Simplified Design of Glued Laminated Timber Girders for the Torsional Moment Caused by Stability Effects

This paper presents a numerical study on the torsional moment in lateral torsional stability analysis of glued laminated timber girders. A numerical model is developed solving the bending-torsion problem. This numerical model according to second order theory also takes single supports at the upper chord into account,which are typical for wide span girders as roof beams with horizontal bracings in order to reduce the relative slenderness of the girders. The numerical studies on straight parallel-chorded glued laminated beams show, that the torsional stresses on buckling girders are in the range of 4-12% of the allowable shear stresses in cross-section at the end supports considering two different curvatures of imperfection. In practice the torsional moment due to stability analysis on the lateral torsional buckling should be derived in a simple and secure way to be able to verify it against the relatively low shear strength of timber without using a calculation according to second order theory.