Coupled local-lateral buckling of I-beams, a finite element model

Coupled local-lateral (distortional) buckling, unlike the usual lateral-torsional buckling in which the cross-section remains rigid in its own plane, involves distortion of web in the cross-section. This type of buckling typically occurs in beams with slender web and stocky flanges. Many studies published in predicting the buckling loads and modes consider a web that is distorted with a cubic shape function. As this assumption may limit the accuracy of the results, a fifth order polynomial is chosen here for the web displacements. The general line-type finite element model used here has two nodes and a maximum of twelve degrees of freedom per node. The model can not only predict the correct coupled mode but is also capable of handling the local buckling of the web. The model has been proved to be accurate and effective.