Study On Local-overall Interactive Flexural-torsional Buckling Of High-strength Steel Welded I-section Beam-columns With Large Web Depth-to-thickness Ratio

With the continuous improvement of steel production technology,high-strength steel has been widely used in many large bridges and building structures at home and abroad because of its remarkable advantages of high bearing capacity and good economic benefit.However,although the high-strength steel members greatly reduces the weight of the structure,but it reduces the section area of the member significantly.The member itself tends to be thiner and slender,and it is easier to exceed the standard limit.The problem of local stability and overall stability becomes the key factor to restrict its application.At present,the local-overall interactive stability for ordinary steel members of research has been relatively mature,but for the interactive stability of high-strength steel,especially the author studies on Q690 high-strength steel members the stability problem,is still relatively short.Therefore,this paper mainly aims at the local-overall interactive flexural-torsional buckling behavior of the member.The Q690 high-strength steel(yield strength of 690 MPa)is selected to be welded and made into I-section beam-columns members with high depth-to-thickness ratio of webs is studied.In this paper,the comprehensive influence of many factors such as residual stress,initial geometric imperfections,material nonlinearity and geometric nonlinearity,and the numerical model is established by ANSYS finite element software and the ultimate bearing capacity of local-overall interactive flexural-torsional buckling of the member is calculated.The influence of factors such as the web depth-to-thickness ratio,flange width-to-thickness ratio,length-to-slenderness ratio,relative eccentricity and steel strength on the ultimate bearing capacity of the members are analyzed and studied.The modified formula for the relevant buckling ultimate bearing capacity is proposed,which based on the existing design codes and takes into account the influence of multiple changing parameters.The results show that the finite element model considering the influence of various factors,which can simulate well the local-overall interactive flexural-torsional buckling behavior of high-strength steel members.With the increase of the web depth-to-thickness ratio,flange width-to-thickness ratio,length-to-slenderness ratio and relative eccentricity,dimensionless ultimate bearing capacity of the members is decreased.Among of them,the flange width-to-thickness ratio has little effect on the dimensionless ultimate bearing capacity of the component.For members with larger web depth-to-thickness ratio,smaller length-to-slenderness ratio and smaller load eccentricity,the form of instability failure is dominated by the local buckling failure;On the contrary,for members with smaller web depth-to-thickness ratio,larger length-to-slenderness ratio and larger load eccentricity,the form of instability failure is dominated by the overall flexural-torsional buckling failure.Compared with ordinary steel members,high-strength steel has better bearing capacity,but its stability decreases.The proposed correction formula proposed in this paper is in good agreement with the finite element results,which can predict the ultimate bearing capacity of the local-overall interactive flexural-torsional buckling of high-strength steel welded I-section beam-columns with large web depth-to-thickness ratio.