been conducted. Local buckling, distortional buckling, lateral-torsional buckling and their interactions were observed in the tests. Then, the tests were modelled by the finite element programme Abaqus and, at the end, the numerical results showed good agreement with the experimental results in terms of axial restraining forces, vertical displacements, critical temperatures and buckling modes. The simulated results were still compared with the predictions from the currently European design rules (EN 1993-1.2:2005), in order to observe if there are safe and consistent regulations for fire design of these members. Finally, the numerical simulations have mainly shown that these design methods for CFS beams may be quite unsafe or over-conservative depending strongly on their boundary conditions.