Influence of load and high temperature on the post‐fire behaviour of high‐strength structural steels

In this work, an experimental campaign was carried out to evaluate the post‐fire mechanical performance of high‐strength steel specimens (grade S700) when being subjected simultaneously to different combinations of tensile load and elevated temperature. To this end, transient‐state tests were firstly carried out to obtain the ‘critical temperature’, i.e., the temperature at which a specimen failed while being simultaneously subjected to tensile load and heated at a constant temperature rate. Secondly, post‐fire tests were performed on unloaded as well as loaded specimens. For that purpose, specimens were heated to temperatures below the critical temperature, cooled down in air and finally submitted to tensile testing. In order to investigate the influence of production route, specimens were extracted from cold‐formed circular hollow sections and hot‐rolled sheets. Moreover, coupons with five different thicknesses were tested to investigate the influence of section thickness on the post‐fire behaviour. Residual values of yield strength, ultimate strength, elastic modulus and ductility were determined from the tests and discussed.