Lateral Torsional Buckling of Wooden Beams with Midspan Lateral Bracing Offset from Section Midheight

Abstract

An energy-based solution is developed for the lateral torsional buckling analysis of wooden beams with a midspan lateral brace subjected to uniformly distributed loads or midspan point load. The predicted critical moments and mode shapes are shown to agree with results based on three-dimensional finite-element analysis. The study indicates that such beams are prone to two buckling patterns: a symmetric mode and an antisymmetric mode. Whether the symmetric or the antisymmetric mode governs the critical moment capacity is shown to depend on the bracing height. A technique is developed to determine the threshold bracing height required to maximize the critical moment. A parametric study is conducted to investigate the effect of lateral bracing and load height effects on the critical moments. Simple design equations are developed to predict critical moments for a practical range of cases. The limitations of the simplified procedure are discussed. For cases outside the scope of the simplified procedure, designers are recommended to adopt the more detailed energy-based solution. Design examples are provided to illustrate the merits and applicability of the proposed procedure in practical situations.