Study Of Local-overall Interactive Flexural-torsional Buckling Of High Strength Steel Welded I-section Beam-columns

High strength steel becomes the new family of constructional steels is a result ofbreakthroughs in steel making technologies, particularly for the born of themicro-alloying technology and the thermo-mechanical control progress. As a result,high strength steels have been used to lots of building and bridge constructions in chinaand other countries, and great economical benefit have been obtained. But comparedwith normal strength steel, high strength steel member’s buckling problems becomemore dominant. In order to increase the ultimate capacity and make the use of steelefficient, plates width-to-thickness ratio should be released appropriately when designthese high strength members.Firstly, this paper presents a finite element model for studying the behavior oflocal-overall interactive flexural-torsional buckling of high strength steel Q460weldedI-section beam-columns which beyond limits of web depth-thickness ratio. Innumerical model, the geometric imperfections and residual stresses were taken intoaccount. The finite element model was validated by comparing the numericalsimulation results with the existing test data. Then, the validated model was used tocarried out a large number of parametric analysis in order to investigate the effectsfrom the web depth-thickness ratio, flange width-thickness ratio, slenderness ratio,eccentricity ratio and steel strength to the local-overall interaction buckling behavior.Finally the modified formulas were proposed for predicting the ultimate capacity of themembers based on the results of parametric analysis and the corresponding designmethods in Chinese structure design codes.The analysis results indicate that the finite element model presented in this paper can simulate the behavior of local-overall interactive flexural-torsional buckling ofwelded I-section steel beam-columns. The ultimate bearing capacity of weldedI-section beam-columns decreases with the web depth-thickness ratio, flangewidth-thickness ratio, slenderness ratio and eccentricity ratio increasing. Steel strengthincreased significantly improves member’s ultimate bearing capacity, Compared withnormal strength steel, The dimensionless ultimate bearing capacity of high strengthsteel members is decreased obviously along with the web depth-thickness andslenderness ratio increasing, but the rate of decrease is slowed down with theeccentricity ratio increasing. The proposed modified formulas are good agreement withthe numerical results.