Flexural-Torsional Buckling Behavior and Design for High-Strength Steel Beams in Fire Conditions

Abstract

Due to its high load-bearing capacity, high-strength steel is progressively more used in present engineering applications. However, the current design codes methodology for the lateral-torsional buckling (LTB) ultimate capacity of laterally unrestrained steel beams is based on experiments limited to room temperature and mild steel. A numerical analysis of steel beams’ ultimate bearing capacity in bending was carried out to evaluate the lateral-torsional bending of different high-strength steels, namely, Q460, Q690, and Q960 steel at high temperatures. As a comparison, the lateral-torsional bending of Q235 steel beam was also studied. Finite element models (FEMs) were generated using Abaqus with taking into account initial geometrical imperfection and residual stress. The validation of the FEMs has been established by comparing the ultimate flexural resistances obtained from previous tests with those from FEM. A number of parametric studies were taken to investigate the effects of different factors such as various span lengths, residual stress, steel grades, temperatures, and cross-section size on the flexural-torsional buckling (FTB) behavior of laterally unrestrained steel beams. Furthermore, the overall bending capacity of laterally unrestrained steel beams has been shown to be deteriorating at high temperatures. In addition, based on findings from the FEMs, design curves were proposed for evaluating the FTB of high-strength steel beams at elevated temperatures. The results were compared with the design curves given by design codes of GB 51249-2017 and EN 1993-1-2.