| The lateral-torsional buckling of thin-walled open section beams is important aspect instructure design .An Investigation across-the-board about this problem is made in this paper. Bymeans of theoretics analysis and finite-element model , an improvement of the steel beambuckling theory in existence is given, and some advice concerning the stability design ofthin-walled open section beams is presented. On the orther side,the stability theory of thin-walledopen section beams under the action of bend-torsion is developed from the presentlyloaded-in-plane stability theory. Based on the newly evolutional stability theory, the stabilitydesign about lateral-torsional buckling of thin-walled open section beams under vertical andhorizontal load is settled in this paper. Firstly , a comprehensive investigation on the two different stability theory of thin-walledopen section beams existing in domestic research these days .The analysis shows that the two eachhas inaccuracy or flaw. By a distinctively technique, a new stability theory of thin-walled opensection beams is obtained . Via the Galerkin method , Coefficients C1,C2 and C3 are recomputedfor simply supported beams.Galerkin's methods are applied. ANSYS software is used in numericalsimulations where the element BEAM189 and SHELL63 are chosen in modeling lateral bucklingphenomena .Base on the result of comparison aboved, some suggestion are given about the designof stability of steel beam . a formula on beam under the two-direction moment and torsion action is theoreticallyderived for the stability design . A FEM verification is carried by the ANSYS software. At last,theformula is compared with the similar one given by《Technical code of cold-formed thin-walledsteel structures》(GB 50018-2002). The result according《Technical code of cold-formedthin-walled steel structures》is higher (about 20%) than that given by the formula in this article,butit could be accepted from the point of application of design practice .
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