Elevated temperature material properties of cold-formed steel hollow sections

• Steady-state and transient-state elevated temperature tests have been conducted on cold-formed steel material.
• Retention factors were derived from the experimental results and compared with provisions in design codes and the literature.
• The retention factors from EN 1993-1-2:2005 were found to be suitable for application to cold-formed steel hollow sections.
• Formulae for the prediction of ultimate strain and fracture strain were proposed.

Elevated temperature material tests on cold-formed steel coupons cut from circular, rectangular and square hollow sections have been conducted, including both steady-state and transient-state tests. The experimental apparatus, methods of testing and results obtained are fully described. Temperature dependent retention factors for stiffness, strength and ductility were determined and compared to those provided in the European Standard EN 1993-1-2:2005 and the Australian Standard AS 4100:1998. It was found that the codified retention factors, despite being derived on the basis of tests on hot-finished material, are also applicable to cold-formed hollow sections. A design proposal from the literature for the prediction of ultimate strain has been also shown to be suitable for application to cold-formed hollow sections. A new expression for predicting strain at fracture has been proposed that provides a lower bound estimate of the test results derived in the current study.