Review of the high temperature mechanical and thermal properties of the steels used in cold formed steel structures – The case of the S280 Gd+Z steel

Abstract

The accuracy of structural fire design of cold-formed steel structures depends on the available predictive models regarding mechanical and thermal properties. The deterioration of mechanical properties, such as yield strength and modulus of elasticity, and the evolution of thermal properties, such as thermal conductivity, thermal elongation and specific heat, with temperature is a key issue in the assessment of the performance of cold-formed steel structural elements in fire. An experimental campaign was undertaken to determine both mechanical and thermal properties of the S280GD+Z steel used in cold-formed steel building construction industry. Tensile coupon tests were carried out to determine the mechanical properties of the S280 GD+Z steel with 2.5mm thickness at temperatures ranging from 20 to 800°C. Thermal properties were assessed using the Transient Plane Source (TPS) equipment. Test results were compared with current design standards and with the ones available in the literature. The proposed predictive equations based on the Ramberg–Osgood model show very good agreement with the experimental results for temperatures beyond 300°C. It was found that some predictive models presented in the EN 1993-1-2:2005 regarding mechanical and thermal properties should be improved. Hence new proposals are presented for both thermal and mechanical properties. Also a modified stress–strain model based on the EN 1993-1-2:2005 formulation is proposed for the S280GD+Z steel.