Research On Flexural-torsional Buckling For Fixed Steel Beams Under Combined Loads

Based on the calculation formula of the critical moment of steel beams proposed by the research group,this paper is aimed at continuing to improve the calculation theory of the critical moment of steel beams.In this study,the critical moments of fixed steel beams under four different boundary conditions for single or combined loads are theoretically derived,including S-S(out-of-plane simple support),C-C(out-of-plane solid support),W-W(out-of-plane constrained warping),and R-R(out-of-plane constrained rotation).According to the results of the integral operation,the calculation formula of the "3C" coefficient corresponding to the full-span uniform load,the mid-span concentrated load and the critical moment of the two concentrated loads in the symmetrical arrangement of the mid-span is given.Besides,the calculation formula of the equivalent bending moment coefficient Cb for the full-span uniform load and the mid-span concentrated load,the full-span uniform load and the two concentrated loads combined with the symmetric arrangement of the mid-span are also given.By comparing with the corresponding coefficients in the 2007 version of EC9 and the 1992 version of EC3,the correctness of the theoretical derivation in this paper is verified.At the same time,the Mtalab and LTBeamN software were used to numerically calculate and finite element simulation of fixed-section steel beams with different sections.The influence law of span,reinforcing flange,load point position and load proportional coefficient on critical moment of fixed steel beam is analyzed.At the end of the paper,the applicability of the existing "4M" form equivalent bending moment coefficient calculation formula to the fixed steel beam is also discussed.