Experimental and numerical study on the behavior of high strength Q960 steel columns after fire exposure

High-strength steel exhibits extensive potential in large-span buildings and bridges. Therefore, it is of great significance to clarify its mechanical properties particularly in the realm of post -fire building repair and reconstruction, making it imperative to elucidate its bearing capacity after exposure to elevated temperatures. To comprehensively investigate the overall stability of high-strength Q960 steel columns under high-temperature conditions, a series of axial compression bearing capacity tests are conducted on eight Q960 steel columns-four of which featured H-shaped sections and the remaining four being box-shaped sections. The design of these members considered the effects of slenderness ratio and temperature. At the same time, the residual stress and geometric initial defects of the steel column were measured. Furthermore, the axial compression model for Q960 steel columns, encompassing both room and high-temperature scenarios, was established using the ABAQUS finite element software. This model duly accounted for the influence of residual stress and geometric initial defects. Subsequently, the test outcomes, encompassing horizontal and vertical displacements, ultimate bearing capacity, and failure mode, were compared with the results obtained from finite element analysis. This comparison serves to validate the accuracy of the model while facilitating parameter analysis. The results based on both the finite element analysis and experimental findings, indicate that when employing the Chinese code GB 50,017-2017, the stability coefficient calculation for Q960 steel columns following high-temperature exposure yields satisfactory safety margins. In light of these findings, a calculation method is proposed to accurately predict the stability coefficient of Q960 steel columns in the aftermath of high-temperature conditions, thus offering a reliable approach for assessing the stability bearing capacity of such columns in such scenarios. By comparing with EN 1993-1-12 and ANSI/AISC 360-22, it is found that EN 1993-1-12 has a better prediction effect, while ANSI/AISC 360-22 is conservative when the slenderness ratio is small.