A NEW DERIVATION OF THE BUCKLING THEORY OF THIN-WALLED BEAMS

Publisher Summary There exist two formulae at present for calculation of flexural–torsional buckling moments of thin-walled beams with monosymmetric I-sections. This chapter compares the stability theories from which these formulae are derived, and presents a buckling analysis of I-sectional beams based on the stability theory of shells, which is certainly superior to the beam theories because fewer assumptions are adopted to establish the shell buckling theory. Totally 36 I-sectional beams are analyzed using the finite element method (FEM) program ANSYS, among which 12 have doubly symmetrical sections, 12 tensile flange strengthened, and 12 compressed flange enlarged. The element SHELL63 is used in the analysis. It is found that the shell buckling analysis verifies the traditional formula, not the newer, seemly more rational theory. The chapter presents a new derivation of the flexural–torsional buckling theory of thin-walled beams. There are great differences in buckling moments of simply supported beams obtained from the traditional and the newly proposed theories, when the beams have monosymmetric cross-sections and are loaded by transverse loads. The cause leading to this unusual inconsistency is analyzed.