The effect of manufacturing process on the post-fire mechanical response of thin-walled ultra-high strength steel (Grade 1200) tubes

This study aims to investigate the effect of manufacturing process on the post-fire mechanical response of Grade 1200 ultra-high strength steel (UHSS) tubes. To this end, the post-fire mechanical properties of “direct-quenched” UHSS (UHSS-DQ) standard tensile coupons are compared to those made of “quenched and tempered” UHSS material (UHSS-QT) with similar original room temperature stress-strain responses. Thus, to compare the post-fire compression behaviour of UHSS-DQ tubular stub columns with those made of UHSS-QT material, a finite element (FE) model is developed in ABAQUS FE software with precise material properties extracted from the results of the post-fire tensile coupon tests. Quasi-static compression tests are then conducted on UHSS-QT tubular stub columns cooled from different fire temperatures to room temperature to validate the FE analysis. Using the results of the tensile coupon tests and the FE analysis on UHSS stub columns, it is shown that the manufacturing process substantially affects the mechanical properties of UHSS stub columns under cooling phase of a fire.