Investigation on post-fire overall stability of restrained Q690 high strength structural steel columns under eccentric compression

In steel structures, steel columns are usually eccentrically compressed while being axially and rotationally restrained by adjacent members, resulting in complex behaviors at and after fire. In addition, steel columns made of high strength structural steel (HSSS) are more prone to fire-induced material strength loss and instability than those made of conventional structural steel. Therefore, investigating the post-fire overall stability of restrained HSSS columns under eccentric compression is crucial for assessing the safety of HSSS structures after fire. This paper firstly presents a parametric study on the post-fire overall stability of restrained Q690 HSSS columns under eccentric compression, based on a verified finite element model built in ABAQUS. Results show that the post-fire overall stability decreases as the slenderness ratio or eccentricity increase, while it increases as the rotational restraint stiffness ratio increases. Under certain circumstances, the post-fire overall stability decreases as the maximum experienced temperature increases, while it increases as the axial restraint stiffness ratio or load ratio increase. Based on the results of parametric study, considering that the post-fire residual deflection should not affect the normal use of the column for possible reuse, an acceptable limit of 1/200 of the column length is proposed. For columns with post-fire residual deflection within the acceptable limit, the coefficients of post-fire overall stability for eccentric compression are compared with those calculated based on the criteria for members subjected to combined bending and axial compression specified in GB 50017-2017, ANSI/AISC 360-22 and EN 1993-1-1: 2022. Results show that the most suitable criterion for assessing the post-fire overall stability of restrained Q690 HSSS columns under eccentric compression is the one specified in EN 1993-1-1: 2022, with the axial compression overall stability coefficients used in the criterion calculated based on the corresponding buckling curve “c”.