Local Buckling of High-Strength Steel Beams Under Bending-Shear Interaction at Elevated Temperatures

High-strength steel is employed in structural engineering due to its excellent mechanical properties. However, research on the local buckling behavior of high-strength steel beams under fire condi-tions remains relatively limited. To understand the local buckling behavior of high-strength steel beam webs under combined bending and shear at elevated temperatures, experimental and numer-ical study was conducted on Q690 steel beams. The experimental program included tests on seven beams considering variations in web height-to-thickness ratios, load ratios, and temperature. Key measurements included the local buckling modes, mid-span deflections, out-of-plane web distor-tions, and temperature evolution. Using ABAQUS finite element software, a validated thermo-mechanical coupling model was developed to comprehensively analyze the influence of multiple parameters, including the web height-to-thickness ratio, flange width-to-thickness ratio, web as-pect ratio, steel strength, load ratio, temperature distribution, residual stresses, and initial geomet-ric imperfections. Based on an analysis of the critical height-to-thickness ratio and critical temper-ature at which buckling occurs due to heating, a method to determine critical temperature was pro-posed for predicting local buckling of steel beam webs under fire conditions. The results indicate that increasing the load ratio from 0.3 to 0.5 reduces the critical temperature by 9.2%. Significant differences were observed in the fire resistance of beams with different steel grades, with Q690 steel beams exhibiting comparatively poorer local buckling performance under fire compared with Q460 and Q960 steel beams. The web height-to-thickness ratio, flange width-to-thickness ratio, and web aspect ratio were found to have minor effects on the critical temperature (within 5%), while residual stresses and initial geometric imperfections had negligible influence. It is recom-mended that the web height-to-thickness ratio of steel beams designed for fire conditions should be limited to less than 102.8ɛk to prevent local buckling at high temperatures. The proposed criti-cal temperature method for predicting local buckling of web under fire demonstrates high accura-cy, with errors within 3%, providing a reliable reference for engineering applications.