Abstract
The present thesis describes a series of theoretical investigations carried out by the Author with a view to contributing towards an understanding of lateral instability in beams and its effects upon beam strength. As far as could be ascertained, this problem had not yet received much detailed consideration. These investigations start from a study of a longitudinal compression layer in a beam, such as the compression flange of a steel I-beam, treated as an ideal free strut under varying end load; and then proceed to consider the effects first of initial lateral curvature in such a layer and then of the relief afforded by a specified type of lateral restraint, taken as provided by the remainder of the beam concerned. From the experience and knowledge thus gained, the wider problem of instability in a simple beam taken as a whole is then treated by the assumption of small initial irregularities such as twist and curvature, the general results being worked out for beams of symmetrical cross section under simple loading conditions. At each stage of these investigations the results are reviewed in so far as they contribute to the general problem, and are illustrated by curves corresponding to typical beam sections and loading cases. Finally, by employing a specified type of initial irregularity, the general theory for a complete beam is applied for comparison with certain experimental data and with relevant clauses in some modern structural engineering specifications. In the course of pursuing the theoretical research into beam instability thus outlined, some methods of treatment are developed which are noted as likely to be of value in the future for the study of certain related structural problems.