Buckling and geometrical nonlinear beam-type analyses of timber structures

An existing co-rotated formulation is presented, and a consistent nonlinear 3D beam element, based on 2nd order theory, and with internal geometric stiffness, is developed for implementation in the formulation. The element proves considerably more accurate with respect to predicting buckling loads in linearized buckling analyses, than the beam elements regularly used in co-rotated formulations. This is also true for nonlinear analysis. The computer program Cfem, which is based on the co-rotated formulation, is used to study several aspects of buckling, mainly lateral torsional buckling, in timber structures. Linearized buckling analyses are used for obtaining simplified or approximate formulas, and nonlinear analyses are used in order to verify these. The problems studied include lateral torsional buckling for beams with eccentricly applied loading and for tapered beams, bracing against lateral torsional buckling, and interaction between flexural and lateral torsional buckling