Fire performance of built-up cold-formed steel columns

Cold-formed steel (CFS) products are nowadays widely used in multiple structural applications, exploring their versatility. More recently CFS products and structural solutions have been used successfully in multi-storey buildings, enabling prefabrication, and easy and fast assembly procedures. To further extend the applicability of such products in new structures, their versatility must be intelligently explored, for instance by combining multiple individual sections effectively to attain higher load-bearing capacity and torsional stiffness. The behaviour of built-up elements has been investigated worldwide in order the address the demands arising from the construction sector about the urgent need for specific guidelines for the design of built-up elements. However, under accidental fire conditions, research on the behaviour of CFS built-up elements is still scarce, and no specific provisions exist for these types of structural elements. In this investigation, the fire performance of short built-up cold-formed steel columns is assessed using experimental tests and numerical modelling. Closed built-up cross-sections were investigated in fire using 3 basic cross-section shapes, namely C, U and Σ. The composite action between the individual shapes and local buckling phenomena was investigated, considering the influence of fastener spacing in the overall behaviour of the short built-up columns in fire