Low‐temperature ductility and structural behaviour of cold‐formed hollow section structures – progress during the past two decades

Abstract Cold‐formed hollow sections are a widely used tubular construction material. The applicability, weldability and reliability of cold‐formed rectangular hollow sections are sometimes questioned because of the consequences of cold forming and inhomogeneous cross‐sections. One of the main concerns is related to the cold‐formed corner areas and possible loss of toughness due to strain ageing in the vicinity of the welds. Conventional hot‐rolled C‐Mn steels are susceptible to strain ageing, and Eurocode 3 includes restrictions on welding in the cold‐formed corner area. Both steelmaking and hot rolling have undergone crucial developments and this has had an impact on cold‐formed hollow sections. Thermomechanically rolled fine‐grain steels became state of the art at the end of the 1990s. This study confirms that cold‐formed EN 10219 hollow sections made of suitable fine‐grain steels have a similar Charpy‐V toughness on the flat face and in the corner, and that even after ageing the transition temperature T40J in the corner area is at a very low level, typically below –50 °C. The load and deformation capacities of X‐ and K‐joints fulfil the requirements without any noticeable ageing effects. The advances in steelmaking and hot rolling enable the manufacturing of reliable and versatile cold‐formed EN 10219 hollow sections for welded structures with good low‐temperature ductility even in the cold‐formed corner area.