Elastic Flexural-Torsional Buckling of Steel I-Section Members Unrestrained Between End Supports
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Warsaw University of Technology, Faculty of Civil Engineering, Al. Armii Ludowej 16, 00-637 Warsaw, Poland
Warsaw University of Technology, Faculty of Civil Engineering, Al. Armii Ludowej 16, 00-637 Warsaw
Submission date: 2020-10-20
Final revision date: 2020-11-03
Acceptance date: 2020-11-04
Publication date: 2021-03-31
Archives of Civil Engineering 2021;67(1):635-656
Elastic instability of steel I-section members has been investigated with regard to axial compression, major axis bending as well as compression and major axis bending, based on the Vlasov theory of thin-walled members. Investigations presented in this paper deal with the energy method applied to the flexural-torsional buckling (FTB) problems of any complex loading case that for convenience of predictions is treated as a superposition of symmetric and antisymmetric components. Firstly, the review of energy equation formulations is presented for the elastic lateral-torsional buckling (LTB) of beams, then the most accurate beam energy equation, so-called the classical energy equation formulated for bisymmetric I-section beams is extended to cover also the beam-column out-of-plane stability problems, referred hereafter to FTB problems. Secondly, for the simple end boundary conditions, the shape functions of twist rotation and minor axis displacement are chosen such that they cover both symmetric and antisymmetric lateral-torsional buckling modes in relation to two lowest eigenvalues of the beam LTB in major axis bending. Finally, the explicit form of the general solution is presented being dependent upon the dimensionless bending moment equations for symmetric and antisymmetric components, and the load factor where the lower k index identifies the load case.
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